A series of 23,24-dihydrodiscodermolide analogues with simplified lactone regions

Structural Refinement of the Tubulin Ligand (+)-Discodermolide to Attenuate Chemotherapy-Mediated Senescence

The natural product (+)-discodermolide (DDM) is a microtubule stabilizing agent and potent inducer of senescence. We refined the structure of DDM and evaluated the activity of novel congeners in triple negative breast and ovarian cancers, malignancies that typically succumb to taxane resistance. Previous structure-activity analyses identified the lactone and diene as moieties conferring anticancer activity, thus identifying priorities for the structural refinement studies described herein. Congeners possessing the monodiene with a simplified lactone had superior anticancer efficacy relative to taxol, particularly in resistant models. Specifically, one of these congeners, B2, demonstrated 1) improved pharmacologic properties, specifically increased maximum response achievable and area under the curve, and decreased EC₅₀; 2) a uniform dose-response profile across genetically heterogeneous cancer cell lines relative to taxol or DDM; 3) reduced propensity for senescence induction relative to DDM; 4) superior long-term activity in cancer cells versus taxol or DDM; and 5) attenuation of metastatic characteristics in treated cancer cells. To contrast the binding of B2 versus DDM in tubulin, X-ray crystallography studies revealed a shift in the position of the lactone ring associated with removal of the C2-methyl and C3-hydroxyl. Thus, B2 may be more adaptable to changes in the taxane site relative to DDM that could account for its favorable properties. In conclusion, we have identified a DDM congener with broad range anticancer efficacy that also has decreased risk of inducing chemotherapy-mediated senescence. SIGNIFICANCE STATEMENT: Here, we describe the anticancer activity of novel congeners of the tubulin-polymerizing molecule (+)-discodermolide. A lead molecule is identified that exhibits an improved dose-response profile in taxane-sensitive and taxane-resistant cancer cell models, diminished risk of chemotherapy-mediated senescence, and suppression of tumor cell invasion endpoints. X-ray crystallography studies identify subtle changes in the pose of binding to β-tubulin that could account for the improved anticancer activity. These findings support continued preclinical development of discodermolide, particularly in the chemorefractory setting.

Ruthenium-catalysed Z-selective cross metathesis of allylic-substituted olefins

The Z-selective cross metathesis of allylic-substituted olefins is explored with recently developed ruthenium-based metathesis catalysts. The reaction proceeds with excellent stereoselectivity for the Z-isomer (typically >95%) and yields of up to 88% for a variety of allylic substituents. This includes the first synthesis of Z-α,β-unsaturated acetals by cross metathesis and their elaboration to Z-α,β-unsaturated aldehydes. In addition, the reaction is tolerant of a variety of cross partners, varying in functionality and steric profile.

The discodermolide hairpin structure flows from conformationally stable modular motifs

(+)-Discodermolide (DDM), a polyketide macrolide from marine sponge, is a potent microtubule assembly promoter. Reported solid-state, solution, and protein-bound DDM conformations reveal the unusual result that a common hairpin conformational motif exists in all three microenvironments. No other flexible microtubule binding agent exhibits such constancy of conformation. In the present study, we combine force-field conformational searches with NMR deconvolution in different solvents to compare DDM conformers with those observed in other environments. While several conformational families are perceived, the hairpin form dominates. The stability of this motif is dictated primarily by steric factors arising from repeated modular segments in DDM composed of the C(Me)-CHX-C(Me) fragment. Furthermore, docking protocols were utilized to probe the DDM binding mode in beta-tubulin. A previously suggested pose is substantiated (Pose-1), while an alternative (Pose-2) has been identified. SAR analysis for DDM analogues differentiates the two poses and suggests that Pose-2 is better able to accommodate the biodata.

Development of practical syntheses of the marine anticancer agents discodermolide and dictyostatin

Initially isolated in trace quantities from deep-sea sponges, the structurally related polyketides discodermolide and dictyostatin share the same microtubule-stabilizing antimitotic mechanism as Taxol. Discodermolide has been the focus of intense research activity in order to develop a practical supply route, and these efforts ultimately allowed its large-scale synthesis and the initiation of clinical trials as a novel anticancer drug. Similarly, the re-isolation and synthesis of dictyostatin continues to stimulate the biological and chemical communities in their quest for the development of new chemotherapeutic agents. This comprehensive review chronicles the synthetic endeavours undertaken over the last 15 years towards the development and realization of practical chemical syntheses of discodermolide and, more recently, dictyostatin, focusing on the methods and strategies employed for achieving overall stereocontrol and key fragment unions, as well as the design and synthesis of novel hybrid structures.

Anticancer drugs from nature--natural products as a unique source of new microtubule-stabilizing agents

This review article provides an overview on the current state of research in the area of microtubule-stabilizing agents from natural sources, with a primary focus on the biochemistry, biology, and pharmacology associated with these compounds. A variety of natural products have been discovered over the last decade to inhibit human cancer cell proliferation through a taxol-like mechanism. These compounds represent a whole new range of structurally diverse lead structures for anticancer drug discovery.

Coumarin-derived discodermolide analogues possessing equivalent antiproliferative activity to the natural product—a further simplification of the lactone region

Analogues of discodermolide in which the complete C-1 to C-7 fragment is replaced with a coumarin moiety display equivalent potency to that of the natural product.