Spirastrellolide B reveals the absolute configuration of the spirastrellolide macrolide core

The new macrolide spirastrellolide B (5) has been isolated from extracts of the marine sponge Spirastrella coccinea collected in Dominica. Chemical transformations of spirastrellolide B have converted it to a bromine-containing crystalline derivative 8 that has a truncated side chain. Single-crystal X-ray diffraction analysis of the derivative 8 has revealed the absolute configuration of the macrolide core of spirstrellolide B to be 3R,7S,9S,11S,13R,14S,17S,20S,21R, 22S,23S,24S,27R,29S,31R,34S,35R,37S,38S.