The structure of an antigenic glycolipid (SL-IV) from Mycobacterium tuberculosis

The structure of an antigenic glycolipid isolated recently from cell walls of various strains of Mycobacterium tuberculosis and believed to be a sulfolipid consisting chiefly of 2,3-di-O-(hexadecanoyl/octadecanoyl)-alpha,alpha-trehalose 2'-sulfate (designated as SL-IV), was reinvestigated by mass spectrometry and nuclear magnetic resonance spectroscopy. The material proved to be a complex mixture of closely related components which are indeed 2,3-di-O-acyltrehaloses. However, no sulfate group was found in the antigen, and revision of its designation as a sulfolipid is therefore required. The lipid substituents comprise an estimated 20% of C14-C19 fatty acids, including tetradecanoic (myristic), 9-tetradecenoic (myristoleic), 9-hexadecenoic (palmitoleic), 9-octadecenoic (oleic), 10-methylhexadecanoic (tuberculopalmitic), and 10-methyloctadecanoic (tuberculostearic) acids in addition to hexadecanoic (palmitic) and octadecanoic (stearic) acids, and approximately 80% of higher, methyl-branched acids. Among the latter are, principally, 2,4-dimethyldocosanoic and 3-hydroxy-2,4,6- trimethyltetracosanoic acids, and a smaller proportion of 2,4,6-trimethyltetracos-2-enoic acid. Numerous further acids, related to those mentioned by methylene homology, are also present in small proportions.