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: ##STR00001## wherein R.sub.3 and R.sub.4 are each independently selected from the group consisting of lower alkyl, phenyl and lower alkyl substituted phenyl, and R.sub.1 and R.sub.2 are each independently either a hydrogen atom or a radical of the formula ##STR00002## wherein R.sub.5 and R.sub.6 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.