Molecular modeling analysis of charge density and heat of fornation by PM3
method as well as C, H NMR and 2D-NMR measurements of histidine (substrate)
and some of its derivatives as histidine decarboxylase inhibitors were performed. It
was established that the atom, usually nitrogen, which forms internal aldimine with
pyridoxal5 -phosphate (PLP), (coenzyme), has negative and almost equal charge in
histidine and ather inhibittors. The preferred ccznfom&on of compounds with higher
inhibitory activity is calculated to be in such a form that the amino group and
imidazole ring have a dihedral angle of 60?. In this conformation, molecules are able
to form internal hydrogen bonds. In contrast, their derivatives with lower activity
have adifferent conformation. NMR measurements support our theoretical calculations