Rogiolenyne A, B, and C: The First Branched Marine C 15 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 (= (−)‐(1 R*, 2 S*, 3 R*, 5 S*, 7 S* )‐2‐(bromomethyl)‐5‐[( Z )‐1‐chlorohex‐3‐en‐5‐ynyl]‐3‐ethyl‐4,8‐dioxabicyclo[5.1.0]octane ; (−)‐ 1 ) while the sponge Spongia zimocca , which grows in the same small area, contains rogiolenyne B (= (−)‐(2 R *3 R *,4 R *,5 R *,7 S *)‐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 C 15 acetogenins. Biogenesis of (−)‐ 1 in L. microcladia is thought to involve C(12) extrusion form a C 15 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 .