Aggregation modes in sheets formed by protected beta-amino acids and beta-peptides.
The crystal structures of four protected beta-amino acid residues, Boc-(S)-beta3-HAla-NHMe (1); Boc-(R)-beta3-HVal-NHMe (2); Boc-(S)-beta3-HPhe-NHMe (3); Boc-(S)-beta3-HPro-OH (6) and two beta-dipeptides, Boc-(R)-beta3-HVal-(R)-beta3-HVal-OMe (4); Boc-(R)-beta3-HVal-(S)-beta3-HVal-OMe (5) have been determined. Gauche conformations about the C(beta)-C(alpha) bonds (theta approximately +/-60 degrees) are observed for the beta3-HPhe residues in and all four beta3-HVal residues in the dipeptides and . Trans conformations (theta is approximately 180 degrees) are observed for beta3-HAla residues in both independent molecules in and for the beta3-HVal and beta3-HPro residues in and , respectively. In the cases of compounds , molecules associate in the crystals via intermolecular backbone hydrogen bonds leading to the formation of sheets. The polar strands formed by beta3-residues aggregate in both parallel (1,3,5) and antiparallel (2,4 fashion. Sheet formation accommodates both the trans and gauche conformations about the C(beta)-C(alpha) bonds.
Sengupta
Anindita
A
Department of Physics, Indian Institute of Science, Bangalore, 560 012, India.
Roy
Rituparna S
RS
Sabareesh
Varatharajan
V
Shamala
Narayanaswamy
N
Balaram
Padmanabhan
P
D000596:Amino Acids / Q000138:chemical synthesis* / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D010455:Peptides / Q000737:chemistry*; D011487:Protein Conformation
D000596:Amino Acids; D010455:Peptides