Asymmetric Synthesis of (2S,3R)-Capreomycidine and the Total Synthesis of Capreomycin IB

A 27 step total synthesis of the tuberculostatic macrocyclic peptide antibiotic capreomycin IB has been accomplished. The synthesis features the use of an enolate−aldimine condensation between a chiral glycine aluminum enolate and the benzyl imine of 3-tert-butyldimethylsiloxy-propanal as a means of preparing the cyclic guanidine amino acid (2S,3R)-capreomycidine. Additionally, a Hofmann rearrangement was exacted on a late-stage pentapeptide in order to transform an asparagine residue into a diaminopropanoic acid residue.