o transfer l-Gal and arabinose from their corresponding donors  (Fig. 12). Both enzymes accept replacements and modifications of the N-acetyl group of the GlcNAc unit [106-108]. FucT VI has been shown to tolerate replacement of the GlcNAc unit with glucal and cyclohexane diol . FucT III and FucT VI have further been used to construct libraries of sialyl Lea or sialyl Lex derivatives using both unnatural donors and unnatural acceptors [110-112].
FucT III and FucT VI have been probed with unnatural donors with a modified purine base. They can tolerate exchange of the guanine by other purine bases such as adenine . These unnatural donors proved to be preparatively efficient in the enzymatic synthesis of Lea or Lex, suggesting that natural sugar nucleotide donors can be replaced with inexpensive ones to lower the cost of enzymatic synthesis.
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