Theoretical calculations on dipyridamole structure allow to explain experimental properties associated to electrochemical oxidation and protonation

PM3 calculations of charge distributions for dipyridamole (DIP) in the neutral, single- and double-ionized states allowed to estimate the first and second ionization potentials. Results are compared with electrochemical oxidation, a sequential two-step process. Single ionization produces a cation radical, the electron being removed from the nitrogen atoms in the substituent positions 2,4,6,8 with participation of the carbons in the pyrimido-pyrimidine ring. Protonation of one of the nitrogens is allowed energetically while a second protonation is forbidden due to the high energy required. Our calculations allow to explain some interesting experimental results related to electrochemical oxidation and protonation of the drug.