Synthesis and structure–activity relationship studies of novel tubulysin U analogues – effect on cytotoxicity of structural variations in the tubuvaline fragment
Synthesis of tubuvaline (Tuv) fragment of tubulysin via diastereoselective dihydroxylation of homoallylamine
摘要:
Tubulysins are natural anticancer molecules that directly bind and inhibit tubulin polymerization in actively dividing cells leading to apoptosis and cell death. Structurally, tubulysins are linear tetrapeptides, constituted by a natural amino acid (Ile) and three non-canonical amino acids (Mep, Tuv, and Tup). Herein, we report a convenient strategy for the practical synthesis of tubuvaline fragment of tubulysin natural products. In this approach, we describe the regioselective ring opening of a chiral aziridine 7 with vinyl Grignard reagent to obtain (R)-tert-butyl(2-methylhex-5-en-3-yl)(tosyl)carbamate 8 which was further subjected to Sharpless asymmetric dihydroxylation with AD-mix-beta resulting in the formation of (2 R,4R)-4-((tert-butoxycarbonyl)amino)-2-(methoxymethoxy)-5-methylhexanoic acid 3 that was finally transformed to tubuvaline by heterocyclization.