Solution structure, dynamics, and proton relaxation mechanisms of natural products and biopolymers. N-acetyl-D-alloisoleucine

The NT1 values of the 13C atoms and the proton-proton scalar coupling established the existence of multiple conformations in N-acetyl-D-alloisoleucine. The principal (x1; X2,1) conformations in solution are those which exist in the crystal. Selective and nonselective proton spin-lattice relaxation rates of the NH, Hα, Hβ, Hγ11, Hγ12, Hγ2, and Hδ yielded Fi ratios (nonselective/monoselective relaxation rate) and cross-relaxation rates, a. The proton relaxation rates yielded correlation times and side chain conformational information and removed the 3Jv ø degeneracy. The proton relaxation mechanism is, within experimental error, exclusively dipolar. This combined scalar coupling constant, 13C, and proton relaxation study of stereochemistry, motion, and relaxation of the first-order couplcd amino acid N-acetyl-D-alloisoleucine establishes the potential of proton relaxation spectroscopy as a technique for studying individual amino acid residues in peptides and proteins. © 1980, American Chemical Society. All rights reserved.