Sulfated glycosaminoglycans (GAGs) and polysaccharides are important biological molecules, a number of which, for example heparin, Fondaparinux Sodium (ARIXTRA®) and Pentosan Polysulfate Sodium (ELMIRON®), have been in clinical use for decades. A variety of sulfated compounds based on new scaffolds have also been recently developed for treatment of various diseases [1,2]. A key step in the preparation of homogeneous sulfated carbohydrates is efficient, reproducible and scalable chemical O- and N-sulfation method. A significant difficulty that arises during attempts to sulfate polyfunctional substrates using conventional approaches is incomplete conversion. Therefore, a reliable and more controllable sulfation protocol is an unmet need for synthetic chemists.
In this presentation we describe a new chemical sulfation method, developed to eliminate this synthetic bottleneck in GAG synthesis. First, we identified that the dipolar solvent, N,N-dimethylformamide (DMF), widely used as a bulk solvent in O-sulfation reactions, while enabling solubilization of the reactants, also uninstalls the newly-formed sulfate groups on reaction substrates. To investigate this problem, we conducted a mechanistic study using real-time NMR spectroscopy to monitor the progress of sulfation reactions distinguishing between conventional and modified approaches. The intriguing findings from the NMR study led us to establish a new sulfation protocol which can efficiently sulfate a wide range of complex carbohydrate substrates with reproducible full conversion. This newly-developed sulfation method both attenuates adverse side reactions and prevents loss of sulfate groups potentially initiated by dipolar solvents throughout the course of reaction, work-up and purification.
The new sulfation method has been successfully applied to O- and N-sulfation of a wide range of substrates . Among these, a library of discrete homogeneous heparan sulfate fragments ranging from mono to octa-saccharides was prepared, which has been exploited to uncover the specific binding interactions of pure GAG fragments with proteins and in metallo-organic complexes [4,5,6]. We also successfully extended this new protocol to sulfate a polyol substrate on a scale of 232 grams in the academic lab and transferred the technology to GMP production (7 kg scale) of a lead drug candidate currently in a human clinical trial.
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- Gorle, A. K.; Rajaratnam, P.; Chang, C.-W.; von Itzstein, M.; Berners-Price, S. J.; Farrell, N. P., Inorg. Chem. 2019. DOI: 10.1021/acs.inorgchem.8b03035