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Part-1Review on Antiulcer LiteratureCNNNOSCH 28080 23Figure 11: Acid-Pump Antagonist.1.4. Classification of PPI’s1.4.1. Irreversible Gastric PPI’s:- Three main structural features of this class ofcompounds are, the substituted pyridine ring; the substituted benzimidazole ring and themethylsulfinyl linking group. Irreversible PPIs lacking one or more of these features arerare. They are further classified according to their chemical structure as follows-1.4.1.1. Pyridinylmethylsulfinyl Benzimidazoles:- The same chemical features areretained by clinically used PPIs, differing only in the substituents present on thebenzimidazole and pyridine ring. Examples of this class include Omeprazole 18,Lansoprazole 19, Rabeprzole 20, Pantoprazole 21 and Esomeprazole 22.1.4.1.2. Pyridylmethylsulfinyl Thienoimidazoles:- In this class, the benzene ring ofimidazole is replaced by thiophene, keeping other structural features same. Examplesinclude saviprazole 24.NO OCF 2 CF 2 CF 2 CF 3SSNHSaviprazole 24NFigure 12: Structures of thienoimidazoles as irreversible gastric proton pump inhibitors.1.4.1.3. Aminobenzylsulfinyl Benzimidazoles:- Here, pyridine ring is replaced bysubstituted aminobenzyl ring. Examples include Leminoprazole 2517