Total synthesis of maytansinoids. Approach to 4,6-bisdemethylmaytansine and 4-demethylmaytansine

Spirastrellolide Studies. Synthesis of the C(1)-C(25) Southern Hemispheres of Spirastrellolides A and B, Exploiting Anion Relay Chemistry

Construction of the C(1)-C(25) southern fragments of both spirastrellolide A and B are described. Highlights of the syntheses include effective use of the three component anion relay chemistry (ARC) tactic recently introduced by our laboratory, a stereoselective spirocyclization via concomitant Ferrier reaction to elaborate the BC spiroketal and use of two dithiane unions to install the A ring as well as C(22)-C(25) fragment. The synthesis proceeded with longest linear sequences of 33 and 32 steps respectively for spirastrellolide A and spirastrellolide B.

Total Synthesis of (-)-Maytansinol

A total synthesis of maytansinol (1) was achieved, in a convergent way, using (3S,6S,7S)-aldehyde 4 and (S)-p-tolyl sulfoxide 3 as fragments. When the anion of 3 was condensed with aldehyde 4, some induction at C(10) was observed (60% de), giving the C(1)-N(19)-open-chain compound 7, after thermal elimination of sulfinate. Pure E/E stereochemistry of the 11,13-diene was obtained. Selective modifications of the functionalities permitted macrocyclization and further elaboration to maytansinol.