Dispersing the crowd: Adopting 13 C direct detection for glycans.

As a direct consequence of technological advancements, the interest in direct detection of low-gamma/low-sensitivity heteronuclei for NMR experiments has been revived. Until recently, experimental development of ¹³ C/ ¹⁵ N detected experiments has been focused on protein NMR. In the present report, we extend the use of ¹³ C-detected experiments to structural studies of glycans in natural abundance. The narrow ¹ H and wider ¹³ C signal dispersion make glycans ideal candidates for heteronuclear detection. We show that ¹³ C-detected HSQC offers a ten-fold increase in ¹³ C dimension resolution compared to the analogous ¹ H-detected HSQC, when the experiments are acquired for the same amount of time. The enhanced resolution comes at the expense of 2 to 3-fold loss in SNR; however, the observed signal loss is a fraction of the theoretical 8-fold difference expected between experiments. Further, we show that by combining a ¹ H constant time element (CT), SMILE data reconstruction and ¹³ C-direct detection, complete resonance assignments of highly degenerate glycan signals are possible. Finally, we demonstrate the potential of our strategy to aid in the assignment of complex glycans, by using a novel ¹³ C-detected version of the CT-HSQC-TOCSY experiment performed on sialyl Lewis X pentasaccharide model system.
Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
(Published by Elsevier Inc.)