Yeast-mediated stereoselective synthesis

Chapters are also included on yeast-mediated stereoselective biocatalysis, stereoselective synthesis of steroids, chemo-enzymatic synthesis of enantiopure arylpropionic acids, supercritical carbon dioxide as a solvent in enzyme catalysis, state-of-the-art techniques in enzyme immobilization, biocatalysis by polyethylene glycol-modified enzymes, and enzymatic deprotection techniques in organic synthesis. 

Bakers s yeast is the most widely employed biocatalyst for asymmetric ketone reductions [43]. A group at Roussel Uclaf described an industrial application of bakers yeast mediated ketone reduction for the synthesis of trimegestone [44], a progestomimetic compound for the treatment of postmenopausal diseases. The key step of the nine-step synthesis is a chemo-, regio- and stereoselective bakers yeast reduction of the triketone 5 (Scheme 4.9). This transformation could not be performed efficiently using nonenzymatic methods. 

A chemo-enzymatic enantiospecific synthesis of (S)-coriolic acid, (13S)-hy-droxy-18 2(9Z,ll ), mediated via immobilized alcohol dehydrogenase of baker s yeast has been described (31). 15,16-Didehydrocoriolic acid, 13-hydroxy-18 3(9Z, 11E, 15Z), was stereoselectively synthesized starting from pent-2-en-4-yn-1 -ol (32). Four stereoisomers of 9,10,13-trihydroxy-18 l(ll ) were derived from methyl 9,10-epoxy-12-octadecenoate. The latter was obtained by partial epoxidation of methyl linoleate. These trihydroxy C j g fatty acids are potential antirice blast fungal substances (33). (115)-Hydroxy-(125,13S)-epoxy-18 2(9Z,15Z) was synthesized from D-mannose (34). 

Stereoselective carbon-carbon bond-forming reactions are among the most useful S5mthetic methods in asymmetric synthesis as they allow the simultaneous creation of up to two adjacent stereocenters. Acyloin formation mediated by thiamine diphosphate-dependent decarboxylase, yeast pyruvate decarboxylase, bacterial benzoylformate decarboxylase, and phenylpyruvate decarboxylase has been reported [142-147]. 

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