Aspartimides DIPEA

As a conclusion from Lansbury s detailed study on a number of peptides and glycosylamines, in addition to 1 equiv. glycosylamine, 1 equiv. of a base is needed for a maximum A -glycopeptide yield, but at the same time aspartimide formation is also promoted. When the peptide is prone to aspartimide formation, and the glycosylamine is not particularly precious, it is recommended to omit DIPEA, and use 2 equiv. of glycosylamine instead. If the peptide is not susceptible to aspartimide formation, excellent JV-glycopeptide yields can be obtained with only 1 equiv. of the glycosylamine, and 1-2 equiv. of DIPEA. 

An example for a complex glycopeptide synthesis plying the aforementioned protocol is illustrated in Scheme 3. The heptasaccharide-glycosylamine 2 was reacted with peptide 3 in the presence of HBTU, HOBt, and 2 equiv. of DIPEA, which furnished 81% of the yV-glycopeptide, 12% of peptide 3, and only 7% of the aspartimide (36). 

Entry H[Pg.334]

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