Enantioselective Hydrogenation of Ethyl 2-Oxo-4-phenylbutyrate on Cinchona-Platinum Catalysts

Enantioselective hydrogenation of ethyl 2-oxo-4-phenylbutyrate to ethyl （R）-2-hydroxy-4-phenyl- bu- tyrate on Pt/γ-Al2O3 modified by 10,11-dihydrocinchonidine was studied by investigating the influences of the amount of modifier, initial concentration of reactant, pressure and temperature on conversion and enantiometric excess in a stirred autoclave and the effects of the liquid velocity, gas velocity, modifier concentration and various catalytic beds in a trickle-bed reactor. The maximum optical yields were about 50% and 60% in the two types of reactors, respectively. It was assumed that the total hydrogenation rate included the reaction rates over the unmodified and modified active sites on platinum surface and a kinetic model, which fitted the experimental data well in autoclave, was obtained. A simplified plug-flow model was proposed to describe the bed average efficiency of trickle-bed reactor.

Highly efficient synthesis of(R)-1,3-butanediol via anti-Prelog reduction of 4-hydroxy-2-butanone with absolute stereoselectivity by a newly isolated Pichia kudriavzevii

(R)-1,3-butanediol is an important pharmaceutical intermediate, and the synthesis of(R)-1,3-butanediol using green biological methods has recently been of interest for industrial application. Here, a novel strain QC-1 that efficiently transforms 4-hydroxy-2-butanone to(R)-1,3-butanediol was isolated from soil samples. Based on morphological, physiological, and biochemical tests and 5.8 S-internal transcribed spacer sequencing, the strain was identified as Pichia kudriavzevii QC-1. The reaction conditions were optimized to 35 ℃, pH 8.0, rotation speed 200 rpm, and 6:5 mass ratio of glucose to 4-hydroxy-2-butanone. Evaluation of the effects of 4-hydroxy-2-butanone concentrations on yield and cell survival rate showed that 85.60 g·L^-1 product accumulated, with an enantiomeric excess of more than 99%, when 30 g·L^-14-hydroxy-2-butanone was added at 0, 10, and 30 h in a 3-L bioreactor. Thus, strain QC-1 showed excellent catalytic activity and stereoselectivity for the synthesis of(R)-1,3-butanediol from 4-hydroxy-2-butanone.

A New Halogenated Biindole and A New Apo-carotenone from Green Alga Chaetomorpha basiretorsa Setchell

A new halogenated biindole and a new apo-carotenone have been isolated from the ethanolic extract of the green alga Chaetomorpha basiretorsa Sethcell. On the basis of chemical and spectroscopic methods including 2D NMR technique, their structures have been elucidated as 4,4′-dichloro-5,5′-dibromo-7,7′-dimethoxy-2,2′-bi-1H-indole and 1′S*,4′R*-8-(4′-hydroxy-2′,6′,6′- trimethylcyclohex-2-enyl)-6-methyloct-3E,5E,7E-trien-2-one, respectively.

Redesign of a short-chain dehydrogenase/reductase for asymmetric synthesis of ethyl (R)-2-hydroxy-4-phenylbutanoate based on per-residue free energy decomposition and sequence conservatism analysis

As an important building block for the synthesis of angiotensin-converting enzyme inhibitors,ethyl(R)-2-hy-droxyl-4-phenylbutanoate[(R)-HPBE]has attracted increasing attention.The key to industrial biosynthesis of(R)-HPBE is a biocatalyst that efficiently reduces ethyl 2-oxo-4-phenylbutanoate(OPBE)with high R-enantiose-lectivity.This paper proposed a strategy for identifying key residues involved in enantioselectivity control based on per-residue free energy decomposition and sequence conservatism analysis.Using this strategy,4 noncon-servative sites with high energy contribution to binding of OPBE were chosen as engineering targets,generating variant Mu27 with 99%conversion and 98%(R)ee value at substrate loading of up to 500 mmol/L.MD simu-lations suggested the higher stability and formation probability of Mu27-OPBEproR prereaction state as key rea-sons for the excellent R-enantioselectivity of Mu27 towards OPBE.The success in this study provides a viable approach for rational design of alcohol dehydrogenases with high enantioselectivity towards unnatural substrates.

A New Bisxanthone from Hypericum japonicum Thunb.ex Murray

A new bisxanthone, named bijaponicaxanthone C, was isolated from the whole plant of Hypericum japonicum. The structure was elucidated as 6-[1’’,5’’,6’’-trihydroxy-2’’’-(β-hydroxy-β- methylethyl)-2’’’,3’’’-dihydrofuran(5’’’,4’’’,3’’,4’’)xanthone-3’’’-oxyl]-1,3,5-trihydroxy-4-isoprenylxant- hone (1) on the basis of the spectral and chemical evidences.

Two pairs of unusual scalemic enantiomers from Isatis indigotica leaves

Two pairs of unusual scalemic enantiomers with a dimethoxyphenyl）ethyl]-2-methoxyindolin-3-one, novel carbon skeleton of 2-[1′-（4＂-hydroxy-3＂,5＂- named isatidifoliumindolinones A-D （1-4）, were isolated from an aqueous extract of lsatis indigotica leaves （da qing ye）. Their structures including absolute configurations were determined by spectroscopic data analysis combined with comparison of their experimental CD and calculated ECD spectra. Validity of the ECD spectra calculation to assign the absolute configurations is discussed. Plausible biosynthetic pathways of 1-4 are proposed. Stereochemistry-dependent activity against LPS-induced NO production in BY2 cells was observed, and among the stereoisomers compound 4 is most active.