First total synthesis of the (±)-2-methoxy-6-heptadecynoic acid and related 2-methoxylated analogs as effective inhibitors of the leishmania topoisomerase IB enzyme

The fatty acids (+/-)-2-methoxy-6Z-heptadecenoic acid, (+/-)-2-methoxy-6-hepta decynoic acid, and (+/-)-2-methoxyheptadecanoic acid were synthesized and their inhibitory activity against the Leishmania DNA topoisomerase IB enzyme (LdTopIB) determined. Both 2-OMe-17: 1 fatty acids were synthesized from 4-bromo-1-pentanol, the olefinic fatty acid in 10 steps and in 7 % overall yield, while the acetylenic fatty acid in 7 steps and in 14 % overall yield. The 2-OMe-17:0 acid was prepared in 6 steps and in 42 % yield from 1-hexa decanol. The 2-OMe-17: 1 acids inhibited LdTopIB, with the acetylenic acid displaying an EC50 = 16.6 +/- 1.1 mu M, but the 2-OMe-17:0 acid did not inhibit LdTopIB. The (+/-)-2-methoxy-6Z-heptadecenoic acid preferentially inhibited LdTopIB over the human TopIB enzyme. Unsaturation seems to be a prerequisite for effective inhibition, rationalized in terms of weak intermolecular interactions between the active site of LdTopIB and either the double or triple bonds of the fatty acids. Toxicity toward Leishmania donovani promastigotes was also investigated, resulting in the order acetylenic > olefinic > saturated with the (+/-)-2-methoxy-6-heptadecynoic acid displaying an EC50 = 74.0 +/- 17.1 mu M. Our results indicate that alpha-methoxylation decreases the toxicity of C-17:1 fatty acids toward L. donovani promastigotes, but improves their selectivity index.