Asymmetric Total Synthesis of Mycobacterial Diacyl Trehaloses Demonstrates a Role for Lipid Structure in Immunogenicity.

The first asymmetric total synthesis of three structures proposed for mycobacterial diacyl trehaloses, DAT, DAT, and DAT is reported. The presence of two of these glycolipids, DAT and DAT, within different strains of pathogenic M. tuberculosis was confirmed, and it was shown that their abundance varies significantly. In mass spectrometry, synthetic DAT possessed almost identical fragmentation patterns to presumptive DAT from H37Rv, but did not coelute by HPLC, raising questions as the precise relationship of the synthetic and natural materials. The synthetic DATs were examined as agonists for signaling by the C-type lectin, Mincle. The small differences in the chemical structure of the lipidic parts of DAT, DAT, and DAT led to drastic differences of Mincle binding and activation, with DAT showing similar potency as the known Mincle agonist trehalose dimycolate (TDM). In the future, DAT could serve as basis for the design of vaccine adjuvants with simplified chemical structure.