The reactivity of the hydroxy-group of methyl β-D-glucopyranoside in the Koenigs–Knorr reaction

Abstract

The relative reactivities of the hydroxy-groups of methyl β-D-glucoside have been studied in the Koenigs–Knorr reaction by condensing it with α-acetobromo-D-[¹⁴C]glucose. The reactivities were based on the yields of the four β-linked disaccharide products, which were determined by measuring their radioactivity using the Van Slyke technique. The Koenigs–Knorr reactions were carried out with silver oxide as the acid acceptor, iodine as a catalyst, and Drierite as the internal desiccant. A large-scale reaction, from which each product was isolated, revealed that the products of this reaction were mainly the β-linked disaccharide glycosides. The order of reactivity was: 6-OH ≫ 3-OH > 4-OH > 2-OH, with an average ratio value of 6·4:1·7:1·2:1·0. Apparently, the difficulties normally encountered in the synthesis of disaccharides with the β(1 → 4)-linkage is due to steric hindrance of the 4-hydroxy-group by the substituent blocking groups, since it is not inherently unreactive compared to the other secondary hydroxy-groups. A new compound, methyl β-sophoroside, has been synthesised.