chemical comparison suggests that the -- n+hme2 group corresponds to the -- n+h3 of histamine , and that the isothiourea group of dimaprit ( which can undergo 1,3-prototropic tautomerism ) may simulate the imidazole ring of histamine and function as a proton transfer agent at h2 receptors .
C0039958
isothiourea
C0058185
dimaprit