A new pulse sequence (excitation-sculptured indirect-detection wealth of structural information (10). They can provide inexperiment, EXSIDE) for measuring long-range heteronuclear formation on dihedral angles via a Karplus equation ( 11). coupling constants has been proposed. The experiment is a band-New proton-detected methods have been presented in recent selective variant of the gradient-HSQC experiment. The initial years to determine long-range heteronuclear coupling conpolarization transfer from 1 H to 13 C and the refocusing of the stants. The J CH can be obtained from E.COSY-like signal antiphase 1 H magnetization after the back-transfer from 13 C to 1 H splitting with 1 J XH in F 1 and n J XH in F 2 . Signals of this kind is unmodulated by any passive homonuclear couplings. This is appear in X-filtered NOESY (12, 13) or X-filtered TOCSY achieved by a variation of the double pulse-field-gradient spin-(14-16) experiments and can be combined with editing and echo technique. The sequence provides pure absorptive lineshapes, selection techniques (17-19). These experiments, however, and long-range heteronuclear coupling constants are J-scaled and are applicable only to protonated carbons. Various other measured along the F 1 (carbon) dimension. Unlike methods where 1D, 2D, and 3D techniques based on HMBC and HSQC the heteronuclear couplings are extracted along the F 2 (proton)
experiment have also been proposed (20-27). The focus in dimension with overlapping homonuclear couplings, in the EX-SIDE spectrum the active coupling constant is measured with no these cases is to extract the heteronuclear coupling constants interference from any passive couplings. As long as one can group in the presence of homonuclear couplings. This is typically subsets of resonances that are not coupled to each other, the achieved by lineshape analysis (in the proton-detection dimethod can be used with multifrequency selection. The applicabilmension) or signal-intensity analysis (analytical, 2D, or 3D ity of the experiment to measure n J CH is demonstrated using methods) or by the use of selective excitation (in the proton strychnine. The unique chemical-shift region of anomeric protons and/or carbon dimensions). A recent review (28) surveys in oligosaccharides and the H1 protons in oligonucleotides makes the various methods for determining scalar coupling conthis method easily applicable for measuring long-range CH coustants (including heteronuclear coupling constants) and their pling constants across the glycosidic bond.