Synthesis of a derivative of racemic 3-hydroxy-2,4,6-trimethyltetracosanoic (mycolipanolic) acid and racemic 2,4,6-trimethyltetracos-2-enoic (mycolipenic) acid

Racemic 2,4-dimethyldocosanol, available from previous studies, was oxidised to the aldehyde using pyridinium chlorochromate. Aldol reaction of 2,4-dimethyldocosanal with methyl propionate afforded racemic methyl 3-hydroxy-2,4,6-trimethyltetracosanoic acid. The hydroxy function was protected as a tert-butyldimethylsilyl ether and the ester functionality hydrolysed to the free acid. Wittig reaction of 2,4-dimethyldocosanal using 1-carboethoxyethylidenetriphenylphosphorane afforded the (E)-stereoisomer following removal of the small quantities of (Z)-isomer by column chromatography. The ethyl ester was hydrolysed to afford racemic 2,4,6-trimethyltetracos-2-enoic acid. These unusual fatty acids are characteristic of Mycobacterium tuberculosis.