A method of treating movement disorders comprises administering to a human or animal subject in need of treatment a therapeutically effective amount of at least one compound according to the following formula: wherein R3 and R4 are each independently selected from the group consisting of lower alkyl, phenyl and lower alkyl substituted phenyl, and R1 and R2 are each independently either a hydrogen atom or a radical of the formula wherein R5 and R6 are each independently selected from the group consisting of H, lower alkyl, phenyl and lower alkyl substituted phenyl, its pharmaceutically acceptable salts, prodrugs, and metabolites thereof.