| Popis: |
The crystal structures of four dipeptides that contain the stereochemically constrained gamma-amino acid residue gabapentin (1-(aminomethyl) cyclohexaneacetic acid Gpn) are described. The molecular conformation of Piv-Pro-Gpn-OH (1), reveals a beta-turn mimetic conformation, stabilized by a ten atom C-H…O hydrogen bond between the Piv CO group and the pro S hydrogen of the Gpn CH2-CO group. The peptides Boc-Gly-Gpn-OH (2),Boc-Aib- Gpn-OH (3),and Boc-Aib-Gpn-OMe (4) form compact,folded structures,in which a distinct reversal of polypeptide chain direction is observed. In all cases, the Gpn residue adopts a gauche, gauche (g,g) conformation about the C alpha-C gamma (tita1) and C beta-C alpha (tita 2) bonds. Two distinct Gpn conformational families are observed. In peptides 1 and 3,the average backbone torsion angle values for the Gpn residue are 98, 1, 62, 2, 73 and 79,while in peptide 2 and 4 the average values are -103, -1, - 46, - 49 and - 92. In the case of 1 and 3,an intramolecular nine membered O-H…O hydrogen bond is formed between the C=O of the preceding residue and the terminal carboxylic acid OH group. All four alpha-gamma dipeptide sequences yield compact folded backbone conformations; this suggests that the Gpn residue may be employed successfully in the design of novel folded structures. |
