Extraction of Distance Restraints from Pure Shift NOE experiments

NMR techniques incorporating pure shift methods to improve signal resolution have recently attracted much attention, owing to their potential use in studies of increasingly complex molecular systems. Extraction of frequencies from these simplified spectra enables easier structure determination, but only a few of the methods presented provide structural parameters derived from signal integral measurements. In particular, for quantification of the nuclear Overhauser effect (NOE) it is highly desirable to utilize pure shift techniques where signal overlap normally prevents accurate signal integration, to enable measurement of a larger number of interatomic distances. However, robust methods for the measurement of interatomic distances using the recently developed pure shift techniques have not been reported to date.
In this work we discuss some of the factors determining the accuracy of measurements of signal integrals in interferogram-based Zangger-Sterk (ZS) pure shift NMR experiments. The ZS broadband homodecoupling technique is used in different experiments designed for quantitative NOE determination from pure shift spectra. It is shown that the techniques studied can be used for quantitative extraction of NOE-derived distance restraints, as exemplified for the test case of strychnine.