Structure and reactions of lactonic and acidic sophorosides of 17-hydroxyoctadecanoic acid

Abstract

The complete structures of the major components of the mixture of lactonic and acidic sophorosides of 17-L-hydroxyoctadecanoic acid, which is produced by a yeast of the genus Torulopsis, have been determined. The principal lactonic component (1) (41%) has acetate groups at the 6′- and 6″-positions and the fatty acid carboxyl group is linked to the 4″-position to form a macrocyclic lactone ring. The other lactonic component (2) (8%) differs from the first only in the absence of the acetate group at the 6′-position. The principal acidic component (5) (31%) also has acetate groups at the 6′- and 6″-positions but the fatty acid carboxyl group is free. The structures were deduced by a combination of glycol cleavage and nuclear magnetic resonance studies and by examination of the products of acetobrominolysis of the acetylated lactones and acid.The 2″,3″-glycol group of the lactones is resistant to oxidation by periodate and by lead tetraacetate in acetic acid. Studies of the rate of glycol cleavage of methyl 4,6-di-O-acyl-β-D-glucopyranosides showed that though an acyl group at C-4 retarded the oxidation of the 2,3-diol it did not stop it completely. The conformation of the lactone ring is probably responsible for the unreactivity of the 2″,3″-glycol group. The lactone ring, however, considerably increases the rate of acetobrominolysis of the fully acetylated lactone compared to that of the acetylated sophorosyl acid methyl ester.