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[摘要]：A practical synthesis of N(alpha)-fluorenylmethoxycarbonyl-N(gamma)-(2,3,4,6-tetra-O-acetyl-alpha -D-glycopyranosyl)-L-asparagine in the gluco and galacto series has been achieved by using the methodology developed by DeShong and co-workers. The resulting alpha-N-linked glycosyl amino acids were used in a linear approach to the synthesis of glycopeptides featuring the unnatural alpha-N-glycosyl linkage. Activation conditions for both C- and N-terminus elongation in solution have been defined. The main side-reaction encountered was the formation of cyclization by-products (aspartimide) from the activated amino acid during C-terminus elongation. Appropriate condensing agents were identified, which allowed a high yield of dipeptide formation and no epimierization of the glycosyl amino acids. Conditions for sugar deacetylation have also been optimized. Solid-phase synthesis (Fmoc protocol) conditions were explored and PyBROP was found to be the reagent of choice for the activaton of glycosyl amino acids. The synthesis of more complex alpha-N-linked glycopeptides has thus become feasible, which will allow the properties of these neo-glycoconjugates to be studied. |
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