The first total synthesis for the (Z)-16-methyl-11-heptadecenoic acid, a novel fatty acid from the sponge Dragmaxia undata, was accomplished in seven steps and in a 44% overall yield. The use of (trimethylsilyl)acetylene was key in the synthesis. Based on a previous developed strategy in our laboratory the best synthetic route towards the title compound was first acetylide coupling of (trimethylsilyl)acetylene to the long-chain protected 10-bromo-1-decanol followed by a second acetylide coupling to the short-chain 1-bromo-4-methylpentane, which resulted in higher yields. Complete spectral data is also presented for the first time for this recently discovered fatty acid and the cis double bond stereochemistry of the natural acid was established. The title compound displayed antiprotozoal activity against Leishmania donovani (IC50 = 165.5 ± 23.4 μM) and inhibited the leishmania DNA topoisomerase IB enzyme (LdTopIB) with an IC50 = 62.3 ± 0.7 μM.

Acetylenic fatty acids are known to display several biological activities, but their antimalarial activity has remained unexplored. In this study, we synthesized the 2-, 5-, 6-, and 9-hexadecynoic acids (HDAs) and evaluated their in vitro activity against erythrocytic (blood) stages of Plasmodiumfalciparum and liver stages of Plasmodiumyoelii infections. Since the type II fatty acid biosynthesis pathway (PfFAS-II) has recently been shown to be indispensable for liver stage malaria parasites, the inhibitory potential of the HDAs against multiple P. falciparum FAS-II (PfFAS-II) elongation enzymes was also evaluated. The highest antiplasmodial activity against blood stages of P. falciparum was displayed by 5-HDA (IC50 value 6.6 μg/ml), whereas the 2-HDA was the only acid arresting the growth of liver stage P. yoelii infection, in both flow cytometric assay (IC50 value 2-HDA 15.3 μg/ml, control drug atovaquone 2.5 ng/ml) and immunofluorescence analysis (IC50 2-HDA 4.88 μg/ml, control drug atovaquone 0.37 ng/ml). 2-HDA showed the best inhibitory activity against the PfFAS-II enzymes PfFabI and PfFabZ with IC50 values of 0.38 and 0.58 μg/ml (IC50 control drugs 14 and 30 ng/ml), respectively. Enzyme kinetics and molecular modeling studies revealed valuable insights into the binding mechanism of 2-HDA on the target enzymes. All HDAs showed in vitro activity against Trypanosomabruceirhodesiense (IC50 values 3.7–31.7 μg/ml), Trypanosomacruzi (only 2-HDA, IC50 20.2 μg/ml), and Leishmaniadonovani (IC50 values 4.1–13.4 μg/ml) with generally low or no significant toxicity on mammalian cells. This is the first study to indicate therapeutic potential of HDAs against various parasitic protozoa. It also points out that the malarial liver stage growth inhibitory effect of the 2-HDA may be promoted via PfFAS-II enzymes. The lack of cytotoxicity, lipophilic nature, and calculated pharmacokinetic properties suggests that 2-HDA could be a useful compound to study the interaction of fatty acids with these key P. falciparum enzymes.2-, 5-, 6-, and 9-hexadecynoic acids (HDAs) were synthesized and evaluated in vitro against various parasitic protozoa. 2-HDA inhibited both liver and blood stage Plasmodium infections and multiple plasmodial FAS-II target enzymes. 2-HDA was further studied through enzyme kinetics, docking studies and for pharmacokinetic properties.

The first total synthesis of the marine cyclopropane fatty acid (±)-17-methyl-trans-4,5-methyleneoctadecanoic acid was accomplished in eight steps and in 9.1% overall yield starting from 1-bromo-12-methyltridecane. The cis analog (±)-17-methyl-cis-4,5-methyleneoctadecanoic acid was also synthesized but in seven steps and in 16.4% overall yield. With the two isomeric cyclopropane fatty acids at hand it was possible to unequivocally corroborate the trans relative configuration of the naturally occurring fatty acid by gas chromatographic co-elution of the corresponding methyl esters. The cis isomer was cytotoxic to Leishmania donovani promastigotes with an IC50 of 300.2 ± 4.2 μM.The first total synthesis of the marine cyclopropane fatty acid (±)-17-methyl-trans-4,5-methyleneoctadeconoic acid (1a) was accomplished in eight steps and in 9.1% overall yield starting from 1-bromo-12-methyltridecane. The cis isomer was cytotoxic to Leishmania donovani promastigotes (IC50 = 300.2 ± 4.2 μM).

The first total synthesis for the (Z)-17-methyl-13-octadecenoic acid was accomplished in seven steps and in a 45% overall yield. The use of (trimethylsilyl)acetylene was key in the synthesis. Based on a previous developed strategy in our laboratory the best synthetic route towards the title compound was first acetylide coupling of (trimethylsilyl)acetylene to the long-chain protected 12-bromo-1-dodecanol followed by a second acetylide coupling to the short-chain 3-methyl-1-bromobutane, which resulted in higher yields. Complete spectral data is also presented for the first time for this recently discovered fatty acid. The title compound displayed antiprotozoal activity against Leishmania donovani (EC50 = 19.8 μg/ml) and inhibited the leishmania DNA topoisomerase IB at concentrations of 50 μM.

The first total syntheses of the naturally occurring acetylenic fatty acids—6-heptadecynoic acid (59% overall yield) and 6-icosynoic acid (34% overall yield)—was accomplished in four steps. Using the same synthetic sequence the naturally occurring fatty acids (6Z)-heptadecenoic acid (46% overall yield) and (6Z)-icosenoic acid (27% overall yield) were also synthesized. The Δ6 acetylenic fatty acids displayed good antiprotozoal activity towards Leishmania donovani promastigotes (EC50 = 1–6 µg/mL), but the 6-icosynoic acid was the most effective in the series. In addition, the (6Z)-icosenoic acid was a much better antiprotozoal compound (EC50 = 5–6 µg/mL) than the (6Z)-heptadecenoic acid (EC50 > 25 µg/mL). The saturated fatty acids n-heptadecanoic acid and n-eicosanoic acid were not effective towards L. donovani, indicating that the Δ6 unsaturation in these fatty acids is necessary for leishmanicidal activity. In addition, both the 6-icosynoic acid and the (6Z)-icosenoic acid were inhibitors of the Leishmania DNA topoisomerase IB enzyme (EC50’s = 36–49 µM), a possible intracellular target for these compounds. This is the first study assessing fatty acids as inhibitors of the Leishmania DNA topoisomerase IB enzyme.

4-Thiatetradecanoic acid exhibited weak antifungal activities against Candida albicans (ATCC 60193), Cryptococcus neoformans (ATCC 66031), and Aspergillus niger (ATCC 16404) (MIC = 4.8–12.7 mM). It has been demonstrated that α-methoxylation efficiently blocks β-oxidation and significantly improve the antifungal activities of fatty acids. We examined whether antifungal activity of 4-thiatetradecanoic acid can be improved by α-substitution. The unprecedented (±)-2-hydroxy-4-thiatetradecanoic acid was synthesized in four steps (20% overall yield), while the (±)-2-methoxy-4-thiatetradecanoic acid was synthesized in five steps (14% overall yield) starting from 1-decanethiol. The key step in the synthesis was the hydrolysis of a trimethylsilyloxynitrile. In general, the novel (±)-2-methoxy-4-thiatetradecanoic acid displayed significantly higher antifungal activities against C. albicans (ATCC 60193), C. neoformans (ATCC 66031), and A. niger (ATCC 16404) (MIC = 0.8–1.2 mM), when compared with 4-thiatetradecanoic acid. In the case of C. neoformans the (±)-2-hydroxy-4-thiatetradecanoic acid was more fungitoxic (MIC = 0.17 mM) than the α-methoxylated analog, but not as effective against A. niger (MIC = 5.5 mM). The enhanced fungitoxicity of the (±)-2-methoxy-4-thiatetradecanoic acid, as compared to decylthiopropionic acid, might be the result of a longer half-life in the cells due to a blocked β-oxidation pathway which results in more time to exert its toxic effects. Thus, these novel fatty acids may have applications as probes to study fatty acid metabolic routes in human cells.

The phospholipid fatty acid composition of the Caribbean sponge Erylus goffrilleri is described for the first time. A total of 70 fatty acids with chain lengths between 13 and 29 carbons were identified in the sponge. Methyl-branched fatty acids predominated in E. goffrilleri suggesting the presence of a considerable number of bacterial symbionts. The novel fatty acids (5Z,9Z)-2-methoxy-5,9-hexadecadienoic acid, (5Z,9Z)-2-methoxy-5,9-octadecadienoic acid, (5Z,9Z)-2-methoxy-5,9-nonadecadienoic acid, and (5Z,9Z)-2-methoxy-5,9-eicosadienoic acid are described for the first time in the literature. In addition, the iso-methyl-branched fatty acids (9Z)-2-methoxy-15-methyl-9-hexadecenoic acid and (5Z,9Z)-2-methoxy-15-methyl-5,9-hexadecadienoic acid, also identified in E. goffrilleri, were identified for the first time in nature. Based on the identified metabolites it is proposed that the unprecedented biosynthetic sequence: i-17:1Δ9 → 2-OMe-i-17:1Δ9 → 2-OMe-i-17:2Δ5,9 might be responsible for the biosynthesis of the novel iso-α-methoxylated fatty acids in E. goffrilleri.

The cyclopropane fatty acids 17-methyl-trans-4,5-methyleneoctadecanoic acid, 18-methyl-trans-4,5-methylenenonadecanoic acid, and 17-methyl-trans-4,5-methylenenonadecanoic acid were characterized for the first time in nature in the phospholipids (mainly PE, PG and PS) of the hermit-crab sponge Pseudospongosorites suberitoides. Pyrrolidine derivatization was the key in identifying the position of the cyclopropyl and methyl groups in the acyl chains and 1H NMR was used to determine the trans stereochemistry of the cyclopropane ring. The phospholipids from the sponge also contained an interesting series of iso-anteiso Δ5,9 fatty acids with chain-lengths between 17 and 21 carbons, with the fatty acids (5Z,9Z)-18-methyl-5,9-nonadecadienoic acid and the (5Z,9Z)-17-methyl-5,9-nonadecadienoic acid being described for the first time in sponges. The anteiso α-methoxylated fatty acid 2-methoxy-12-methyltetradecanoic acid was also identified for the first time in nature in the phospholipids of this interesting marine sponge. The novel cyclopropyl fatty acids could have originated from the phospholipids of a cyanobacterium living in symbiosis with the sponge.