An access to various sulfation patterns in dermatan sulfate: chemical syntheses of sulfoforms of trisaccharide methyl glycosides

摘要

The syntheses are reported for the first time of #alpha#-L-IdopA2SO_3-(1->3)-#beta#-D-GalpNAc4SO_3-(1->4)-#alpha#-L-IdopA2SO_3-(1->OMe), its disulfated analogue #alpha#-L-IdopA2SO_3-(1->3)-#beta#-D-GalpNAc-(1->4)-#alpha#-L-IdopA2SO_3-(1->OMe), and of #beta#-D-GalpNAc4SO_3-(1->4)-#alpha#-L-IdopA2SO_3-(1->3)-#beta#-D-GalpNAc4SO_3-(1->OMe), which represent structural fragments of dermatan sulfate, unavailable directly by chemical or enzymatic degradation of the glycosaminoglycan polymer. These molecules were readily obtained from a pair of key disaccharide intermediates, in which the relative difference of stability of the D-Ga1NAc- 4-hydroxy protecting groups (acetate or pivalate) toward saponification conditions access to various sulfoforms from a common precursor. For the preparation of these blocks, the 4-O-pivaloyl-D-galacto moiety was readily obtained through a one-pot stereospecific intramolecullar nucleophilic displacement on an easily available 3-O-pivaloyl-D-gluco precursor, and the L-IdoA moiety through selective radical oxidation of C-6 of a L-ido 4,6-diol derivative withoxoammonium salts.