Silicon Effect on the Enantioselective Transcyanation of Acetyltrimethylsilane Examined by Different Oxynitrilases

The synthesis of optically active （R）- and （S）-2-trimethylsilyl-2-hydroxyl propionitrile by enantioselective transcyanation of acetyltrimethylsilane with acetone cyanohydrin was successfully carded out using defatted plum, loquat , peach, almond or apple seed meals as （R）-oxynitrilase source and using Manihot esculenta leaves as （S）-oxynitrilase source in a biphasic system with good conversion and high enantiomeric excess. Comparative study demonstrated that silicon atom in substrate showed great effect on the reaction and due to the unique characteristics of silicon atom, both the substrate conversion and the product e.e. of the transcyanation of acetyltrimethylsilane were much higher than those of its carbon counterpart 3,3-dimethyl-2-butanone for all examined oxynitrilases.

Enzymatic Enantioselective Synthesis of (R)-2-Trimethylsilyl-2-hydroxyl-propionitrile by Defatted Apple Seed Meal

The enantioselective synthesis of ( R ) 2 trimethylsilyl 2 hydroxyl propionitrile by ( R ) oxynitrilase contained in defatted apple seed meal in a biphasic system was successfully performed. The influences of some factors on the reaction were investigated systematically. Diisopropyl ether was found to be the best for this reaction among all the organic solvents examined. The optimal concentration of defatted apple seed meal, aqueous phase content, concentrations of acetyltrimethylsilane and acetone cyano^hydrin, buffer pH, reaction temperature were 4% ( W/V ), 23% ( V/V ), 20 mmol·L -1 , 40 mmol·L -1 , pH=5 0 and 40 ℃, respectively, under which the initial reaction rate, substrate conversion and product enantiomeric excess were 9 4 mmol·L -1 ·h -1 , 99% and >99%, respectively.

Asymmetric Syntheses Aided by Biocatalysts

This article summarizes the achievements of the authors' group in the area of biocatalyst catalyzed organic reactions in recent 10 years. A strain of Geotrichum sp. obtained by screening is capable of stereoselectively reducing a number of carbonyl compounds. In many cases, the stereochemistry is complementary with that obtained by baker's yeast. Therefore, this micro organism provides a useful pathway to the preparation of alcohol compounds with specific configurations. On the other hand, a number of plant sources have been screened for oxynitrilases and the hydrocyanation reactions of various arylcarboxaldehydes have been investigated. A “micro aqueous reaction system' was invented, by which a series of novel optically active cyanohydrins were prepared. On this basis, a high through put continuous reaction system has been designed. This paper also describes examples of the syntheses of bio active compounds by using the optically active compounds obtained from the above mentioned catalytic reactions as precursors.