Formation of borate complexes of inosamines (aminodeoxyinositols) and their separation by paper electrophoresis

Abstract

The electrophoretic mobility of an inosamine in borate buffer is very dependent on configuration, and a set of 10 inosamines showed a wide range of mobilities. The order of mobilities within the set changed as the pH of the buffer was changed in the range 7.7-9.5. Paper electrophoresis in borate buffers can effectively separate mixtures of inosamines. The probable site of reaction between an inosamine and borate ions has been identified for some isomers. In aminodeoxy-scyllo-inositol and 3-amino-3-deoxy-epi-inositol the amino group is involved in the formation of a tridentate borate complex of adamantane-type structure, which is electrically neutral over the above range of pH values. Aminodeoxy-scyllo-inositol simultaneously combines with a second molecule of borate, forming a bis-tridentate complex with one anionic centre. There is evidence that in other isomers protonation of the amino group and formation of anionic borate complexes at hydroxyl groups are not independent reactions. Paper electrophoresis in non-complexing buffers provides evidence for the relative basicities of inosamines. DL-2-Amino-2-deoxy-epi-inositol, which has an interaction between axial amino and hydroxyl group in the preferred conformation, was the strongest base in the set, whereas the bases with an axial amino group free of such an interaction were the weakest. Inosamines form N-carboxyl derivatives in the normal way on exposure to carbon dioxide in the presence of strong alkali.