FR66979 REQUIRES REDUCTIVE ACTIVATION TO CROSS-LINK DNA EFFICIENTLY

The activity of FR66979 as a DNA-DNA interstrand cross-linking agent in the absence of exogenous reducing agents was re-examined. Samples of FR66979 prepared by hydrogenation of FR900482 (H-2/Pd-C) were quite active whereas reduction of FR900482 with sodium borohydride afforded inactive or very weakly active FR66979 samples. Rigorous purification of FR66979 from either source abolished the observed cross-linking activity thus indicating that FR66979 does not efficiently cross-link DNA in the absence of exogenous reducing agents. LC-MS analysis of active samples indicated the possible presence of the over-reduced impurity 3, below. The DNA-DNA cross-link arising from the same sample was identical in structure to that formed by reductively activated FR66979.