Practical and stereoselective synthesis of a pentacyclic guanidine system: Synthetic studies toward ptilomycalin A and related compounds

Symmetrical pentacyclic guanidine compounds 3a-c have been synthesized based on the construction of 2,5-disubstituted pyrrolidines via sequential 1,3-dipolar cycloaddition and the formation of pentacyclic guanidine via guanylation followed by double N,O-acetalization. The present synthesis will provide a potential route for the synthesis towards ptilomycalin A (1) and 13,13,15-isocrambescidin 800 (2). (C) 1999 Elsevier Science Ltd. All rights reserved.