Communication: Synthesis of Me α-L-Rhap-(1↠3)-2-O-Me-α-L-Rhap And Me 2,3,4-Tri-O-Me-α-L-Fucp-(1↠3)-α-L-Rhap-(1↠3)-2-O-Me-α-L-Rhap : Oligosaccha-Ride Segments of Phenolic Glycolipids inMycobacterium Bovis BcgandTuberculosis Strain Canetti

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Abstract
The revived interest in phenolic glycolipids of pathogenic mycobacteria is evoked by a widespread1-3 use of Mycobacterium (M.) leprae specific antigen for serodiagnosis of leprosy patients. As a consequence, a few phenolic glycolipids of other mycobacterias were isolated and structurally elucidated. Recently Vercellone and Puzo4 reported the isolation of new phenolic glycolipids not yet described in M. bovis BCG. The combination of sugars in one of the glycolipids was identified as 3-O-(α-L-rhamnopyranosyl)-2-O-methyl-α-L-rhamnopyranoside (1) which is closely related to the trisaccharide segment (2) of M. tuberculosis strain Canetti.5 The latter contains 2,3,4-tri-O-methyl-L-fucopyranosyl monosaccharide α-linked to 3′ position of 1. It has been emphasised that new found glycolipids of M. bovis BCG could share common epitopes with those of M. tuberculosis, thus leading to false positive immunoabsorbent assay tests during screening of tuberculosis patients. In addition, there is concern regarding the involvement of one of the new found glycolipids in the stimulation of T suppressor cells, thus adding to the conflicting results noted in the protection of M. tuberculosis by M. bovis BCG. In essence the new found phenolic glycolipids of M. bovis BCG are associated with interesting but unclear biological profiles. We now report the synthesis of these closely related oligosaccharides, 1 (R = Me) and 2 (R = Me).