Rc. Crouch et Ge. Martin, LONG-RANGE H-1-N-15 CORRELATION AT NATURAL-ABUNDANCE USING GRADIENT-ENHANCED INVERSE-DETECTION, Journal of heterocyclic chemistry, 32(5), 1995, pp. 1665-1669
Inverse-detected heteronuclear shift correlation efficiency has been s
ignificantly augmented by the incorporation of pulsed field gradients
(PFG). Phase-cycling requirements for t(1)-noise suppression in gradie
nt-enhanced experiments are, for the most part, obviated, making it fe
asible to acquire data in one or a few transients/t(1) increment. The
benefits which accrue for H-1-C-13 correlation (using GHMQC, GHMBC, an
d variants of GHMQC-TOCSY) are well documented. Less obvious is the in
creased facility with which long-range H-1-N-15 correlation spectra ca
n be acquired. An IDR-(Inverted Direct Response)-GHMQC-TOCSY was used
to establish unequivocal proton resonance assignments for the alkaloid
ajmaline. Long-range H-1-N-15 heteronuclear couplings to the two nitr
ogen atoms of ajmaline were then probed using a gradient-enhanced H-1-
N-15 heteronuclear shift correlation experiment derived from HMQC. Lon
g-range H-1-N-15 couplings in ajmaline are assigned for the first time
.