Conformation of cydo(L-Alanylglycyl-ε-aminocaproyl), a Cyclized Dipeptide Model for a β Bend. 2. Synthesis, Nuclear Magnetic Resonance, and Circular Dichroism Measurements

Abstract

cyclo(L-Alanylglycyl-ε-aminocaproyl) has been synthesized by means of classical solution techniques. The Ala-Gly moiety of this molecule is constrained to form a β bend because of the closure of the ring by the five-carbon alkyl chain of the e-aminocaproyl residue. 13C NMR spectroscopic measurements indicate the absence of rapid internal segmental motion. Reorientation takes place by means of anisotropic rotational diffusion. 1H NMR spectroscopic measurements show that the molecule has little flexibility and that its predominant backbone conformation is a type II β bend, with a strongly bent NH&O=C bond in the ε-aminocaproyl residue. Circular dichroism measurements confirm this conclusion. I..