Enantioselective Synthesis and Antifungal Activity of C18 Polyacetylenes

Fungal pathogens cause serious crop diseases and decrease crop yields and quality. Polyacetylene alcohols are plant secondary metabolites and bioactive against various pathogenic fungi. They are, however, difficult to synthesize. In the present study, an efficient and highly enantioselective method (>98% ee) was established and employed to achieve the synthesis of the natural C18 polyacetylenes (S,E)-octadeca-1,9-dien-4,6-diyn-3-ol 1, (3R,10R,E)-octadeca-1,8-dien-4,6-diyne-3,10-diol 2, and their analogs. The title compounds were structurally characterized and biologically evaluated for fungicidal activities. The compounds exhibited high potencies against eight pathogenic fungal species tested, such as Colletotrichum gloeosporioiles, Bipolaris sorokiniana, Fusarium graminearum, and Fusarium pseudograminearum, with half-maximum effective concentrations ranging from 8 to 425 μg/mL, being similar to those of the fungicide thiophanate-methyl (3-408 μg/mL). These compounds are potential natural fungicides and fungicide lead candidates for further structural and property improvements.