Functional groups glycosylation process

Transferases catalyze the transfer of functional groups such as methyl, hydroxymethyl, formal, glycosyl, acyl, alkyl, phosphate, and sulfate groups by means of a nucleophilic substitution reaction. They are not widely used in industrial processes however, there are a few examples of industrial processes that utilize transferases. 

Nickel-catalyzed ketone and aldehyde hydrosilylations have been developed with well-defined Ni(II) hydrides using phosphine anilide ligands (Scheme 3-84). This process is tolerant of a variety of functional groups including aryl halides. In mechanistically distinct processes, nickel(O) complexes of NHCs were shown to catalyze ketone hydrosilylations using carbohydrate-derived silanes in a process that allows reductive glycosylations of ketones. Chemoselectivity of the latter method was optimal in the presence of Ti(OR)4 additives. 

For both N- and O-substituted alkyl groups, initial hydroxylation results in the formation of alcohol intermediates that are generally unstable and, unless rapidly glycosylated, decompose to liberate formaldehyde in the case of a methyl group. These processes are referred to as iV- and O-dealkylations. Further oxidation of C-alkyl-derived alcoholic functions to corresponding carboxylic acids is generally slow and is probably of limited relevance to selectivity. In the case of carboxylic acids, rates of glucose ester formation may also be sufficiently rapid to further reduce the opportunity for decarboxylation. 

Addition of glycosyl radicals to alkenes is a key process in the synthesis of C-glycosides, which are well known to have potent antiviral, antibacterial, and antitumor activities. While various methods for the synthesis of C-glycosides under ionic conditions have been developed, the importance of radical-mediated synthesis should be stressed because of the mild reaction conditions employed. As radicals are neutral species, various polar functional groups in carbohydrate molecules are compatible under the reaction conditions, and the reaction is sometimes carried out without protecting the hydroxyl and amino groups. 

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