CALOUNDRIN-B AND FUNICULATIN-A - NEW POLYPROPIONATES FROM SIPHONARIIDLIMPETS

Two new polypropionates, caloundrin B (11), systematic name 1(3,7)]dec -3''-yl)-5-hydroxy-4-methylheptan-3-one, and funiculatin A (12), syste matic name (2 ]nona-3',7'-dien-3'-yl)-4,6-dimethylnon-6-en-3-one have been isolated from Siphonaria zelandica and S. funiculata respectively . The structures of the new compounds were deduced by two-dimensional n.m.r. spectroscopy, particularly long-range C-13-H-1 correlation spec troscopy (HEjrsc), by biosynthetic reasoning and by comparison with th e known polypropionates denticulatin A (5), siphonarin B (8), muamvati n (9) and baconipyrone C (14). Information about the relative stereoch emistry of the tricyclic ring system of (11) and the bicyclic ring sys tem of (12) was deduced from coupling constant values, and by n.O.e. d ifference and NOESY experiments, and was confirmed by molecular modell ing studies. The relative stereochemistry of the side chains and the a bsolute stereochemistry were inferred from biosynthetic comparison wit h the above known polypropionates, and by correlation of funiculatin A with denticulatin A (5) of known absolute stereochemistry. The stereo chemistry at C 10 of funiculatin A (position 2 of the non-6-en-3-one c hain) could not be unambiguously determined. A third new polypropionat e funiculatin B, epimeric with funiculatin A at C 10, was isolated and partially characterized.