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

Abstract

We 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.

Synthesis and Structure-Activity Relationship Studies of Dioxane- and Oxathiane-Based Analogs of (–)-Zampanolide

“…In order to assess the microtubule-binding affinity of analogs 4-8 and establish a possible relationship with their cellular activity, we have investigated their ability to displace the fluorescent taxol analog Flutax-2 from cross-linked microtubules. [43] As discussed previously, [19] the binding data obtained for covalent binders in a displacement assay do not represent bona fide thermodynamic binding constants. Rather, this assay produces what we call apparent binding constants (Kbapp).…”

“…Zampanolide analogs 4-8 were all to be prepared according to the same convergent approach that we had successfully followed in our total synthesis of 1 and of different types of previous analogs (Scheme 1). [10,12,19] Thus dioxane-and oxathiane-based alcohols 10 and 11, respectively, would be esterified with acid 9 and the esters would then be elaborated into aldehydes 12 and 13 via an intramolecular HWE reaction as the macrocyclization step.…”

“…No difference in activity against A2780 and A2780AD cells was observed for 4, 5, or 7; the same is true for natural (−)https://doi.org/10.26434/chemrxiv-2024-nwb48 ORCID: https://orcid.org/0000-0002-0747-9734 Content not peer-reviewed by ChemRxiv. License: CC BY-NC 4.0 zampanolide (1) [10] and almost all of our previously reported analogs, [10,12,17,19] whose cellular potency is not affected by Pgp-overexpression. It has been suggested that the cellular potency of covalent microtubule inhibitors is inherently insensitive to overexpression of the Pgp efflux pump.…”

“…Rather, this assay produces what we call apparent binding constants (Kbapp). [19] While Kbapp values cannot be reliably compared to each other or to true Kb's, they are indicative of the efficiency of the overall reaction of a covalent ligand with polymerized tubulin.…”

“…This has included investigations of modifications of the C(19)-side chain, [6,10,11] the tetrahydropyran ring, [10,[12][13][14][15][16][17] and, most recently, the macrolide backbone. [18,19] As part of these studies, work in our own laboratory has revealed that 13-desmethylene-(−)zampanolide (2) (Fig. 1) inhibits human cancer cell growth with the same potency as 1.…”