摘要:
An isomeric form of the immunosuppressive agent, rapamycin, exists in equilibrium with the pyrano form of rapamycin in solution. The isomer was isolated and a method to completely (>95%) convert the pyrano form of rapamycin into this isomer by treatment with excess Grignard reagent was discovered. The structure of the isomer, characterized by C-13-NMR and COSY H-1-NMR, is proposed to be an oxepane 3, formed via hemiketal formation of the C-9 hydroxyl with the C-14 (central) carbonyl of the "tricarbonyl" system.