646
3
Chemical Glycosylation Reactions
⊡ Scheme 77
2,3,5,6-Tetrafluoro-4-(2,3,4,6-tetra-O-acetyl or O-benzyl-β-D-glucopyranosyloxy) pyridine as glycosyl donors
⊡ Scheme 78
MOP Ribofuranosyl donors in the synthesis of 1,2-cis furanosyl nucleosides
6.3.2 Esterification and Phosphorylation of Unprotected MOP Glycosides
MOP glycosyl donors have been used in stereocontrolled esterification and phosphorylation,
leading to glycosyl 1,2-cis-1-carboxylates or glycosyl 1,2-cis-glycosyl-1-phosphates in one
step. Treatment of MOP donor 475 in acetonitrile or DMP with an excess (20–200 equiv.) of
a carboxylic acid under anhydrous conditions led to the corresponding D-glycosyl carboxylate
477, in excellent yields [228]. Moreover, treatment of 6-O-tert-butyldiphenylsilyl MOP donor
478 with only 1.5 equiv. of the corresponding carboxylic acid in CH 2 Cl 2 resulted in the formation of 1,2-cis-glycosyl carboxylate 479 ( > Scheme 81a). Treatment of β-D-galactopyranosyl,
and 2-azido-2-deoxy-α-D-galactopyranosyl MOP donors 475 and 471, respectively with
3
Chemical Glycosylation Reactions
⊡ Scheme 77
2,3,5,6-Tetrafluoro-4-(2,3,4,6-tetra-O-acetyl or O-benzyl-β-D-glucopyranosyloxy) pyridine as glycosyl donors
⊡ Scheme 78
MOP Ribofuranosyl donors in the synthesis of 1,2-cis furanosyl nucleosides
6.3.2 Esterification and Phosphorylation of Unprotected MOP Glycosides
MOP glycosyl donors have been used in stereocontrolled esterification and phosphorylation,
leading to glycosyl 1,2-cis-1-carboxylates or glycosyl 1,2-cis-glycosyl-1-phosphates in one
step. Treatment of MOP donor 475 in acetonitrile or DMP with an excess (20–200 equiv.) of
a carboxylic acid under anhydrous conditions led to the corresponding D-glycosyl carboxylate
477, in excellent yields [228]. Moreover, treatment of 6-O-tert-butyldiphenylsilyl MOP donor
478 with only 1.5 equiv. of the corresponding carboxylic acid in CH 2 Cl 2 resulted in the formation of 1,2-cis-glycosyl carboxylate 479 ( > Scheme 81a). Treatment of β-D-galactopyranosyl,
and 2-azido-2-deoxy-α-D-galactopyranosyl MOP donors 475 and 471, respectively with