Total Synthesis of (-)-Spirotryprostatin B and Three Stereoisomers We thank NIH NIGMS (GM-30859) for financial support, Prof. A. J. Shaka and N. D. Taylor for DPFGSE experiments, Prof. H. Osada for providing spectral data for natural 1, and Prof. R. M. Williams and P. R. Sebahar for providing spectral data and a sample of synthetic ent-21. We are also grateful to Prof. R. M. Williams and Prof. S. J. Danishefsky for open exchange of information prior to publication. NMR and mass spectra were determined at UC Irvine with instruments purchased with the assistance of the NSF and NIH shared instrumentation programs.