Mannosylation intramolecular

Ziegler and coworkers prearranged a glycoside by employing a succinyl tether between C-6 of a mannosyl donor and C-3 of glucosyl acceptor [151,152]. They found that the nature of the glycosyl acceptor and the length of the tether affected the anomeric selectivity of the intramolecular mannosylation (Scheme 4.4d) [153]. 

Seeking for general and highly stereoselective P-mannosylation, our attention was drawn to the approach based on the emerging concept of intramolecular aglycon... 

The aromatic phenol was varied to explore the scope of the O-to-C conversion with mannosyl phosphates. Using phosphate 9, the a-C-mannosides of 2-naphthol and 3-benzyloxy phenol (23 and 25, Table 1) were synthesized in excellent yield. O-Mannosides were obtained exclusively with less nucleophilic aromatic systems, such as 3-acetoxy phenol. Several non-phenolic aromatic systems were unsuccessful in the formation of C-aryl or O-aryl glycosides. Reaction of 9 with furan, thiophene, trimethoxybenzene, and indole in the presence of TMSOTf did not result in any product formation. Interestingly, activation of 9 in the absence of any aromatic nucleophiles gave 26 as the major product via an intramolecular C-glycosylation (Figure 1) (79). 

Ito, Y, Ohnishi, Y, Ogawa, T, Nakahara, Y, Highly optimized (i-mannosylation via 4-methoxybenzyl-assisted intramolecular aglycon delivery, Synlett, 10, 1102-1104, 1998. 

In addition, a polymer-supported version of the intramolecular aglycon delivery was explored [148]. In this system, mannosyl thioglycoside 93 bound to polyethylene glycol (PEG) via a p-alkoxybenzyl linker was subjected to the two-step sequence and the resultant fi-manno-glycoside is specifically released into the non-polymeric phase, while most of the by-products remain bound to the polymer. 

On treatment with NIS, TfOAg a mixture of the 2,6-tethered 6 and phenyl tetra-O-acetyl-l-thio-a-D-mannopyranoside underwent (l- 6)-cyclization of 6 and slower 3-a-mannosylation of the product, the former step being favoured by its intramolecular character in this one-pot procedure. a-D-Man-(l- 3)-[a-D-Man-(l- 6)]-a-D-ManOMe was consequently made in 30% yield. Alternatively this trisaccharide was made in 42% yield by direct selective mannosylation with the O-acetylated trichloroacetimidate (2 equiv) of p-nitrophenyl a-D-man-nopyranoside. The product was converted to the p-acrylamide glycoside and copolymerized with 2-acrylamido-N,iV-dimethylamine to give a product tested for lectin binding. ... 

Beignet J, Tierman J, Woo CH, Kariuki BM, Cox LR (2004) Stereoselective synthesis of allyl-C-mannosyl compounds use of a temporary silicon connection in intramolecular allylations strategies with allyl silanes. J Org Chem 69 6341-6356... 

To obtain more support for the remote participation of 3-0-acyl and 6-0-acetyl groups in mannosyl donors, Kim and co-workers carried out experiments to trap anomeric oxocarbenium ion intermediates by the intramolecular nucleophilic attack of the trichloroacetimidoyl group at the 0-3 position of mannosyl donors the activation of 72 with 1-benzenesulfinyl piperidine (BSP) and Tf20 afforded... 

Barresi and Hindsgaul have published an improvement on their intramolecular preparation of 3-D-mannopyranosyl disaccharides (see Vol. 25, p. 38). In closely parallel work which uses a silicon bridging atom rather than carbon. Stork and Kim have published a further intramolecular method for preparing p-mannosyl compounds (Scheme 13). ... 

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