A short synthesis of the C15–C21 segment of (+)-discodermolide, based on an asymmetric approach from achiral 2-methyl-1,3-propanediol to versatile enantiopure stereotriads

Total synthesis of the marine natural product (+)-discodermolide in multigram quantities

The novel polyketide (+)-discodermolide was isolated in very small quantities from sponge extracts. This compound is one of several microtubule stabilizers showing promise as novel chemotherapeutic agents for the treatment of cancer. The clinical evaluation of this and similar compounds is hampered by lack of material, and at present, the only way to obtain the necessary quantities is total chemical synthesis.

A second-generation total synthesis of (+)-discodermolide: the development of a practical route using solely substrate-based stereocontrol

A novel total synthesis of the complex polyketide (+)-discodermolide, a promising anticancer agent of sponge origin, has been completed in 7.8% overall yield over 24 linear steps, with 35 steps altogether. This second-generation approach was designed to rely solely on substrate control for introduction of the required stereochemistry, eliminating the use of all chiral reagents or auxiliaries. The common 1,2-anti-2,3-syn stereotriad found in each of three subunits, aldehyde 9 (C(1)-C(5)), ester 40 (C(9)-C(16)), and aldehyde 13 (C(17)-C(24)), was established via a boron-mediated aldol reaction of ethyl ketone 15 and formaldehyde, followed by hydroxyl-directed reduction to give 1,3-diol 14. Alternatively, a surrogate aldehyde 22 was employed for formaldehyde in this aldol reaction, leading to the beta-hydroxy aldehyde 20 as a common building block, corresponding to the discodermolide stereotriad. Key fragment unions were achieved by a lithium-mediated anti aldol reaction of ester 40 and aldehyde 13 under Felkin-Anh control to provide (16S,17S)-adduct 51 and a boron-mediated aldol reaction between enone 10 and aldehyde 9, exploiting unprecedented remote 1,6-stereoinduction, to give the (5S)-adduct 57.