Aromatic aldehydes as substrates for yeast and yeast alcohol dehydrogenase

The conversion of benzaldehyde to optically active L-phenylacetyl carbinol by yeast fermentation is a key step in the manufacture of L-ephedrine.' Typical fermentation raw materials are molasses, which provides a source of hexoses for glycolysis, and benzaldehyde.L-phenylacetyl carbinol formation is catalyzed by the pyruvate decarboxylase complex.'In the carboligase reaction, pyruvate is decarboxylated to active acetaldehyde which forms the carbinol product in the presence of benzaldehyde cosub-~t r a t e .~' ~ Quantitative conversion of benzaldehyde to phenylacetyl carbinol is never achieved and usually some of the benzaldehyde is reduced to benzyl alcoh01.~*~Benzoic acid may also be produced at very low levek7It has previously been reported* that Saccharomyces cerevisiae can also catalyze the conversion of 3-methoxy-4-hydroxy benzaldehyde and 3,4-methylenedioxybenzaldehyde to the corresponding optically active acyloin compounds ~(-)-3-methoxy-4-hydroxyphenylacetyl carbinol and ~(-)-3,4-methylenedioxyphenylacetyl carbinol respectively.Under these conditions, side reactions involving formation of the corresponding substituted aromatic alcohols are likewise usually formed.Selected strains of Aerobacter aerogenes can also catalyze the conversion of