DA 4643 is one of histamine H2-receptor antagonistic. Two histamine H2-receptor antagonists of the phenylformamidine type, mifentidine (N-isopropyl-N'-(4-1H-imidazol-4-yl-phenyl) formamidine dihydrochloride; I) and DA 4643 (N-methyl-N'-(3-(2-guanidinothiazol-4-yl)-phenyl) formamidine dihydrochloride; II), have been investigated by experimental physico-chemical studies and theoretical conformational analysis. Both mifentidine and DA 4643 interact with the histamine H2-receptor at the same site, utilizing in the binding process the same, or closely similar, receptor structural features.
