The first total synthesis of cis, cis-ceratospongamide (cyclo [l-Pro-l-Ile-Me-oxazoline-l-Phe-l- Pro-thiazole-l-Phe-]) was accomplished and confirmed by X-ray crystal analysis. The heating of cis, cis-ceratospongamide in DMSO converted it not to the trans, trans isomer but to the trans, trans-[d-allo-Ile]-ceratospongamide, which was confirmed by total synthesis. Its solution conformation was constructed by the dynamic simulated annealing method using ...