The present invention relates to substantially pure piperidine derivative compounds of the formulae: ##STR1## wherein R.sub.1 is hydrogen or hydroxy;R.sub.2 is hydrogen;or R.sub.2 and R.sub.2 taken together form a second bond between the carbon atoms bearing R.sub.1 and R.sub.2 ;R.sub.3 is --COOH or --COOR.sub.4 ;R.sub.4 has 1 to 6 carbon atoms;A, B, and D are the substituents of their respective rings each of which may be different or the same and are hydrogen, halogens, alkyl, hydroxy, alkoxy, or other substituents.A process of preparing such piperidine derivative compounds in substantially pure form is also disclosed.