1-Amino-2-phenylcyclopentane-1-carboxylic acid: A conformationally restricted phenylalanine analogue

(Chemical Equation Presented) DFT calculations at the B3LYP/6-311G(d,p) level have been used to investigate the intrinsic conformational preferences of 1-amino-2-phenylcyclopentane-1-carboxylic acid (c₅Phe), a constrained analogue of phenylalanine in which the α and β carbons are included in a cyclopentane ring. Specifically, the N-acetyl-N′-methylamide derivatives of the cis and trans stereoisomers, where cis and trans refer to the relative position between the amino group and the phenyl ring, have been calculated. Solvent effects have been examined using a self-consistent reaction field (SCRF) method. Results indicate that the conformational space of the cis stereoisomer is much more restricted than that of the trans derivative both in the gas phase and in solution.