Synthesis Of Sugar Amino Acid Conjugates

The first synthetic reports of sugar amino acid conjugation appeared in the early 1970s. Most of those studies were directed to the synthesis of nucleoside antibiotics containing hexuronic acids conjugated to a-amino acids [11]. The first suggestions that unnatural compounds were of synthetic interest appeared in two separate papers published in 1976. Yoshimura and coworkers demonstrated that a hexosaminuronic acid could be conjugated to a glucosamine via an amide bond [42]. These scientists were clearly influenced by earlier work on nucleoside antibiotics. Nonetheless, they

Figure 20

did make amido-bonded disaccharides for the first time. Because one sugar was an acid and the other an amine, these systems were self-terminating (Fig. 21).

Fuchs and Lehmann first demonstrated that homo-oligomers of sugar amino acids could be prepared. In their reaction, a glucose-derived sugar amino acid possessing an anomeric carboxylate and a C4 amino group was polymerized under basic conditions [43]. After the reaction mixture had been heated for 4 h at 100°C, a water-insoluble precipitate formed (Fig. 22). The products were not rigorously characterized, but there was evidence that the precipitate was composed of dimers, trimers, and tetramers.

Although these two reports clearly demonstrated the feasibility of using sugar amino acids in the production of novel and unnatural compounds, it was nearly 20

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