Compounds of formula (I) and their salts in which R1 is optionally substituted phenyl, R2 is alkyl, cycloalkyl or optionally substituted amino, or R2 and R3 together with the nitrogen and carbon atoms to which they are attached form an optionally substituted heterocyclic ring or R3 and R4 together with the nitrogen atom to which they are attached form an optionally substituted heterocyclic ring and R5 is H, halo, alkyl, alkoxy, trifluoromethyl or a group of formula S(O)mR8 in which m is 0, 1 or 2 and R8 is alkyl have utility in the treatment of diabetes particularly in the treatment of hyperglycaemia.