The first total synthesis for the novel fatty acid (±)-2-methoxy-6-icosynoic acid was accomplished in seven steps and in a 14% overall yield starting from 2-(4-bromobutoxy)- tetrahydro-2H-pyran. The title compound displayed an EC50 = 23 ± 1 µM against the human SHSY5Y neuroblastoma cell line and an EC50 = 26 ± 1 µM against the human adenocarcinoma cervix cell line (HeLa) after 48 h of exposure. The corresponding non-methoxylated analog 6- icosynoic acid did not display cytotoxicity (EC50 > 500 µM) towards the studied cell lines as well as the 2-methoxyicosanoic acid (EC50 > 300 µM). The critical micelle concentration (CMC = 20–30 µM) for the (±)-2-methoxy-6-icosynoic acid was also determined. It was found that α- methoxylation decreases the CMC of a fatty acid.

The natural fatty acids (5Z)-5-pentacosenoic and (9Z)-9-pentacosenoic acids were synthesized for the first time in eight steps starting from either 4-bromo-1-butanol or 8-bromo-1-butanol and in 20-58% overall yields, while the novel fatty acids 5-pentacosynoic and 9-pentacosynoic acids were also synthesized in six steps and in 34-43% overall yields. The Δ5 acids displayed the best IC50’s (24-38 µM) against the HIV-1 reverse transcriptase (RT) enzyme, comparable to nervonic acid (IC50 = 12 µM). The Δ9 acids were not as effective towards HIV-RT with the (9Z)-9-pentacosenoic acid displaying an IC50 = 54 µM. Fatty acid chain length and position of the unsaturation was critical for the observed inhibition. Molecular modeling studies indicated the structural determinants underlying the biological activity of the most potent compounds. These results provide new insights into the structural requirements that must be present in fatty acids so as to enhance their inhibitory potential towards HIV-RT.