Preferred conformation of peptides based on cycloaliphatic C(alpha,alpha)-disubstituted glycines: 1-amino-cycloundecane-1-carboxylic acid (Ac11c).
Two complete series of N-protected oligopeptide esters to the pentamer level from 1-amino-cycloundecane-1-carboxylic acid (Ac11c), an alpha-amino acid conformationally constrained through a medium-ring C(i)alpha<-->C(i)alpha cyclization, and either the L-Ala or Aib residue, along with the N-protected Ac11c monomer and homo-dimer alkylamides, have been synthesized by solution methods and fully characterized. The preferred conformation of these model peptides has been assessed in deuterochloroform solution by FT-IR absorption and 1H-NMR techniques. Furthermore, the molecular structures of one derivative (Z-Ac11c-OH) and two peptides (the tripeptide ester Z-Aib-Ac11c-Aib-OtBu and the pentapeptide ester Z-Ac11c-(Aib)2-Ac11c-Aib-OtBu) have been determined in the crystal state by X-ray diffraction. The experimental results support the view that beta-bends and 3(10)-helices are preferentially adopted by peptides rich in Ac11c, the second largest cycloaliphatic C(alpha,alpha)-disubstituted glycine known. This investigation has allowed the authors to approach the completion of a detailed conformational analysis of the whole 1-amino-cycloalkane-1-carboxylic acid (Ac(n)c, with n = 3-12) series, which represents the prerequisite for their recent proposal of the 'Ac(n)c scan' concept.
Saviano
M
M
Biocrystallography Research Centre, CNR, Department of Chemistry, University of Naples Federico II, Napoli, Italy.
Iacovino
R
R
Benedetti
E
E
Moretto
V
V
Banzato
A
A
Formaggio
F
F
Crisma
M
M
Toniolo
C
C
D000146:Acids, Carbocyclic / Q000737:chemistry*; D019281:Dimerization; D005998:Glycine / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D010455:Peptides / Q000737:chemistry*; D011487:Protein Conformation; D013055:Spectrophotometry, Infrared; D014961:X-Ray Diffraction
D000146:Acids, Carbocyclic; D010455:Peptides; D005998:Glycine