Toward aplyronine payloads for antibody-drug conjugates: total synthesis of aplyronines A and D.

The aplyronines are a family of antimitotic marine macrolides that disrupt cytoskeletal dynamics by dual targeting of both actin and tubulin. Given their picomolar cytotoxicity profile and unprecedented mode of action, the aplyronines represent an excellent candidate as a novel payload for the development of next-generation antibody-drug conjugates (ADCs) for cancer chemotherapy. Enabled by an improved second-generation synthesis of the macrolactone core 5, we have achieved the first total synthesis of the most potent congener aplyronine D together with a highly stereocontrolled synthesis of aplyronine A. To facilitate step economy, an adventurous site-selective esterification of the C7 hydroxyl group was performed to install the N,N,O-trimethylserine pharmacophore to directly afford aplyronines A and D. Toward the assembly of ADCs incorporating an aplyronine warhead, the C29-ester derivative 4 featuring an Fmoc-amino substituted linker attached to the actin-binding tail region was also prepared by adapting this flexible endgame.

Synthetic studies toward the brasilinolides: controlled assembly of a protected C1-C38 polyol based on fragment union by complex aldol reactions.

The brasilinolides are an architecturally complex family of 32-membered macrolides, characterised by potent immunosuppressant and antifungal properties, which represent challenging synthetic targets. By adopting a highly convergent strategy, a range of asymmetric aldol/reduction sequences and catalytic protocols were employed to assemble a series of increasingly elaborate fragments. The controlled preparation of suitable C1-C19 and C20-C38 acyclic fragments 5 and 6, containing seven and 12 stereocentres respectively, was first achieved. An adventurous C19-C20 fragment union was then explored to construct the entire carbon chain of the brasilinolides. This pivotal coupling step could be performed in a complex boron-mediated aldol reaction to install the required C19 hydroxyl stereocentre when alternative Mukaiyama-type aldol protocols proved unrewarding. A protected C1-C38 polyol 93 was subsequently prepared, setting the stage for future late-stage diversification toward the various brasilinolide congeners. Throughout this work, asymmetric boron-mediated aldol reactions of chiral ketones with aldehydes proved effective both for controlled fragment assembly and coupling with predictable stereoinduction from the enolate component.

Total synthesis and biological evaluation of simplified aplyronine analogues as synthetically tractable anticancer agents.

The aplyronines are a family of highly cytotoxic marine natural products with potential application in targeted cancer chemotherapy. To address the severe supply issue, function-oriented molecular editing of their macrolactone scaffold led to the design of a series of simplified aplyronine analogues. Enabled by a highly convergent aldol-based route, the total synthesis of four analogues was achieved, with a significant improvement in step economy versus previous compounds, and their cancer cell growth inhibition in the HeLa cell line was determined. The modular strategy presented offers a means for significantly shortening their chemical synthesis to facilitate the continued development of this promising class of anticancer agent.

Toward the total synthesis of the brasilinolides: stereocontrolled assembly of a C1-C19 polyol segment.

Two highly convergent syntheses of a fully protected C1-C19 polyol subunit of the brasilinolide family of immunosuppressive macrolides are described, exploiting boron-mediated 1,5-anti aldol couplings to form the C8-C9 and C13-C14 bonds.

Toward the total synthesis of the brasilinolides: construction of a differentially protected C20-C38 segment.

An efficient, convergent synthesis of a differentially protected C20-C38 segment of the brasilinolides is described. Iterative 1,4-syn aldol additions and ketone reductions were employed to construct the two related stereotetrads, while a sequence of Horner-Wadsworth-Emmons (HWE) coupling, CBS reduction, and Sharpless AE installed the epoxy alcohol functionality.