Evaluation of Kochetkov Hemiaminal hydrolysis under acidic, alkaline, and neutral conditions

The most common precursors to synthetic glycoproteins are reducing end glycosyl amines. To afford these amines, a carbohydrate is reacted with an excess of an ammonia source to yield the β-anomer, exclusively, in a reaction known as the Kochetkov amination. Although this process is the state-of-the-art method to synthesize non-functionalized, β-amino (βA) glycans, misconceptions surrounding the stability of these amines has limited their use in subsequent reactions. Here, we investigated the stability of seven amino sugars in the neutral, acidic, and basic conditions they would be subject to in common reactions using amines. In neutral and basic conditions, the amino sugars proved relatively stable with the fastest time to 50% hydrolysis being four days for only one carbohydrate. However, acidic conditions promoted rapid hydrolysis, with all amino sugars reaching over 97% hydrolysis within 2 h. Finally, we performed a bioconjugation using fluorescein isothiocyanate and βA-difucosyllactose, revealing sufficient stability of the amino product for a successful subsequent reaction.