Synthesis and evaluation of radamide analogues, a chimera of radicicol and geldanamycin.

Previously, we reported the Hsp90 inhibitory activity of radamide, an open chain amide chimera of geldanamycin and radicicol. Attempts to further expand upon structure-activity relationships for this class of Hsp90 inhibitors led to the preparation of a series of radamide analogues focused on differing tether lengths and quinone mimics. In addition, the cup-shaped conformation adopted by the two natural products when bound to the Hsp90 N-terminal ATP binding pocket suggests that conformationally biased compounds may demonstrate improved binding and inhibition. The preparation and evaluation of radamide analogues with cis/trans alpha,beta-unsaturated amides yielded compounds that exhibit improved antiproliferative activity. In addition, several analogues demonstrated the ability to induce degradation of Hsp90-dependent oncogenic signaling proteins in vitro, a hallmark of Hsp90 N-terminal inhibition.