Azidonitration of D-galactal and D-glucal

Azidonitration of D-galactal and D-glucal

Scheme 2 The synthesis of 2-deoxy-2-amino glucosides from glycals.

dine, which is an extremely powerful electrophile that promotes the ^-attack of a nucleophile at the anomeric carbon. Chain elongation can be achieved if the nucle-ophile is another glycal or a suitably differentiated glycosyl acceptor. Several procedures for the conversion of the 2-sulfonamide to the free amine have been reported and depend on the arylsulfonamide employed. Benzenesulfonamide can be converted to the corresponding amine by treatment with excess sodium in ammonia [26]. When 9-anthracenesulfonamide is used, conversion to the free amine can be achieved by treatment with thiophenol, 1,3-propanedithiol, or diisopropylethylamine. The milder reaction conditions required to cleave 9-anthracenesulfonamide derivatives are more likely to be compatible with other functional groups on the carbohydrate [30].

Since d-galactose is the C4 epimer of d-glucose, the selective inversion of the configuration at C4 on d-glucosamine derivatives provides efficient access to the corresponding d-galactosamine derivatives (Scheme 4). In this way, construction of GAG oligosaccharides may incorporate d-glucosamine units, which can then be inverted at C4 to afford the corresponding galactosaminoglycan. This C4 inversion has been achieved by formation of the C4 triflate followed by nucleophilic displacement

Scheme 3 Iodosulfonamidation of glycals to form 2-deoxy-2-amino glucosides.

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