- Metabolites of the Anaerobic Degradation of n-Hexane by Denitrifying Betaproteobacterium Strain HxN1
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The constitutions of seven metabolites formed during anaerobic degradation of n-hexane by the denitrifying betaproteobacterium strain HxN1 were elucidated by comparison of their GC and MS data with those of synthetic reference standards. The synthesis of 4-methyloctanoic acid derivatives was accomplished by the conversion of 2-methylhexanoyl chloride with Meldrum's acid. The β-oxoester was reduced with NaBH4, the hydroxy group was eliminated, and the double bond was displaced to yield the methyl esters of 4-methyl-3-oxooctanoate, 3-hydroxy-4-methyloctanoate, (E)-4-methyl-2-octenoate, and (E)- and (Z)-4-methyl-3-octenoate. The methyl esters of 2-methyl-3-oxohexanoate and 3-hydroxy-2-methylhexanoate were similarly prepared from butanoyl chloride and Meldrum's acid. However, methyl (E)-2-methyl-2-hexenoate was prepared by Horner–Wadsworth–Emmons reaction, followed by isomerization to methyl (E)-2-methyl-3-hexenoate. This investigation, with the exception of 4-methyl-3-oxooctanoate, which was not detectable in the cultures, completes the unambiguous identification of all intermediates of the anaerobic biodegradation of n-hexane to 2-methyl-3-oxohexanoyl coenzyme A (CoA), which is then thiolytically cleaved to butanoyl-CoA and propionyl-CoA; these two metabolites are further transformed according to established pathways.
- Küppers, Julian,Mitschke, Nico,Heyen, Simone,Rabus, Ralf,Wilkes, Heinz,Christoffers, Jens
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p. 373 - 380
(2019/11/19)
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- 2-Amino-5,6-difluorophenyl-1 H-pyrazole-Directed PdII Catalysis: Arylation of Unactivated β-C(sp3)-H Bonds
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Palladium-catalyzed arylation of unactivated β-C(sp3)-H bonds in carboxylic acid derivatives with aryl iodides is described for the first time using 2-amino-5,6-difluorophenyl-1H-pyrazole as an efficient and readily removable directing group. Two fluoro groups are installed at the 5- and 6-position of the anilino moiety in 2-aminophenyl-1H-pyrazole, clearly enhancing the directing ability of the auxiliary. In addition, the protocol employs Cu(OAc)2/Ag3PO4 (1.2/0.3) as additives, evidently reducing the stoichiometric amount of expensive silver salts. Furthermore, this process exhibits high β-site selectivity, compatibility with diverse substrates containing α-hydrogen atoms, and excellent functional group tolerance.
- Yang, Jinyue,Fu, Xiaopan,Tang, Shibiao,Deng, Kezuan,Zhang, Lili,Yang, Xianjin,Ji, Yafei
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p. 10221 - 10236
(2019/08/20)
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- Ferric(III) Chloride Catalyzed Halogenation Reaction of Alcohols and Carboxylic Acids Using α,α-Dichlorodiphenylmethane
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A new method for chlorination of alcohols and carboxylic acids, using α,α-dichlorodiphenylmethane as the chlorinating agent and FeCl3 as the catalyst, was developed. The method enables conversions of various alcohols and carboxylic acids to their corresponding alkyl and acyl chlorides in high yields under mild conditions. Particulary interesting is the observation that the respective alkyl bromides and iodides can be generated from alcohols when either LiBr or LiI are present in the reaction mixtures.
- Lee, Chang-Hee,Lee, Soo-Min,Min, Byul-Hana,Kim, Dong-Su,Jun, Chul-Ho
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supporting information
p. 2468 - 2471
(2018/04/25)
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- Unactivated C(sp3)-H hydroxylation through palladium catalysis with H2O as the oxygen source
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A novel palladium catalyzed hydroxylation of unactivated aliphatic C(sp3)-H bonds was successfully developed. Different from conventional methods, water serves as the hydroxyl group source in the reaction. This new reaction demonstrates good reactivity and broad functional group tolerance. The C-H hydroxylated products can be readily transformed into various highly valuable chemicals via known transformations. Based on experimental and theoretical studies, a mechanism involving the Pd(ii)/(iv) pathway is proposed for this hydroxylation reaction.
- Hu, Jiantao,Lan, Tianlong,Sun, Yihua,Chen, Hui,Yao, Jiannian,Rao, Yu
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p. 14929 - 14932
(2015/10/06)
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- Methylation-dependent acyl transfer between polyketide synthase and nonribosomal peptide synthetase modules in fungal natural product biosynthesis
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Biochemical studies of purified and dissected fungal polyketide synthase and nonribosomal peptide synthetase (PKS-NRPS) hybrid enzymes involved in biosynthesis of pseurotin and aspyridone indicate that one α-methylation step during polyketide synthesis is a prerequisite and a key checkpoint for chain transfer between PKS and NRPS modules. In the absence of the resulting γ-methyl feature, the completed polyketide intermediate is offloaded as an α-pyrone instead of being aminoacylated by the NRPS domain. These examples illustrate that precisely timed tailoring domain activities play critical roles in the overall programming of the iterative PKS (and NRPS) functions.
- Zou, Yi,Xu, Wei,Tsunematsu, Yuta,Tang, Mancheng,Watanabe, Kenji,Tang, Yi
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supporting information
p. 6390 - 6393
(2015/02/19)
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- Hypervalent iodine catalyzed hofmann rearrangement of carboxamides using oxone as terminal oxidant
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Hofmann rearrangement of carboxamides to carbamates using Oxone as an oxidant can be efficiently catalyzed by iodobenzene. This reaction involves hypervalent iodine species generated in situ from catalytic amount of PhI and Oxone in the presence of 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) in aqueous methanol solutions. Under these conditions, Hofmann rearrangement of various carboxamides affords corresponding carbamates in high yields.
- Yoshimura, Akira,Middleton, Kyle R.,Luedtke, Matthew W.,Zhu, Chenjie,Zhdankin, Viktor V.
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p. 11399 - 11404
(2013/02/23)
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- Chili pepper fruits: Presumed precursors of fatty acids characteristic for capsaicinoids
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Capsaicin is a molecule unique to fruits from the genus Capsicum. It is responsible for the pungent sensation and displays valuable pharmacological properties. Despite the fruits' economic importance and decades of research, the regulation of the content of capsaicinoids in individual fruits is not completely elucidated, and no agricultural cultivation of chili of defined pungency is assured. Precursor candidates of the fatty acid moiety of the capsaicinoids, especially for the unique 8-methyl-trans-6-nonenoic acid, were examined. Thioesters, acyl-ACP and acyl-CoA, were isolated from the placenta of Capsicum fruits by means of DEAE-Sepharose chromatography, selectively converted to the corresponding N-butylamides, and analyzed by GC-MS. Fatty acid moieties characteristic for capsaicinoids were identified. In two different varieties (Capsicum chinense var. Habanero orange and Capsicum annuum var. Jalapeno) it was shown that the fatty acid pattern corresponds to the distribution pattern of the capsaicinoids formed up to this time. The acyl-thioester fractions contained already the 8-methyl-trans-6-nonenoic acid.
- Thiele, Roland,Mueller-Seitz, Erika,Petz, Michael
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experimental part
p. 4219 - 4224
(2010/03/31)
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- The Synthesis of the High-Potency Sweetener, NC-00637. Part 3: The Glutamyl Moiety and Coupling Reactions
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The synthesis of the high-potency sweetener, NC-00637 (1), required selective preparation of the γ-protected glutamic acid. Coupling of the three components could be performed in any order, but the final route involved N-acylation of the protected L-glutamic acid with the acid chloride derived from (S)-2-methylhexanoic acid. Activation of the α-carboxyl group allowed condensation with 5-amino-2-cyanopyridine (4). Saponification of the γ-ester 19 then provided the sweetener 1.
- Ager, David J.,Babler, Scott,Erickson, Robert A.,Froen, Diane E.,Kittleson, Jeannine,Pantaleone, David P.,Prakash, Indra,Zhi, Ben
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- The synthesis of the high-potency sweetener, NC-00637. Part 1: The synthesis of (S)-2-methylhexanoic acid
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The synthesis of the high potency sweetener candidate NC-00637 (1) required large quantities of (S)-2-methylhexanoic acid (2). This acid was first prepared in small quantities by the use of chiral auxiliaries. For large quantities, resolution by classical means and an enzymatic method were investigated. Asymmetric hydrogenation provided a workable solution.
- Ager, David J.,Babler, Scott,Froen, Diane E.,Laneman, Scott A.,Pantaleone, David P.,Prakash, Indra,Zhi, Ben
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p. 369 - 378
(2013/09/06)
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- Structures of cribochalines A and B, branched-chain methoxylaminoalkyl pyridines from the micronesian sponge, Cribochalina sp. absolute configuration and enantiomeric purity of related O-methyl oximes
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Two new 3-alkyl pyridines, cribochalines A (2) and B (3), were isolated from the North Pacific sponge Cribochalina sp. The known related oxime, ikimine A, was shown to be a 2.8:1 mixture of the (S)- and (R)-enantiomers. Cribochaline A exhibited antifungal activity against Candida albicans ATCC and Fluconazole-resistant strains C. albicans 96-489, C. krusei and C. glabrata. (C) 2000 Elsevier Science Ltd.
- Nicholas, Gillian M.,Molinski, Tadeusz F.
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p. 2921 - 2927
(2007/10/03)
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- Phenylglycine methyl ester, a useful tool for absolute configuration determination of various chiral carboxylic acids
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A new chiral anisotropic reagent, phenylglycine methyl ester (PGME), developed for the elucidation of the absolute configuration of chiral α,α- disubstituted acetic acids, has turned out to be applicable to other substituted carboxylic acids, such as chiral α-hydroxy-, α-alkoxy-, and α- acyloxy-α,α-disubstituted acetic acids, as well as to chiral β,β- disubstituted propionic acids. Because a carboxylic moiety is convertible from other functional groups, e.g., ozonolysis of an olefin and oxidative cleavage of a glycol, the present findings can expand the utility of the PGME method to the absolute configuration determination of various types of organic compounds, even those which initially lack oxygen functions. Several examples of the combination of chemical reactions and the PGME method are described.
- Yabuuchi, Tetsuya,Kusumi, Takenori
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p. 397 - 404
(2007/10/03)
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