Sulfatides of Mycobacterium tuberculosis: the structure of the principal sulfatide (SL-I).

The gross structural features of five families of multiacylated trehalose 2-sulfates elaborated by Mycobacterium tuberculosis strain H37Rv are described. The principal sufatide SL-I is a 2,3,6,6'-tetraacyl-alpha,alphs'-D-trehalose 2'-sulfate, whose component carboxylate substituents (and homolgy) were previously established. In the present study the specific locations of the acyl substituents were assigned. The desulfated glycolipid (SL-I-CF) was methanolyzed on a column of diethylaminoethylcellulose (free base form), affording tri-, di-, and monoacylated trehalose mixtures. The most abundant diacyltrehalose generated was identified as 6,6'-bis-(2,4,6,8,10,12,14,16-octamethyl-17-hydroxydotriaconta-noyl)trehalose (6,6'-bis(C40-hydroxyphthioceranoyl)trehalose), along with lower and higher homologues.A small amount (about 15%) of the unhydroxylated analogue (phthioceranate) was also recognized. From the monoacylated carbohydrate mixture (chiefly 6-(C40-hydroxyphthioceranoyl)trehalose) surviving trehalose monopalmitate(s) were isolated by preparative gas chromatography of the trimethylsilylated products. Trehalose 2-palmitate was identified as the principal component. Small amounts of the 3 isomer may also be present, but no 6-palmitate was detectable. Gentle acidic solvolysis, which minimizes the possibility of acyl migrations, afforded a different diacyltrehalose, identified by mass spectrometry of the permethylated derivative as principally 2-palmitoyl(stearoyl)-3-phthioceranoyltrehalose. A variant in which hydroxyphthioceranate substitutes at the 3 position was also recognized. The results indicate that the biological acylation processes at the trehalose core are not entirely specific, but instead yield an SL-I family, for the chief member of which a logical structural expression is deduced.