Total synthesis of bleomycin A(sub 2) and related agents. 1. Synthesis and DNA binding properties of the extended C-terminus: tripeptide S, tetrapeptide S, pentapeptide S, and related agents

A concise, diastereocontrolled process yields bleomycin A(sub 2) subunits and optically-active tripeptide S, tetrapeptide S, and pentapeptide S. Absolute DNA binding constants reveal the influence of linking chain substituents on DNA binding strength and the binding site size of the agent. Calculated binding site sizes reveal that the tripeptide S subunit of bleomycin A(sub 2) is fully-bound to duplex DNA.