TiCl4 promoted menthyl ester chiral auxiliary mediated synthesis of chiral syn-β-amino esters and applications of a representative syn-β-amino ester
摘要:
beta-Amino esters were obtained in up to 78% yield with 72:28-96:4 diastereomeric ratios by the reaction of the chiral titanium enolate of menthyl esters, prepared using the TiCl4/Et3N reagent system with prochiral imines. A representative syn-beta-amino ester derivative has been used for the resolution of racemic mandelic acid to obtain a sample with >99% ee in a single step. A representative syn-beta-amino ester was converted to the corresponding N-deprotected amino ester using the Pd-C/HCOOH reagent system, and then to the corresponding beta-amino acid using the glacial CH3COOH/HCl reagent system, and to the corresponding beta-lactam derivative with partial epimerization by the reaction using C2H5MgBr. (C) 2010 Elsevier Ltd. All rights reserved.
TiCl4 promoted menthyl ester chiral auxiliary mediated synthesis of chiral syn-β-amino esters and applications of a representative syn-β-amino ester
摘要:
beta-Amino esters were obtained in up to 78% yield with 72:28-96:4 diastereomeric ratios by the reaction of the chiral titanium enolate of menthyl esters, prepared using the TiCl4/Et3N reagent system with prochiral imines. A representative syn-beta-amino ester derivative has been used for the resolution of racemic mandelic acid to obtain a sample with >99% ee in a single step. A representative syn-beta-amino ester was converted to the corresponding N-deprotected amino ester using the Pd-C/HCOOH reagent system, and then to the corresponding beta-amino acid using the glacial CH3COOH/HCl reagent system, and to the corresponding beta-lactam derivative with partial epimerization by the reaction using C2H5MgBr. (C) 2010 Elsevier Ltd. All rights reserved.
Treatment of (−)-menthyl carboxylates(2) with 2 equiv of p-tolylsulfinylcarbanion(1) afforded the corresponding opticallyactive β-keto sulfoxides(3) together with opticallyactivemethyl p-tolyl sulfoxide. The enantiomeric purity and the predominant configuration of the products were discussed.
Candida rugosa lipase: Enantioselectivity enhancements in organic solvents
作者:Rose A. Persichetti、Jim J. Lalonde、Chandrika P. Govardhan、Nazer K. Khalaf、Alexey L. Margolin
DOI:10.1016/0040-4039(96)01430-x
日期:1996.9
Chiral resolutions of carboxylic acids (1-3) and alcohol (4) were carried out through esterification or transesterification in organic solvents using cross-linked enzyme crystals (CLEC(R)) of Candida rugosa lipase (CRL). Comparison of these results with those of elude CRL reveal significant differences. As was seen in resolution through hydrolysis,(1) a marked improvement in enantioselectivity is realized with the CLEC. Additionally, the stability afforded the enzyme in CLEC form leads to a higher activity in organic solvent. Copyright (C) 1996 Elsevier Science Ltd
Facile synthesis of chiral O-alkyl enol ethers
作者:Florence Charbonnier、Albert Moyano、Andrew E. Greene
DOI:10.1021/jo00387a038
日期:1987.5
Biocatalytic enantiomeric resolution of l-menthol from an eight isomeric menthol mixture through transesterification
The four diastereomers of menthol and their enantiomers, namely DL-menthol, DL-neomenthol, DL-neoisomenthol and DL-isomenthol, were synthesised by the hydrogenation of thymol to yield an eight isomer liquid menthol. A suitably selective lipase was sought to preferentially esterify L-menthol in organic solvent, hence simplifying separation from the diasteromeric mix through distillation. From an initial screen a commercial Pseudomonas fluorescens lipase (Amano AK) was selected, and vinyl acetate was chosen as a suitable irreversible acyl donor for transesterification. The reaction reagent ratios were optimised, and an enantiomeric excess (ee) of L-menthol of greater than 95% was reproducibly achievable at a conversion of 30% DL-menthol (0.68 M) at <= 50 degrees C. On the basis of the composition of liquid menthol the reaction had a diastereomeric excess (de) of 82%. The enzyme was recycled 150 times in 5 ml batch reactions using liquid menthol and achieving an overall yield of 184.3 g DL-menthol/g commercial enzyme preparation. The by-product acetic acid, formed by hydrolysis of menthyl acetate, was found to cause a high degree of enzyme inactivation.The resolution reaction was scaled up 400 fold to 2 L and the enzyme recycled 38 times with an average conversion of the available L-menthol of 59% and a volumetric productivity of 1.2 g/L/h. (C) 2011 Elsevier B.V. All rights reserved.
NAGAO, Y.;HAGIWARA, Y.;TOHJO, T.;HASEGAWA, Y.;OCHIAI, M.;SHIRO, M., J. ORG. CHEM., 53,(1988) N5, C. 5983-5986
作者:NAGAO, Y.、HAGIWARA, Y.、TOHJO, T.、HASEGAWA, Y.、OCHIAI, M.、SHIRO, M.