Rogiolenyne A,B, and C: The First Branched Marine C15 Acetogenins. Isolation from the Red Seaweed Laurencia microcladia or the Sponge Spongia zimocca of II Rogiolo

It is shown here that the red seaweed Laurencia microcladia, collected off the torrent II Rogiolo, south of Livorno, contains rogiolenyne A (= (?)-(1R*,2S*,3R*,5S*,7S*)-2-(bromomethyl)-5-(Z)-1-chlorohex-3-en-5-ynyl]-3-ethyl-4,8-dioxabicyclo5.1.0]octane; (?)- 1 ) while the sponge Spongia zimocca, which grows in the same small area, contains rogiolenyne B (= (?)-(2R*3R*,4R*,5R*,7S*)-3-(bromomethyl)-5-chloro-7-(Z)-1-chlorohex-3-en-5-ynyl]-2-ethyloxepan-4-ol; (?)- 4a ) and its acetate, rogiolenyne C((?)- 4b ). These structures, which are based on extensive NMR and MS data and on chemical transformation, are the first examples of branched marine C₁₅ acetogenins. Biogenesis of (?)- 1 in L. microcladia is thought to involve C(12) extrusion form a C₁₅ linear tetraen-1-yne precursor via H⁺-induced cyclopropane ring closure, followed by Br⁺-induced cyclopropane ring opening, aided by C–O^? attack (Scheme 2). It is also proposed that transfer of (?)- 1 to S. zimocca is followed by epoxide ring opening by Cl^? to give (?)- 4a and acetylation to give (?)- 4b .