A re-investigation of the mycolic acids of Mycobacterium avium

The isolation of the complete wax ester fraction of M. avium is described for the first time, including the trans-cyclopropane A as a major component. The mixture of minor trans-alkene wax diacids included the isomer B in which the methyl-substituent is on the distal carbon adjacent to the alkene. [Display omitted] •The in-tact wax ester fraction of M. avium is isolated for the first time, including a trans-cyclopropane with a distal methyl substituent as a major component.•The components correlate well with those partially reported earlier.•The mixtures of wax esters or of the corresponding wax diacids each contained minor amounts of a trans-alkene previously believed to have a methyl-substituent on the adjacent carbon proximal to the hydroxy-acid.•In both cases, it is now shown that the isomer in which the methyl-substituent is on the distal carbon adjacent to the alkene is also present.•In the case of the wax-diacid, this was the major isomer.•This isomer relates directly to the major trans-cyclopropane wax ester, and its isolation may be of value in analysing the rates of biochemical leading to different mycolic acids and wax esters. Mycolic acid methyl esters were extracted from Mycobacterium avium by a mild saponification protocol, designed to preserve labile components. The resulting mixture of α-, keto- and wax ester mycolates was accompanied by some degraded ω-carboxymycolic acid dimethyl esters, whose overall structures were found to support previous studies. Chromatography of the mono-carboxylic mycolates gave an inseparable mixture of keto- and wax ester mycolates and separate α-mycolates. Reduction of the ketomycolate components allowed isolation and characterisation of intact wax ester mycolates for the first time. Minor α- and ω-carboxymycolates were detected in which methyl branches were located on either the proximal or distal sides of trans-alkene groups.