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The phospholipid fatty acid composition of Malvaviscus arboreus DC. (Malvaceae) and Allamanda cathartica L. (Apocynaceae) was studied. The fatty acids, 17-methyl-5,9-octadecadienoic acid, 16-methyl-5,9-octadecadienoic acid, and 5,9-nonadecadienoic acid were identified in the phospholipid (mainly phosphatidylcholine) extract of M. arboreus by GC-MS. 17-Methyl-5,9-octadecadienoic acid was also identified in A. cathartica . This is the first report of iso - anteiso branched Δ5,9 fatty acids from a plant source.

The dimethyl disulfide derivatization of ethyl (9Z,12Z)-9,12-octadecadienoate and ethyl (9E,12E)-9,12-octadecadienoate was studied. These methylene-interrupted dienes were reacted with dimethyl disulfide and I2 for 72 h at 50°C and the tetrahydrothiopyran, thietane, and tetrahydrothiophene derivatives thus obtained were analyzed by gas chromatography-mass spectrometry. Each configurational isomer displayed a unique gas chromatography trace for the 4-, 5- and 6-membered ring cyclization products thus obtained. Therefore, the cis-cis and trans-trans double bond stereochemistry of 9,12-octadecadienoates can now be determined by dimethyl disulfide derivatization.

A stereoselective synthesis for the (5 Z ,9 Z )-14-methyl-5,9-pentadecadienoic acid and the monounsaturated analog ( Z )-14-methyl-9-pentadecenoic acid was accomplished in six to seven steps where double alkyne coupling was the key step. This synthesis will facilitate the study of the topoisomerase I inhibitory profile of this important class of fatty acids.

The reaction of dimethyl disulfide in I 2 with a series of methylene-interrupted methyl dienoates was examined. In all cases ring-closure occurs and thietane formation competes favorably with tetrahydrothiophene formation. When the I 2 concentration was increased, tetrahydrothiopyran formation was observed. These results are explained in terms of two distinct reaction pathways.

1. 1. The phospholipid fatty acid compositions of the sponges Ircinia strobilina , Ircinia felix , Ircinia campana , Ircinia sp., Spongia tubulifera and Dysidea etherea were studied, revealing the presence, besides other common fatty acids, of considerable amounts (2–5%) of the novel 23-methyl-5,9-tetracosadienoic acid (1). 2. 2. The demospongic acids, 5,9-tetracosadienoic acid, 23-methyl-5,9-tetracosadienoic acid (1), and 5,9-pentacosadienoic acid, were particularly abundant in sponges of the genus Ircinia , in contrast to the most common 5,9-hexacosadienoic acid found in other species. These findings are discussed in terms of the taxonomy of the Dictyoceratida. 3. 3. The complete characterization of the novel phospholipid fatty acid 23-methyl-5,9-tetracosadienoic acid (1) is presented.

The hitherto unknown 2,6-hexadecadiynoic acid, 2,6-nonadecadiynoic acid, and 2,9-hexadecadiynoic acid were synthesized in two steps and in 11-18% overall yields starting from either 1,5-hexadiyne or 1,8-nonadiyne. Among all the compounds 2,6-hexadecadiynoic acid displayed the best overall antifungal activity against both the fluconazole-resistant Candida albicans strains ATCC 14053 and ATCC 60193, with a minimum inhibitory concentration (MIC of 11 microM), and against Cryptococcus neoformans ATCC 66031 (MIC < 5.7 microM). 2,9-Hexadecadiynoic acid did not display any significant cytotoxicity against the fluconazole-resistant C. albicans strains, but it showed fungitoxicity against C. neoformans ATCC 66031 with a MIC value of < 5.8 microM. Other FA, such as 2-hexadecynoic acid, 5-hexadecynoic acid, 9-hexadecynoic acid, and 6-nonadecynoic acid were also synthesized and their antifungal activities compared with those of the novel acetylenic FA. 2-Hexadecynoic acid, a known antifungal FA, exhibited the best antifungal activity (MIC = 9.4 microM) against the fluconazole-resistant C. albicans ATCC 14053 strain, but it showed a MIC value of only 100 microM against C. albicans ATCC 60193. 2,6-Hexadecadiynoic acid and 2-hexadecynoic acid also displayed a MIC of 140-145 microM toward Mycobacterium tuberculosis H37Rv in Middlebrook 7H12 medium. In conclusion, 2,6-hexadecadiynoic acid exhibited the best fungitoxicity profile compared with other analogues. This diynoic FA has the potential to be further evaluated for use in topical antifungal formulations.

The phospholipid fatty acid composition of Holothuria mexicana was investigated, and the novel 7-methyl-6-octadecenoic acid was identified. Structural characterization was accomplished by means of pyrrolidide derivatization and total synthesis. Other interesting phospholipid fatty acids in H. mexicana were 7-eicosenoic acid, 13-tricosenoic acid, 7-methyl-6-hexadecenoic acid, and 2-hydroxy-15-tetradecenoic acid.