EXCITATION-SCULPTURED INDIRECT-DETECTION EXPERIMENT (EXSIDE) FOR LONG-RANGE CH COUPLING-CONSTANT MEASUREMENT

A new pulse sequence (excitation-sculptured indirect-detection experim ent, 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 from H-1 t o C-13 and the refocusing of the antiphase H-1 magnetization after the back-transfer from C-13 to H-1 is unmodulated by any passive homonucl ear couplings. This is achieved by a variation of the double pulse-hel d-gradient spin-echo technique. The sequence provides pure absorptive lineshapes, and long-range heteronuclear coupling constants are J-scal ed and measured along the F-1 (carbon) dimension. Unlike methods where the heteronuclear couplings are extracted along the F-2 (proton) dime nsion with overlapping homonuclear couplings, in the EXSIDE spectrum t he 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 multifrequ ency selection. The applicability of the experiment to measure (n)J(CH ) is demonstrated using strychnine. The unique chemical-shift region o f anomeric protons in oligosaccharides and the H1' protons in oligonuc leotides makes this method easily applicable for measuring long-range CH coupling constants across the glycosidic bond. (C) 1996 Academic Pr ess, Inc.