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71.
Mugford PF Magloire VP Kazlauskas RJ 《Journal of the American Chemical Society》2005,127(18):6536-6537
Subtilisin Carlsberg-catalyzed hydrolysis of N-chloroacetyl p-toluenesulfinamide favored cleavage of the sulfinamide (S(O)-N) bond with a minor amount ( approximately 25%) of the expected carboxamide (C(O)-N) bond. The sulfinamide hydrolysis was enantioselective (E approximately 17) and yielded remaining starting material enriched in the R-enantiomer and achiral product, sulfinic acid and chloroacetamide, as confirmed by mass spectra and NMR. In contrast, the related subtilisin BPN' and E favored the carboxamide hydrolysis. Hydrolysis of the pseudo-symmetrical N-p-toluoyl p-toluenesulfinamide, which contains a sulfinamide and a carboxamide in similar steric and electronic environments, gave only sulfinamide cleavage (>10:1) for subtilisin Carlsberg, showing that sulfinamide cleavage is the preferred path even when a similar carboxamide is available. 相似文献
72.
Although lipase from Pseudomonas cepacia (PCL) shows high enantioselectivity towards many secondary alcohols, it usually exhibits only low to moderate enantioselectivity towards primary alcohols. To increase this enantioselectivity, we optimised the reaction conditions for the PCL-catalysed hydrolysis of esters of three chiral primary alcohols: 2-methyl-3-phenyl-1-propanol 1, 2-phenoxy-1-propanol 2 and solketal 3. The enantioselectivity towards 1-acetate increased from E=16 to 38 upon changing the solvent from ethyl ether/phosphate buffer to 30% n-propanol in phosphate buffer and increased again to E ≥190 upon changing the substrate from 1-acetate to 1-heptanoate. The same changes increased the enantioselectivity towards alcohol 2 from E=17 to 70, but did not significantly increase the enantioselectivity towards alcohol 3. The best solvent was similar to the solvent used to crystallise the open form of PCL and likely stabilises the open form of PCL. This stabilisation may increase the enantioselectivity by removing kinetic contributions from a non-enantioselective lid-opening step. We determined the kinetic contribution of the lid-opening step by measuring the interfacial activation of PCL. The activation energy for the PCL-catalysed hydrolysis of ethyl acetate was at least 2.6 kcal/mol lower in the presence of a water–organic solvent interface. 相似文献
73.
Bornscheuer UT Kazlauskas RJ 《Angewandte Chemie (International ed. in English)》2004,43(45):6032-6040
Biocatalysis has expanded rapidly in the last decades with the discoveries of highly stereoselective enzymes with broad substrate specificity. A new frontier for biocatalysis is broad reaction specificity, where enzymes catalyze alternate reactions. Although often under-appreciated, catalytic promiscuity has a natural role in evolution and occasionally in the biosynthesis of secondary metabolites. Examples of catalytic promiscuity with current or potential applications in synthesis are reviewed here. Combined with protein engineering, the catalytic promiscuity of enzymes may broadly extend their usefulness in organic synthesis. 相似文献
74.
Synthetic chemists often exploit the high enantioselectivity of lipases to prepare pure enantiomers of primary alcohols, but the molecular basis for this enantioselectivity is unknown. The crystal structures of two phosphonate transition-state analogs bound to Burkholderia cepacia lipase reveal this molecular basis for a typical primary alcohol: 2-methyl-3-phenyl-1-propanol. The enantiomeric alcohol moieties adopt surprisingly similar orientations, with only subtle differences that make it difficult to predict how to alter enantioselectivity. These structures, along with a survey of previous structures of enzyme bound enantiomers, reveal that binding of enantiomers does not involve an exchange of two substituent positions as most researchers assumed. Instead, the enantiomers adopt mirror-image packing, where three of the four substituents at the stereocenter lie in similar positions. The fourth substituent, hydrogen, points in opposite directions. 相似文献
75.
Cheeseman JD Corbett AD Gleason JL Kazlauskas RJ 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(6):1708-1716
Current drug discovery using combinatorial chemistry involves synthesis followed by screening, but emerging methods involve receptor-assistance to combine these steps. Adding stoichiometric amounts of receptor during library synthesis alters the kinetics or thermodynamics of the synthesis in a way that identifies the best-binding library members. Three main methods have emerged thus far in receptor-assisted combinatorial chemistry: dynamic combinatorial libraries, receptor-accelerated synthesis, and a new method, pseudo-dynamic libraries. Pseudo-dynamic libraries apply both thermodynamics and kinetics to amplify library members to easily observable levels, and attain selectivity heretofore unseen in receptor-assisted systems. 相似文献
76.
Hydrolase-catalyzed biotransformations in deep eutectic solvents 总被引:1,自引:0,他引:1
Hydrolases show good catalytic activity in deep eutectic solvents, despite the presence of urea, which can denature enzymes, or alcohols, which can interfere with hydrolase-catalyzed reactions. 相似文献
77.
N. I. Aizatskii V. N. Boriskin A. N. Dovbnya V. V. Zakutin V. A. Kushnir V. A. Mitrochenko N. G. Reshetnyak V. P. Romas’ko Yu. Ya. Volkolupov M. A. Krasnogolovets 《Technical Physics》2003,48(2):245-249
A study is made of the generation of electron beams in a system consisting of eight secondary-emission cathodes arranged at regular intervals in the azimuthal direction inside a coaxial cylindrical anode in crossed electric and magnetic fields. In this system with an azimuthally nonuniform electric field, secondary-emission multiplication of electrons is realized and beam generation is achieved. With a cathode voltage of ∼37 kV and a magnetic field of ∼3000 Oe, the total current of all the beams amounts to ∼35 A, the microperveance of each beam being ∼0.7 μA/V3/2. 相似文献
78.
79.
The tandem synthesis of naphthoquinones was conducted from the reaction of laccase-generated quinones and acyclic dienes via Diels-Alder reaction. This reaction was carried out under mild condition in aqueous medium and yielded naphthoquinones up to 80%. In addition, the effect of solvent was also investigated and water was shown to be optimal for this reaction. 相似文献
80.
S. Pozdniakova R. Ragauskas A. Dikčius A. Padarauskas 《Analytical and bioanalytical chemistry》1999,363(1):124-125
A capillary electrophoretic method for the determination of EDTA has been developed. EDTA was converted to Ni(II)-EDTA prior
to separation, separated from Fe(III)-EDTA, thiosulphate, bromide and polythionates using a fused silica capillary (57 cm
× 75 μm I.D.) filled with a borate buffer (50 mmol L–1; pH 8.5; applied voltage, 30 kV) and detected at 214 nm. The separation time is about 6 min. The detection limit achieved
is 2 × 10–6 mol L–1 for EDTA. This method was applied for the determination of free EDTA in used fixing solutions.
Received: 27 February 1998 / Revised: 28 April 1998 / Accepted: 20 May 1998 相似文献