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 3 R,7 S,9 S,11 S,13 R,14 S,17 S,20 S,21 R, 22 S,23 S,24 S,27 R,29 S,31 R,34 S,35 R,37 S,38 S .