O-Glycosyl Donors
3.4
567
5.4
2 -Carboxybenzyl Furanosyl Donors. Acceptor-Dependent Stereoselective
β-D-Arabinofuranosylation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 635
5.4.1
Synthesis of an Octaarabinofuranoside
Based on Stereoselective α-D-Arabinofuranosylation . . . . . . . . . . . . . . . . . . . . . . . . . 637
5.5
2 -(Allyloxycarbonyl)benzyl (ACB) Glycosides: New “Latent” Donor
for the Preparation of “Active” 2-Azido-2-deoxy BC Glycosyl Donors . . . . . . . . . 639
5.6
Synthesis of Oligosaccharides Based on BC Glycosyl Donors . . . . . . . . . . . . . . . . . 640
5.6.1
Synthesis of Trisaccharide 431, the Repeat Unit
of the O-Antigen Polysaccharide from Danish Helicobacter pylori Strains . . . . . 640
5.6.2
Synthesis of Tetrasaccharide 438 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 641
5.6.3
Synthesis of Tetrasaccharide Repeat Unit from E. coli O77 . . . . . . . . . . . . . . . . . . . . 641
5.6.4
Total Synthesis of Agelagalastatin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 643
5.7
Conversion of 2 -Carboxybenzyl Glycosides into other Glycosyl Donors . . . . . . . 643
5.8
2 -Carboxybenzyl Glycosides as Glycosyl Donors for C-Glycosylation . . . . . . . . 644
6
O-Heteroaryl Glycosyl Donors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 644
6.1
2-Pyridyl 2,3,4,6-tetra-O-benzyl-D-glucosides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 644
6.2
O-Hetaryl Glycosides by Schmidt’s Group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 644
6.3
3-Methoxy-2-pyridyl (MOP) Glycosides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 645
6.3.1
Coupling of Unprotected MOP Glycosyl Donors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 645
6.3.2
Esterification and Phosphorylation of Unprotected MOP Glycosides . . . . . . . . . . . 646
6.3.3
MOP Glycosides in Oligosaccharide Synthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 649
6.4
6-Nitro-2-benzothiazolyl Glycosides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 649
7
Miscellaneous O-Glycosyl Donors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 651
Abstract
O-Glycosyl donors, despite being one of the last successful donors to appear, have developed
themselves into a burgeoning class of glycosyl donors. They can be classified in two main
types: O-alkyl and O-aryl (or hetaryl) glycosyl donors. They share, however, many characteristics, they can be (1) synthesized from aldoses, either by modified Fisher glycosidation
(O-alkyl) or by nucleophilic aromatic substitution (O-aryl or O-hetaryl), (2) stable to diverse
chemical manipulations, (3) directly used for saccharide coupling, and (4) chemoselectively
activated. Among these, n-pentenyl glycosides stand apart. They were the first O-alkyl glycosyl donors to be described and have paved the way to many conceptual developments in
oligosaccharide synthesis. The development of the chemoselectivity-based “armed-disarmed”
approach for saccharide coupling, including its stereoelectronic or torsional variants, now
extended to other kinds of glycosyl donors, was first recognized in n-pentenyl glycosides.
The chemical manipulation of the anomeric substituent in the glycosyl donor to induce reactivity differences between related species (sidetracking) was also introduced in n-pentenyl
glycosides. An evolution of this concept, the “latent-active” strategy for glycosyl couplings,
first described in thioglycosyl donors (vide infra), has been elegantly applied to O-glycosyl
donors. Thus, allyl and vinyl glycosides, 2-(benzyloxycarbonyl)benzyl (BCB) glycosides and
2 -carboxybenzyl (CB) glycosides are useful “latent-active” glycosyl pairs. Finally, unprotect-
3.4
567
5.4
2 -Carboxybenzyl Furanosyl Donors. Acceptor-Dependent Stereoselective
β-D-Arabinofuranosylation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 635
5.4.1
Synthesis of an Octaarabinofuranoside
Based on Stereoselective α-D-Arabinofuranosylation . . . . . . . . . . . . . . . . . . . . . . . . . 637
5.5
2 -(Allyloxycarbonyl)benzyl (ACB) Glycosides: New “Latent” Donor
for the Preparation of “Active” 2-Azido-2-deoxy BC Glycosyl Donors . . . . . . . . . 639
5.6
Synthesis of Oligosaccharides Based on BC Glycosyl Donors . . . . . . . . . . . . . . . . . 640
5.6.1
Synthesis of Trisaccharide 431, the Repeat Unit
of the O-Antigen Polysaccharide from Danish Helicobacter pylori Strains . . . . . 640
5.6.2
Synthesis of Tetrasaccharide 438 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 641
5.6.3
Synthesis of Tetrasaccharide Repeat Unit from E. coli O77 . . . . . . . . . . . . . . . . . . . . 641
5.6.4
Total Synthesis of Agelagalastatin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 643
5.7
Conversion of 2 -Carboxybenzyl Glycosides into other Glycosyl Donors . . . . . . . 643
5.8
2 -Carboxybenzyl Glycosides as Glycosyl Donors for C-Glycosylation . . . . . . . . 644
6
O-Heteroaryl Glycosyl Donors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 644
6.1
2-Pyridyl 2,3,4,6-tetra-O-benzyl-D-glucosides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 644
6.2
O-Hetaryl Glycosides by Schmidt’s Group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 644
6.3
3-Methoxy-2-pyridyl (MOP) Glycosides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 645
6.3.1
Coupling of Unprotected MOP Glycosyl Donors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 645
6.3.2
Esterification and Phosphorylation of Unprotected MOP Glycosides . . . . . . . . . . . 646
6.3.3
MOP Glycosides in Oligosaccharide Synthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 649
6.4
6-Nitro-2-benzothiazolyl Glycosides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 649
7
Miscellaneous O-Glycosyl Donors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 651
Abstract
O-Glycosyl donors, despite being one of the last successful donors to appear, have developed
themselves into a burgeoning class of glycosyl donors. They can be classified in two main
types: O-alkyl and O-aryl (or hetaryl) glycosyl donors. They share, however, many characteristics, they can be (1) synthesized from aldoses, either by modified Fisher glycosidation
(O-alkyl) or by nucleophilic aromatic substitution (O-aryl or O-hetaryl), (2) stable to diverse
chemical manipulations, (3) directly used for saccharide coupling, and (4) chemoselectively
activated. Among these, n-pentenyl glycosides stand apart. They were the first O-alkyl glycosyl donors to be described and have paved the way to many conceptual developments in
oligosaccharide synthesis. The development of the chemoselectivity-based “armed-disarmed”
approach for saccharide coupling, including its stereoelectronic or torsional variants, now
extended to other kinds of glycosyl donors, was first recognized in n-pentenyl glycosides.
The chemical manipulation of the anomeric substituent in the glycosyl donor to induce reactivity differences between related species (sidetracking) was also introduced in n-pentenyl
glycosides. An evolution of this concept, the “latent-active” strategy for glycosyl couplings,
first described in thioglycosyl donors (vide infra), has been elegantly applied to O-glycosyl
donors. Thus, allyl and vinyl glycosides, 2-(benzyloxycarbonyl)benzyl (BCB) glycosides and
2 -carboxybenzyl (CB) glycosides are useful “latent-active” glycosyl pairs. Finally, unprotect-