Microwave-accelerated Fischer glycosylation

Abstract

Fischer glycosylation has been used for decades for the synthesis of simple alkyl and aryl glycosides from free sugars. The reaction proceeds under reflux in the presence of catalytic acid with the alcohol as solvent. The main deficiency of this reaction is the long reaction time required. In this study microwave heating has been utilized for the Fischer glycosylation reaction of N-acetyl-D-glucosamine, N-acetyl-Dgalactosamine, D-glucose, D-galactose and D-mannose with a variety of alcohols (methanol, ethanol, benzyl alcohol and allyl alcohol). Remarkable acceleration of the glycosylation reactions (minutes compared to hours) over conventional reflux heating was observed with good yields and production of the α-glycoside as the dominant product.

1,2-cis Alkyl glycosides: straightforward glycosylation from unprotected 1-thioglycosyl donors

“…The stereoselectivity of glycosylation with unprotected D-glucose, D-mannose and disaccharide donors and propargyl alcohol spanned from modest to high (Table 2, entries 1, [9][10][11][12][13]. It is noteworthy that the major product from phenyl 1-thio-α-D-mannoside is the β (cis) anomer (Table 2, entry 10) that is formed.…”

Synthesis, physico-chemical properties and complexing abilities of new amphiphilic ligands from d-galacturonic acid

“…Reactions were very fast with complete consumption of the starting material (<10 min), good yields and modified glycoside ratios compared to that of thermal activation. 28 An efficient glycosidation and/or esterification of D-glucuronic acid and its 6,1-lactone under solvent-free microwave irradiation has also been recently reported. 29 D-Glucuronic acid derivatives were obtained with different regioselectivities from those obtained using a thermal activation.…”

Microwave-assisted synthesis of long-chain alkyl glucopyranosides

“…Fischer glycosylation of fatty alcohols has been employed despite the low solubility of glucose in long-chain fatty alcohols. [7][8][9][10][11] By this methodology, it is usual to obtain a mixture of four isomers: the kinetic furanosides and the thermodynamic pyranosides with the major axial anomeric configuration. A protected glucose is used in the Koenigs-Knorr [12][13][14][15] and the Helferich [15][16][17][18][19][20][21][22] glycosylations of fatty alcohols.…”

“…[18][19][20][21][22] Compared to conventional methods, reactions under microwaves usually show noticeable improvements such as shorter reaction times, high yields and these can be carried out in solvent-free conditions. Microwave-assisted Fischer glycosylation is feasible for short chain alcohols, 9,10 but in the case of fatty alcohols (octanol 10 and decanol 11 ), yields can be diminished due to decomposition of glucosides. Microwave-assisted solvent-free Helferich glycosylation has been reported by Limousin et al for the preparation of decyl glucosides with good yields.…”

“…Microwave-assisted solvent-free Helferich glycosylation has been reported by Limousin et al for the preparation of decyl glucosides with good yields. 11 From the literature on microwave-assisted glycosylation, [9][10][11] we can conclude first that the a anomer is usually the major one; however, little information can be found concerning the control and evolution of the anomeric ratio. Secondly, no information is given about the evolution of yield, which is of importance because of the possible degradation of saccharides.…”