CHEMICAL SYNTHESIS OF MENINGOCOCCAL GROUP A OLIGOSACCHARIDES

合成控制大小寡糖的研究正在进行中

The synthesis of controlled size oligosaccharides is being pursued in order to provide material for the preparation of conjugates. These conjugates will make it possible to determine the effects of oligosaccharide size on immunogenicity of a conjugate vaccine. An appropriate solid phase support has been prepared. This support incorporates a four-carbon spacer arm which is attached to the support by a selectively cleavable disulfide bond. The support has been found to bear derivatizable groups at a concentration of 50 mmoles/gm. It was determined that the conventional b-cyanoethyl protected phosphitylating reagent, required to complete the synthesis of the activated monomer, would not be optimal for this synthesis, therefore a benzyl protected phosphitylating reagent was prepared. This reagent was preferable because it uses the same protective group as is already present in the carbohydrate moiety of the monomer. In contrast to the case of the b-cyanoethyl protected intermediate, the phosphite enantiomers of the a-anome of the benzyl protected intermediate copurify. This makes the essential separation of anomers much less labor intensive. The required monomer, 2-acetamido-3-0-acetyl-4-0-benzyl-2-deoxy-6- fluorenylmethoxycarbonyl-a-D-mannopyranosyl-N, N-diisopropy-0-benzyl-phosphoramidite, was prepared, purified and characterized. This monomer has been used to prepare a tetrasaccharide attached to the solid phase. Measurement of coupling efficiency indicated that the synthesis can be readily extended to produce a 20-mer. Work is now progressing on the efficient removal of the saccharide from the support.