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Part-1Review on Antiulcer LiteratureClHOONML 3000 69Hayashi et al., 103 have reported the proton pump inhibitory effects of syntheticcompounds with the scopadulan ring system, which have ether linkages at C-6, C-13and/or C-18 positions. Tert-butyldimethylsilyl ethers of 5-methylenecycloheptene andrelated compounds 70-72 were shown to be novel proton pump inhibitors.OOIIOH70OTBSOTBS71IOTBSJain et al., 104 have designed a variety of novel mononuclear and condensed pyrimidineanalogs of omeprazole replacing the pyridine heterocycle of conventional PSMBs with its3-aza isoster, pyrimidine. The rationale behind their work is that the weakly basic natureof pyrimidine (pKa-1.31) as compared to pyridine (pKa-5.2), has the N 1 and N 3 ofpyrimidine less electron donating than the pyridine nitrogen. 105 This makes the formationof sulfenamide intermediate difficult. (Figure 20)72A review of a basic literature on organic & the heterocyclic chemistry reveals that indeedpyrimidine ring is the ring of choice.37