2,6-Hexadecadiynoic acid and 2,6-nonadecadiynoic acid: Novel synthesized acetylenic fatty acids as potent antifungal agents

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 mu M), and against Cryptococcus neoformans ATCC 66031 (MIC < 5.7 mu M). 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 mu M. 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 mu M) against the fluconazole-resistant C. albicans ATCC 14053 strain, but it showed a MIC value of only 100 mu M against C. albicans ATCC 60193. 2,6-Hexadecadiynoic acid and 2-hexadecynoic acid also displayed a MIC of 140-145 mu M toward Mycobacterium tuberculosis H(37)Rv 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.