A-Anomeric linkage

It should be noted that the addition of aminocyclitol derivatives to glycals catalyzed by boron trifluoride etherate also affords l,2-d5 -aminoglycosides stereo-selectively. Thus, the glycosyl product 54 with an a-anomeric linkage was obtained in 65% yield by addition of the alcohol 53 to the glycal 35 [48] (compounds 53, 54). 

Note the various ways in which the a anomeric linkage is designated in the different types of structures. Realizing the structure of melibiose we can deduce compounds A and B and their related products. 

The configuration of each anomeric hydroxyl group that forms a polymer linkage is fixed, and the type of linkage has a significant effect on the physical properties of the polymer, as will be seen. 

A (1—>5)-linkage for the polyribose is expected to be a preponderant linkage, based on the relative reactivities of primary and secondary hydroxyl groups 2 and on the tendency 1 of D-ribose to adopt the furanose form. However, the anomeric configuration of the polyribose is, most probably, a mixture of a-D and /3-d linkages, since a mixture of D-ribose and adenine, under the influence of polyphosphoric acid esters,w gave, among other products, approximately equal proportions of adenosine and its a-D isomer. 2... 

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