Carbohydrate amino acids: the intrinsic conformational preference for a beta-turn-type structure in a carbopeptoid building block.
Infrared ion-dip spectroscopy coupled with DFT and ab initio calculations are used to establish the intrinsic conformational preference of the basic structural unit of a peptide mimic, a cis-tetrahydrofuran-based "carbopeptoid" (amide-sugar-amide), isolated at low temperature in the gas phase. The carbopeptoid units form a beta-turn-type structure, stabilized by an intramolecular NH --> O=C hydrogen bond across the sugar ring, thus forming a 10-membered, C10 turn. Despite the clear preference for C10 beta-turn structures in the basic unit, however, the presence of multiple hydrogen-bond donating and accepting groups also generates a rich conformational landscape, and alternative structures may be populated in related molecules. Calculations on an extended, carbopeptoid dimer unit, which includes an alternating amide-sugar-amide-sugar-amide chain, identify conformers exhibiting alternative hydrogen-bonding arrangements that are somewhat more stable than the lowest-energy double beta-turn forming conformer.
Jockusch
Rebecca A
RA
Chemistry Department, Physical and Theoretical Chemistry Laboratory, South Parks Road, Oxford OX1 3QZ, UK. rebecca.jockusch@utoronto.ca
Talbot
Francis O
FO
Rogers
Paul S
PS
Simone
Michela I
MI
Fleet
George W J
GW
Simons
John P
JP
D000596:Amino Acids / Q000737:chemistry*; D002241:Carbohydrates / Q000737:chemistry*; D005663:Furans / Q000737:chemistry; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation; D009842:Oligopeptides / Q000138:chemical synthesis / Q000737:chemistry*; D012680:Sensitivity and Specificity; D013055:Spectrophotometry, Infrared / Q000379:methods
D000596:Amino Acids; D002241:Carbohydrates; D005663:Furans; D009842:Oligopeptides; C018674:tetrahydrofuran