Glycosyl amides

The use of N-glycosyl amides as glycosyl donors was reported by Pleuss and Kunz [240]. These amides were activated by Ph3P and CBr4 to produce bromo-N-imidates, which were spontaneously converted into the corresponding bromide concomitant with releasing nitrile, and then coupled with alcohols by activation with AgOTf (Scheme 5.86). 

The glycosyl azide (7) (7.80 g, 20.9 mmol) is dissolved in 50 mL dry methanol and the solution placed under an inert atmosphere. 10% Pd on activated charcoal (300 mg) is added and the reaction maintained under a constant pressure of H2 with vigorous stirring for 24 h at room temperature. The suspension is filtered through celite and the solvent removed under reduced pressure to yield 6.70 g of the title compound as a colorless syrup (92%). The residue can be used immediately for the preparation of glycosyl amide (9). FAB MS (C14H21NO9) 347.12 m/z (%) 169 (79), 331 [M-NH2J+ (34), 370 [M-nNa]+ (100). 

The use of A-glycosyl amides as glycosyl donors has been recently reported [578]. These amides 266 are activated by the Appel reagent to form the intermediate imidoyl bromide 267. The addition of alcohols and AgOTf to the mixture resulted in the formation of glycosides 268 (Scheme 4.52). 

Pleuss, N, Kunz, H, A-Glycosyl amides removal of the anomeric protecting group and conversion into glycosyl donors, Angew. Chem. Int. Ed., 42, 3174-3176, 2003. 

Maunier, V, Boullanger, P, Lafont, D, A one-pot synthesis of glycosyl amides from glycosyl azides using a modified Staudinger reaction, J. Carbohydr. Chem., 16, 231-235, 1997. 

Isomerization. Overman rearrangement of imino ethers of glycals favors the generation of P-glycosyl amides. Interestingly, more ionic Pd species favor the a-isomers. 

L. Kovacs, E. 6sz, V. Domokos, W. Holzer, and Z. Gyorgydeak, An easy access to anomeric glycosyl amides and imines (Schiff bases) via transformation of glycopyranosyl trim-ethylphosphinimides, Tetrahedron, 57 (2001) 4609-4621. 

Song X, Lasanajak Y, Xia B, Smith DF, Cummings RD (2009) Fluorescent glycosyl-amides produced by microscale derivatization of firee glycans for natmal glycan microarrays. ACS Chem Biol 4 741-750... 

This review is devoted to the description of synthetic strategies for glycodendrimers synthesis. Dendrimers can be classified into three categories carbohydrate-coated, carbohydrate-centered and carbohydrate-based dendrimer. In this paper we will focus on the third one, in which the core unit is originated from a monosaccharide. Compare to classical Pamam, Boltorn cores, carbohydrate units add much more three dimension information, coded in the chirality in almost each carbon. Various coupling chemistry have been developed and are presented here glycosylation, amide bound formation, and click chemistry (thiol-ene reaction, epoxide - thiol reaction). 

To form an anomeric N-acyl glycosylamine, the unsubstituted glyco-sylamine is usually used " but this form is quite labile and prone to potential anomerization and dimerization. Here the azide function was directly converted into its corresponding glycosyl amide without previous reduction to an amine. A modified Staudinger reaction was used with trimethylphosphine in the presence of different amino acids derivatives, for instance 26 activated with HOBt to give 27 (Scheme 5). 

Esterification Cmbonate formation Glycosylation Amidation Phosphorylation Action onto fimctional groups... 

In the chemo-enzymatic synthesis of LLG-3 performed by Withers et al. [34], the glycoside of 8-0-Me-Neu5Ac with glycolic acid 59 was synthesized from NeuSAc derivative 58 by a chemical method because of the absence of a sialyltransferase capable of sialyltransfer to the hydroxyl group of the glycosyl amide in the penultimate sialic acid residue and an 8-O-methyltransferase for NeuAc (Scheme 11.10). 

Scheme 16.12 Three-component Staudinger-type reaction with ji-glycosyl azide 4 stereose-lectively leads to the ji-glycosyl amides 48. a-Clycosyl amides can only be obtained from a-glycosyl azide 49 with strong acylating agents to prevent complete anomerization of the Intermediate lmlnophosphorane °...

---