Ultrasound-induced scission of the glycosidic bond in disaccharides

The products originating from the scission of the glycosidic bond by ultrasound were investigated for lactose (4-O-β-d-galactopyranosyl-d-glucopyranose), melibiose (6-O-α-d-galactopyranosyl-d-glucopyranose) and trehalose (1,1-O-α, α-d-glucopyranosyl-d-glucopyranose). A comparison with the product formation of radiolysis reveals that for ultrasound the reactions also start from sugar radicals, produced by abstraction of carbon-bonded hydrogens by OH- and H-radicals. From these radicals, only those that are directly located at this bond or can be transferred by rearrangement into a position adjacent to this bond contribute to the scission of the glycosidic bond: C-1′, C-5′, C-4 for lactose; C-1′, C-5′, C-6 for melibiose and C-1 (=C-1′), C-5 (=C-5′) for trehalose. Based on the yields of the characteristic products for the different radicals it can be concluded that the reaction predominantly starts from the radical at C-1′ for lactose and melibiose and from C-1 (=C-1′) for trehalose. From the product formation it can be further deduced that the radical-induced scission is mainly determined by hydrolytic processes, fragmentation by radical rearrangement being of minor importance. The ratio of hydrolysis to fragmentation reactions reveals that in sonolysis this is still more pronounced than in radiolysis (lactose: sonolysis 8.2, radiolysis 4.2; melibiose: sonolysis 23.5, radiolysis 16.2).