Abstract: A substantially pure compound of the formula: ##STR1## wherein each of R.sub.1 and R.sub.2, independently, is H, CH.sub.3, CF.sub.3, F, Cl, Br, I, OH, OCH.sub.3, OCF.sub.3, SH, SCH.sub.3, NH.sub.2, N.sub.3, NO.sub.2, CN, COOH, CONH.sub.2, CH.sub.2 CONH.sub.2, or SO.sub.2 NH.sub.2 ;R.sub.3 is H, CH.sub.3, COOH, CONH.sub.2, or COOR where R is C.sub.1-4 alkyl;each R.sub.4, independently, is H or C.sub.1-6 alkyl;X is CH.sub.2, CH.sub.2 CH.sub.2, CH.dbd.CH, or CH.sub.2 CH.sub.2 CH.sub.2 ; ##STR2## each Z, independently, is H, CH.sub.3, or Q where Q is a hydrophobic acyl, benzoyl, phenacetyl, benzyloxycarbonyl, alkoxycarbonyl, or N-methyl-dihydropyridine-3-carbonyl linked to N by an amide bond which is cleavable by an endogenous central nervous system enzyme;D is H or ##STR3## where R.sub.5 is H or C.sub.