The conjugation of serotype 31 pneumococcal polysaccharide and CRM197 in N,N-dimethylformamide

Traditionally, PCV (pneumococcal conjugate vaccine) was prepared by the coupling of aldehyde-activated polysaccharide, with a carrier protein via NaCNBH3 (sodium cyanoborohydride) mediated reductive amination in water. However, the reaction is very slow and may take up to several days, which is a significant burden for pharmaceutical companies. Here we report the detailed reaction process of the reductive amination of structurally reassigned serotype 31 polysaccharide and cross reacting material (CRM197) in an organic solvent (N,N-dimethylformamide, DMF) by using STAB (sodium triacetoxyborohydride). The product has been characterized by size exclusion chromatography, nuclear magnetic resonance and transmission electron microscopy. Compared with the traditional method, the reaction can finish within hours and elicited a comparable immune response. The new strategy has the potential of being applied in the preparation of next-generation polysaccharide conjugate vaccines.