813 813 (1~{S},3~{R},11~{R},13~{S},14~{Z},18~{E})-1,8,14,17,17-pentamethyl-5,13-bis(oxidanyl)-2-oxatricyclo[9.9.0.0^{3,9}]icosa-4,7,9,14,18-pentaen-6-one 813