Enzyme-mediated regioselective acylations of sophorolipids

Enzymatic synthesis of well-defined sophorolipid analogues for evaluation of their bioactivities and as new building blocks for the preparation of glycolipid-based amphiphilic polymers is described. Lipase Novozym 435 from Candida antarctica has been shown to be an efficient catalyst for acylation of sophorolipids esters. A mixture of sophorolipids produced by Torulopsis bombicola was esterified by reaction with sodium alcoxide. The alkyl esters of sophorose lipids were subjected to Novozym 435 catalyzed acylation in dry tetrahydrofuran (THF) with vinyl acrylate and vinyl acetate to diacyl derivatives. The reactions were highly regioselective, and exclusive acylation of the hydroxyl groups on C-6' and C-6" took place. Methyl ester in the absence of the acylating agent, or with the agent at a concentration less than equimolar, gave sophorolactone (9). Careful analysis of the spectral data revealed it to be a synthetic analogue of microbially produced macrolactone. Sophorolactone (9) differs in the site at which the sophorose ring is attached to the fatty acid. Specifically, in 9, unlike the natural sophorolipids, the fatty acid carboxyl carbon is linked to the C-6" hydroxyl, not to the C-4" hydroxyl. Subsequent acrylation of 9 catalyzed by Novozym 435 led to the formation of the C-6' monoacryl derivative linked only to the primary site.