- Absolute configuration and polymorphism of 2-phenylbutyramide and α-methyl-α-phenylsuccinimide
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Crystal structures of racemic and homochiral forms of 2-phenylbutyramide (1) and 3-methyl-3-phenylpyrrolidine-2,5-dione (2) were investigated in detail by a single crystal X-ray diffraction study. Absolute configurations of the homochiral forms of 1 and 2, obtained by chromatographic separation of racemates, were determined. It was revealed that racemate and homochiral forms of 1 are very similar in terms of supramolecular organization (H-bonded ribbons) in crystal, infrared (IR) spectral characteristics, and melting points. The presence of two different molecular conformations in homochiral forms of 1 allowed mimicking of crystal packing of the H-bonded ribbons in racemate 1. Two polymorph modifications (monoclinic and orthorhombic) comprising very similar H-bonded zigzag-like chains were found for the homochiral forms of compound 2 that were significantly different in terms of crystal structure, IR spectra, and melting points from the racemic form of 2. Unlike compound 1, homochiral forms of compound 2 have a higher density than the corresponding racemate which contradicts the Wallach rule and indicates that, in this case, homochiral forms are more stable than racemate forms.
- Khrustalev, Victor N.,Sandhu, Bhupinder,Bentum, Samuel,Fonari, Alexandr,Krivoshein, Arcadius V.,Timofeeva, Tatiana V.
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p. 3360 - 3369
(2014/07/21)
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- Probing the enantioselectivity of a diverse group of purified cobalt-centred nitrile hydratases
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In this study a diverse range of purified cobalt containing nitrile hydratases (NHases, EC 4.2.1.84) from Rhodopseudomonas palustris HaA2 (HaA2), Rhodopseudomonas palustris CGA009 (009), Sinorhizobium meliloti 1021 (1021), and Nitriliruptor alkaliphilus (iso2), were screened for the first time for their enantioselectivity towards a broad range of chiral nitriles. Enantiomeric ratios of >100 were found for the NHases from HaA2 and CGA009 on 2-phenylpropionitrile. In contrast, the Fe-containing NHase from the well-characterized Rhodococcus erythropolis AJ270 (AJ270) was practically aselective with a range of different α-phenylacetonitriles. In general, at least one bulky group in close proximity to the α-position of the chiral nitriles seemed to be necessary for enantioselectivity with all NHases tested. Nitrile groups attached to a quaternary carbon atom were only reluctantly accepted and showed no selectivity. Enantiomeric ratios of 80 and >100 for AJ270 and iso2, respectively, were found for the pharmaceutical intermediate naproxennitrile, and 3-(1-cyanoethyl)benzoic acid was hydrated to the corresponding amide by iso2 with an enantiomeric ratio of >100.
- Van Pelt,Zhang,Otten,Holt,Sorokin,Van Rantwijk,Black,Perry,Sheldon
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experimental part
p. 3011 - 3019
(2011/06/17)
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- Synthesis of chiral disulfides: Potential reagents for enantioselective sulfurization
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Synthesis of chiral phosphorothioates for use as antisense oligonucleotides might benefit from the use of chiral disulfides. This paper reports the synthesis of chiral analogs of phenylacetyl disulfide and of 5-methyl-3H-1,2,4-dithiazol-3-one from the same set of 2-arylalkanoic acids. The X-ray crystal structures of the disulfides derived from (R) and [S]-2-phenylpropanoic acid establish the stereochemistry and the helicity of these materials, and density functional theory calculations suggest that the high specific rotations can be due to preferred retention of this helicity in solution. Chiral HPLC showed that the final products were formed with enantiomeric purities from 86.1% to >99.9%.
- Mukhlall, Joshua A.,Noll, Bruce C.,Hersh, William H.
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scheme or table
p. 199 - 212
(2012/01/06)
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- Enantioselective hydrolysis of various racemic α-substituted arylacetonitriles using Rhodococcus sp. CGMCC 0497
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The enantioselective hydrolysis of 17 racemic α-substituted arylacetonitriles by Rhodococcus sp. CGMCC 0497 is described. The corresponding (R)-amides and (S)-acids were obtained with excellent enantiomeric excess in most cases. The effect of steric and electronic factors on the outcome of the reactions are discussed here. The results prove that nitrile-converting enzymes are efficient tools for the synthesis of sterically unencumbered chiral α-arylpropionic acids and amides.
- Wu, Zhong-Liu,Li, Zu-Yi
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p. 3305 - 3312
(2007/10/03)
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- Enantioselective biotransformations of racemic α-substituted phenylacetonitriles and phenylacetamides using Rhodococcus sp. AJ270
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Rhodococcus sp. AJ270 is an efficient whole-cell system able to catalyze the stereoselective conversions of racemic α-substituted phenylacetonitriles and amides under very mild conditions into enantiopure carboxylic acids and derivatives. The nitrile hydratase involved generally has a broad substrate spectrum against phenylacetonitriles irrespective of the electronic nature of the α-substituent while the amidase is very sensitive to both the electronic and steric factors of the substituent of amides. The overall enantioselectivity of nitrile hydrolysis is mainly determined by the combination of selectivities of nitrile hydratase and of amidase, with the latter being a major contributor. The amidase has high S-enantiocontrol against amides while the nitrile hydratase exhibits low R-selectivity against nitriles. The scope and limitations of this enantioselective biotransformation process are discussed. Copyright (C) 2000 Elsevier Science Ltd.
- Wang, Mei-Xiang,Lu, Gang,Ji, Gai-Jiao,Huang, Zhi-Tang,Meth-Cohn, Otto,Colby, John
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p. 1123 - 1135
(2007/10/03)
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- Biosynthesis of porphyrins and related macrocycles. Part 52.1'2 Synthesis of 1-SH11-4Hjporphobilinogen and the (11R)enantiomer for stereochemical studies on hydroxymethylbilane synthase (porphobilinogen deaminase)
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A synthetic route is devised for the synthesis of (115)-[11-2H,]porphobilinogen la and of the (1 lβ)-enantiomer Ib. Their absolute configurations and enantiomeric purity are established by degradation to a derivative of [2-2H,]glycine of known stereochemistry. Methods are then developed, based on the synthesis of chiral imidate esters, for determination of the configuration of [2H1]-labelled aminomethylpyrroles by converting them into [2H,]-labelled amidines followed by analysis using 'H-NMR. The labelled samples of PEG la and Ib serve as substrates for hydroxymethylbilane synthase and the products are trapped as [2H1]-labelIed aminomethylbilanes 7c and 7d. Their configurations are determined by the NMR assay to demonstrate that as PBG 1 is enzymically converted into the aminomethylbilane 7, there is overall retention of configuration at the aminomethyl carbon. The Royal Society of Chemistry 1999.
- Neidhart, Werner L.,Anderson, Paul C.,Hart, Graham J.,Battersby, Alan R.
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p. 2677 - 2689
(2007/10/03)
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- Stereoselective Hydrolysis of Nitriles and Amides Under Mild Conditions Using a Whole Cell Catalyst
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An immobilised whole cell Rhodococcus sp. (SP 361) has been shown to be an effective catalyst for the stereoselective hydrolysis of both racemic and prochiral nitrile containing compounds. 2-Alkyl-arylacetonitriles 6a-8a were hydrolysed to (S)-acids and (R)-amides whereas the closely related substrate 9a gave the (R)-acid.A series of prochiral dinitriles 10a-13a were hydrolysed to the corresponding (S)-acids with e.e.'s 22-84percent.Models to account for the stereoselectivity of the enzymic hydrolyses have been proposed.
- Beard, Timothy,Cohen, Mark A.,Parratt, Julian S.,Turner, Nicholas J.,Crosby, John,Moilliet, Jock
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p. 1085 - 1104
(2007/10/02)
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- Enantioselective hydrolysis of nitriles and amides using an immobilised whole cell system
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An immobilised whole cell catalyst SP361 has been shown to hydrolyse a range of 2-alkyl arylacetonitriles 1a-3a and amides 2b, 3b with good to excellent enantioselectivity. The absolute configuration of the derived amides and/or carboxylic acids shows remarkable changes according to the structure of the nitrile substrate.
- Cohen,Parratt,Turner
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p. 1543 - 1546
(2007/10/02)
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