Anomeric alkylations, glycosylation methods

Another method for synthesis of useful derivatives of L-acosamine and L-daunosamine from rhamnal 23 was based on addition of chlorosulfonyl isocyanate to 2,3-unsaturated pyranosides 73 [66,67]. Since the anomeric alkyl substituent in this reaction ends up as the carbamate ester, aUyl glycoside securing easy deprotection was chosen for elaborating this reaction into large laboratory scale technical process. Method development for acosam-inal derivative 74 involved multiparameter optimization of the isocyanate addition step by exploration of the reaction response surface. The final daunosaminyl glycosylation synthon 76 was obtained in overall 35% yield (Scheme 12) [68]. 

Bryan et al. have also constructed microarrays of carbohydrates using physical absorption [73], They demonstrated that a library of glycosyl lipids containing saturated alkyl chains at the anomeric position was mostly retained on a polystyrene surface and could be used in biological assays. However, the hydrophobicity of the alkyl chain interfered significantly with the synthesis and purification of the glycosyl lipids. They searched for an alternative method to overcome this problem and developed the 1,3-dipolar cycloaddition strategy described in Section 4.2.1 [43]. 

The advantages of the anomeric 0-alkylation and glycosylation via locked anomeric configuration methods are ... 

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