Regioselective enzyme-catalyzed synthesis of sophorolipid esters, amides, and multifunctional monomers

Novel enzyme-mediated synthetic routes were developed to provide a new family of sophorolipid derivatives and glycolopid-based amphiphilic monomers. These compounds are of great interest for their potential use in immunoregulation, as well as for other biological properties. In the present work, an efficient lipase-catalyzed conversion of sophorolipid ethyl ester to (a) the 6'-monoacylated derivatives using Novozym 435, (b) 6-monoacylated derivatives using Lipase PS-C, (c) secondary amide derivatives using Novozym 435, and (d) 6',6-diacylated amide derivatives using Novozym 435 in an one-pot reaction and (e) the regioselective monoacylation of an amide derivative at the 6'- and 6-positions using Novozym 435 and Lipase PS-C, respectively, are described. The ethyl ester produced by esterification of the sophorolipid mixture with sodium ethoxide was subjected to acylation catalyzed by Novozym 435 in dry tetrahedrofuran (THF) with vinyl acetate and vinyl methacrylate to produce 6'-monoacylated derivatives. In contrast, Lipase PS-C catalyzed acylations of sophorolipid ethyl ester in dry THF with vinyl acetate and vinyl methacrylate to give the corresponding 6'-monoacylated derivatives. Novozym 435 mediated amidation of sophorolipid ethyl ester in dry THF with phenethylamine, tyramine, p-methoxyphenethylamine, 2-(p-tolyl)ethylamine, and p-fluorophenethylamine generated the corresponding secondary amides but not tertiary amides. The formation of diacyl derivatives of amides was achieved by their treatment with vinyl acetate and vinyl methacrylate in dry THF using Novozym 435 as catalyst. The conversion of sophorolipid ethyl ester to the same diacyl derivatives of amide (i.e., both amidation and acylation) in high yield was also demonstrated in dry THF by a one-pot reaction using Novozym 435. Furthermore, regioselective monoacylation of a sophorolipid amide at 6' and 6 in dry THIP with vinyl acetate and vinyl methacrylate using Novozym 435 and Lipase PS-C was also demonstrated.