1H NMR signal at 2.10 ppm in the spectrum of KMnO4-bleached heparin sodium: identification of the chemical origin using an NMR-only approach

Abstract

The recently revised European Pharmacopeia and US Pharmacopeia heparin sodium monographs include nuclear magnetic resonance (NMR) tests on both identity and purity. In KMnO(4)-bleached heparin, an unidentified NMR signal is present at 2.10ppm at a level of 15-20% of the mean of signal height of the major glucosamine (GlcNAc/GlcNS,6S) anomeric proton signal at 5.42ppm and of the major iduronic acid (IdoA2S) anomeric proton signal at 5.21ppm. According to the new monographs, no unidentified signals greater than 4% should be detected at that position. Thus, the material did not meet the acceptance criterion. The signal at 2.10ppm has been present at the same level in all released MSD KMnO(4)-bleached heparin sodium batches analyzed over the past 10years. The signal is a result of the KMnO(4) bleaching. No (oversulfated) chondroitin sulfate or dermatan sulfate was detected in this material. A comprehensive NMR study using long-range heteronuclear 2D techniques identifies this signal at 2.10ppm as originating from the acetyl methyl group of (6-sulfated) 2-N-acetyl-2-deoxy-glucono-1,5-lactone. This modified monosaccharide is formed by the KMnO(4) oxidation of the reducing end of a terminal N-acetylglucosamine.