- Asymmetric hydrogenation of an α-unsaturated carboxylic acid catalyzed by intact chiral transition metal carbonyl clusters-diastereomeric control of enantioselectivity
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Twenty clusters of the general formula [(μ-H)2Ru3(μ3-S)(CO)7(μ-P-P?)] (P-P? = chiral diphosphine of the ferrocene-based Walphos or Josiphos families) have been synthesised and characterised. The clusters have be
- Abdel-Magied, Ahmed F.,Doverbratt, Isa,Haukka, Matti,Nordlander, Ebbe,Raha, Arun K.,Rahaman, Ahibur,Richmond, Michael G.,Singh, Amrendra K.,Theibich, Yusuf
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- Asymmetric [2,3]-Wittig rearrangements with chiral, phosphorus anion-stabilizing groups
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The [2,3]-Wittig rearrangement of a chirally-modified phosphorus stabilized anion proceeds readily and with excellent diastereo- and enantioselectivity for alkyloxymethyl and (Z)-2-butenyloxymethyl derivatives.
- Denmark, Scott E.
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- Conformational study of poly(N-propargylamides) having bulky pendant groups
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N-Propargylamides having chiral centers at the α-carbon of the amide groups, 1-3, were polymerized with (nbd)Rh+[η6-C6H5B-(C 6H5)3] to afford polymers with moderate molecular weights (Mn = 6000-32 000) in good yield. The 1H NMR spectra demonstrated that the polymers have stereoregular structures (cis = 100%). The polymers were proven to take a helical conformation with an excess of one- handed screw sense in CHCl3, which was supported by their intense CD effects and large optical rotations. It was confirmed that the helical structure was stabilized not only by the steric repulsion but also by the intramolecular hydrogen bonds between the pendant groups. CD spectroscopic study showed that the helical structure is more stable than that of the polymers without a branch at the α-position, which allowed the polymers to exist in the helical state in various solvents. The electronic absorption, CD effects, and optical rotations of the polymers closely correlated to the extent of the hydrogen bonding between the pendant amide groups.
- Tabei, Junichi,Nomura, Ryoji,Masuda, Toshio
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- Diastereomeric control of enantioselectivity: Evidence for metal cluster catalysis
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Enantioselective hydrogenation of tiglic acid effected by diastereomers of the general formula [(μ-H)2Ru3(μ3-S)(CO) 7(μ-P-P*)] (P-P* = chiral Walphos diphosphine ligand) strongly supports catalysis by intact Ru
- Abdel-Magied, Ahmed F.,Singh, Amrendra K.,Haukka, Matti,Richmond, Michael G.,Nordlander, Ebbe
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- Palladium nanoparticle-graphene catalysts for asymmetric hydrogenation
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We report for the first time the application of palladium nanoparticle-graphene (Pd/Gn) catalysts in the asymmetric hydrogenation of aliphatic α,β-unsaturated carboxylic acids using cinchonidine as chiral modifier. Pd/Gns were prepared by deposition-preci
- Sz?ri, Korne?l,Puskás, Robert,Sz?ll?si, Gyo?rgy,Bertóti, Imre,Szépv?lgyi, János,Bartók, Mihály
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- Chiral 2-alkylbranched acids, esters and alcohols. Preparation and stereospecific flavour evaluation
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Racemic 2-alkylbranched acids are transformed to diastereomeric derivatives with (S)-2-hydroxy-3-phenylpropionic acid-N-methylamide of (S)-(-)-1-phenylethylamine and separated by liquid chromatography to pure diastereoisomers, which are subsequently hydrolyzed to yield optically pure acids. Enantiomeric alcohols are generated by LiAlH4-reduction of the corresponding acids, esters are synthesized by different methods. The odour impression of the enantiomeric compounds is investigated.
- Rettinger,Burschka,Scheeben,Fuchs,Mosandl
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- Toosendanin relatives, trypanocidal principles from Meliae Cortex
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Africa Trypanosomiasis remains a serious health problem, but the approved drugs for this disease are so few that novel trypanocidal compounds are demanded. In search for trypanocidal principles from medicinal plants, we found MeOH extracts of Meliae Cortex with potent activity through the screening from about 300 kinds of methanolic extract. By bioassay-guided fractionation from this extract through the liquid–liquid partition and subsequent chromatographic technique using silica gel and ODS, finally we disclosed toosendanin (1) and its relatives as active principles. These active congeners showed not only potent trypanocidal activity but also little cytotoxicity to display the excellent selective index. Taking the isolated amount as well as trypanocidal activity into consideration, 1 was disclosed to be the responsible active principle in Meliae Cortex. Additionally, the derivatives of 1 were chemically prepared from 1 and bioactivity of them were also evaluated. Through the comparison with their trypanocidal activity among the isolated relatives and the synthesized derivatives of 1, the epoxide moiety was revealed to be essential for their potent trypanocidal activity. Furthermore, 3-O-acetyl group and 7-hydroxyl group were presumed to be important functional groups and introduction of methylpropionyl group into hemiacetal hydroxy moiety was clarified to enhance their typanocidal activity.
- Mifundu, Michel N.,Murakami, Nobutoshi,Kawano, Tomikazu,Tamura, Satoru
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- Achiral amine additives in the enantioselective hydrogenation of aliphatic α,β-unsaturated acids over cinchonidine-modified Pd/Al 2O3 catalyst
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The effect of the achiral amine additive structure was studied on the enantioselective hydrogenation of (E)-2-methyl-2-butenoic acid and (E)-2-methyl-2-hexenoic acid over Pd/Al2O3 catalyst modified by cinchonidine. It was found that
- Makra, Zsolt,Sz?ll?si, Gy?rgy,Bartók, Mihály
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- Synthesis and evaluation of a new steroidal BINAP type phosphine
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The short and high yielding synthesis of a new cis-configured bissteroidal phosphine 7 is reported. The comparison of these new phosphines as ligands in ruthenium-based hydrogenation catalysts with the previously synthesized diastereomeric trans-configured phosphines 20 shows that the steroid backbone exerts only a minor influence on the enantioselection of the ruthenium catalysts and confirms that the bissteroidal phosphines behave as 'pseudo'-enantiomers in spite of their diastereomeric nature. Evidence is presented that the mode of catalyst preparation, i.e. catalyst structure, is the crucial reaction parameter which mainly determines the enantiomeric excess of the hydrogenation products. (C) 2000 Elsevier Science Ltd.
- Enev,Harre,Nickisch,Schneider,Mohr
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- Eight new diterpenoids and two new nor-diterpenoids from the stems of Croton cascarilloides
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From the stems of Croton cascarilloides, eight new diterpenoids, named crotocascarins A-H (1-8), having a crotofolane skeleton were isolated along with two new nor-diterpenoids (9 and 10), named crotocascarins α and β, derived through rearrangement of the crotofolane skeleton. The structures of these compounds were elucidated by means of extensive one- and two-dimensional NMR spectroscopic analyses. The absolute structures of the diterpene moiety were determined by application of the circular dichroism (CD) rule for the γ-lactone ring. The relative structures of the two crotofolanes (1 and 2) and one rearranged compound (9) were confirmed by X-ray crystallographic analyses. Compounds 1, 2 and 9 possessed 2-methylbutyric acid in their molecules, the absolute configuration of which was found to be 2S by comparison of its HPLC behavior with that of an authentic sample. Therefore, the absolute structures of these crotocascarins (1, 2 and 9) were unambiguously determined. The absolute structures of crotofolanes are reported for the first time in this paper.
- Kawakami, Susumu,Toyoda, Hiroki,Harinantenaina, Liva,Matsunami, Katsuyoshi,Otsuka, Hideaki,Shinzato, Takakazu,Takeda, Yoshio,Kawahata, Masatoshi,Yamaguchi, Kentaro
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- Anti-inflammatory and anti-oxidant potential of the root extract and constituents of doronicum austriacum
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Background: Doronicum austriacum Jacq., Asteraceae, is a plant which is used in traditional alpine medicine. Historical sources describe the medical use of the root, but up until now only a few studies evaluated its pharmacological properties. The evaluation of the dichloromethane extract, and its major compounds for their anti-inflammatory and anti-oxidant potential was performed in macrophages J774A.1 and C6 astrocytes. Nitric oxide (NO) and reactive oxygen species (ROS) release, as well as nitrotyrosine formation, were evaluated. Moreover, in order to evaluate the potential anti-proliferative activity, under the same experimental conditions, 3-(4,5-dimethyltiazol-2yl)-2,5-phenyl-2H-tetrazolium bromide (MTT) assay was also performed. Our results indicate that Doronicum austriacum has a significant effect in inhibiting both pro-inflammatory and pro-oxidative mediators. All isolated compounds were able to significantly inhibit NO and ROS release both in macrophage and in astrocytes cells, even if the effect was more pronounced in macrophage. In articular, among the tested compounds, 6,12-dihydroxy-(?)-2S-tremetone exerted stronger activity. Both extract and single compounds did not affect cellular viability. This study provides evidence for the pharmacological anti-inflammatory and anti-oxidant potential of Doronicum austriacum extract. These effects could be due to the activity of its major constituents and subsequent identification of benzofurans as a promising compound class to combat inflammation and related diseases.
- Marzocco, Stefania,Adesso, Simona,Alilou, Mostafa,Stuppner, Hermann,Schwaiger, Stefan
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- Limonoids from the seeds of a hainan mangrove, xylocarpus granatum
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Ten new limonoids, hainangranatumins A-J (1-10), and 25 known compounds were isolated from seeds of a Chinese mangrove, Xylocarpus granatum, collected on Hainan Island. Hainangranatumins A-E (1-5) and I and J (9 and 10) are 9,10-seco-mexicanolides, whereas hainangranatumin F (6) is a limonoid possessing an 8α,30α-epoxy ring and a C1-C29 oxygen bridge. Hainangranatumin G (7) is a limonoid with a central pyridine ring, and hainangranatumin H (8) is a phragmalin 1,8,9-ortho ester. The relative configurations of hainangranatumins A and B were established by means of single-crystal X-ray diffraction analysis, and their absolute configurations were assigned on the basis of the specific rotation of the free acids obtained from alkaline hydrolysis. This is the first report of X-ray crystallographic structures of 9,10-seco-mexicanolides with a flexible C2-C 30-C8 linkage. Hainangranatumins I and J (9 and 10), unusual 9,10-seco-mexicanolides with a C9-C30 linkage, are proposed to be artifacts derived from hainangranatumin C and xylomexicanin A, respectively.
- Pan, Jian-Yu,Chen, Shi-Lin,Li, Min-Yi,Li, Jun,Yang, Mei-Hua,Wu, Jun
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- Anti-inflammatory components of Chrysanthemum indicum flowers
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One new octulosonic acid derivative, chrysannol A (1), along with 17 known compounds (2-18), were isolated from Chrysanthemum indicum flowers. Their structures were determined from 1D NMR, 2D NMR, HR-ESI-MS spectral data, and comparisons with previous reports. The effects of these compounds on lipopolysaccharide (LPS)-induced nitric oxide (NO) and tumor necrosis factor alpha (TNF-α) production by RAW 264.7 cells were investigated. Compound 8 showed the highest inhibition of NO production of 46.09% at a concentration of 10.0 μM. Compounds 7, 10, 11, and 16 inhibited TNF-α secretion at all concentration tested (0.4, 2.0, and 10.0 μM), with inhibition values ranging from 22.27% to 33.13%. In addition, compound 8 and 9 decrease COX-2 and iNOS protein on Western blot analysis in dose dependent manner.
- Luyen, Bui Thi Thuy,Tai, Bui Huu,Thao, Nguyen Phuong,Cha, Ji Yun,Lee, Hoon Yeon,Lee, Young Mi,Kim, Young Ho
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- Weakly anti-inflammatory limonoids from the seeds of xylocarpus rumphii
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Seven new limonoids, namely, xylorumphiins E-J (1-2 and 4-7) and 2-hydroxyxylorumphiin F (3), along with three known derivatives (8-10), were isolated from the seeds of Xylocarpus rumphii. 2-Hydroxyxylorumphiin F (3) and xylorumphiin I (6) displayed moder
- Sarigaputi, Chanin,Sommit, Damrong,Teerawatananond, Thapong,Pudhom, Khanitha
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- Asymmetric hydrogenation of α,β-unsaturated carboxylic acids in supercritical carbon dioxide
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Hydrogenation of tiglic acid in supercritical CO2 catalyzed by a chiral H8-BINAP-Ru(II) complex proceeds cleanly with cis stereochemistry to afford 2-methylbutanoic acid in up to 89% ee and over 99% yield.
- Xiao, Jianliang,Nefkens, Sylvia C. A.,Jessop, Philip G.,Ikariya, Takao,Noyori, Ryoji
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- Bioactive constituents from chinese natural medicines. XXXI.1 hepatoprotective principles from sinocrassula indica: Structures of sinocrassosides A8, A9, A10, A11, and A12
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The methanolic extract from the whole plant of Sinocrassula indica (Crassulaceae) was found to show hepatoprotective effect on D-galactosamineinduced cytotoxicity in primary cultured mouse hepatocytes. From the methanolic extract, five new acylated flavon
- Ninomiya, Kiyofumi,Morikawa, Toshio,Xie, Haihui,Matsuda, Hisashi,Yoshikawa, Masayuki
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- ASYMMETRIC SYNTHESIS BY CHIRAL RUTHENIUM COMPLEXES. XI. ASYMMETRIC HYDROGENATION OF TIGLIC ACID IN THE PRESENCE OF PHOSPHINE SUBSTITUTED RUTHENIUM CARBONYL CARBOXYLATES
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The enantioface-discriminating hydrogenation of tiglic acid in the presence of (-)-DIOP substituted carbonyl carboxylato complexes of ruthenium has been investigated in order to identify the factors affecting the stereoselectivity of this reaction.The carboxylato ligand present in the catalytic intermediate does not seem to make a significant contribution to the stereoselectivity of this process.The stereoselectivity seems to be associated with the presence of the optically active phosphine.The catalytic system develops during the reaction through intermediates having a higher enantioface-discriminating activity than the initial and the final ruthenium complexes.
- Matteoli, Ugo,Menchi, Gloria,Frediani, Piero,Bianchi, Mario,Piacenti, Franco
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- Optically active alkylvinylpyridines: Synthesis of (±)-(S)-6-(1-methylpropyl)-2-vinylpyridine
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A generalizable procedure for the preparation of optically active 6-alkyl-2-vinylpyridines from chiral 2-alkylpyridines without loss of optical purity is reported.
- Chelucci
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- Anacolosins A-F and Corymbulosins X and Y, Clerodane Diterpenes from Anacolosa clarkii Exhibiting Cytotoxicity toward Pediatric Cancer Cell Lines
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An extract of the plant Anacolosa clarkii was obtained from the NCI Natural Products Repository, and it showed cytotoxic activity toward several types of pediatric solid tumor cell lines. Bioassay-guided fractionation led to the purification of eight new clerodane diterpenes [anacolosins A-F (1-6) and corymbulosins X and Y (7 and 8)] and two known compounds (9 and 10) that contained an isozuelanin skeleton. The structures of the new natural products were determined using 1D and 2D NMR and HRESIMS data, while the relative and absolute configurations of the compounds were assessed using a combination of 1H NMR coupling constant data, ROESY experiments, ECD (electronic circular dichroism) and VCD (vibrational circular dichroism) spectroscopy, chemical methods (including Mosher and 2-naphthacyl esterification), and chiral HPLC analyses. The purified natural products exhibited a range of cytotoxic activities against cell lines representing four pediatric cancer types (i.e., rhabdomyosarcoma, Ewing sarcoma, medulloblastoma, and hepatoblastoma) with total growth inhibitory (TGI) values in the range 0.2-4.1 μM. The rhabdomyosarcoma and medulloblastoma cell lines showed higher sensitivity to compounds 1-4, which are the first compounds reported to contain an isozuelanin skeleton and feature keto carbonyl groups at the C-6 positions. In contrast, the hepatoblastoma cell line was modestly more sensitive to 7-10, which contained a C-6 hydroxy group moiety.
- Cai, Shengxin,Risinger, April L.,Petersen, Cora L.,Grkovic, Tanja,O'Keefe, Barry R.,Mooberry, Susan L.,Cichewicz, Robert H.
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- Synthesis, isolation, stereostructure and cytotoxicity of paclitaxel analogs from cephalomannine
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Four paclitaxel derivatives were afforded by preparative HPLC separation of two pairs of diastereoisomers, which were obtained by catalytic hydrogenation and epoxidation of the C-13 side-chain double bond of cephalomannine, a naturally occurring paclitaxel analog. The four paclitaxel derivatives were analyzed using NMR, CD spectroscopy, and side-chain hydrolysis in order to measure their optical rotations and GC characteristics. In this way, the stereoconfigurations of the products were determined. Evaluation of the compounds' activity indicated that they had differing cytotoxic activities: compound 5 had superior activity in BCG-823 tumor cells compared to paclitaxel, while compound 7 had superior activity in HCT-8 and A549 tumor cells compared to paclitaxel. These results indicate that the stereoconfiguration of the paclitaxel N-acyl side chain has a significant impact on its activity.
- Gao, Feng,Wang, Dan,Huang, Xing
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- Movement to the Clinic of Soluble Epoxide Hydrolase Inhibitor EC5026 as an Analgesic for Neuropathic Pain and for Use as a Nonaddictive Opioid Alternative
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This report describes the development of an orally active analgesic that resolves inflammation and neuropathic pain without the addictive potential of opioids. EC5026 acts on the cytochrome P450 branch of the arachidonate cascade to stabilize epoxides of polyunsaturated fatty acids (EpFA), which are natural mediators that reduce pain, resolve inflammation, and maintain normal blood pressure. EC5026 is a slow-tight binding transition-state mimic that inhibits the soluble epoxide hydrolase (sEH) at picomolar concentrations. The sEH rapidly degrades EpFA; thus, inhibiting sEH increases EpFA in vivo and confers beneficial effects. This mechanism addresses disease states by shifting endoplasmic reticulum stress from promoting cellular senescence and inflammation toward cell survival and homeostasis. We describe the synthesis and optimization of EC5026 and its development through human Phase 1a trials with no drug-related adverse events. Additionally, we outline fundamental work leading to discovery of the analgesic and inflammation-resolving CYP450 branch of the arachidonate cascade.
- Hammock, Bruce D.,McReynolds, Cindy B.,Wagner, Karen,Buckpitt, Alan,Cortes-Puch, Irene,Croston, Glenn,Lee, Kin Sing Stephen,Yang, Jun,Schmidt, William K.,Hwang, Sung Hee
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- Concerted action of P450 plus helper protein to form the amino-hydroxy-piperidone moiety of the potent protease inhibitor crocapeptin
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The crocapeptins are described here as cyclic depsipeptides, isolated from cultures of the myxobacterium Chondromyces crocatus. Structure elucidation of the compounds revealed a cyanopeptolin-like skeleton, containing the characteristic amino-hydroxy-piperidone (Ahp)-heterocycle. Like the cyanopeptolins, the myxobacterial crocapeptins proved to be serine protease inhibitors. The nonribosomal origin of the peptide was confirmed by mutagenesis experiments, and the biosynthesis gene cluster was sequenced. It could be shown that the Ahp-heterocycle originates from a proline residue in the precursor molecule precrocapeptin, which is converted to crocapeptin by the tailoring enzymes CpnE and CpnF. Conversion of precrocapeptin isolated from a cpnF mutant into crocapeptin was achieved using recombinant CpnF, a cytochrome P450 enzyme responsible for hydroxylation of the proline residue in precrocapeptin. Addition of protein CpnE resulted in strongly increased conversion rates toward Ahp containing product. A mutant with 10-fold increased production of crocapeptin A was created through insertion of the Pnpt-promotor in front of the NRPS gene.
- Viehrig, Konrad,Surup, Frank,Harmrolfs, Kirsten,Jansen, Rolf,Kunze, Brigitte,Mueller, Rolf
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- The origin of the enantioselection in the ruthenium(II)-catalyzed asymmetric hydrogenation of α,β-unsaturated carboxylic acid
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Using our chiral atropisomeric bisphosphines ruthenium(II) complexes, asymmetric hydrogenations of tiglic acid and its isomer were carried out. A possible enantioselective mechanism was considered on the basis of their different results on hydrogenation pressure effects.
- Yoshikawa,Murata,Yamamoto,Inoguchi,Achiwa
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- New synthesis of optically pure α-branched aliphatic carboxylic acids from amidines
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A range of amidines containing amino acid function was easily prepared in good yields from simple starting materials. Starting from L- or D- proline and linear symmetric ketones, optically pure amidines were prepared. Hydrolysis of these amidines afforded optically pure branched aliphatic carboxylic acids.
- Cassani, Flavio,Celentano, Giuseppe,Erba, Emanuela,Pocar, Donato
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- Cytotoxic Nitrogenated Azaphilones from the Deep-Sea-Derived Fungus Chaetomium globosum MP4-S01-7
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Eight new nitrogenated azaphilones (1-8) and two known compounds (chaetoviridin A and chaetoviridin E, 9, 10) were isolated from the culture of the deep-sea-derived fungus Chaetomium globosum MP4-S01-7. The absolute configurations of new compounds were elucidated by HSQC-HECADE NMR data, J-based configuration analysis, and modified Mosher's method and finally verified by comparison of recorded and computed NMR chemical shifts from quantum chemical calculations coupled with a statistical procedure (DP4+). All of the compounds were evaluated for their in vitro cytotoxicities against the gastric cancer cell lines MGC803 and AGS, and most of them showed significant inhibition on cancer cell viability at 10 μM. Among them, compounds 1, 2, and 5 exerted the most potent cytotoxic activities, with IC50 values less than 1 μM. Further studies showed that compound 2 inhibited cell cycle progression, and both compounds 1 and 2 induced apoptosis of gastric cancer cells in a concentration-dependent manner.
- Chen, Jing,Cheng, Gang,Cheng, Xiang-Dong,Liao, Yan-Yan,Qin, Jiang-Jiang,Shao, Zongze,Wang, Weiyi,Yang, Jing
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- General synthesis of novel chiral ruthenium catalysts and their use in asymmetric hydrogenation
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The first general synthesis of mononuclear hexacoordinate chiral ruthenium-complexes is presented. Four chiral ruthenium(II)(2-methylallyl)2 complexes containing Diop, Chiraphos, Norphos, and Binap were prepared in 50-71% yield under mild conditions, and were found to be effective for asymmetric hydrogenation of unsaturated carboxylic acids to give the corresponding saturated derivatives attaining 90% optical purity.
- Genet,Mallart,Pinel,Juge,Laffitte
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- Simple azo dyes provide access to versatile chiroptical switches
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Azo dyes have played an important role in the development of the chemical industry for 150 years. The azo-core of these dyes can undergo trans to cis photoisomerization, which allows azobenzene derivatives to act as light triggered molecular switches. Here, we showed that simple derivatization of Sudan I provides access to chiroptical molecular switches, and that the properties of these switches can be readily tuned by modification of the molecular structure. The synthesis, characterization, photoisomerization, thermal stability, chiral HPLC resolution, determination of absolute configuration and chiroptical properties of chiroptical switches based on Sudan I are reported. ortho-difluorinated Sudan I derivatives have improved thermal stabilities and switching properties compared to switches based on Sudan I itself. Transfer of stereochemical information from a non-racemic chiral unit to the π-conjugated system of the dye and exciton-coupled circular dichroism are both observed. The chiral unit influences the geometry and hence the spectra of cis and trans-isomers differently, which is the mechanistic basis of chiroptical switching. The azo-core of dyes can undergo trans to cis photoisomerization, which allows azobenzene derivatives to act as light triggered molecular switches. Simple derivatization of Sudan I using a chiral auxiliary provides access to chiroptical molecular switches. The properties of these switches can be readily tuned by modification of the molecular structure.
- Anger, Emmanuel,Fletcher, Stephen P.
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- Moluccensins A-G, phragmalins with a conjugated C-30 carbonyl group from a krishna mangrove, Xylocarpus moluccensis
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Seven new phragmalins with a C-30 carbonyl moiety, named moluccensins A-G (1-7), among which moluccensins A-F, possessing a Δ8,14 double bond, and moluccensin G (7), containing conjugated Δ8,9 and Δ14,15 double bonds, were
- Li, Min-Yi,Yang, Sheng-Xin,Pan, Jian-Yu,Xiao, Qiang,Satyanandamurty, Tirumani,Wu, Jun
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- Hydrogenation of (E)-2-methyl-2-butenoic acid over cinchona-modified Pd catalyst in the presence of achiral amines: Solvent and modifier effect
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The effect of the solvent, modifier structure and concentration on the enantioselective hydrogenation of (E)-2-methyl-2-butenoic acid over Pd/Al 2O3 modified by cinchona alkaloids was influenced by the addition of achiral amines to t
- Makra, Zsolt,Szollosi, Gy?rgy
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- Limonoids and tirucallane derivatives from the seeds of a krishna mangrove, xylocarpus moluccensis
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Six new phragmalins, moluccensins H-M (1-6), two new andirobin-type limonoids, moluccensins N and O (7, 8), and two new tirucallane derivatives, moluccensins P and Q (9, 10), were isolated from seeds of an Indian mangrove, Xylocarpus moluccensis, together with the known compound 3β,22S- dihydroxytirucalla-7,24-dien-23-one. The structures of these compounds were established on the basis of spectroscopic data. Moluccensins H-L were phragmalins with a C-30 carbonyl group, and moluccensin M was a unique ring-D-opened 16-norphragmalin. Moluccensins H-J possess conjugated Δ8,9 and Δ14,15 double bonds, moluccensins K and L contain a Δ8,14 double bond, and moluccensin M has a characteristic C15-C30 linked five-membered lactone ring. Moluccensins H and I showed moderate insecticidal activity against the fifth instar larvae of Brontispa longissima (Gestro) at a concentration of 100 mg/L.
- Wu, Jun,Yang, Sheng-Xin,Li, Min-Yi,Feng, Gang,Pan, Jian-Yu,Xiao, Qiang,Sinkkonen, Jari,Satyanandamurty, Tirumani
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- A crotofolane-type diterpenoid and a rearranged nor-crotofolane-type diterpenoid with a new skeleton from the stems of Croton cascarilloides
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From the stems of Croton cascarilloides collected in the Okinawa Islands, a structurally rare crotofolane-type diterpenoid (1) and a rearranged nor-crotofalane, a new skeletal diterpenoid (2) were isolated. The structures were determined by X-ray crystallographic analyses, establishing their absolute stereostructures for the first time. Compound 2 was probably biosynthesized from 1 through several steps, such as decarboxylation, oxidation, C-C bond migration.
- Kawakami, Susumu,Matsunami, Katsuyoshi,Otsuka, Hideaki,Shinzato, Takakazu,Takeda, Yoshio,Kawahata, Masatoshi,Yamaguchi, Kentaro
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- Structural insights into the catalytic mechanism of lovastatin hydrolase
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The lovastatin hydrolase PcEST from the fungus Penicillium chrysogenum exhibits enormous potential for industrial-scale applications in single-step production of monacolin J, the key precursor for synthesis of the cholesterol-lowering drug simvastatin. This enzyme specifically and efficiently catalyzes the conversion of lovastatin to monacolin J but cannot hydrolyze simvastatin. Understanding the catalytic mechanism and the structure-function relationship of PcEST is therefore important for further lovastatin hydrolase screening, engineering, and commercial applications. Here, we solved four X-ray crystal structures, including apo PcEST (2.3 ?), PcEST in complex with monacolin J (2.48 ?), PcEST complexed with the substrate analog simvastatin (2.4 ?), and an inactivated PcEST variant (S57A) with the lovastatin substrate (2.3 ?). Structure-based biochemical analyses and mutagenesis assays revealed that the Ser57 (nucleophile)-Tyr170 (general base)-Lys60 (general acid) catalytic triad, the hydrogen-bond network (Trp344 and Tyr127) around the active site, and the specific substrate-binding tunnel together determine efficient and specific lovastatin hydrolysis by PcEST. Moreover, steric effects on nucleophilic attack caused by the 2',2-dimethybutyryl group of simvastatin resulted in no activity of PcEST on simvastatin.Onthe basis of structural comparisons, we propose several indicators to define lovastatin esterases. Furthermore, using structure-guided enzyme engineering, we developed a PcEST variant, D106A, having improved solubility and thermostability, suggesting a promising application of this variant in industrial processes. To our knowledge, this is the first report describing the mechanism and structure-function relationship of lovastatin hydrolase and providing insights that may guide rapid screening and engineering of additional lovastatin esterase variants.
- Liang, Yajing,Lu, Xuefeng
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- Enantioselective Catalytic Transfer Hydrogenation of α,β-Unsaturated Carboxylic Acids with Formates Catalyzed by Novel Ruthenium Phosphine Complexes
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Hydrogen transfer from the formic acid/triethylamine (5:2) azeotrope to α,β-unsaturated carboxylic acids is effectively catalyzed by ruthenium complexes of general formula 3-C3H5)(diphosphine).If a chiral diphosphine is employed, the saturated acids are obtained in up to 93percent ee, the most active and selective catalyst being formed with BINAP.
- Brown, John M.,Brunner, Henri,Leitner, Walter,Rose, Michael
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- Convenient enzymatic resolution of (R,S)-2-methylbutyric acid catalyzed by immobilized lipases
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The application of several immobilized lipases has been explored in the enantioselective esterification of (R,S)-2-methylbutyric acid, an insect pheromone precursor. With the use of Candida antarctica B, using hexane as solvent, (R)-pentyl 2-methylbutyrat
- Mittersteiner, Mateus,Linshalm, Bruna Luiza,Vieira, Ana Paula Furlan,Brondani, Patrícia Bulegon,Scharf, Dilamara Riva,de Jesus, Paulo Cesar
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- Granatumins A-G, limonoids from the seeds of a Krishna mangrove, Xylocarpus granatum
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Seven new limonoids (1-7), named granatumins A-G, were isolated from seeds of an Indian mangrove (Xylocarpus granatum) collected from the wetlands of Krishna estuary, Andhra Pradesh. The known compounds khayasin T, tigloylseneganolide A, 6-deoxyswietenine
- Li, Min-Yi,Yang, Xiao-Bo,Pan, Jian-Yu,Feng, Gang,Xiao, Qiang,Sinkkonen, Jari,Satyanandamurty, Tirumani,Wu, Jun
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- Isolation, absolute configurations and bioactivities of pestaphilones A–I: Undescribed methylated side chain containing-azaphilones from Pestalotiopsis oxyanthi
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Nine undescribed side chain containing azaphilones, pestaphilones A–I, were isolated from the Anoectochilus roxburghii endophytic fungus Pestalotiopsis oxyanthi. The structures of these isolates were identified by spectroscopic data, electronic circular dichroism (ECD) calculations and comparisons, quantum-chemical 13C NMR calculations with DP4+ probability analysis, Rh2(OCOCF3)4-induced ECD, acetonide formation, selective oxidation reaction and X-ray crystallographic data. Structurally, pestaphilones A–I were the first azaphilones characteristically formed via a methyl group at C-9 in the C7 side chain. More importantly, a selective oxidation reaction was firstly set up to resolve the absolute configuration of flexible side chain containing azaphilones, and an acetonide formation based Rh2(OCOCF3)4-induced ECD experiment was performed to identify the configurations of the oxygenated pyranoquinone core in the azaphilones. In bioassay, pestaphilones A–F displayed potential immunosuppressive activity in concanavalin A (Con A)-induced T lymphocyte proliferation, with IC50 values ranging from (9.36 ± 1.14) μM to (35.21 ± 3.25) μM.
- Chen, Xia,Deng, Mengyi,Gu, Lianghu,Qi, Changxing,Qiao, Yuben,Shi, Zhengyi,Wang, Jianping,Zhang, Yonghui,Zhu, Hucheng
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- Bioactive constituents from the leaves of Croton tiglium
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Fifteen compounds, including five new phorbol esters (1-5) and ten known metabolites were isolated from the leaves of Croton tiglium. The structures of new compounds 1-5 were determined by comprehensive analysis of the HRESIMS, IR, 1D and 2D NMR spectral
- Duan, Li-Kun,Feng, Jin-E.,He, Hong-Ping,Huang, Chun-Qiu,Jiang, Zhi-Yong,Li, Xiao-Fei,Li, Yuan,Liu, Chun-Jiang,Shi, Sheng-Li,Zuo, Ai-Xue
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- Calyhedins I–VI: Resin glycosides from the rhizomes of Calystegia hederacea
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Six previously undescribed resin glycosides, calyhedins I–VI, were isolated from the rhizomes of Calystegia hederacea Wall., which are the first genuine resin glycosides isolated from C. hederacea. The structures of calyhedins I–VI were determined based on spectroscopic data and chemical evidence. All the compounds have macrolactone structures (jalapins), and their sugar moieties were partially acylated by five organic acids. Calyhedins I, II–V, and VI have 27-, 28-, and 23-membered rings, respectively, and calyhedins IV–VI are the first jalapins with a sugar chain consisting of seven monosaccharides. Additionally, the cytotoxic activity of calyhedins II and III toward HL-60 human promyelocytic leukemia cells was evaluated. Both compounds demonstrated almost the same activity as the positive control, cisplatin.
- Kinjo, Junei,Matsubara, Souta,Nohara, Toshihiro,Okawa, Masafumi,Ono, Masateru,Shimohara, Takaaki,Tsuchihashi, Ryota,Yasuda, Shin,Yoshimitsu, Hitoshi,Yuhara, Nobuyoshi,Zhou, Jian-Rong
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- Enantioselective Enzymatic Reduction of Acrylic Acids
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An ene-reductase (ERED 36) with broad substrate specificity was identified, and optimization studies led to the development of an enzymatic protocol for the reduction of α,β-unsaturated acids under mild, aqueous conditions. The substrate scope includes aromatic- A nd aliphatic-substituted acrylic acids, as well as cyclic α,β-substituted acrylic acids, yielding chiral α-substituted acids with exquisite levels of enantioselectivity (>99% ee).
- An, Chihui,Shaw, Megan H.,Tharp, Annika,Verma, Deeptak,Li, Hongming,Wang, Heather,Wang, Xiao
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supporting information
p. 8320 - 8325
(2020/11/03)
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- Total synthesis of (S)-(+)-ent-phomapyrones B and surugapyrone B
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Phomapyrone B (1), the 2-pyrones isolated from the phytopathogenic fungus Leptosphaeria maculans, has been synthesized as the enantiomeric form starting from (S)-2-methylbutanol (4). Surugapyrone B (3) isolated from Streptmyces sp. USF-6280 as an antioxidant has also been synthesized as a natural form. The absolute configuration of phomapyrone B (1) was estimated to be the (R)-form and that of surugapyrone B (3) being the (S)-form. A series of 2-pyrone derivatives 17 have been synthesized through the established procedure and their DPPH radical-scavenging activities have also been evaluated.
- Ohmukai, Hiroaki,Sugiyama, Yasumasa,Hirota, Akira,Kirihata, Mitsunori,Tanimori, Shinji
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p. 1090 - 1100
(2019/12/24)
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- Electrocatalytic asymmetric hydrogenation of α,β-unsaturated acids in a PEM reactor with cinchona-modified palladium catalysts
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We have developed an electrocatalytic asymmetric hydrogenation reaction using a proton-exchange membrane (PEM) reactor that employs a polymer electrolyte fuel cell and industrial electrolysis technologies. Reasonable enantioselectivities and excellent current efficiencies were obtained in the asymmetric hydrogenation of α-phenylcinnamic acid under mild conditions without adding a supporting electrolyte. The current density was crucial to achieving the improved results observed.
- Atobe, Mahito,Fukazawa, Atsushi,Hashimoto, Yasushi,Sato, Yasushi,Tanaka, Kenta
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- Effect of particle restructuring during reduction processes over polydopamine-supported Pd nanoparticles
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The effect of catalyst restructuring on the polydopamine-supported Pd catalyzed transfer hydrogenation of ethyl 4-nitrobenzoate and the catalytic hydrogenation of (E)-2-methyl-2-butenoic acid is reported. Transmission electron microscopy investigation of different catalyst pre-treatment and reaction conditions revealed high catalytic activity in both reactions unless drastic aggregation of the active metal occurred. In the transfer hydrogenation reaction aggregation was primarily dependent on the H-source used, while in the catalytic hydrogenation additives in combination with the reductive environment led to extensive Pd aggregation and thus decreased catalytic activity. The enantioselective hydrogenation of (E)-2-methyl-2-butenoic acid showed increased enantioselectivity and decreased conversion with increased particle size.
- Gazdag, Tamás,Baróthi, ádám,Juhász, Koppány Levente,Kunfi, Attila,Németh, Péter,Sápi, András,Kukovecz, ákos,Kónya, Zoltán,Szori, Kornél,London, Gábor
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p. 484 - 491
(2018/12/13)
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- Hydrogen/deuterium isotopic labeling study of enantioselective hydrogenation of (E)-2-Methyl-2-butenoic acid over a cinchonidine-modified Pd/C catalyst
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In the enantioselecitve hydrogenation of (E)-2-methyl-2butenoic acid (1) over a cinchonidine-modified Pd/C catalyst, the addition of hydrogen preferentially proceeds from the Re-Si enantioface of the C=C double bond of 1 to yield (S)-2methylbutanoic acid ((S)-3). Double bond migration of 1 takes place under the reaction conditions and is followed by immediate hydrogenation to yield 3 in a poor enantiomeric purity. Deuterium labeling experiments at 0.1 MPa and 1.9 MPa of D2verified the previous assumption of competitive double bond migration. The combination of isotopic labeling experiments and chiral analysis revealed that the double bond migration of 1 proceeds with the same enantiofacial differentiation as the hydrogenation of 1. Thus, interaction of 1 with cinchonidine adsorbed on the Pd surface may control the configuration of the double bond migration and the hydrogenation.
- Sugimura, Takashi,Tomatsuri, Satoshi,Fujita, Morifumi,Okamoto, Yasuaki
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p. 1737 - 1742
(2019/10/01)
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- Chemoenzymatic Cascade Synthesis of Optically Pure Alkanoic Acids by Using Engineered Arylmalonate Decarboxylase Variants
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Arylmalonate decarboxylase (AMDase) catalyzes the cofactor-free asymmetric decarboxylation of prochiral arylmalonic acids and produces the corresponding monoacids with rigorous R selectivity. Alteration of catalytic cysteine residues and of the hydrophobic environment in the active site by protein engineering has previously resulted in the generation of variants with opposite enantioselectivity and improved catalytic performance. The substrate spectrum of AMDase allows it to catalyze the asymmetric decarboxylation of small methylvinylmalonic acid derivatives, implying the possibility to produce short-chain 2-methylalkanoic acids with high optical purity after reduction of the nonactivated C=C double bond. Use of diimide as the reductant proved to be a simple strategy to avoid racemization of the stereocenter during reduction. The developed chemoenzymatic sequential cascade with use of R- and S-selective AMDase variants produced optically pure short-chain 2-methylalkanoic acids in moderate to full conversion and gave both enantiomers in excellent enantiopurity (up to 83 % isolated yield and 98 % ee).
- Enoki, Junichi,Mügge, Carolin,Tischler, Dirk,Miyamoto, Kenji,Kourist, Robert
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p. 5071 - 5076
(2019/03/17)
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- dM-Dim for carboxylic acid protection
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The 1,3-dithian-2-yl-methyl (Dim) and its analogous groups including dimethyl-Dim (dM-Dim) can provide a new dimension of orthogonality for carboxylic acid protection. They can be deprotected under nearly neutral oxidative conditions. In this paper, the protection of carboxylic acid with dM-Dim, deprotection of dM-Dim ester with sodium periodate, stability of dM-Dim protected carboxylic acid under acidic and basic conditions, and selective deprotection of dM-Dim protected carboxylic acids in the presence of tertiary butyl and methyl esters are presented.
- Shahsavari, Shahien,Wigstrom, Travis,Gooding, James,McNamara, Chase,Fang, Shiyue
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supporting information
p. 1763 - 1766
(2018/04/06)
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- Novel iridium complex of spirophosphine-carboxylic acid, preparation method and application thereof
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The invention relates to an iridium complex of spirophosphine-carboxylic acid, a preparation method and application thereof. The iridium complex of spirophosphine-carboxylic acid is a compound with a structure shown as formula (I), wherein n=0-3; and the values of R1, R2, R3, R4, R5, R6 and R7 are defined as claim 1. Substituted 7-carboxyl-7'-diarylphosphino-1, 1'-spirobiindane is taken as the ligand to from carboxylic acid anion under the action of alkali, and then complexation with an iridium precursor is carried out to obtain different iridium/spirophosphine-carboxylic acid complexes. The iridium complex of spirophosphine-carboxylic acid provided by the invention can catalyze the asymmetric hydrogenation reaction of a variety of unsaturated carboxylic acids, and show high activity and enantioselectivity, thus having good industrialization prospects. (formula (I)).
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Paragraph 0081-0085
(2017/05/20)
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- Neutral iridium catalysts with chiral phosphine-carboxy ligands for asymmetric hydrogenation of unsaturated carboxylic acids
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We developed neutral iridium catalysts with chiral spiro phosphine-carboxy ligands (SpiroCAP) for asymmetric hydrogenation of unsaturated carboxylic acids. Different from the cationic Crabtree-type catalysts, the iridium catalysts with chiral spiro phosphine-carboxy ligands are neutral and do not require the use of a tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (BArF?) counterion, which is necessary for stabilizing cationic Crabtree-type catalysts. Another advantage of the neutral iridium catalysts is that they have high stability and have a long lifetime in air. The new iridium catalysts with chiral spiro phosphine-carboxy ligands exhibit unprecedented high enantioselectivity (up to 99.4% ee) in the asymmetric hydrogenations of various unsaturated carboxylic acids, particularly for 3-alkyl-3-methylenepropionic acids, which are challenging substrates for other chiral catalysts.
- Yang, Shuang,Che, Wen,Wu, Hui-Ling,Zhu, Shou-Fei,Zhou, Qi-Lin
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p. 1977 - 1980
(2017/03/09)
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- Three new resin glycosides compounds from Argyreia acuta and their α-glucosidase inhibitory activity
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Three new phenolic compounds, acutacoside C (1), acutacoside D (2) and acutacoside E (3) were isolated from the aerial part of Argyreia acuta. The oligosaccharide chain was composed of two glucoses and three rhamnoses, and the aglycone was (11S)-hydroxyhexadecanoic acid (jalapinolic acid). The core of the three compounds was operculinic acid B, which was rare in resin glycosides. Their structures were established by a combination of spectroscopic and chemical methods. Compounds 1-3 have been evaluated for inhibitory activity against α-glucosidase, which all showed weak inhibitory activities.
- Wang, Li,Yan, You-Shao,Cui, Hong-Hua,Yin, Yong-Qin,Pan, Jie-Tao,Yu, Bang-Wei
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supporting information
p. 537 - 542
(2017/01/13)
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- Asymmetric Hydrogenation of α-Substituted Acrylic Acids Catalyzed by a Ruthenocenyl Phosphino-oxazoline-Ruthenium Complex
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Asymmetric hydrogenation of various α-substituted acrylic acids was carried out using RuPHOX-Ru as a chiral catalyst under 5 bar H2, affording the corresponding chiral α-substituted propanic acids in up to 99% yield and 99.9% ee. The reaction could be performed on a gram-scale with a relatively low catalyst loading (up to 5000 S/C), and the resulting product (97%, 99.3% ee) can be used as a key intermediate to construct bioactive chiral molecules. The asymmetric protocol was successfully applied to an asymmetric synthesis of dihydroartemisinic acid, a key intermediate required for the industrial synthesis of the antimalarial drug artemisinin.
- Li, Jing,Shen, Jiefeng,Xia, Chao,Wang, Yanzhao,Liu, Delong,Zhang, Wanbin
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supporting information
p. 2122 - 2125
(2016/06/01)
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- Phenolics from durian exert pronounced NO inhibitory and antioxidant activities
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Durian, known as the king of fruits, is native to Southeast Asia and popular in many countries. Bioactivity-guided fractionation of the peel of durian was applied to determine its bioactive constituents. Four novel phenolics, along with 16 known, were pur
- Feng, Jianying,Wang, Yihai,Yi, Xiaomin,Yang, Weimin,He, Xiangjiu
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p. 4273 - 4279
(2016/06/15)
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- Two pentasaccharide resin glycosides from Argyreia acuta
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Two new compounds of acutacosides 1 and 2, pentasaccharide resin glycosides were isolated from the aerial parts of Argyreia acuta. The core of the two compounds was operculinic acid A, and they were esterfied at the same position, just one substituent group was linked at C-2 of Rha. The absolute configuration of the aglycone in the two compounds was established by Mosher's method, which was (11S)-hydroxyhexadecanoic acid (jalapinolic acid). Their structures were established by a combination of spectroscopic and chemical methods.
- Yin, Yong-Qin,Pan, Jie-Tao,Yu, Bang-Wei,Cui, Hong-Hua,Yan, You-Shao,Chen, Yan-Fen
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- Structural and functional analysis of the loading acyltransferase from avermectin modular polyketide synthase
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The loading acyltransferase (AT) domains of modular polyketide synthases (PKSs) control the choice of starter units incorporated into polyketides and are therefore attractive targets for the engineering of modular PKSs. Here, we report the structural and biochemical characterizations of the loading AT from avermectin modular PKS, which accepts more than 40 carboxylic acids as alternative starter units for the biosynthesis of a series of congeners. This first structural analysis of loading ATs from modular PKSs revealed the molecular basis for the relaxed substrate specificity. Residues important for substrate binding and discrimination were predicted by modeling a substrate into the active site. A mutant with altered specificity toward a panel of synthetic substrate mimics was generated by site-directed mutagenesis of the active site residues. The hydrolysis of the N-acetylcysteamine thioesters of racemic 2-methylbutyric acid confirmed the stereospecificity of the avermectin loading AT for an S configuration at the C-2 position of the substrate. Together, these results set the stage for region-specific modification of polyketides through active site engineering of loading AT domains of modular PKSs.
- Wang, Fen,Wang, Yanjie,Ji, Junjie,Zhou, Zhan,Yu, Jingkai,Zhu, Hua,Su, Zhiguo,Zhang, Lixin,Zheng, Jianting
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p. 1017 - 1025
(2015/07/27)
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- Jalapinoside, a macrocyclic bisdesmoside from the resin glycosides of ipomea purga, as a modulator of multidrug resistance in human cancer cells
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The first macrocyclic bisdesmoside resin glycoside, jalapinoside (4), was purified by preparative-scale recycling HPLC from the MeOH-soluble extracts of Ipomoea purga roots, the officinal jalap. Purgic acid C (3), a new glycosidic acid of ipurolic acid, was identified as 3-O-β-d-quinovopyranoside, 11-O-β-d-quinovopyranosyl-(1→2)-O-β-d-glucopyranosyl-(1→3)-O-[β-d-fucopyranosyl-(1→4)]-O-α-l-rhamnopyranosyl-(1→2)-O-β-d-glucopyranosyl-(1→2)-O-β-d-quinovopyranoside (3S,11S)-dihydroxytetradecanoic acid. The acylating residues of this core were acetic, (+)-(2S)-methylbutanoic, and dodecanoic acids. The site of lactonization was defined as C-3 of the second saccharide moiety. Reversal of multidrug resistance by this noncytotoxic compound was evaluated in vinblastine-resistant human breast carcinoma cells.
- Bautista, Elihü,Fragoso-Serrano, Mabel,Pereda-Miranda, Rogelio
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p. 168 - 172
(2015/02/05)
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- Batatins VIII-XI, glycolipid ester-type dimers from ipomoea batatas
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Sweet potato (Ipomoea batatas) is native to the tropics of Central and South America, where many varieties have been consumed for more that 5000 years. In developing countries, this crop is a recognized effective food for fighting malnutrition. Purification of the minor lipophilic glicolipids found in the n-hexane-soluble resin glycosides from the white-skinned variety was performed by preparative-scale recycling HPLC. Application of column overload, peak shaving, heart cutting, and recycling techniques permitted the purification of four new oligosaccharide ester-type dimer derivatives of jalapinolic acid, batatins VIII-XI (1-4). The structural characterization of these complex lipo-oligosaccharides was performed through NMR spectroscopy and MS, indicating that batatins VIII-XI (1-4) possess an oligomeric structure consisting of two pentasaccharide units of the known simonic acid B.
- Rosas-Ramírez, Daniel,Pereda-Miranda, Rogelio
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- Enantioselective hydrogenation of α,β-unsaturated carboxylic acid over cinchonidine-modified Pd nanoparticles confined in carbon nanotubes
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We report the enantioselective hydrogenation of α,β-unsaturated acid catalyzed by Pd nanoparticles in carbon nanotubes (CNTs) taking the advantage of the channels as nanoreactors. The Pd nanocatalyst inside the channels of CNTs shows higher activity and e
- Guan, Zaihong,Lu, Shengmei,Li, Can
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- Application of acyclic chiral auxiliaries on alkylation reactions
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The application in alkylation reactions of an acyclic chiral auxiliary is described. The synthesis is straightforward from a chiral primary amine and a double acylation. A characteristic of this auxiliary is its modular design formed by an achiral part (acyl) and a chiral component (primary amine) so it can be tuned for different reactions without difficulty. The alkylation proceeds with excellent diastereoselectivity because the conformational flexibility of the enolate is restricted by the formation of a chelate and the allylic 1,3-strain.
- Gardu?o-Castro, Monserrat H.,Hernández-Rodríguez, Marcos
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supporting information
p. 193 - 196
(2014/01/06)
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- Enantioselective hydrogenation of α,β-unsaturated carboxylic acids on Pd nanocubes
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Pd nanocubes of 6-19 nm in size were synthesized using a seeded growth method and examined for enantioselective hydrogenation of α,β- unsaturated carboxylic acids. It was found that the Pd nanocubes had two types of active sites on the planes and at the edges, respectively. Small nanocubes having a higher edge/plane ratio were more active in enantioselective hydrogenation of α,β-unsaturated carboxylic acids, but afforded a lower enantioselectivity because their sharp edges could not offer stable adsorption of the chiral modifier and the reaction intermediates. In contrast, large nanocubes with a higher fraction of flat planes provided a higher enantioselectivity but a much lower activity.
- Chen, Chunhui,Zhan, Ensheng,Ta, Na,Li, Yong,Shen, Wenjie
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p. 2620 - 2626
(2013/09/24)
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- Memory of chirality in rebound cyclizations of α-amide radicals
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Reduction of (S)-N-(2-bromoallyl)-N-(tert-butyl)-2-methyl-3- phenylpropanamide with tributyltin hydride provides (3S,4S)-3-benzyl-1-(tert- butyl)-3,4-dimethylpyrrolidin-2-one with about 80% retention of chirality at the stereocenter adjacent to the amide carbonyl group. This memory of chirality is suggested to occur by transfer of chirality from a stereocenter to an axis, then from the axis back to a new stereocenter.
- Sasmal, Aniruddha,Taniguchi, Tsuyoshi,Wipf, Peter,Curran, Dennis P.
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supporting information
p. 1 - 5
(2013/03/13)
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- Metal-free, hydroacylation of CC and NN bonds via aerobic C-H activation of aldehydes, and reaction of the products thereof
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In this report, a thorough evaluation of the use of aerobically initiated, metal-free hydroacylation of various CC and NN acceptor molecules with a wide range of aldehydes is presented. The aerobic-activation conditions that have been developed are in sharp contrast to previous conditions for hydroacylation, which tend to use transition metals, peroxides that require thermal or photochemical degradation, or N-heterocyclic carbenes. The mildness of the conditions enables a number of reactions involving sensitive reaction partners and, perhaps most significantly, allows for α-functionalised chiral aldehydes to undergo radical-based hydroacylation with complete retention of optical purity. We also demonstrate how the resulting hydroacylation products can be transformed into other useful intermediates, such as γ-keto- sulfonamides, sultams, sultones, cyclic N-sulfonyl imines and amides.
- Chudasama, Vijay,Akhbar, Ahmed R.,Bahou, Karim A.,Fitzmaurice, Richard J.,Caddick, Stephen
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p. 7301 - 7317
(2013/10/22)
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- Pentasaccharide resin glycosides from Ipomoea cairica and their cytotoxic activities
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Six partially acylated pentasaccharide resin glycosides, cairicosides A-F, were isolated from the aerial parts of Ipomoea cairica. These compounds were characterized as a group of macrolactones of simonic acid A, partially acylated with different organic acids. The lactonization site of 11S-hydroxyhexadecanoic acid (jalapinolic acid) was bound to the second saccharide moiety at C-3 in cairicosides A-E, while at C-2 in cairicoside F. Structures were established by spectroscopic and chemical methods. Compounds cairicosides A-E exhibited moderate cytotoxicity against a small panel of human tumor cell lines with IC50 values in the range of 4.28-14.31 lM.
- Yu, Bangwei,Luo, Jianguang,Wang, Junsong,Zhang, Dongming,Yu, Shishan,Kong, Lingyi
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p. 421 - 427
(2014/03/21)
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- Enantioselective hydrogenation of α-substituted acrylic acids catalyzed by iridium complexes with chiral spiro aminophosphine ligands
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Highly active: Iridium complexes with chiral spiro aminophosphine ligands were synthesized and applied as catalysts for the asymmetric hydrogenation of α-substituted acrylic acids (see scheme). The complexes were highly active catalysts, showing turnover frequencies of up to 6000 h-1, and catalyst loadings could be reduced to 0.01 mol %. Copyright
- Zhu, Shou-Fei,Yu, Yan-Bo,Li, Shen,Wang, Li-Xin,Zhou, Qi-Lin
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supporting information; experimental part
p. 8872 - 8875
(2012/10/08)
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- Efficient cluster-based catalysts for asymmetric hydrogenation of α-unsaturated carboxylic acids
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The new clusters [H4Ru4(CO)10(μ-1,2-P- P)], [H4Ru4(CO)10(1,1-P-P)] and [H 4Ru4(CO)11(P-P)] (P-P=chiral diphosphine of the ferrocene-based Josiphos or Walphos ligand families) have been synthesised and characterised. The crystal and molecular structures of eleven clusters reveal that the coordination modes of the diphosphine in the [H4Ru 4(CO)10(μ-1,2-P-P)] clusters are different for the Josiphos and the Walphos ligands. The Josiphos ligands bridge a metal-metal bond of the ruthenium tetrahedron in the "conventional" manner, that is, with both phosphine moieties coordinated in equatorial positions relative to a triangular face of the tetrahedron, whereas the phosphine moieties of the Walphos ligands coordinate in one axial and one equatorial position. The differences in the ligand size and the coordination mode between the two types of ligands appear to be reflected in a relative propensity for isomerisation; in solution, the [H4Ru4(CO)10(1,1-Walphos)] clusters isomerise to the corresponding [H4Ru4(CO) 10(μ-1,2-Walphos)] clusters, whereas the Josiphos-containing clusters show no tendency to isomerisation in solution. The clusters have been tested as catalysts for asymmetric hydrogenation of four prochiral α-unsaturated carboxylic acids and the prochiral methyl ester (E)-methyl 2-methylbut-2-enoate. High conversion rates (>94 %) and selectivities of product formation were observed for almost all catalysts/catalyst precursors. The observed enantioselectivities were low or nonexistent for the Josiphos-containing clusters and catalyst (cluster) recovery was low, suggesting that cluster fragmentation takes place. On the other hand, excellent conversion rates (99-100 %), product selectivities (99-100 % in most cases) and good enantioselectivities, reaching 90 % enantiomeric excess (ee) in certain cases, were observed for the Walphos-containing clusters, and the clusters could be recovered in good yield after completed catalysis. Results from high-pressure NMR and IR studies, catalyst poisoning tests and comparison of catalytic properties of two [H4Ru4(CO)10(μ-1,2-P-P)] clusters (P-P=Walphos ligands) with the analogous mononuclear catalysts [Ru(P-P)(carboxylato)2] suggest that these clusters may be the active catalytic species, or direct precursors of an active catalytic cluster species. Copyright
- Moberg, Viktor,Duquesne, Robin,Roehrs, Oliver,Nachtigall, Jonny,Nordlander, Ebbe,Contaldi, Simone,Monari, Magda,Damoense, Llewellyn,Green, Michael,Hutton, Alan T.,Santelia, Daniela,Haukka, Matti
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p. 12458 - 12478,21
(2020/08/24)
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- Discovery of tetrasubstituted pyrazines as semiochemicals in a sexually deceptive orchid
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Sexually deceptive orchids employ mimicry of insect sex pheromones to exploit a diverse group of pollinators. The chemical structures of five semiochemicals (1-3, 7, 8) produced by populations of the warty hammer orchid, Drakaea livida, pollinated by a thynnine wasp in the genus Catocheilus were elucidated. With the exception of (2,5-dimethylpyrazin-3-yl)methyl 3-methylbutanoate (7), all active compounds were tetrasubstituted pyrazines, including hydroxymethyl (1) and ester (2 and 3) trimethylpyrazine derivatives. Male Catocheilus wasps were responsive to all of these compounds in GC-EAD experiments.
- Bohman, Bjoern,Jeffares, Lynne,Barrow, Russell A.,Phillips, Ryan D.,Peakall, Rod,Flematti, Gavin,Dixon, Kingsley W.,Byrne, Lindsay T.,Skelton, Brian W.
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p. 1589 - 1594,6
(2020/09/09)
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- Medicinal flowers. XXXV. Nor-oleanane-type and acylated oleanane-type triterpene saponins from the flower buds of Chinese Camellia japonica and their inhibitory effects on melanogenesis
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The methanolic extract and its 1-butanol-soluble fraction from the flower buds of Camellia japonica, cultivated in Yunnan Province, China, showed inhibitory effects on melanogenesis in theophylline-stimulated B16 melanoma 4A5 cells. From the 1-butanol-soluble fraction, a new 28-nor-oleanane-type and three new oleanane-type triterpene saponins, sanchakasaponins A-D, were isolated together with four known triterpene saponins. Their chemical structures were elucidated on the basis of chemical and physicochemical evidence. The inhibitory effects on melanogenesis in theophylline-stimulated B16 melanoma 4A5 cells and structure-activity relationships of the saponins were investigated.
- Fujimoto, Katsuyoshi,Nakamura, Seikou,Nakashima, Souichi,Matsumoto, Takahiro,Uno, Kaoru,Ohta, Tomoe,Miura, Tomoko,Matsuda, Hisashi,Yoshikawa, Masayuki
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p. 1188 - 1194,7
(2020/08/31)
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- TPAP-catalyzed direct oxidation of primary alcohols to carboxylic acids through stabilized aldehyde hydrates
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We present a simple, mild, and highly effective method for the direct conversion of primary alcohols to carboxylic acids. TPAP serves as the catalyst, and NMO?H2O plays a dual role, acting as the co-oxidant and as a reagent for aldehyde hydrate stabilization. This previously unknown stabilizing effect of geminal diols by N-oxides is the key for the efficiency of the overall transformation.
- Schmidt, Andrea-Katharina C.,Stark, Christian B. W.
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supporting information; experimental part
p. 4164 - 4167
(2011/10/08)
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- Calysolins I-IV, resin glycosides from calystegia soldanella
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Four new resin glycosides having intramolecular cyclic ester structures (jalapins), named calysolins I-IV (1-4), were isolated from the methanol extract of leaves, stems, and roots of Calystegia soldanella, along with one known jalapin (5) derivative. The structures of 1-4 were determined on the basis of spectroscopic data and chemical evidence. They fall into two types, one having a 22-membered ring (1 and 4) and the other with a 27-membered ring (2 and 3). The sugar moieties of 1-4 were partially acylated by some organic acids. Compound 4 is the first example of a hexaglycoside of jalapin.
- Takigawa, Ayako,Muto, Haruka,Kabata, Kiyotaka,Okawa, Masafumi,Kinjo, Junei,Yoshimitsu, Hitoshi,Nohara, Toshihiro,Ono, Masateru
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experimental part
p. 2414 - 2419
(2012/01/15)
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