Development of Programmed Oligosaccharide Synthesis on Nucleic Acid Template

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The objective of this project is to develop new methodology for oligosaccharide synthesis on DNA templates. We hypothesized that glycosyl donors having nucleobases would be aligned on DNA template due to the hydrogen bonding between complementary base pairs and glycosylation would proceeds upon addition of activators of glycosyl donors, resulting in the selective synthesis of target sequence of oligosaccharides. It also provides a new concept for the direct conversion of genetic sequence of DNA to olitosaccharide sequence.For the aforementioned purpose, we decided to design and synthesize nucleothio-glycosides, which are thioglycosides linked with nucleobases by covalent bonds, because thioglycosides are stable and can be activated by specific activators, and hence, they are used as glycosyl donors in plenty examples of oligosaccharide synthesis.First, a benzenethiol part having thymidine(T) was prepared from bromobenzene in 8 steps and then reacted with galactosyl acetate to afford th … More iogalactoside linked with thymidine(T)(T-Gal). In addition, Gal having adenosine(A-Gal) and N-acetyl-glucosamine linked with A(A-GlcNAc) were prepared in a similar manner. Recently, more convenient synthetic routes of these nucleothioglucosides were established.Secondly, it was found that glycosylation of T-Gal with glucose derivatives gave the desired disaccharides such as Gal(β1→4) Glc in a fairly good yield, proving the possibility of glycosylation of nucleobase-linked thioglycosides. However, glycosylation of T-Gal with glycosyl acceptors having adenosine units and A-GlcNAc with several acceptors were not successful under these reaction conditions, possibly because Lewis acidity of promoters is neutralized by adenosine moiety of these substrates. Therefore, we have tested several reaction conditions(activators, solvent, and temperature) and finally found that a combination of Tol-SCl & AgOTf(OTf=triflate) gave the target disaccharides in moderate or high chemical yields.As for DNA template to program oligosaccharide sequences, we have synthesized A, T, G, and C derivatives having glycine backbone. Coupling reactions of these parts to obtain DNA template is now underway. In the next experiments, preparation and other nucleothioglucosides such as CMP-NeuNAc and G-Glc, and glycosylation of these glycosyl donors as well as the aforementioned glycosides, T-Gal and A-GlcNAc, with glycosyl acceptors in the presence of DNA-template will be examined. Less