THE SYNTHESIS AND X-RAY STRUCTURES OF THE GEOMETRIC ISOMERS OF 1-AMINO-1,2-CYCLOPENTANEDICARBOXYLIC ACID

The geometric isomers of 1-amino-1,2-cyclopentanedicarboxylic acid were isolated as the hydrolysis products of 2-cyclopentanecarboxylic acid-5,5'-hydantoin. The hydantoin ester was formed from ethyl -2-oxocyclopentanecarboxylate via a Bucherer-Bergs reaction. Hydrolysis of the hydantoin at elevated temperatures gave a mixture of trans- and cis-1-amino-1,2-cyclopentanedicarboxylic acids indicating epimerization during hydrolysis. The trans product has not been described previously and the cis not extensively characterized. X-ray crystallography reveals that both isomers are zwitterionic in the solid state and the cis isomer molecules are linked by unusually strong hydrogen bonding. Structures were confirmed by C-13 NMR, X-ray crystallography, and elemental analysis. Physical data are also presented.