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Owing to our current interest in synthesizing and evaluating the antiulcer and antisecretory activity of bicyclic compounds, a series of 1(or 3),4,6,7-tetrahydropyrano- and 1(or 3),4,6,7-tetrahydrothiopyrano-[3,4-d]imidazoles was synthesized and tested. The biological results were compared with those of some previously described 4,5,6,7-tetrahydroimidazo-[4,5-c]pyridine and 4,5,6,7-tetrahydrobenzimidazole derivatives.

The synthesis of some 7- and 9-methyltetracyclines is reported together with the biological activity of the new compounds.

As the ultimate result of a long-term search for new bicyclic molecules potentially endowed with antiulcer and/or antisecretory activity, simple urea derivatives of 2-guanidino-4,5,6,7-tetrahydrothiazolo[5,4-c]pyridine [(VIII), Fig. 1; X = 0, R = alkyl], displaying a strong inhibition of stress- and ASA-induced gastric ulcers and of basal gastric secretion, were found. Their potency does compare very favourably with that of cimetidine and ranitidine and approaches that of famotidine. On spontaneously beating guinea pig atria they behaved as inhibitors of the histamine H2-receptor. In contrast with cimetidine and ranitidine but like other recently described inhibitors (famotidine included), the most active compounds (VIII) caused a surmountable antagonism only at low concentrations and an unsurmountable antagonism at higher concentrations. The onset of action was slow, while the inhibitory effect was hardly reversed by washing. The rational development of the research and the synthetic approach, as well as a quantitative assessment of both in vitro and in vivo potencies in comparison with the best known, clinically used drugs, are shown in detail.

The remarkable antiulcer and antisecretory activity of some previously described 4,5,6,7-tetrahydroimidazo[4,5-c]pyridine derivatives prompted us to further investigate related bicyclic systems. Accordingly, a series of 5-amino- and 5-aminomethyl-4,5,6,7-tetrahydrobenzimidazoles, regiospecifically alkylated in position 1, were synthesized and tested. Only a few 1-ethyl-5-amino derivatives displayed a reasonable antiulcer activity in comparison with our former class of compounds.

New thioureas and ureas with an interesting anti-ulcer and antisecretory activity are disclosed. The chemical synthesis, determination of the structure, and structure-activity relationships of the compounds are discussed.