Direct synthesis of maradolipids and other trehalose 6-monoesters and 6,6'-diesters.

It was shown that reaction of trehalose with 1 equiv of a fatty acid in pyridine promoted by 1 equiv of the uronium-based coupling agent 2-(1H-benzotriazole-1-yl)-1,1,3,3-tetramethyluronium tetrafluoroborate (TBTU) at room temperature gives a good yield of the primary ester accompanied by small amounts of the diprimary ester using hexanoic, palmitic, and oleic acids as examples. Reactions using 2 equiv of the fatty acids gave the symmetrical diesters. The monoesters were reacted with different fatty acids to give nonsymmetric 6,6'-diesters in very good yields. Compounds synthesized include the most abundant component of the very complex maradolipid mixture, 6-O-(13-methyltetradecanoyl)-6'-O-oleoyltrehalose, and a component potentially present in this mixture, 6-O-(12-methyltetradecanoyl)-6'-O-oleoyltrehalose, a derivative of an ante fatty acid. The C5-C6 rotameric populations of 6-O-monoesters, symmetrical 6,6'-diesters, and 2,6,6'-triesters of fatty acids were calculated from the values of the H5-H6R and H5-H6S coupling constants and found to be similar to those found for glucose. The rotameric populations of the monosubstituted glucose residues in the 2,6,6'-triesters was altered considerably to favor the gt rotamer, presumably because of attraction between the 2- and 6'-fatty acid chains.