Formal enantiospecific synthesis of (+)-FR900482.

The enantiospecific synthesis of FK973, and thus a formal enantiospecific synthesis of the antitumor antibiotic (+)-FR900482, is reported. Addition of aniline 8 to chiral epoxide 9, prepared from l-vinylglycine, afforded amino alcohol 12. After protection of the aliphatic nitrogen with the 9-phenylfluoren-9-yl group, to preserve the acidic stereocenter from racemization, formation of the aziridine 14 and intramolecular condensation under basic conditions gave azocinone 15. Hydroxymethylation at the benzylic position was achieved by a process involving methylenation, epoxidation, and hydrogenolysis; the absolute stereochemistry of the resulting alcohol 23 was determined by X-ray crystallographic analysis. The hydroxyl group of 23 was carbamoylated, and the aromatic amine was deprotected electrochemically and then oxidized to give an unstable hydroxylamine that was immediately protected as acetate 26. Oxidation of 26 with DMP, followed by hydrazinolysis of the acetyl group led to spontaneous closure of the resulting N-hydroxyamino ketone to hemiketal 28, which can be considered as a fully protected precursor of FR900482 and derivatives. Acid treatment to remove the protecting groups and acetylation afforded the triacetate FK973.