Synthesis and Structure‐Activity Relationship Studies of C(13)‐Desmethylene‐(−)‐Zampanolide Analogs

Abstract

AbstractWe describe the synthesis and biochemical and cellular profiling of five partially reduced or demethylated analogs of the marine macrolide (−)‐zampanolide (ZMP). These analogs were derived from 13‐desmethylene‐(−)‐zampanolide (DM‐ZMP), which is an equally potent cancer cell growth inhibitor as ZMP. Key steps in the synthesis of all compounds were the formation of the dioxabicyclo[15.3.1]heneicosane core by an intramolecular HWE reaction (67–95 % yield) and a stereoselective aza‐aldol reaction with an (S)‐BINOL‐derived sorbamide transfer complex, to establish the C(20) stereocenter (24–71 % yield). As the sole exception, for the 5‐desmethyl macrocycle, ring‐closure relied on macrolactonization; however, elaboration of the macrocyclization product into the corresponding zampanolide analog was unsuccessful. All modifications led to reduced cellular activity and lowered microtubule‐binding affinity compared to DM‐ZMP, albeit to a different extent. For compounds incorporating the reactive enone moiety of ZMP, IC50 values for cancer cell growth inhibition varied between 5 and 133 nM, compared to 1–12 nM for DM‐ZMP. Reduction of the enone double bond led to a several hundred‐fold loss in growth inhibition. The cellular potency of 2,3‐dihydro‐13‐desmethylene zampanolide, as the most potent analog identified, remained within a ninefold range of that of DM‐ZMP.