“…Because the resorcylic acid macrolactone 30 exhibits potent Hsp90 inhibitory activity, total synthesis, medicinal chemistry, and biology of 30 have been intensively explored; chemistry and biology of 30 were recently reviewed by Kitson and Moody [68]. Attachment of alkaloid scaffolds to the resorcinol moiety of radicicol resulted in potent anticancer derivatives, NVP-AUY922 (32), CCT018159 (33), and AT13387 (34) (Fig. Although 30 is one of the most potent natural Hsp90 inhibitors (IC 50 at nanomolar levels) [71,72], it was inactive in vivo, failing to inhibit the tumor growth in an animal model.…”