There are described compounds of formula I,
wherein one of R¹ and R² represents halogen or alkyl C₁₋₆, and the other represents hydrogen,
R³ represents alkyl C₁₋₆,
and pharmaceutically acceptable salts thereof.
Processes for making the compounds and pharmaceutical compositions containing them, e.g. for the treatment of conditions in which gastric acid has a pathological role, are also disclosed.