Total Synthesis of Pyrrole-Imidazole Alkaloid (+)-Cylindradine B.

Cylindradines A and B are members of the oroidin-derived pyrrole-imidazole alkaloid (PIA) family. They possess a characteristic pyrrole-3-carbamoyl moiety, which is unusual among PIAs. We achieved a total synthesis of (+)-cylindradine B by applying a Pictet-Spengler-type reaction followed by oxidative cyclization in the presence of hypervalent iodine to construct the pyrrole-3-carbamoyl and cyclic guanidine with N,N'-aminal moieties at C6 and C10.