Structure of mycolic acids and an intermediate in the biosynthesis of dicarboxylic mycolic acids

Abstract

The lipids of mycobacteria contain mycolic acids, which are α-alkyl, β-hydroxy acids with 70 to 80 carbon atoms. Mycolic acids isolated from a strain of Mycobacterium paratuberculosis can be written , and three types of compounds are studied: (I) R with two cyclopropanes; (II) R with a keto group; (III) R with a carboxyl group. The elucidation of the structure of the dicyclopropanic mycolic acid (I) is carried out by mass spectrometry of the acetylated ester, after a chromic oxidation, and R is: In the keto mycolic acid (II) R would appear to be: In the dicarboxylic mycolic acid (III) R is HOCO–(CnH2n–2) with n = 32 to 39. Etemadi [7] suggested that the dicarboxylic acids are produced from the keto mycolic acids by a biological Baeyer-Villiger oxidation, therefore he postulated an ester of the dicarboxylic acid (III) as an intermediate. This compound (IV) was isolated, and its structure is established by alkaline hydrolysis, pyrolytic gas chromatography and mass spectrometry: This compound, named “mycolic wax”, has either a free carboxyl, or is linked to glycerol to form a 1-monoglyceride; this glyceride is identified by mild hydrolysis and periodate oxidation on thin layer chromatography. Some further comments on the biogenesis of mycolic acids are added.