Selective J ‐resolved‐HMQC‐1 and ‐2, new methods for measuring proton–proton coupling constants in strongly coupled spin systems

Efficient pulse sequences for measuring 1 H– 1 H coupling constants ( J HH ) in strongly coupled spin systems, named selective J ‐resolved‐HMQC‐1 and ‐2, have been developed. In the strongly coupled spin systems such as ‐CH 2 ‐CH A (OH)‐CH B (OH)‐CH 2 ‐, measurements of 3 J HAHB are generally difficult owing to the complicated splitting caused by the adjacent CH 2 protons. For easier and accurate measurements of 3 J HAHB in such a spin system, a selective excitation pulse is incorporated into the J ‐resolved HMQC pulse sequence. In the proposed methods, only two strongly coupled protons, H A and H B which are excited by a selective pulse, are observed as J ‐resolved HMQC signals. The cross peaks of H A and H B appear as doublets owing to 3 J HAHB along the F 1 dimension in the selective J ‐resolved HMQC‐1 and ‐2 experiments. The efficiency of the proposed pulse sequences has been demonstrated in application to the stereochemical studies of the complicated natural product, monazomycin. Copyright © 2011 John Wiley & Sons, Ltd.