Results from the analysis of the synthesized AMS-maleimide 6-MHA was first chlorinated with oxalyl chloride to yield 6-MHC (Figure ). The reaction completion was checked by 1 H NMR, as reported (Figure in SI) . Then, AMS was esterified with 6-MHC, yielding AMS-maleimide with a degree of esterification of 1.42 and maleimide content of 3.2 mmol g -1 , as previously determined by quantitative 1 H NMR (Figure in SI). The chemical structure of AMS-maleimide was precisely determined by C APT, 1 H- C HSQC, 1 H-13 C HMBC NMR, and FTIR (Figure in SI). Some results were also given in a recent work [11]. C APT and 1 H-13 C HMBC NMR analyses were partly hampered by a decrease of the intensity of the peaks assigned to the protons on the carbohydrates rings. This phenomenon is due to partial esterification, which increases the number of neighboring protons. This, in turn, leads to a greater number of peaks in the spectrum, each with reduced intensity. Essentially, the incomplete esterification process creates a more complex environment where protons are in closer proximity, resulting in a more intricate and less intense peak pattern with decreased intensities . 1 H-13 C HSQC yielded light cross-peaks corresponding to the carbons and hydrogens on the rings of AMS-maleimide. We can find only few reports on the use of 1 H-15 N HMBC for the characterization of nitrogencontaining organic molecules in the literature . This type of spectroscopy is largely less used than 1 H-13 C 2D because of the lower natural abundance of N atoms, despite its high sensitivity enabled by the large dispersion of N chemical shifts (approximately 1000 ppm) . In this NMR study of AMS-maleimide, 1 H-15 N HMBC at natural abundance was used to confirm the presence of grafted maleimide groups by identifying multiple bond long-range 1 H-15 N couplings. 6-MHA was first analyzed( Figure and Table in SI). On the 1 H-15 N HMBC spectrum of 6-MHA (Figure , top), the nitrogen atom with a chemical shift of 152.0 ppm gave a 2 J correlation response with the protons labelled Hb and 3 J correlation responses with the protons Ha and Hc, in agreement with the structure of 6-MHA. The absence of longer-range 1 H-15 N couplings is in agreement with literature, where the longest couplings are usually 3 J or 4 J 47 . The 1 H-15 N HMBC spectrum of AMS-maleimide was then recorded (Figure , bottom). The correlation responses between the nitrogen atom and the protons Ha and Hb were obtained again with only a minor variation of the chemical shift of the nitrogen atom (Table in SI). While the intensity of the peak assigned to the Hb-N correlation was largely reduced and hardly distinguishable from noise signals, the peak assigned to the Hc-N correlation, yet visible on the spectra of 6-MHA, was absent. This could be explained by the decreased solubility of AMSmaleimide in DMSO-d6 compared to 6-MHA and/or by the high viscosity of the solution of AMS-maleimide in DMSO-d6, which could reduce the translational motion of the macromolecules and thus increase the relaxation time of their atoms . Nevertheless, in this case, 1 H- N HMBC was profitably used to further confirm the structure of AMS-maleimide, clearly demonstrating the esterification reaction with 6-MHA.