Conformations of β-amino acid residues in peptides: X-ray diffraction studies of peptides containing the achiral residue 1-aminocyclohexaneacetic acid, β3,3Ac6c

✍ Scribed by Prema G. Vasudev; Rajkishor Rai; Narayanaswamy Shamala; Padmanabhan Balaram

• Publisher: Wiley (John Wiley & Sons)
• Year: 2008
• Tongue: English
• Weight: 837 KB
• Volume: 90
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.20957

✦ Synopsis

Abstract

The conformational preferences of the 3,3‐disubstituted β‐amino acid residue, 1‐aminocyclohexaneacetic acid (β^3,3^Ac~6~c) 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 β‐position restricts the values of the torsion angles ϕ (NC^β^) and θ (C^β^C^α^) to approximately gauche values (±60°). Relatively few intramolecularly hydrogen bonded conformations are observed. In the dipeptide Boc‐β^3,3^Ac~6~c‐β^3,3^Ac~6~c‐NHMe a C~6~ hydrogen bond is observed. In Piv‐Pro‐β^3,3^Ac~6~c‐NHMe a C~11~ hydrogen bonded hybrid αβ 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 β‐residues, including β^2,2^Ac~6~c. © 2008 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 90: 138–150, 2008.

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