Specific deuteration of a trimannoside confirms the existence of a disputed interresidue nuclear Overhauser enhancement.

The relative orientation of the 3-arm of N-linked glycans in solution can be determined, in part, by two interresidue nuclear Overhauser enhancements. The existence of one of these enhancements, that observed to the H5 proton of the (alpha 1,3)-linked mannose (attached to the core beta-linked mannose) upon irradiation of the beta-linked mannose H2 proton, has been disputed by other investigators (Homans, S. W., Dwek, R. A., Fernandes, D. L., and Rademacher, T. W. (1983) FEBS Lett. 164, 231-235). To demonstrate unequivocally the existence of this interresidue enhancement, we have synthesized a mannotrioside to model the corresponding moiety in N-linked glycans. Just as in N-linked glycans, the disputed enhancement cannot be directly observed due to spectral overlap with other enhancements but is detectable by careful quantitative analysis. By employing specifically deuterated derivatives of the mannotrioside, however, the disputed enhancement can be directly visualized.