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Synthesis of C-linked carbo-β2-amino acids and β2-peptides: design of new motifs for left-handed 12/10- and 10/12-mixed helices†
Gangavaram V. M. Sharma,Nelli Yella Reddy,Rapolu Ravi,Bommagani Sreenivas,Gattu Sridhar,Deepak Chatterjee,Ajit C. Kunwar,Hans-Jörg Hofmann
Organic & Biomolecular Chemistry Pub Date : 10/02/2012 00:00:00 , DOI:10.1039/C2OB26615F
Abstract

C-linked carbo-β2-amino acids (β2-Caa), a new class of β-amino acid with a carbohydrate side chain having D-xylo configuration, were prepared from D-glucose. The main idea behind the design of the new β-amino acids was to move the steric strain of the bulky carbohydrate side chain from the Cβ- to the Cα-carbon atom and to explore its influence on the folding propensities in peptides with alternating (R)- and (S)-β2-Caas. The tetra- and hexapeptides derived were studied employing NMR (in CDCl3), CD, and molecular dynamics simulations. The β2-peptides of the present study form left-handed 12/10- and 10/12-mixed helices independent of the order of the alternating chiral amino acids in the sequence and result in a new motif. These results differ from earlier findings on β3-peptides of the same design, containing a carbohydrate side chain with D-xylo configuration, which form exclusively right-handed 12/10-mixed helices. Quantum chemical calculations employing ab initio MO theory suggest the side chain chirality as an important factor for the observed definite left- or right-handedness of the helices in the β2- and β3-peptides.

Graphical abstract: Synthesis of C-linked carbo-β2-amino acids and β2-peptides: design of new motifs for left-handed 12/10- and 10/12-mixed helices
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