Peptic ulcer disease occurs when offensive factors involving gastric acid secretion are strong or defensive factors of gastric mucous are weak. For the treatment of peptic ulcer disease, various drugs such as antacid, anticholinergic agent, H2-receptor antagonist, and proton pump inhibitor have been used. The advent of omeprazole as a proton pump inhibitor has rekindled research activities in this field.
However, it has been pointed out that proton pump inhibition by omeprazole is irreversible, thereby incurring long-term inhibition of gastric acid secretion, which may induce side effects. Accordingly, various attempts to develop a reversible proton pump inhibitor are being made. For example, imidazopyridine derivatives are disclosed in WO 98/37,080 (AstraZeneca AB), WO 00/17,200 (Byk Gulden Lomberg Chem.), and U.S. Pat. No. 4,450,164 (Schering Corporation) as a reversible proton pump inhibitor. Further, pyrimidine derivatives are also disclosed in European Patent No. 775,120 (Yuhan Corp.).