Investigation of the action of Taka-amylase A [EC 3. 2.1.1] on phenyl a-maltosides, in which the terminal C-4 was modified, revealed that the hydroxyl of the terminal C-4 in phenyl a-maltoside was almost indifferent to the enzymatic action. However, it was found that inversion of the configuration of the terminal C-4 considerably retarded the enzymatic action. Syntheses of new derivatives and analogues of phenyl a-maltoside are also described.