Glycosylation with 2-Acetamido-2-deoxyglycosyl Donors at a Low Temperature: Scope of the Non-Oxazoline Method

Abstract

A direct construction of 1,2-trans-β-linked 2-acetamido-2-deoxyglycosides was investigated. The 3,4,6-tri-O-benzyl- and 3,4,6-tri-O-acetyl-protected glycosyl diethyl phosphites and 4,6-O-benzylidene-protected galactosyl diethyl phosphite each reacted with a variety of acceptor alcohols in the presence of a stoichiometric amount of Tf2NH in CH2Cl2 at -78 °C to afford the corresponding β-glycosides in good to high yields with complete stereoselectivity. Some experiments provided strong evidence that the corresponding oxazolinium ions are not responsible for the reaction. We demonstrated that glycosylations with the corresponding glycosyl imidate and thioglycoside also proceeded at a low temperature, indicating the possibility of these donors being attractive alternatives to the phosphite. A plausible reaction mechanism, which features glycosyl triflimide and contact ion pair as reactive intermediates, is proposed on the basis of the results obtained with 2-acetamido-2-deoxymannosyl donors.

Synthesis of Type-I and Type-II LacNAc-Repeating Oligosaccharides as the Backbones of Tumor-Associated Lewis Antigens

“…This approach was found useful to obtain good yields for the acceptors containing a primary hydroxyl group, but the reactions for those containing a secondary hydroxyl still gave moderate yields. Meanwhile, Hashimoto and coworkers used triflimide to convert glycosyl diethylphosphite to α-glycosyl triflimide for the subsequent glycosylation, which successfully avoided the oxazoline formation ( 82 , 83 ).…”

Stereoselective Synthesis of 1,1′‐Disaccharides by Organoboron Catalysis

“…This combination was expected to be one of the most challenging because both the acceptor and donor have lower reactivity compared to substrates without 2-amino groups. [2,21] After investigating a variety of combinations of N-protecting groups on the acceptors and donors, [17] the reaction of N-NapSO 2 -protected glucosamine with N-Troc-protected galactosamine in the presence of 10 mol % of borinic acid catalyst was found to furnish the desired product (3 mG) in 44 % yield with perfect anomeric selectivity. We finally focused on the reaction with lyxose-derived phosphite because 1,1'-lyxoside is the core scaffold of natural products such as avilamycin A.…”

Nitrogen-Centered Radical Mediated Anomeric Specific Cascade Amidoglycosylation of Glycals

“…[9][10][11][12] Since some of the mono 2-amino-2-deoxysugars are naturally available or easily prepared, they have widely employed in synthesis of 2-amino-2-deoxyglycosides. 5,13 And many different types of glycosamide precursors, including thioglycoside [14][15][16][17] , trichloroacetimidate, [18][19][20] phosphate ester 21,22 , and OABz 23 , have been extensively explored. However, these protocols commonly start from glycosamides with masking amino groups [24][25][26] such as Azide 16,[27][28][29] , PhthN 30 , AcNH 21,31,32 or TrocNH 33 .…”