Application of baker's yeast in bioorganic synthesis

Baker's yeast has been widely used as a biocatalyst in organic synthesis, primarily because it is inexpensive and readily available. The majority of studies on the biotransformation capability of yeast deal with reductions of carbonyl groups and carbon–carbon double bonds. Reactions involving carbon–carbon bond formation are of great interest in chemical synthesis. Most of these biocatalytic reactions have been carried out in aqueous media. The conversion of benzaldehyde and pyruvate to L-phenylacetyl carbinol (a precursor of ephedrine) was one of the first commercial processes to utilize an enzyme biotransformation step. During this biotransformation, a proportion of the benzaldehyde is also reduced to benzyl alcohol. Detailed investigations have been carried out on factors affecting product formation by whole yeast cells, mainly in aqueous systems. The reaction mechanisms involved in pyruvate decarboxylase mediated formation of L-phenylacetyl carbinol have been reported. Recent studies on biocatalysis of benzaldehyde and substituted benzaldehyde to benzyl alcohol by whole cells of wild-type and mutant strains of baker's yeast in nonconventional media have established the effects of organic solvents and substrate hydrophobicity on reaction performance. The effect of solvent and substituted benzaldehyde substrate hydrophobicity on the kinetics of yeast alcohol dehydrogenase catalyzed reactions in nonconventional media will also be discussed. Key words: Saccharomyces, baker's yeast, biotransformations, organic synthesis.