Conformational analysis of [n-demethyl-Tyr(OCH3)-3]RA-VII, conformationally restricted model approach.

A molecular design was carried out in a way that locked the type II β-turn conformation of RA-VII, which was isolated from Rubia cordifolia and R.akane, by removing the N-methyl group of the Tyr-3 residue. Conformational analysis of [N-Demethyl-Tyr(OCH3)-3]RA-VII, derived from RA-VII by hepatic microsomal biotransformation, was conducted by 2D-NMR techniques, temperature effect on NH protons, and NOE experiments. It showed a restricted conformational state with a typical type II β-turn structure between Ala-2 and Tyr-3 in solution.