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

Abstract

The fatty acids (±)-2-methoxy-6Z-heptadecenoic acid (1), (±)-2-methoxy-6-heptadecynoic acid (2) and (±)-2-methoxyheptadecanoic acid (3) were synthesized and their inhibitory activity against the Leishmania DNA topoisomerase IB enzyme (LdTopIB) determined. Acids 1 and 2 were synthesized from 4-bromo-1-pentanol, the former in ten steps and in 7% overall yield, while the latter in seven steps and in 14% overall yield. Acid 3 was prepared in six steps and in 42% yield from 1-hexadecanol. Acids 1–3 inhibited the LdTopIB enzyme following the order 2 > 1 ⪢ 3, with 2 displaying an EC50 = 16.6 ± 1.1 μM and 3 not inhibiting the enzyme. Acid 1 preferentially inhibited the LdTopIB enzyme 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 towards Leishmania donovani promastigotes was also investigated resulting in the same order 2 > 1 > 3, with 2 displaying an EC50 = 74.0 ± 17.1 μM. Our results indicate that α-methoxylation decreases the toxicity of C17:1 fatty acids towards L. donovani promastigotes, but improves their selectivity index.

Novel Very Long‐Chain α‐Methoxylated Δ5,9 Fatty Acids from the Sponge Asteropus niger Are Effective Inhibitors of Topoisomerases IB

“…The inhibitory activities of 1a – 1b towards either L TopIB or h TopIB were determined as previously described [13]. One unit of both enzymes was assayed in a plasmid DNA relaxation assay for 30 min at 37 °C in the presence of 0.15 – 10 mg/mL of 1a – 1b .…”

“…Since we did not have the corresponding C 27 non-methoxylated Δ5,9 FA at hand, it was not possible to test how the C-2 methoxy group affected the binding to h TopIB. However, out of the 2-methoxylated FA that we have tested so far [13], acids 1a – 1b are certainly the best inhibitors of h TopIB. This result implies that the very long chains are indeed needed for an effective h TopIB inhibition.…”

“…For example, it can be speculated that the α-methoxy functionality in the FA will make additional favorable binding interactions between the FA and the h TopI enzyme as the acidity of the FA is expected to increase (pKa 3.5 vs. 4.8) and the extra oxygen of the methoxy group can provide an additional hydrogen bond acceptor (HBA) in the molecule. In fact, we have previously shown that the (±)-2-methoxy-6-heptadecynoic acid is a better inhibitor (EC 50 = 16.6 μM) of the Leishmania donovani DNA topoisomerase IB enzyme ( L TopIB) than 6-heptadecynoic acid (EC 50 = 71.7 μM) [13]. Interestingly, the latter two acids were not as effective towards the h TopIB enzyme [13].…”

“…In fact, we have previously shown that the (±)-2-methoxy-6-heptadecynoic acid is a better inhibitor (EC 50 = 16.6 μM) of the Leishmania donovani DNA topoisomerase IB enzyme ( L TopIB) than 6-heptadecynoic acid (EC 50 = 71.7 μM) [13]. Interestingly, the latter two acids were not as effective towards the h TopIB enzyme [13]. In fact, all the short-chain FA that we have tested so far have been more effective towards L TopIB than h TopIB [13].…”

“…Interestingly, the latter two acids were not as effective towards the h TopIB enzyme [13]. In fact, all the short-chain FA that we have tested so far have been more effective towards L TopIB than h TopIB [13]. …”