Study of structure-activity relationships for neurotransmitters using molecular electric field mapping: histamine and some of its H2-receptor agonists.

Molecular electric field mapping has been carried out to study structure-activity relationships for neutral and cationic forms of histamine and some of its agonists which are thiazole derivatives. Optimised geometries and Mulliken charges at the atomic sites were obtained using the PM3 method. Electric field values near the N3-H bond in histamine and those near substituents at the C2 position in the agonists have been found to correlate reasonably well with observed activities. Electric fields near the sulphur atom in thiazoles indicate that involvement of this site in hydrogen bonding with the H2-receptor is unlikely.