Excitation-Sculptured Indirect-Detection Experiment (EXSIDE) for Long-Range CH Coupling-Constant Measurement

Abstract

A new pulse sequence (excitation-sculpturedindirect-detectionexperiment, EXSIDE) for measuring long-range heteronuclear coupling constants has been proposed. The experiment is a band-selective variant of the gradient–HSQC experiment. The initial polarization transfer from1H to13C and the refocusing of the antiphase1H magnetization after the back-transfer from13C to1H is unmodulated by any passive homonuclear couplings. This is achieved by a variation of the double pulse-field-gradient spin-echo technique. The sequence provides pure absorptive lineshapes, and long-range heteronuclear coupling constants areJ-scaled and measured along theF1(carbon) dimension. Unlike methods where the heteronuclear couplings are extracted along theF2(proton) dimension with overlapping homonuclear couplings, in the EXSIDE spectrum the active coupling constant is measured with no interference from any passive couplings. As long as one can group subsets of resonances that are not coupled to each other, the method can be used with multifrequency selection. The applicability of the experiment to measurenJCHis demonstrated using strychnine. The unique chemical-shift region of anomeric protons in oligosaccharides and the H1′ protons in oligonucleotides makes this method easily applicable for measuring long-range CH coupling constants across the glycosidic bond.