Total synthesis and structure-activity relationship of a cytotoxic polycyclic ether gymnocin-A

Gymnocin-A is a polycyclic ether toxin, isolated from the notorious red tide dinoflagellate, Karenia mikimotoi. Structurally, it is characterized by 14 contiguous and saturated ether rings and a 2-methyl-2-butenal side chain. The toxin is a rare polycyclic ether natural product that exhibits cytotoxicity against P 388 murine leukemia (IC50 = 1.3 mu g/mL); however, the biological mechanism of action remains unknown to date. We have accomplished a highly convergent and efficient total synthesis of gymnocin-A by using our developed B-alkyl Suzuki-Miyaura coupling-based methodology. The convergent nature of our synthesis is well suited for preparation of various structural analogues of gymnocin-A to explore the structure-activity relationship (SAR). The results of SAR studies indicated that an alpha,beta-unsaturated aldehyde functionality of the side chain and the molecular length of the polycyclic ether skeleton were the crucial structural elements required for cytotoxicity.