STUDIES ON THE CONFORMATION OF HEPARIN BY H-1 AND C-13 NMR-SPECTROSCOPY

A convolution-difference 270-MHz 1H NMR spectrum of heparin has afforded a complete set of interproton coupling data for the major constituent residues of heparin, i.e., α-L-idopyranosyluronic acid 2-sulfate and 2-deoxy-2-sulfamino-α-D-glucopyranose 6-sulfate. According to these data, the conformation of the iduronic acid residue is 1C4(L) or a slightly distorted form thereof, whereas that of the aminodeoxyhexose residue is 4C1(D); the exocyclic CH2OSO3 group of the latter residue favors the gauche, gauche rotamer. The 5-proton of each residue exhibits selective line broadening and a large chemical shift displacement in the p region of the uronide carboxyl group, which indicates that these particular protons are in close proximity within the molecule. This observation helps to define a solution conformation for the polyelectrolyte chain. Other information on stereochemical aspects, and on pH and temperature effects, is provided by 13C NMR spectra. The latter are utilized also to highlight differences between beef lung (B type) and hog mucosal (A type) heparins, associated with the presence of minor constituent sugar residues, particularly through the acquisition of a difference 13C spectra. It is also shown that signal dispersion in 13C spectra of heparin is satisfactory at relatively low field (22.6 MHz) as well as at 67.9 MHz, provided that conditions of pH and ionic strength are optimized. © 1979, American Chemical Society. All rights reserved.