Conformations of beta-amino acid residues in peptides: X-ray diffraction studies of peptides containing the achiral residue 1-aminocyclohexaneacetic acid, beta3,3Ac6c.
The conformational preferences of the 3,3-disubstituted beta-amino acid residue, 1-aminocyclohexaneacetic acid (beta3,3Ac6c) have been investigated by determining the crystal structures of the parent amino acid, the hydrochloride derivative, 10 protected derivatives and di and tripeptides. The symmetrical cyclohexyl substituent at the beta-position restricts the values of the torsion angles phi (N--C(beta)) and theta (C(beta)--C(alpha)) to approximately gauche values (+/-60 degrees ). Relatively few intramolecularly hydrogen bonded conformations are observed. In the dipeptide Boc-beta(3,3)Ac6c-beta(3,3)Ac6c-NHMe a C6 hydrogen bond is observed. In Piv-Pro-beta(3,3)Ac6c-NHMe a C11 hydrogen bonded hybrid alphabeta turn is characterized. In a majority of cases the amino group occupies the axial position in the cyclohexane ring. The conformations observed are compared with crystallographically observed structures for other beta-residues, including beta(2,2)Ac6c.
Vasudev
Prema G
PG
Department of Physics, Indian Institute of Science, Bangalore 560 012, India.
Rai
Rajkishor
R
Shamala
Narayanaswamy
N
Balaram
Padmanabhan
P
D000596:Amino Acids / Q000737:chemistry*; D018360:Crystallography, X-Ray; D003510:Cyclohexanes / Q000737:chemistry*; D006860:Hydrogen Bonding; D008958:Models, Molecular; D008968:Molecular Conformation; D010455:Peptides / Q000737:chemistry*; D013237:Stereoisomerism; D014961:X-Ray Diffraction
D000596:Amino Acids; D003510:Cyclohexanes; D010455:Peptides