Asymmetric Total Synthesis and Structural Revision of DAT₂, an Antigenic Glycolipid from Mycobacterium tuberculosis

DAT₂ is a member of the diacyl trehalose family (DAT) of antigenic glycolipids located in the mycomembrane of Mycobacterium tuberculosis (Mtb). Recently it was shown that the molecular structure of DAT₂ had been incorrectly assigned, but the correct structure remained elusive. Herein, the correct molecular structure of DAT₂ and its methyl-branched acyl substituent mycolipanolic acid is determined. For this, four different stereoisomers of mycolipanolic acid were prepared in a stereoselective and unified manner, and incorporated into DAT₂. A rigorous comparison of the four isomers to the DAT isolated from Mtb H37Rv by NMR, HPLC, GC, and mass spectrometry allowed a structural revision of mycolipanolic acid and DAT₂. Activation of the macrophage inducible Ca²⁺-dependent lectin receptor (Mincle) with all four stereoisomers shows that the natural stereochemistry of mycolipanolic acid / DAT₂ provides the strongest activation, which indicates its high antigenicity and potential application in serodiagnostics and vaccine adjuvants.