Conformation of Achiral α/β Hybrid Peptides Containing Glycine and 1‐Aminocyclohexaneacetic Acid

• Published in: ChemistrySelect (Weinheim) Vol. 7; no. 10
• Main Authors: Shankar, Sudha, Jyothi, Deeti, Rahim, Junaid ur, Pal, Purna Chandra, Singh, Umesh Prasad, Rai, Rajkishor
• Format: Journal Article
• Language: English
• Published: 15.03.2022
• Subjects: conformation; helices; hybrid peptides; X-ray crystallography; Β-β disubstituted-β-amino acid
• ISSN: 2365-6549; 2365-6549
• DOI: 10.1002/slct.202104453

The present work describes the conformation of achiral α/β hybrid peptides, Boc‐Gly‐β3,3‐Ac6c‐NHMe (P1), Boc‐Gly‐β3,3‐Ac6c‐Gly‐OMe (P2), and Boc‐Gly‐β3,3‐Ac6c‐Gly‐β3,3‐Ac6c‐OMe, (P3) using X‐ray crystallography. Peptides P1 and P2 adopt C11 and C12 folded conformations, respectively. The directionality of the hydrogen bond observed in P1 is opposite to that observed in peptide P2. In case of tetrapeptide P3, no such hydrogen bond is observed. Further, the solvent titration experiment establishes the similar intramolecular hydrogen bonding as observed in the crystals. In P1 and P2, the amino group of β3,3‐Ac6c occupies equatorial orientations, while in the case of peptide P3, it occupies axial and equatorial orientations for residues β3,3‐Ac6c(2) and β3,3‐Ac6c(4), respectively. The average (ϕ,θ,ψ) torsional preferences of β3,3‐Ac6c in achiral α/β peptides are somewhat different from that of chiral α/β peptides. α/β hybrid peptides Boc‐Gly‐β3,3‐Ac6c‐NHMe (P1) and Boc‐Gly‐β3,3‐Ac6c‐Gly‐OMe (P2) display C11 and C12 intramolecular hydrogen‐bonds, respectively. The directionality of the hydrogen bond observed in P1 is opposite to that observed in peptide P2. No intramolecular hydrogen bond is observed in peptide Boc‐Gly‐β3,3‐Ac6c‐Gly‐β3,3‐Ac6c‐OMe, P3.