An olefin metathesis approach to 36- and 72-membered archaeal macrocyclic membrane lipids

An olefin metathesis approach, which has been successfully applied to an efficient synthesis of archaeal 36- and 72-membered macrocyclic membrane lipids (1, 2a, and 2b), is reported. In the presence of a Grubbs' ruthenium-alkylidene complex, RuCl2(=CHPh)(PCy3)(2) (3), a ring-closing metathesis (RCM) reaction of alpha,omega-diene 5 efficiently proceeded in 79% yield under high dilution conditions to give 36-membered 6. By changing the reaction conditions, a acyclic diene metathesis (ADM) product 7 was predominantly formed from the same substrate 5. The acyclic product 7 was subsequently subjected to the RCM reaction under high dilution conditions to provide 72-membered compound 8 in 45% yield. Final catalytic hydrogenation of 6 and 8 afforded the 36-membered lipid I and a mixture of the 72-membered lipid 2a and 2b, respectively. The present synthetic method appears to be of significant advantage for the synthesis of such giant ring structures of the 36- and 72-membered lipids, because both of the macrocylic lipids can be obtained in a short step at will from the same starting material only by changing the order and conditions of the metathesis reaction.