title: Stereochemistry and synthetic applications of products of fermentation of alpha,beta-unsaturated aromatic aldehydes by baker's yeast.
abstract: Baker's yeast fermenting on D-glucose converts 2-substituted C6-C3 alpha,beta-unsaturated aromatic aldehydes into the corresponding 3-phenylprop-2-en-1-ols and 3-phenylpropan-1-ols, and into the 4-substituted (2S,3R)-5-phenylpent-4-en-2,3-ols. The formation of the C6-C3 alcohols from the aldehydes by baker's yeast was already known, but the production of the methyl diols is new. The conversion of C6-C3 alpha,beta-unsaturated aldehydes into the C6-C5 methyl diols can be viewed as the overall consequence of two distinct chemical operations: (1) addition of a C2 unit equivalent to acetaldehyde onto the Si-face of the carbonyl carbon of the unsaturated aldehyde forms the (R)-alpha-hydroxy ketone in an acyloin-type condensation, and (2) reduction of this intermediate on the Re-face of the carbonyl gives the diol actually isolated. There is some tolerance by the enzymic system(s) involved in the reaction(s) leading from the C6-C3 alpha,beta-unsaturated aromatic aldehydes to the 4-substituted (2S,3R)-5-phenylpent-4-en-2,3-ols as far as the structure of the aromatic aldehydes and the substitutents in the alpha position are concerned, but acetaldehyde is the only aldehyde accepted as second terminus of the reaction. However, synthetic alpha-hydroxy ketones, prepared from aldehydes that cannot be directly converted by yeast into the corresponding methyl diols, are reduced by yeast. This indicates that the reason direct conversion of the aldehydes does not occur is that these materials probably cannot be accepted as substrates by the condensing enzyme(s). The (2S,3R)-diols can be used instead of natural carbohydrates as starting materials for the synthesis of optically active forms of natural products belonging to different structural classes. Applications of these diols in the synthesis of L-daunosamine, the natural form of vitamin E and other products are discussed.
mesh_terms: D000447:Aldehydes / Q000138:chemical synthesis / Q000378:metabolism*; D005285:Fermentation; D066298:In Vitro Techniques; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D013237:Stereoisomerism; D013379:Substrate Specificity; D014810:Vitamin E / Q000096:biosynthesis
chemical_list: D000447:Aldehydes; D014810:Vitamin E