a-D-Trehalose present in Mycobacterium phleiMixtures of dimycolates of a-u-trehalose (cord factor) and monomycolates have been isolated from Mycohacterium phlei and separated as trimethylsilyl derivatives according to the polarity of the fatty acid residues. The free glycolipids can be recovered by mild hydrolysis. Silylation and desilylation reactions did not induce any isomerisation.The structure of these trehalose esters has been determined by using a series of reactions elaborated on synthetic acyl-sugar models. Free hydroxyl groups are transformed into tetrahydropyran ethers, deacylated by dimsyl sodium, methylated and the sugar derivatives are hydrolyzed. The O-methylsugars obtained contain a methyl ether group located at the position where the acyl group was present initially. Identification by gas chromatography of the 0-methyl-sugars thus allows the location of the fatty acid residues in the glycolipid. It has been demonstrated that no migration occurs.Two types of 6-monomycoloyl-a-~-trehalose have been isolated, differing by the nature of the mycolic acid residues. One of them, called MA, contains "a-phlei mycolic acid". The other one, called M,, contains "y-phlei mycolic acid" which is the ester of 2-eicosanol with the co-carboxyl function of a dicarboxylic mycolic acid.

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