DFT calculations at the B3LYP/6-311G(d,p) level have been used to investigate the intrinsic conformationalpreferences of 1-amino-2-phenylcyclopentane-1-carboxylic acid (c
5Phe), a constrained analogue ofphenylalanine in which the
![](/images/gifchars/alpha.gif)
and
![](/images/gifchars/beta2.gif)
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 relativeposition between the amino group and the phenyl ring, have been calculated.
Solvent effects have beenexamined using a self-consistent reaction field (SCRF) method. Results indicate that the conformationalspace of the
cis stereoisomer is much more restricted than that of the
trans derivative both in the gasphase and in
solution.