MECHANISMS OF FERULIC ACID CONVERSIONS TO VANILLIC ACID AND GUAIACOL BY RHODOTORULA-RUBRA

Resting cells of Rhodotorula rubra converted trans-ferulic acid (1) to vanillic acid (2), then to guaiacol (3) and protocatechuic acid (4), under aerobic conditions. In an argon atmosphere, R. rubra transformed ferulic acid to vanillic acid and 4-hydroxy-3-methoxystyrene (5). Met abolites were isolated by solid-phase extraction and characterized by mass spectrometry, H-1, and C-13-nuclear magnetic resonance spectrosco py (NMR). The biotransformation of ferulic acid to vanillic acid by R. rubra cell-free extracts required CoA, ATP, and NAD+. Mass spectromet ry and C-13-NMR were used to demonstrate the incorporation of oxygen f rom (H2O)-O-18 during the conversion of ferulic acid to vanillic acid. The results suggest a parallel between this bioconversion reaction an d the beta-oxidation of fatty acids. Proton-carbon correlation NMR spe ctroscopy was used to demonstrate the specific incorporation of deuter ium from D2O into guaiacol obtained from vanillic acid. The incorporat ion of deuterium implicates the involvement of a quinoid vanillic acid tautomer as an intermediate in the decarboxylation reaction.