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Synthesis of Linear and Hyperbranched Stereoregular Aminopolysaccharides by Oxazoline Glycosylation
Published in Raphael M. Ottenbrite, Sung Wan Kim, Polymeric Drugs & Drug Delivery Systems, 2019
Jun-Ichi Kadokawa, Hideyuki Tagaya, Koji Chiba
Glycosylation, a reaction for the synthesis of glycosides, usually involves the condensation of a protected glycose derivative (glycosyl donor) with an appropriate aglycon derivative (glycosyl acceptor). The development of stereoselective glycosylation made it possible to synthesize virtually any desired sugar compound [6]. However, synthesis of polysaccharides by glycosylations as the polymerization reaction has not been well established yet. Only a few methods such as orthoester and Koenigs-Knorr glycosylations have been used for the synthesis of polysaccharides (Scheme 2) [2b, 7]. Scheme 2.
Precise Preparation of Functional Polysaccharides Nanoparticles by an Enzymatic Approach
Published in Raj K. Keservani, Anil K. Sharma, Rajesh K. Kesharwani, Drug Delivery Approaches and Nanosystems, 2017
Alternative to such chemical glycosylations, in vitro reaction approach by enzymatic catalysis has been significantly developed in recent years, so-called ‘enzymatic glycosylation’ because enzymatic reaction is the superior method in terms of stereo- and regioselectivities compared with that by chemical catalysis (Shoda, 2001; Shoda et al., 2003). Similar to the general chemical glycosylation, the enzymatic glycosylation for the formation of a glycosidic linkage between an anomeric carbon of a monosaccharide and one of hydroxy groups of the other monosaccharide can be realized by the reaction of a activated glycosyl donor at the anomeric position with a glycosyl acceptor, where these substrates can be employed in their unprotected forms beside the anomeric position of the glycosyl donor (Figure 4.2). In the enzymatic glycosylation, first, the glycosyl donor is recognized by a catalytic center of enzyme to form a glycosyl-enzyme complex. Then, the complex is attacked by the hydroxy group of the glycosyl acceptor in the stereo- and regioselective manners according to specificity of each enzyme, leading to the direct formation of the unprotected glycoside. Thus, repetition of the enzymatic glycosylations, i.e., enzymatic polymerization, forms polysaccharides with well-defined structure. Amongst the six main classes of enzymes, i.e., oxidoreductase (EC1), transferase (EC2), hydrolase (EC3), lyase (EC4), isomerase (EC5), and ligase (EC6), transferase (glycosyl transferase) and hydrolase (glycosyl hydrolase) have been practically applied as catalysts for the in vitro enzymatic synthesis of polysaccharides via the glycosylations (Blixt and Razi, 2008; Thiem and Thiem, 2008). The former glycosyl transferase is mainly subclassified into synthetic enzymes (Leloir glycosyl transferases), phosphorolytic enzymes (phosphorylases), and sucrases (Seibel et al., 2006a, 2006b). Leloir glycosyl transferases are the biologically important catalysts because they conduct the role to synthesize saccharide chains in vivo. However, Leloir glycosyl transferases are generally transmembrane-type proteins, present in fewer amounts in nature, and unstable for isolation and purification. Therefore, in vitro approach by Leloir glycosyl transferase catalysis has hardly been employed for practical synthesis of polysaccharides.
An expedient, chemoselective N-chloroacetylation of aminoalcohols under metal-free bio-compatible conditions
Published in Green Chemistry Letters and Reviews, 2018
Chloroacetyl chloride (CAC) (29) plays multiple roles in synthetic and biological chemistry as a bifunctional linker (30), protecting group (31) for alcohols and amines, in dendrimer synthesis (32–36), and as a glycosyl donor in oligosaccharide synthesis (33, 35, 37, 38).