An Asymmetric, Chemo-Enzymatic Synthesis ofO-Acetylcyanohydrins

Minor enantiomer recycling – a strategy to improve enantioselectivity

In enantioselective reactions, the major, desired enantiomer is commonly obtained along with the minor, undesired enantiomer. By continuous recycling of this undesired enantiomer back to starting material, products with improved enantiomeric purity can be obtained. Such in situ minor enantiomer recycling can be accomplished by coupling the catalytic reaction to an exergonic transformation of a sacrificial reagent. The method has been applied to the synthesis of O-acylated cyanohydrins, which serve as starting materials for a variety of biologically active compounds.

Obtaining enriched compounds via a tandem enantioselective reaction and kinetic resolution polishing sequence

Herein we describe a tandem method of coupling an enantioselective reaction with a nonenzymatic kinetic resolution to prepare highly enantioenriched compounds. The procedure employs a moderately selective enantioselective reaction on a ketone or aldehyde to form an enriched alcohol followed by a kinetic resolution of the alcohol to generate ee's of >99% in yields greater than what is possible with a kinetic resolution. This method highlights an avenue to quickly acquire highly enriched compounds without developing and optimizing a new methodology.

In situ evaluation of lipase performances through dynamic asymmetric cyanohydrin resolution

A dynamic resolution process based on multiple reversible cyanohydrin formation coupled to lipase-mediated transesterification is demonstrated. The resulting process resulted in the efficient evaluation of complex lipase performances in asymmetric cyanohydrin acylate synthesis. Dynamic systems were generated and resolved in situ, and the effects of the reaction conditions could be directly monitored for the overall system. By this concept, the enzyme activity, chemo- and stereoselectivity for all involved substrates could be simultaneously evaluated.