[Synthesis, physical-chemical properties and pharmacologically-oriented screening studies on budipine and related...

1-Alkyl-4,4-diphenylpiperidines 5-23 are accessible in a simple manner and with attractive yields by regioselective reaction of piperidine derivatives like 1, 2, 3 or particularly 3-aroyl-4-aryl-4-hydroxypiperidines 4, which can be varied widely at the nitrogen atom, with benzene under Friedel-Crafts conditions. The physico-chemical parameters, which are important for the transport and the distribution of a drug in a living system, are discussed for the 1-tert-butyl derivative 13 (budipine) (pKa, partition coefficient P, saturation concentration Cs, surface activity, protein binding). Rapid absorption of this drug in man is indicated by the size of the permeability coefficient PM of the passive transport through artificial phospholipid collodium membranes as well as the invasion curves calculated from PM. According to pharmacological screening tests, most of the compounds of this class show marked antagonistic activity against experimentally generated pathological states in mice (tremorine and reserpine antagonism) which suggest their potential use in the therapy of Parkinson's disease. 13 has been selected for detailed investigations. Structure-activity analyses did not readily demonstrate the presence of a relationship between the type of alkyl substituent at the piperidine nitrogen atom and the pharmacological screening results obtained.