REVISED STRUCTURE AND CONVERGENT SYNTHESIS OF NEMERTELLINE, THE NEUROTOXIC QUATERPYRIDINE ISOLATED FROM THE HOPLONEMERTINE SEA WORM

The correct structure of the quaterpyridine nemertelline first isolate d from hoplonemertine sea worms has been identified as 2 (3,2':3',4 '' :2 '',3triple prime-quaterpyridine). The natural product was synthesiz ed using palladium(0)-catalyzed cross-coupling of 3-(tributylstannyl)- 2,3'-bipyridine (3) and 4-chloro-2,3'-bipyridine (4). The bipyridines were prepared in the presence of the Pd catalyst by cross-coupling 2-b romo-3-(tributylstannyl)pyridine (5) and 2,4-dichloropyridine with 3-d iethyl(pyridyl)borane, respectively. X-ray analysis confirmed the stru cture of 2 and provided its conformation in the solid state. The proto n NMR spectrum of 2 identifies it as the natural product first reporte d in 1976.