A convenient synthesis of nucleoside monophosphate-N-acetylneuraminic acids (NMP-Neu5Ac)

Docking-guided rational engineering of a macrolide glycosyltransferase glycodiversifies epothilone B

Glycosyltransferases typically display acceptor substrate flexibility but more stringent donor specificity. BsGT-1 is a highly effective glycosyltransferase to glycosylate macrolides, including epothilones, promising antitumor compounds. Here, we show that BsGT-1 has three major regions significantly influencing the glycodiversification of epothilone B based on structural molecular docking, "hot spots" alanine scanning, and site saturation mutagenesis. Mutations in the PSPG-like motif region and the C2 loop region are more likely to expand donor preference; mutations of the flexible N3 loop region located at the mouth of the substrate-binding cavity produce novel epothilone oligosaccharides. These "hot spots" also functioned in homologues of BsGT-1. The glycosides showed significantly enhanced water solubility and decreased cytotoxicity, although the glycosyl appendages of epothilone B also reduced drug permeability and attenuated antitumor efficacy. This study laid a foundation for the rational engineering of other GTs to synthesize valuable small molecules.

Microbial glycosyltransferases for carbohydrate synthesis: alpha-2,3-sialyltransferase from Neisseria gonorrheae

The alpha-2,3-sialyltransferase from Neisseria gonorrheae was overproduced in E. coli for exploitation of its substrate specificity and synthetic utility. Several potential acceptor substrates were synthesized in this study, including mono- and oligosaccharides, glycolipids, and glycopeptides and their sulfate derivatives. Some CMP-sialic acid derivatives with modification at the C-5 position were also prepared for evaluation as donor substrates. It was found that the enzyme exhibits a broader acceptor substrate specificity when compared to other sialyltransferases, though the donor specificity is quite limited. Application of the enzyme to the preparative synthesis of representative sialyl glycoconjugates has been demonstrated. On the basis of this work and the work of others, this enzyme is the most versatile and synthetically useful among all sialyltransferases known to date, especially for the synthesis of sulfate-containing glycoconjugates.

Ceramide-1-phosphate sugars: new types of glycophospholipids

Ceramide-1-phosphate sugars were synthesized by direct glycosyl phosphite/phosphate and O-glycosyl trichloroacetimidate/phosphate exchange reactions, respectively. Thus, ceramide-1-O-phosphoric acid 5 gave with sialyl phosphite 1 as sialyl donor directly beta-linked sialyl phosphate 6; deprotection afforded the corresponding glycophospholipid ceramide-1-phosphate N-acetylneuraminate 7. Similarly, from O-glucosyl- and O-galactosyltrichloroacetimidate 10 and 13 with phosphoric acid derivative 5 glycosyl ceramide-1-phosphate sugars 12 and 15, respectively, were obtained.