Configurational assignment of optically active hydroperoxy homoallylic alcohols and the corresponding diols by circular dichroism and multidimensional gas chromatography

Allylic hydroperoxides are a class of compounds of versatile synthetic utility. Optically active diastereomeric hydroperoxy homoallylic alcohols and their corresponding diols are easily available through horseradish peroxidase (HRP)-catalyzed kinetic resolution of racemic hydroperoxides. Here we describe the assignment of the absolute configuration of the optically active products and substrates obtained after HRP-catalysis by the circular dichroism exciton chirality method. Moreover, the analytical-scale separation of the enantiomers based on multidimensional gas chromatography on chiral columns is presented. Since the enantiomeric elution order on the ciral columns was constituted, the absolute stereochemistry of optically active allylic diols can easily be deduced by their retention times on β-cyclodextrins. Chirality 9:69–74, 1997. © 1997 Wiley-Liss, Inc.     

Synthesis and stereochemical characterization of optically active 1,2-diarylethane-1,2-diols: useful chiral controllers in the Ti-mediated enantioselective sulfoxidation

The series of phenylsubstituted 1,2-diphenylethane-1,2-diols 2a-h was prepared in high chemical (70--80%) and optical yields (approximately 90%) by Sharpless syn-dihydroxylation of the corresponding (E)-1,2-diarylethenes, in turn obtained by McMurry or Wittig reactions. The enantiomeric excesses of the samples were determined by HPLC analysis using Chiralcel OD chiral stationary phase (CSP). This CSP was able to resolve all the diols, except for 2g, with alpha values ranging between 1.10--1.64. In all cases the (R,R) antipode was eluted first. (R,R) absolute configuration was assigned to the dextrorotatory (CHCl(3)) diols 2a--h by analyzing the CD spectra of their 2,2-dimethyl-1,3-dioxolanes 3a--h. In fact, the CD spectra of all these dioxolanes present a positive couplet (210--180 nm range) which can be nonempirically related to an (R,R) absolute configuration of the two stereocenters.     

Synthesis of racemic and optically active glycidic ethers,precursors of liquid crystalline polyethers

A series of racemic and optically active oxiranes, bearing mesogenic groups, precursors of liquid crystalline polyethers, has been synthesized from epichlorohydrin or glycidol. The enantiomeric excess of the optically active oxiranes has been determined by chiral stationary phase HPLC. Compounds bearing 4-cyanobiphenyl mesogenic group exhibit monotropic liquid crystalline behavior. A transfer of chirality to the mesophase has been observed for the optically active oxiranes, which present a cholesteric phase. Chirality 10:779–785, 1998. © 1998 Wiley-Liss, Inc.     

Chemoenzymatic synthesis of optically active, biodegradable polymers based on phenyl- and naphthyl-ethanols esterified with divinyladipate

For the purpose of developing a new synthetic polymer containing an asymmetric molecule branch, three racemic alcohols, i.e. 1-phenylethanol, 1-(4-methylphenyl)ethanol and 1-(2-naphthyl)ethanol, were esterified enzymatically with divinyladipate using a lipase from Pseudomonas cepacia. The enzymatic acylation of alcohols produced monoacylated products. Optically active polymerizable monomers, (R)-vinyl adipic acid (phenyl-1-yl) ethyl ester, (R)-vinyl adipic acid (4-methylphenyl-1-yl) ethyl ester and (R)-vinyl adipic acid (2-naphthyl-1-yl) ethyl ester with enantiometric excesses over 99%, 96% and 99%, respectively, were obtained. Each optically active monomer was then subjected to free radical polymerization, to give polymers having a number average molecular weight of 2.9 x 10(3) - 2.2 x 10(4). These polymers are considered useful as optically active polymers having biodegradability.     

Synthetic Racemate and Enantiomers of Cytosporone E,a Metabolite of an Endophytic Fungus,Show Indistinguishably Weak Antimicrobial Activity

The racemate and the enantiomers of cytosporone E [3-heptyl-4,5,6-trihydroxyphthalide (1)], a metabolite of the endophytic fungus, CR200 (Cytospora sp.), were synthesized. The key steps were (i) Sharpless asymmetric dihydroxylation of an alkene (8) and (ii) HPLC separation of the enantiomers of tert-butyldimethylsilyl ether (12) on a chiral stationary phase. The racemate and enantiomers of cytosporone E showed only weak antimicrobial activity with no difference among them.     

Synthesis of chiral vicinal diols and analysis of them by capillary zone electrophoresis

This paper describes an improved access to 1,4-bis (9-O-quininyl) phthalazine [(QN)(2)PHAL], a very useful chiral ligand for catalytic asymmetric dihydroxylation (AD), by using CaH(2) as acid-binding reagent in a high yield under mild conditions. The application of (QN)(2)PHAL to the AD reactions of eight olefins exhibited excellent enantioselectivity and activity with corresponding chiral vicinal diols. Furthermore, a capillary zone electrophoresis method was developed to separate the aforementioned chiral vicinal diols by using of neutral beta-cyclodextrin (beta-CD) as chiral selector and borate as running buffer. High resolution was achieved under the optimal conditions of beta-CD 2.2% (w/v), pH 10, 200 mM borate buffer at 15 kV, and 20 degrees C within 15 min. The relative standard deviations of the corrected peak areas and migration time were less than 3.9% and 1.3%, respectively. In addition, the developed method was successfully applied to the determination of the purity and the enantiomeric excesses value (%ee) of the AD reaction products.     

Highly selective anti-Prelog synthesis of optically active aryl alcohols by recombinant Escherichia coli expressing stereospecific alcohol dehydrogenase

Biocatalytic asymmetric synthesis has been widely used for preparation of optically active chiral alcohols as the important intermediates and precursors of active pharmaceutical ingredients. However, the available whole-cell system involving anti-Prelog specific alcohol dehydrogenase is yet limited. A recombinant Escherichia coli system expressing anti-Prelog stereospecific alcohol dehydrogenase from Candida parapsilosis was established as a whole-cell system for catalyzing asymmetric reduction of aryl ketones to anti-Prelog configured alcohols. Using 2-hydroxyacetophenone as the substrate, reaction factors including pH, cell status, and substrate concentration had obvious impacts on the outcome of whole-cell biocatalysis, and xylose was found to be an available auxiliary substrate for intracellular cofactor regeneration, by which (S)-1-phenyl-1,2-ethanediol was achieved with an optical purity of 97%e.e. and yield of 89% under the substrate concentration of 5 g/L. Additionally, the feasibility of the recombinant cells toward different aryl ketones was investigated, and most of the corresponding chiral alcohol products were obtained with an optical purity over 95%e.e. Therefore, the whole-cell system involving recombinant stereospecific alcohol dehydrogenase was constructed as an efficient biocatalyst for highly enantioselective anti-Prelog synthesis of optically active aryl alcohols and would be promising in the pharmaceutical industry.     

Enantioselective synthesis and antioxidant activity of 3‐(3,4‐dihydroxyphenyl)‐glyceric acid—Basic monomeric moiety of a biologically active polyether from Symphytum asperum and S. caucasicum

The racemic and enantioselective synthesis of a novel glyceric acid derivative, namely, 2,3‐dihydroxy‐3‐(3,4‐dihydroxyphenyl)‐propionic acid as well as the antioxidant activities is described. The virtually pure enantiomers, (+)‐(2R,3S)‐2,3‐dihydroxy‐3‐(3,4‐dihydroxyphenyl)‐propionic acid and (?)‐(2S,3R)‐2,3‐dihydroxy‐3‐(3,4‐dihydroxyphenyl)‐propionic acid were synthesized for the first time via Sharpless asymmetric dihydroxylation of trans‐caffeic acid derivatives using the enantiocomplementary catalysts, (DHQD)₂‐PHAL and (DHQ)₂‐PHAL. The determination of enantiomeric purity of the novel chiral glyceric acid derivatives was performed by high‐performance liquid chromatographic techniques on the stage of their alkylated precursors. The novel glyceric acid derivatives show strong antioxidant activity against hypochlorite and N,N‐diphenyl‐N‐picryl‐hydrazyl free radical. Their antioxidant activity is about 40‐fold higher than that of the corresponding natural polyether and three‐fold higher of trans‐caffeic acid itself. Chirality, 2010. © 2010 Wiley‐Liss, Inc.     

Chiral separation machinery using new crystalline inclusion hosts: Match/mismatch in the enantiomer recognition of (R,S)-1-methoxy-2-propanol effected by a borneol/fenchol building block exchange in the host molecule

New chiral host molecules 1 and 2 involving a bulky terpenoid unit and aromatic ethyne spacer groups were synthesized using Pd-catalyzed cross-coupling reactions of (+)-2α-ethynyl-2β-hydroxybornane (4) or (+)-2α-ethynyl-2β-hydroxyfenchane (5) with 9,10-dibromoanthracene. Host compounds 1 and 2 from crystalline inclusions with 1-methoxy-2-propanol (3) in 1:1 and 1:2 stoichiometry, respectively. In the case of 1, complete enantiomer resolution (ee > 99%) of 3 is effected in one cocrystallization step. However, constitutional isomer 2 failed in the enantiomer separation of 3, which might be explained due to the different crystal lattice buildup of these cocrystals. Chirality 9:203–210, 1997. © 1997 Wiley-Liss, Inc.