Mammalian milk or colostrum usually contains a variety of milk oligosaccharides in addition to lactose (Galβ1-4Glc) as the predominant saccharide. Almost all of them have a lactose unit at their reducing ends and also contain galactose (Gal), N-acetylglucosamine (GlcNAc), fucose (Fuc), N-acetyl or N-glycolylneuraminic acid (Neu5Ac and Neu5Gc, respectively), or N-acetylgalactosamine (GalNAc) residues. For example, human milk contains more than 250 varieties of oligosaccharides at a concentration of 12–13 g/L (see Note 1). Around 170 of the more than 250 chemical structures have been characterized to date.1 In this chapter of the series, the potential utilization of milk oligosaccharides is discussed as a unique research tool to solve the unanswered questions related to galectins.
Cellulose is a natural polysaccharide, and is functionally classified as a structural polysaccharide. Its superior strength is attributed to the fact that it is composed of multiple molecular chains, and it has a structure known as cellulose I crystal that exhibits a high crystalline modulus. The fact that such an agglomeration of polymers can be synthesized by enzymatic proteins suggests that cellulose biosynthesis is a mechanism designed to synthesize the strongest possible structure by controlling the polymer chains at ambient temperature and pressure in aqueous solvents. In comparison with the typical formation process for general-purpose polymers, which involves high temperature, high pressure, and harsh solvents, the enzyme cellulose synthase possesses an extremely sophisticated “green” mechanism for controlling polymer structure.
In this paper, I will describe efforts to reconstitute the cellulose-synthesizing activity of cellulose synthase, the mechanism of which we have been seeking to elucidate for more than 10 years.
Cyclodextrins (CDs) are cyclic oligomers of α-1,4-D-glucopyranoside. Because the central cavities of CDs can be used to encapsulate small molecules, cyclic hexamer to octamer (CD6–8) have been widely used. While CD-hundreds are known for large CDs, the synthesis of the only CD5 had been only one reported for small CDs. Smaller CDs, such as CD4 and CD3, have never been synthesized because their molecular sizes are too small for the pyranose ring to adopt a stable chair-type conformation. In this report, we describe the chemical synthesis of both CD4 and CD3. The development of a specific bridging group between the 3- and 6-oxygen positions (O-3 and O-6) of D-glucose led to the successful synthesis of these compounds. In other words, the adoption of this bridging group provides both the stereoselective glycosylation reaction and the supple conformation of the pyranose ring, which are required for the synthesis of CD4 and CD3.
