RATIONALIZING THE ORIGIN OF SOLERONE (5-OXO-4-HEXANOLIDE) - BIOMIMETIC SYNTHESIS AND IDENTIFICATION OF KEY METABOLITES IN SHERRY WINE

A biomimetic synthesis of solerone (5-oxo-4-hexanolide, 1) using both enzymatic and acid-catalyzed reactions was performed. Starting from L- glutamic acid 5-ethyl ester (2) enzymatic oxidative deamination follow ed by subsequent decarboxylation of the corresponding 2-oxoglutaric ac id Ei-ethyl ester (3) led to ethyl 4-oxobutanoate (4). In the presence of pyruvate, 4 served as key substrate for a novel acyloin condensati on catalyzed by pyruvate decarboxylase (EC 4.1.1.1) from Saccharomyces cerevisiae. Finally, the resulting ethyl 4-hydroxy-5-oxo-hexanoate (5 ) was easily converted into solerone (1) in the presence of acid. The acyloin condensation of 3 with acetaldehyde to ethyl 5-hydroxy-4-oxohe xanoate (6) revealed an alternative route to solerone (1). Acid-cataly zed lactonization of 6 produced 4-oxo-5-hexanolide (7) as well as 5 an d 1 via keto-enol tautomerization. Confirming the relevance of the pro posed biogenetic pathway, the solerone precursors 2-6 as well as delta -lactone 7 were identified in sherry by GC/MS analysis for the first t ime.