CHIROSPECIFIC SYNTHESIS OF (1S,3R)-1-AMINO-3-(HYDROXYMETHYL)CYCLOPENTANE, PRECURSOR FOR CARBOCYCLIC NUCLEOSIDE SYNTHESIS - DIECKMANN CYCLIZATION WITH AN ALPHA-AMINO-ACID

Carbocyclic nucleosides are important isosteres of nucleosides possessing a variety of antiviral and antineoplastic activities. We report here a new method for the chirospecific synthesis of (1S,3R)-1-amino-3-(hydroxymethyl)cyclopentane. This compound is a key precursor for the synthesis of some carbocyclic nucleosides. The method involves (1) an improved synthesis of (S)-2-aminoadipic acid; (2) Dieckmann cyclization of this alpha-amino acid to an aminocyclopentanone; and (3) elaboration of the latter to the target (1S,3R)-l-amino-3-(hydroxymethyl)cyclopentane. The starting (S)-2-aminoadipic acid delta-methyl ester was prepared enantiomerically pure from (S)-aspartic acid in 51% overall yield. Dieckmann condensation converted this amino acid to a (methoxycarbonyl)-cyclopentanone, and reduction of the ketone followed by elimination yielded (S)-3-[N-(9-phenylfluoren-9-yl)amino]-1-(methoxycarbonyl)cyclopentene. Reduction of the double bond gave a mixture of the cis and trans diastereomers. This mixture was converted to a single diastereomer by epimerization and trapping of the cis isomer as (1S,4R)-2-(9-phenylfluoren-9-yl)-2-azabicyclo[2.2.1]heptan-3-one. Hydrolytic cleavage of the lactam followed by reduction gave (IS,3R)-1-amino-3-(hydroxymethyl)-cyclopentane.