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 (MIC = 11 μM) and against Cryptococcus neoformans ATCC 66031 (MIC < 5.7 μM). The 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 μM. Other fatty acids, such as 2-hexadecynoic acid, 5-hexadecynoic acid, 9-hexadecynoic acid, and 6-nonadecynoic acid were also synthesized and their antifungal activities compared. The 2-hexadecynoic acid, a known antifungal fatty acid, exhibited the best antifungal activity (MIC = 9.4 μM) against the fluconazole resistant C. albicans ATCC 14053 strain, but it showed a MIC value of only 100 μM against C. albicans ATCC 60193. The fatty acids 2,6-hexadecadiynoic acid and 2-hexadecynoic acid also displayed a MIC of 140–145 μM towards Mycobacterium tuberculosis H37Rv in Middlebrook 7H12 medium. In conclusion, 2,6-hexadecadiynoic acid exhibited the best fungitoxicity profile compared to other analogues. This diynoic fatty acid has the potential to be further evaluated for use in topical antifungal formulations.
Carballeira, Néstor M., David Sanabria, Clarisa Cruz, Keykavous Parang, Baojie Wan, and Scott Franzblau. "2, 6-Hexadecadiynoic acid and 2, 6-nonadecadiynoic acid: novel synthesized acetylenic fatty acids as potent antifungal agents." Lipids 41, no. 5 (2006): 507-511.