The hydroxy mycolic acids shown in Figure i, below, were prepared. Hydroxymycolic acids having the same chain lengths as these synthetic hydroxy mycolic acids have been isolated from Microbacterium bovis BCG and have also been detected amongst the mycolic acids of Mycobacterium tuberculosis.Figure i: The hydroxy mycolic acids synthesised in this study.An attempt was also made to synthesise the three different keto mycolic acids shown in Figure ii, below.
Figure ii: The keto mycolic acids synthesised in this study.
Unfortunately, during the final deprotection of the β-hydroxyl group and the acid OH of the keto mycolic acids, using basic media, epimerisation occurred at the a-methyl-ketone position of each of the keto mycolic acids shown above.
After many trial reactions, a new method was formulated, in which the final
deprotection could be carried out in acid media, resulting in the synthesis of a single enantiomer of the keto mycolic acid, Figure iii, below:
Figure iii: Using acid media for the final deprotection step resulted in a single enantiomer of keto mycolic acid
It would now be possible to obtain the other keto mycolic acids as single enantiomers, by applying this protection/deprotection method to their synthesis.
Biological testing was carried out using ELISA assays to determine the ability of the different mycolic acids to differentiate between TB positive and TB negative sera. Testing was also carried out on mouse models to determine the structural features of the mycolic acids required to elicit an inflammatory response.