P-Mannopyranosides

Figure 2. Natural entities containing p-mannopyranosidic linkages...

Yamanoi, T, Nakamura, K, Takeyama, H, Yanagihara, K, Inazu, T, 1,2-Cw-p-mannopyranoside formation by the dimethylphosphinothioate method, Chem. Lett., 343-346, 1993. 

Crich, D. Chemistry of glycosyl triflates Synthesis of P-mannopyranosides. J. Carbohydr. Chem. 2002, 21, 667-690. 

Hycosylation. Hindered thioglycosides are activated by PhSOTf and the process permits the direct formation of p-mannopyranosides. 

Figure 3.32 Base-catalysed hydrolyses of aryl a-glucopyranosides and aryl a- and P-mannopyranosides.

Some derivatives of methyl 4,6-0-benzylidene-a- and /3-p-mannopyranoside have been described by P. J. Garegg, Arkiv. Kemi, 255 (1964). 

Using a related anomeric radical inversion concept, Curran has synthesized P-mannopyranosides from their corresponding a-epimers via an intramolecular 1,6-... 

P-Mannopyranosides. Mixed silyl acetals are formed expediently from a cimethylsilyl-tethered sugar unit in which one is mannosyl phenyl sulfoxide. It simply ni olves admixture of two equimolar sugars with 1 equiv. of MCjSiClj in the presence of )MAP and imidazole. The addition of 2,6-di-t-butylpyridine and Tf O at -100° followed warming completes the glycosylation. 

Crich D. Chemistry of glycosyl triflates synthesis of p-mannopyranosides. J Carbohydr Chem 2002 21 667-690. 

Yamazaki N, Eichenberger E, Curran DP (1994) Synthesis of p-mannopyranoside from a-epimers by radical inversiotL 1,6-hydrogen transfer reactions of 2-0-(2-bromoaryl) dimethylsilyl-a-methyl-D-marmopyranosides. Tetrahedron Lett 35 6623-6626... 

Abstract The genesis and development of the 4,6-( -benzylidene acetal method for the preparation of p-mannopyranosides are reviewed. Particular emphasis is placed on the influence of the various protecting groups on stereoselectivity and these effects are interpreted in the framework of a general mechanistic scheme invoking a series of solvent-separated and contact ion pairs in dynamic equilibrium with a covalent a-glycosyl trifluoromethanesulfonate. 

While it is usually considered most efficient to conduct polymer-supported glycosylation by an acceptor-bound strategy [132, 133], consideration of the hydrolytic and thermal instability of the mannosyl triflate intermediates initially led to the development of a donor-bound strategy for the supported synthesis of the p-mannopyranosides. Thus, a polystyrylboronate resin was employed to capture a 4,6-diol leading to a resin bound donor that was activated and coupled under the standard BSP conditions. Excellent p-selectivities were obtained and the products cleaved from the resin with aqueous acetone (Scheme 11) [88]. 

A further route to P-mannopyranosides involves use of the 1,2-anhydride 33, made by the Danishefsky method from tri-O-benzyl-D-glucal. Epoxide ring opening with alcohols in the presence of zinc chloride gives P-glucosides which, by oxidation and reduction, lead to the P-mannosides including P-mannosyl disaccharides. Danishefsky has also adapted compound 33 for use as a precursor of a-glucosides. Treated with tributylstannylated alochols in the presence... 

The classical problem in carbohydrate chemistry of the stereocontrolled synthesis of p-mannopyranosides was largely solved by the introduction of the 4,6-0-benzylidene acetal controlled method in the mid-1990s. The main drawback to this method,... 

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