SYNTHESIS OF DERIVATIVES OF FK-506 AND FR-900520 - MODIFICATIONS AT THE BINDING DOMAIN

The synthesis of 9-deoxo-FK 506 (13a), 9-deoxo-FR 900520 (13b), 9-deoxo-10(R)-deoxy-FR 900520 (14) and its 10(S) isomer 15 is described. Radical deoxygenation/elemination of the 9-di-hydro-9,10-thiocarbonates 5a,5b,6a and 6b gave the 9,10 unsaturated compounds 7a (7b) or 8a (8b) which were further transferred by hydration or hydrogenation. Different E/Z ratios of 7a (7b) were obtainted when nBu3SnH or [(CH3)3Si]3SiH in combination with AIBN or Et3B were used, allowing the selective preparation of both isomers. Two possible reaction mechanisms are discussed.