α-Selective Glucosylation Can Be Achieved with 6-O-para-Nitrobenzoyl Protection

Abstract

A systematic study of the effect of various 6-O-acyl groups on anomeric selectivity in glucosylations with thioglycoside donors was conducted. All eight different esters were found to induce moderate-to-high α-selectivity in glucosylation with L-menthol with the best being 6-O-p-nitrobenzoyl. The effect appears to be general across various glucosyl acceptors, glucosyl donor types, and modes of activation. No evidence was found in favor of distal participation.

Acetal Substitution Reactions: Stereoelectronic Effects, Conformational Analysis, Reactivity vs Selectivity, and Neighboring-Group Participation

“…Other authors have observed that nitrobenzoate groups at C-6 of glucose derivatives can lead to high diastereoselectivity. 106 Traditionally, it is believed that participation by alkoxy groups is not possible. 107,108 A number of observations in the literature, however, suggest that a benzyloxy group can engage with an electrophilic center elsewhere in the molecule.…”

“…Other authors have observed that nitrobenzoate groups at C-6 of glucose derivatives can lead to high diastereoselectivity. 106…”

Formation of β-Configured Thioglycosides ofd-Glucosamine andd-Galactosamine and Synthesis of Protected Human Milk Oligosaccharides

“…We were curious to investigate whether this procedure could also be employed to generate thioglycosides of GlcNAc as a single β-anomer and later convert the 2-NHAc functionality to substituents such as 2-azido that are more compatible with oligosaccharide synthesis (Scheme ). Although a good protocol for the synthesis of 2-azido α-thioglycosides exists, it could be beneficial to also have a good synthesis of its anomer, as we have recently demonstrated that glycosyl donor stereochemistry can have a vast impact of glycosylation selectivity. , …”

Lewis Acid Promoted Deprotection of Benzylidene Acetals and p-Methoxybenzyl Ethers with Mercaptoacid Acid as Scavenger

“…Protecting groups remain essential in many aspects of multistep synthetic organic chemistry. , In carbohydrate chemistry, in particular they offer a welcomed increase in lipophilicity that improves solubility in cold organic solvents and allows handling by extraction procedures. Protecting groups are furthermore capable of perturbing reactivity and selectivity due to mechanistic participation, , bulk, , or their electronic properties. Since the installment and cleavage of protecting groups are nonconstructive reactions, achieving high chemical yields for these manipulations are of great importance.…”