Synthesis and biochemical evaluation of the CBI-PDE-I-dimer, a benzannelated analog of (+)-CC-1065 that also produces delayed toxicity in mice

A practical synthesis of CBI (2) was developed and applied to the synthesis of benzannelated analogs of CC-1065, including CBI-PDE-I-dimer (13) and CBI-bis-indole [(+)-A'BC]. The CBI-PDE-I-dimer was shown to have similar DNA sequence selectivity and structural effects on DNA as (+)-CC-1065. Of particular importance was the observed duplex winding effect that has been associated with the pyrrolidine ring of the nonalkylated subunits of (+)-CC-1065 and possibly correlated with its delayed toxicity effects. The effect of CBI-PDE-I-dimer was also compared to (+)-CC-1065 in the inhibition of duplex unwinding by helicase II and nick sealing by T4 ligase and found to be quantitatively similar. The in vitro and in vivo potencies of the CBI compounds corresponded very closely to the corresponding CPI derivatives. Finally, CBI-PDE-I-dimer was like (+)-CC-1065 in causing delayed toxicity in mice.