P-mannoside linkage

The potential of the mannuronate ester donors in the formation of the p-mannosidic linkage has been demonstrated with the construction of a mannuronic acid alginate pentamer using a convergent orthogonal glycosylation.64... 

Scheme 9.12 Reverse use of a polymer support for the synthesis of P-mannoside linkage. The synthetic helper arm (MPEG), together with other polymer-bound by products, is removed from the desired product by simple precipitation.

Beta-mannosidase and P-mannanase cleave the P-mannoside linkages in P-l,4-D-... 

Nagai, H, Matsumura, S, Toshima, K, Environmentally benign and stereoselective formation of p-mannosidic linkages utilizing 2,3-di-0-benzyl-4,6-0-benzylidene-protected mannopyranosyl phosphite and montmorillonite K-10, Carbohydr. Res., 338, 1531-1534, 2003. 

SCHEME 15.22 Total synthesis of complex type 2 undecasaccharide-aspargine 189. Construction of the P-mannosidic linkage in the key trisaccharide 182 and preparation of core heptasaccharide 185. 

El Ashry ESH, Rashed N, Ibrahim ESI. Strategies of synthetic methodologies for constructing p-mannosidic linkage. Curr Org Syn 2005 2 175-213. 

In order to access only the required stereoisomer, it is essential that the geometries of the glycosidic bonds are controlled. Some linkages are particularly difficult to form, for example p-mannosidic linkages, even though they are abundant within... 

Figure 8.5 Fungal metabolites containing a p-mannoside linkage.

This chapter has illustrated the importance of the P-mannosidic linkage within biological systems, and problems encountered with its synthesis. A number of chemical preparative methods have been compared, but it is obvious that there is no one, ideal method of universal utility. As with all carbohydrate chemistry, a careful assessment of the proposed preparative route must be performed before a specific technique for the incorporation of the p-mannosidic linkage is selected and pursued. 

Next, a p-mannoside linkage must be established and two major problems must be overcome because commonly used neighboring groups, and the anomeric effect lead to the formation of the undesired a-mannosides. 

This chapter reviews methods for the construction of P-mannosidic linkages. Together with the more popular protocols, less widespread and emerging approaches are also covered in the hope they will stimulate further progress. 

Silver cations on the surface of insoluble catalysts anchor mannosyl bromides from the a-side [52]. As a consequence, highly reactive alcohols can attack the anomeric center from the P-side in an Sn2 type reaction, thus leading to P-mannosidic linkages. The first application of this principle was reported by Perlin [53] in 1961 who condensed the cyclic carbonate-protected mannosyl bromide [54] 2 and the reactive aglycone 3 under silver oxide activation to afford the first synthetic disaccharide (4) that contains a P-mannopyranosidic linkage (Scheme 2). 

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