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Part-1Review on Antiulcer LiteratureNNPyridinepKa : 5.2NPyrimidinepKa : 1.31The weekly basic nature of pyrimidine (pKa 1.31) is striking in relation to pyridine(pKa 5.2). It is understandable as in inductive effect (depletion of π-electrons), caused byinsertion of the avidly electron-attracting second nuclear nitrogen atom. Pyrimidine maytherefore be likened more to beta-nitropyridine (pKa 0.8), which contains the equallystrongly electron-attracting nitro group, than to the parent pyridine. A cursory review ofthe literature does reveal successful use of this logic. Replacement of the pyridine ringwith less basic isosteric pyrimidine ring has also been reported by Japanese workers 81 .They have evaluated2-(1H-benzoimidazole-2-sulfinylmethyl)-4-dimethylaminopyrimidine-5-carboxy-licacid ethyl ester 43 for its proton pump inhibition. It was foundto have marked proton pump inhibitory activity with IC 50 of 7.5 µm as compared toomeprazole IC 50 of 5.8 µm.NONSNONH43NOIt really appears difficult that in this system the formation of the disulfide intermediate islikely. This is owing to the poor availability of electrons on pyrimidine and its nitrogens.38