- A Novel Chiral Ferrocenyl Phosphine Ligand from Sugar: Applications in Rh-Catalyzed Asymmetric Hydrogenation Reactions
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(Matrix Presented) A new chiral ferrocenyl diphosphine ligand 3 was synthesized from readily available D-mannitol. Rh-complex with this ligand showed high enantioselectivity and reactivity in the asymmetric hydrogenation of dehydroamino acid derivatives and itaconic acid derivatives. Up to over 99% ee and 10 000 TON were achieved with this catalytic system.
- Liu, Duan,Li, Wenge,Zhang, Xumu
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Read Online
- STUDIES ON AI-77s, MICROBIAL PRODUCTS WITH GASTROPROTECTIVE ACTIVITY. STRUCTURES AND THE CHEMICAL NATURE OF AI-77s
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The structures and chemical nature of a novel gastroprotective substance AI-77-B (1) and its analogues AI-77-C (2), D (3), F (4) and G (5), which are produced by Bacillus pumilus AI-77, are described.The structure of 1 was confirmed to be 6-amino>-4(S),5(S)-dihydroxy-6-oxo-3(S)-aminohexanoic acid by X-ray in combination with chemical studies and the structures of 2, 3, 4 and 5 were determined by chemical syntheses from 1 and spectral analyses.
- Shimojima, Yukiji,Hayashi, Hiroshi,Ooka, Tadaaki,Shibukawa, Mitsuru,Iitaka, Yoichi
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- ASYMMETRIC HYDROGENATION CATALYZED BY AMINOPHOSPHINE-PHOSPHINITERHODIUM COMPLEXES DERIVED FROM NATURAL AMINOALCOHOLS AND X-RAY CRYSTAL STRUCTURE OF (1,5-CYCLOOCTADIENE)-(S)-N-(DIPHENYLPHOSPHINO)-2-DIPHENYLPHOSPHINOXYMETHYLPYRROLIDINERHODIUM(I) PERCHLORATE
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From the cheap and readily available amino alcohols (S)-pyrrolidinemethanol ((S)-prolinol), and (S)-α-N-ethyl-aminobutanol, we have obtained two new aminophosphine-phosphinite ligands: (S)-N-(diphenylphosphino)-2-diphenylphosphinooxymethylpyrrolidine ((S)-Prolophos) and (S)-1-diphenylphosphinoxy-2-N-ethyl-N-diphenylphosphinoaminobutane ((S)-Butaphos).The rhodium(I) complexes of these phosphines act as efficient homogeneous hydrogenation catalysts at ambient temperature and pressures for dehydro N-acetyl amono acids, dehydro N-benzoyl amino acids and itaconic acid.An X-ray diffraction study of the complex *THF has been shown that the crystals belong to the monoclinic space group P21 with a 10.680(2), b 10.448(2), c 18.207(3) Angstroem and β 104.97(1)o.Refinements based on 2105 significant counter reflections led to a final R value of 0.060.The cation is in a distorted square planar geometry, the rhodium atom being bound to the two phosphorus atoms and to the two double bonds of the diene molecule.
- Cesarotti, E.,Chiesa, A.,Ciani, G.,Sironi, A.
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- Rapid Room-Temperature Gelation of Crude Oils by a Wetted Powder Gelator
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Phase-selective organogelators (PSOGs) not only exhibit ability to phase-selectively congeal oil from oily water but also allow easy separation of gelled oil from the body of water. However, all hitherto reported PSOGs either necessitate carrier solvents for their dissolution or suffer from an extremely slow action in gelling oil in the powder form. A previously unexplored generally applicable wetting strategy is now described to dramatically enhance, by up to two orders of magnitude, gelling speed of the resultant wet but non-sticky gelator in the powder form in crude oils of widely ranging viscosities. Such unprecedented rapid gelling speeds enable rapid gelation of six types of (un)weathered crude oils within minutes at room temperature, making PSOGs one step closer to their eventual practical uses as one of important oil spill control technologies.
- Ren, Changliang,Shen, Jie,Chen, Feng,Zeng, Huaqiang
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- Acetylation under ultrasonic conditions: Convenient preparation of N-acetylamino acids
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An efficient and simple method of preparation of acetylamino acids from amino acids under ultrasonic conditions is described. The reactions proceed without racemization and the yields are almost quantitative.
- Veera Reddy,Ravindranath
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Read Online
- Paecilopeptin, a new cathepsin S inhibitor produced by Paecilomyces carneus.
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Paecilopeptin, a novel cathepsin S inhibitor, was produced and isolated from the culture supernatant of the fungal strain, Paecilomyces carneus. A spectroscopic analysis revealed the planar structure of paecilopeptin to be acetyl-Leu-Val-CHO. The stereochemistry of the constituent amino acids was analysed by chiral HPLC after oxidation and 6N HCl hydrolysis of paecilopeptin. The total synthesis of paecilopeptin was completed in six steps. Paecilopeptin inhibited human cathepsin S with an IC50 value of 2.1 nM in vitro.
- Shindo, Kazutoshi,Suzuki, Hidefumi,Okuda, Toru
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Read Online
- Structure-activity relationship studies of dipeptide-based hepsin inhibitors with Arg bioisosteres
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Hepsin is a type II transmembrane serine protease (TTSP) associated with cell proliferation and overexpressed in several types of cancer including prostate cancer (PCa). Because of its significant role in cancer progression and metastasis, hepsin is an attractive protein as a potential therapeutic and diagnostic biomarker for PCa. Based on the reported Leu-Arg dipeptide-based hepsin inhibitors, we performed structural modification and determined in vitro hepsin- and matriptase-inhibitory activities. Comprehensive structure-activity relationship studies identified that the p-guanidinophenylalanine-based dipeptide analog 22a exhibited a strong hepsin-inhibitory activity (Ki = 50.5 nM) and 22-fold hepsin selectivity over matriptase. Compound 22a could be a prototype molecule for structural optimization of dipeptide-based hepsin inhibitors.
- Kwon, Hongmok,Ha, Hyunsoo,Jeon, Hayoung,Jang, Jaebong,Son, Sang-Hyun,Lee, Kiho,Park, Song-Kyu,Byun, Youngjoo
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supporting information
(2020/12/25)
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- Oxidative damage of proline residues by nitrate radicals (NO3): A kinetic and product study
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Tertiary amides, such as in N-acylated proline or N-methyl glycine residues, react rapidly with nitrate radicals (NO3) with absolute rate coefficients in the range of 4-7 × 108 M-1 s-1 in acetonitrile. The major pathway proceeds through oxidative electron transfer (ET) at nitrogen, whereas hydrogen abstraction is only a minor contributor under these conditions. However, steric hindrance at the amide, for example by alkyl side chains at the α-carbon, lowers the rate coefficient by up to 75%, indicating that NO3-induced oxidation of amide bonds proceeds through initial formation of a charge transfer complex. Furthermore, the rate of oxidative damage of proline and N-methyl glycine is significantly influenced by its position in a peptide. Thus, neighbouring peptide bonds, particularly in the N-direction, reduce the electron density at the tertiary amide, which slows down the rate of ET by up to one order of magnitude. The results from these model studies suggest that the susceptibility of proline residues in peptides to radical-induced oxidative damage should be considerably reduced, compared with the single amino acid.
- Nathanael, Joses G.,Nuske, Madison R.,Richter, Annika,White, Jonathan M.,Wille, Uta
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supporting information
p. 6949 - 6957
(2020/10/02)
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- GRANZYME B DIRECTED IMAGING AND THERAPY
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Provided herein are heterocyclic compounds useful for imaging Granzyme B. Methods of imaging Granzyme B, combination therapies, and kits comprising the Granzyme B imaging agents are also provided.
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Page/Page column 108; 109
(2019/09/04)
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- Oxidative Damage in Aliphatic Amino Acids and Di- and Tripeptides by the Environmental Free Radical Oxidant NO3?: the Role of the Amide Bond Revealed by Kinetic and Computational Studies
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Kinetic and computational data reveal a complex behavior of the important environmental free radical oxidant NO3? in its reactions with aliphatic amino acids and di- and tripeptides, suggesting that attack at the amide N-H bond in the peptide backbone is a highly viable pathway, which proceeds through a proton-coupled electron transfer (PCET) mechanism with a rate coefficient of about 1 × 106 M-1 s-1 in acetonitrile. Similar rate coefficients were determined for hydrogen abstraction from the α-carbon and from tertiary C-H bonds in the side chain. The obtained rate coefficients for the reaction of NO3? with aliphatic di- and tripeptides suggest that attack occurs at all of these sites in each individual amino acid residue, which makes aliphatic peptide sequences highly vulnerable to NO3?-induced oxidative damage. No evidence for amide neighboring group effects, which have previously been found to facilitate radical-induced side-chain damage in phenylalanine, was found for the reaction of NO3? with side chains in aliphatic peptides.
- Nathanael, Joses G.,Wille, Uta
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p. 3405 - 3418
(2019/03/11)
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- Oxidative functionalization of aliphatic and aromatic amino acid derivatives with H2O2 catalyzed by a nonheme imine based iron complex
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The oxidation of a series of N-acetyl amino acid methyl esters with H2O2 catalyzed by a very simple iminopyridine iron(ii) complex 1 easily obtainable in situ by self-assembly of 2-picolylaldehyde, 2-picolylamine, and Fe(OTf)2 was investigated. Oxidation of protected aliphatic amino acids occurs at the α-C-H bond exclusively (N-AcAlaOMe) or in competition with the side-chain functionalization (N-AcValOMe and N-AcLeuOMe). N-AcProOMe is smoothly and cleanly oxidized with high regioselectivity affording exclusively C-5 oxidation products. Remarkably, complex 1 is also able to catalyze the oxidation of the aromatic N-AcPheOMe. A marked preference for the aromatic ring hydroxylation over Cα-H and benzylic C-H oxidation was observed, leading to the clean formation of tyrosine and its phenolic isomers.
- Ticconi, Barbara,Colcerasa, Arianna,Di Stefano, Stefano,Lanzalunga, Osvaldo,Lapi, Andrea,Mazzonna, Marco,Olivo, Giorgio
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p. 19144 - 19151
(2018/05/31)
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- MODULATORS OF SESTRIN-GATOR2 INTERACTION AND USES THEREOF
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The present invention provides compounds, compositions thereof, and methods of using the same.
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- Cinnamic acid derivative with aldose reductase inhibitory activity as well as preparation method and application thereof
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The invention discloses a cinnamic acid derivative with aldose reductase inhibitory activity, a preparation method thereof and an application of the cinnamic acid derivative in preparation of a medicine used for treating diabetic complications and diseases caused by oxidative stress. The structure of the compound is shown in a formula I. The preparation method comprises the following steps: firstly reacting substituted benzaldehyde with substituted acetic acid or acid anhydride thereof to obtain substituted cinnamic acid, then reacting with a diamine compound protected by N-tertiary butoxy acyl to obtain substituted cinnamoyl diamide protected by N-tertiary butoxy acyl; and carrying out tertiary butoxy acyl deprotection on the substituted cinnamoyl diamide protected by N-tertiary butoxy acyl, and then reacting with natural or non-natural N-acyl alpha-amino acid, so that the cinnamic acid derivative is obtained. The cinnamic acid derivative compound disclosed by the invention has excellent inhibitory activity on aldose reductase and excellent antioxidant activity and can be applied to preparation of a medicine used for treating the diabetic complications, especially diabetic retinopathy, senile dementia due to diabetes and nerve ending disturbance, as well as diseases caused by the oxidative stress.
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Paragraph 0087; 0091; 0107
(2017/09/01)
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- MODULATORS OF SESTRIN-GATOR2 INTERACTION AND USES THEREOF
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The present invention provides compounds, compositions thereof, and methods of using the same.
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- Peptide Tyrosinase Activators
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Peptides that increase melanin synthesis are provided. These peptides include pentapeptides YSSWY, YRSRK, and their variants. The peptides may activate the enzymatic activity of tyrosinase to increase melanin synthesis. The pharmaceutical, cosmetic, and other compositions including the peptides are also provided. The methods of increasing melanin production in epidermis of a subject are provided where the methods include administering compositions comprising an amount of one or more peptides effective to increase the melanin production. The methods also include treating vitiligo or other hypopigmentation disorders with compositions including one or more peptides.
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- Salt complexes of two-component N-acylamino acid diastereoisomers: Self-assembly studies and modulation of gelation abilities
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The self-assemblies and gelation of various organic solvents by salt complexes of two-component N-acylamino acid diastereoisomers are described. The potent organogelator, N-(2-aminoethyl)-α-[-(1-oxoheptadecyl)amino]phenyl) propanamide, was mixed with various N-acyl leucines having different fatty alkyl chain lengths at a ratio of 1:1. In some cases, their complexation resulted in modulations of the current gelation abilities. When the l-form of the organogelator was used for mixing, the gelation ability appeared to be independent of the hydrophobic nature of the N-acyl leucine. This is not observed when the racemate form of the organogelator was used. Moreover, a minimum gelation concentration (MGC) in aromatic solvents as well as improvements of the gelation ability such as formation of a robust hydrogel in water, gelation of the R-propylene carbonate, and unexpected gelation of pyridine were observed. The supramolecular gels were analyzed by Fourier Transform-Infrared (FT-IR), 1H nuclear magnetic resonance (NMR) spectroscopies, and rheology analysis. The phase transition temperatures (T g-s) were determined using differential scanning calorimetry (DSC). Homogeneity of the gel networks was observed by field emission scanning microscopy (FE-SEM) and transmission electron microscopy (TEM). The lamella structure was confirmed by X-ray diffraction (XRD).
- Delbecq, Frederic,Masuda, Yuki,Ogue, Yuki,Kawai, Takeshi
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supporting information
p. 6588 - 6593,6
(2012/12/12)
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- Electron-donating and rigid p-stereogenic bisphospholane ligands for highly enantioselective rhodium-catalyzed asymmetric hydrogenations
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More electron donating, more rigid: A new highly electron-donating P-stereogenic bisphospholane ligand (ZhangPhos) was synthesized in a practical and highly enantioselective manner from a commercially available chiral source. Better or comparable enantioselectivities and reactivities than TangPhos were achieved in rhodium-catalyzed hydrogenation of various functionalized olefins (see scheme; nbd=3,5-norbornadiene). Copyright
- Zhang, Xiaowei,Huang, Kexuan,Hou, Guohua,Cao, Bonan,Zhang, Xumu
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supporting information; experimental part
p. 6421 - 6424
(2010/12/19)
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- D-aminoacylase mutants
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The present invention provides mutant D-aminoacylases and use thereof. The mutant D-aminoacylases are hard to be inhibited by the substrate and, comprise the amino acid sequences of the D-aminoacylase derived from Alcaligenes denitrificans subsp. xylosoxydans MI-4 strain, wherein amino acid residues at specific sites have been modified. The mutants of the present invention have high reaction specificity as well as resistance to inhibition by the substrate. The present invention enables high-yield production of D-amino acids using higher concentrations of N-acyl-DL-amino acid as the substrate. The mutants of the present invention are useful in producing D-tryptophan in particular.
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- Asymmetric catalysis based on chiral phospholanes and hydroxyl phospholanes
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Chiral phosphine ligands derived from chiral natural products including D-mannitol and tartaric acid. The ligands contain one or more 5-membered phospholane rings with multiple chiral centers, and provide high stereoselectivity in asymmetric reactions.
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(2010/02/06)
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- ASYMMETRIC SYNTHESIS CATALYZED BY TRANSITION METAL COMPLEXES WITH CYCLIC CHIRAL PHOSPHINE LIGANDS
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The present invention relates to rigid chiral ligands usefull in making catalysts for asymmetric synthesis. More particularly, the present invention relates to new monodentate and bidentate cyclic chiral phosphine ligands which are formed into catalysts to provide high selectivity of the enantiomeric structure of the end-product.
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- Synthesis of ortho-phenyl substituted MeO-BIPHEP ligand and its application in Rh-catalyzed asymmetric hydrogenation
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A new BIPHEP-type ligand with phenyl groups at the 3,3′-positions, o-Ph-MeO-BIPHEP 3 was prepared. This ligand afforded excellent enantioselectivities when used in the Rh-catalyzed asymmetric hydrogenation of α-dehydroamino acid derivatives. The strong influence of o-phenyl groups of the ligand on the enantioselectivities of the reaction has been demonstrated by a comparison with its parent ligand MeO-BIPHEP.
- Wu, Shulin,He, Minsheng,Zhang, Xumu
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p. 2177 - 2180
(2007/10/03)
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- Inhibition of peptidylglycine α-amidating monooxygenase by exploitation of factors affecting the stability and ease of formation of glycyl radicals
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Peptidylglycine α-amidating monooxygenase catalyzes the biosynthesis of peptide hormones through radical cleavage of the C-terminal glycine residues of the corresponding prohormones. We have correlated ab initio calculations of radical stabilization energies and studies of free radical brominations with the extent of catalysis displayed by peptidylglycine α-amidating monooxygenase, to identify classes of inhibitors of the enzyme. In particular we find that, in closely related systems, the substitution of glycolate for glycine reduces the calculated radical stabilization energy by 34.7 kJ mol -1, decreases the rate of bromination with N-bromosuccinimide at reflux in carbon tetrachloride by a factor of at least 2000, and stops catalysis by the monooxygenase, while maintaining binding to the enzyme.
- Barratt, Brendon J. W.,Easton, Christopher J.,Henry, David J.,Li, Iris H. W.,Radom, Leo,Simpson, Jamie S.
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p. 13306 - 13311
(2007/10/03)
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- Efficient chemoenzymatic synthesis of enantiomerically pure α-amino acids
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A general two-step chemoenzymatic synthesis for enantiomerically pure natural and nonnatural α-amino acids is presented. In the first step of the sequence, the ubiquitous educts aldehyde, amide and carbon monoxide react by palladium-catalyzed amidocarbonylation to afford the racemic N-acyl amino acids in excellent yields. In the second step, enzymatic enantioselective hydrolysis yields the free optically pure a-amino acid and the other enantiomer as the N-acyl derivative, both in optical purities of 85-99.5% ee. The advantage of the chemoenzymatic process compared to other amino acid synthesis are demonstrated by the preparation of various functionalized (-OR, -Cl, -F, -SR) α-amino acids on a 10-g scale.
- Beller, Matthias,Eckert, Markus,Geissler, Holger,Napierski, Bernd,Rebenstock, Heinz-Peter,Holla, E. Wolfgang
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p. 935 - 941
(2007/10/03)
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- Pronase catalysed peptide syntheses
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A mixture of proteases from Streptomyces griseus (pronase), displaying a very broad substrate tolerance in the hydrolysis of peptides, has been studied for the first time systematically regarding their substrate specificity in peptide synthesis. It is demonstrated that pronase can be employed successfully for the formation of dipeptides with yields up to 95%. Pronase has also been employed successfully as catalyst for the enzyme assisted synthesis of a hexapeptide.
- Lobell, Mario,Schneider, Manfred P.
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p. 319 - 325
(2007/10/03)
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- Enantioselective hydrolytic reactions of rice bran lipase (RBL): A first report
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Enantioselectivity has been observed in the hydrolysis of racemic N-acetyl amino acid esters with rice bran lipase (RBL). The enzyme shows selectivity towards the (S)-enantiomer. Products with high enantiomeric excess (e.e. >99%) are obtained depending upon the hydrophobicity of the amino acid as well as that of the leaving group.
- Fadnavis,Jadhav, Vasudev
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p. 2361 - 2366
(2007/10/03)
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- Cosmetic composition
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A composition suitable for topical application to mammalian skin and hair for inducing, maintaining or increasing hair growth comprises a hair growth promoter chosen from glutamine derivatives and salts thereof. The composition preferably also comprises an activity enhancer which may be chosen from hair growth stimulants, penetration enhancers and cationic polymers.
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- Cosmetic composition containing DOPA derivatives
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A composition for topical application to human hair or skin contains a chemical analogue of dihydroxyphenyl alanine (DOPA). This chemical analogue can be absorbed by skin or by a hair follicle and metabolised in-vivo, thus leading to the formation of melanin in skin or to the growth of melanin-pigmented hair. Consequently the composition can give controlled skin darkening to mimic sun-induced tanning or can bring about the growth of dar hair in place of the grey or white hair.
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- A novel tea-bag methodology for enzymatic resolutions of α-amino acid derivatives in reverse micellar media
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A novel tea bag methodology for resolution of methyl esters of N-acetyl- α-amino acids in reverse micellar medium of bis(2-ethylhexyl) sulfosuccinate sodium salt (AOT) in isooctane-chloroform using immobilized enzymes or microbial cells is presented. The methodology effectively solves the problems of substrate solubility, product separation and surfactant recycling and provides products in high yields (80 to 90%) and excellent optical purities (% ee 97 to >99%).
- Bhalerao,Rao,Fadnavis
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p. 2109 - 2118
(2007/10/02)
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- Cosmestic composition
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A composition suitable for topical application to mammalian skin and hair for inducing, maintaining or increasing hair growth comprises a hair growth promoter chosen from glutamic acid derivatives and salts thereof. The composition preferably also comprises an activity enhancer which may be chosen from hair growth stimulants, penetration enhancers and cationic polymers.
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- Selectivity in Carbonic Anhydrase Catalyzed Hydrolysis of Standard N-Acetyl-DL-amino Acid Methyl Esters
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Carbonic anhydrase-catalyzed hydrolysis of some standard N-acetyl-DL-amino acid methyl esters proceeds with high enantioselectivity.This enzyme hydrolyses selectively D amino acid derivatives in contrast to proteases which have a L stereoselectivity. Key Words: carbonic anhydrase, hydrolysis, N-acetyl-DL-amino acid methyl esters, enantioselectivity.
- Chenevert, Robert,Rhlid, Rachid Bel,Letourneau, Martin,Gagnon, Rene,D'Astous, Linda
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p. 1137 - 1140
(2007/10/02)
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- Hair growth composition containing citric acid esters
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Triesters of citric acid are used for inducing, maintaining or increasing hair growth. Compositions for topical application to mammalian hair or scalp comprise an effective amount of from 1% to 99% by weight of an ester of citric acid having the structure (1): where, R1, R2 and R3 each independently represent a branched or unbranched alkyl, alkenyl, aryl, alkylaryl or arylalkyl group, each said group having from 1 to 18 carbon atoms, R4 represents -H, or a branched or unbranched saturated or unsaturated acyl, alkyl, aryl, alkylaryl or aylalkyl group having from 1 to 18 carbon atoms, in the presence of a cosmetically acceptable vehicle for the citric acid ester and in the absence of solid absorbent for the ester;, said effective amount of said ester being sufficient to increase hair growth in the rat, when said composition is applied topically thereto over a period of no more than three months, by at least 10% more than that obtainable using a control composition from which the said ester has been omitted, in accordance with the Rat Hair Growth Test.
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- Cosmetic composition
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A composition suitable for topical application to mammalian skin and hair for inducing, maintaining or increasing hair growth comprises a hair growth promoter chosen from N-acylated amino-acids, in which the acyl group has from 2 to 20 carbon atoms, together with a cosmetically acceptable vehicle for the hair growth promoter.
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- Catalysis by β-cyclodextrin in the reaction of p-nitrophenyl acetate with α-amino acids
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The reactions of p-nitrophenyl acetate, 1, with both enantiomers of the following α-amino acids: alanine (2a), methionine (2b), leucine (2c), and tryptophan (2d), were studied in the presence of β-cyclodextrin (β-CD).All the reactions were catalyzed by β-
- Barra, Monica,Rossi, Rita H. de
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p. 1124 - 1130
(2007/10/02)
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- Efficient Asymmetric Hydrogenations of (Z)-2-Acetamidoacrylic Acid Derivatives with the Cationic Rhodium Complex of (2S,4S)-MOD-BPPM
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The preparation of (2S,4S)-MOD-BPPM ((2S,4S)-N-(t-butoxycarbonyl)-4-phosphino>-2-phosphino>methyl>pyrrolidine) and its application to highly effective asymmetric hydrogenations of (Z)-2-acetamidoacrylic acid derivatives are described.
- Takahashi, Hisashi,Achiwa, Kazuo
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p. 305 - 308
(2007/10/02)
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- O.N-Bis(diphenylphosphino) Derivatives of Chiral trans- and cis-2-Aminocyclohexanols: Synthesis and Enantioselective Behaviour as Ligands in Rh-based Homogeneous Hydrogenation Catalysts
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trans- and cis-2-Methylamino cyclohexanols (MAC) were prepared in enantiomerically pure forms and transformed into O.N-bis(diphenylphosphino) derivatives ("PONP").An analogous trans-1R;2R-aminocyclohexanol PONP could only be isolated in an impure form, whereas the attempted synthesis of PONP's of diastereomeric trans-2-(N-α-phenylethylamino)-cyclohexanols failed.Cationic Rh(I)-chelates of the new PONP's catalyzed the enantioselective hydrogenation of dehydro-α-acylamino acids with /= 97percent ee.A comparison of the enantiodiscriminating properties of the MAC-PONP's with structurally related chiral ligands leads to surprising conclusions.
- Pracejus, H.,Pracejus, G.,Costisella, B.
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p. 235 - 245
(2007/10/02)
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- ENANTIOSELECTIVE HYDROLYSIS BY BAKER'S YEAST - II. ESTERS OF N-ACETYL AMINO ACIDS
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D-N-Acetyl amino acid esters were obtained via enantioselective hydrolysis of their racemates by use of fermenting yeast.Evidence is given that proteinases are the enzymes involved.
- Glaenzer, B. I.,Faber, K.,Griengl, H.
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p. 771 - 778
(2007/10/02)
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- Asymmetric Hydrogenation Catalyzed by Rhodium Complex with a New Chiral Bisphosphine Derived from L-Threonine
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A new chiral bisphosphine, (2R,3S)-1,2-bis(diphenylphosphino)-3-'Boc-aminobutane (RS-5), was prepared from L-threonine.Mesylation of 'Boc-L-threonine methyl ester (2) and subsequent reduction with sodium borohydride gave the alcohol (10), which was treated with potassium carbonate to afford a key intermediate, (2S,3S)-1-'Boc-3-methyl-2-aziridinemethanol (SS-7b).Mesylation of SS-7b, followed by treatment with sodium diphenylphosphide afforded the new chiral bisphosphine (RS-5).The structure of RS-5 was confirmed by the X-ray analysis of its crystalline CuCl complex (RS-12).The cationic rhodium (I) complexes prepared from RS-5 and RS-12 are efficient asymmetric hydrogenation catalysts for N-acyldehydroamino acids, giving (S))-N-acylamino acids in high optical yields (83-94percentee).
- Saito, Kunio,Saijo, Shigeyoshi,Kotera, Keishi,Date, Tadamasa
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p. 1342 - 1350
(2007/10/02)
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- Asymmetric Synthesis. Asymmetric Catalytic Hydrogenation Using Chiral Chelating Six-Membered Ring Diphosphines
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Rhodium(I) catalysts formed by the two chiral chelating six-membered ring diphosphines, 2,4-bis(diphenylphosphino)pentane (skewphos) and 1,3-bis(diphenylphosphino)butane (chairphos), are efficient catalysts for the hydrogenation of amino acid precursors.The two chiral phosphines differ in that skewphos probably adopts a chiral conformation whereas chairphos probably adopts an achiral conformation.This comparison evidences the importance of ring conformations in determining optical yields.The mechanism of asymmetric hydrogenation is discussed, and a number of particular and general conclusions are drawn which may prove useful in predicting optical yields from asymmetric synthesis.
- MacNeil, Patricia A.,Roberts, Nicholas K.,Bosnich, B.
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p. 2273 - 2280
(2007/10/02)
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- A New Chiral Rhodium(I) Complex of (2R,3R)-2,3-Bis(diphenylphosphino)butane for Asymmetric Hydrogenations
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Rhodium(I) complexes of the new chiral ligand (2R,3R)-2,3-bis(diphenylphosphino)butane (4) - which is easily prepared from natural tartaric acid - hydrogenate α-(acylamino)acrylic acids to natural (S)-acylamino acids in high chemical (95-100percent) and optical (80-100percent) yields.
- Koettner, Johann,Greber, Gerd
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p. 2323 - 2325
(2007/10/02)
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