Cocaine and 3 beta-(4'-substituted phenyl)tropane-2 beta-carboxylic acid ester and amide analogues. New high-affinity and selective compounds for the dopamine transporter

Several 2 beta-carboxylic acid ester and amide analogues of cocaine and of 3 beta-(4'-substituted phenyl)tropane-2 beta-carboxylic acid were prepared. The binding affinities of these compounds, and of some previously prepared analogues, at the dopamine (DA), norepinephrine (NE), and serotonin (5-HT) transporters were determined. The phenyl esters of 3 beta-(4'-methylphenyl)- and 3 beta-(4'-chlorophenyl)tropane-2 beta-carboxylic acid are highly potent and highly selective for the DA transporter. The isopropyl esters of 3 beta-(4'-chlorophenyl)- and 3 beta-(4'-iodophenyl)tropane-2 beta-carboxylic acid also possess high DA affinity and show significant DA transporter selectivity. Similarly, the phenyl and isopropyl ester analogues of cocaine are much more selective for the DA transporter than cocaine. Tertiary amide analogues of cocaine and of 3 beta-(4'-substituted phenyl)tropane-2 beta-carboxylic acids are more potent inhibitors of radioligand binding at the DA transporter than the primary and secondary amide analogues. In particular, 3 beta-(4'-chlorophenyl)tropane-2 beta-N-morpholinocarboxamide as well as the 3 beta-(4'-chlorophenyl)- and 3 beta-(4'-iodophenyl)tropane-2 beta-N- pyrrolidinocarboxamides possess high affinity and selectivity for the DA transporter. The N,N-dimethylamide cocaine analogue is the most selective cocaine amide derivative for the DA transporter. High correlation between the inhibition of radioligand binding and inhibition of uptake at the DA, NE, and 5-HT transporter was found for a selected group of analogues. Within this group, one compound, the isopropyl ester of 3 beta-(4'-iodophenyl)-tropane-2 beta-carboxylic acid, was found to be more potent in the inhibition of radioligand binding than in the inhibition of DA uptake. Taken together with its high potency and selectivity at the DA transporter, this suggests that this compound may be a lead in the development of a cocaine antagonist.

Synthesis, ligand binding, and QSAR (CoMFA and classical) study of 3 beta-(3'-substituted phenyl)-, 3 beta-(4'-substituted phenyl)-, and 3 beta-(3',4'-disubstituted phenyl)tropane-2 beta-carboxylic acid methyl esters

Several new 3 beta-(4'-substituted phenyl)-, 3-beta-(3'-substituted phenyl)-, and 3 beta-(3',4'-disubstituted phenyl)tropane-2 beta-carboxylic acid methyl esters were prepared and assayed for inhibition of [3H]WIN 35,428 binding to the dopamine transporter. The 3 beta-(3',4'-dichloro) and 3 beta-(4'-chloro-3'-methyl) analogues (2w and 2y; RTI-111 and RTI-112, respectively) with IC50 values of 0.79 and 0.81 nM showed the highest affinity. The contributions of quantitative structure-activity relationship (QSAR) models derived from the classical and comparative molecular field analysis (CoMFA) approaches to rational drug design were examined. CoMFA models were derived using steric and electrostatic potentials with SYBYL default values while the classical models were derived from pi and MR parameters. Using a 12-compound training set, both models were used for predicting the binding affinity of compounds both inside and outside the training set. The CoMFA study provided new insight into the steric and electrostatic factors influencing binding to the DA transporter and provided additional support for our original finding that CoMFA is useful in predicting and designing new compounds for study. The classical QSAR models, which were easier to obtain, suggest that the distribution property (pi) of the compounds is an important factor. Overall, the SAR, CoMFA, and conventional QSAR studies elaborated some features of the cocaine binding site pharmacophore and provided useful predictive information.

3-Aryl-2-(3'-substituted-1',2',4'-oxadiazol-5'-yl)tropane analogues of cocaine: affinities at the cocaine binding site at the dopamine, serotonin, and norepinephrine transporters

Previous studies have shown that 3 beta-(substituted phenyl)tropan-2 beta-carboxylic acid esters possess high affinity for the cocaine binding site on the dopamine transporter both in vitro and in vivo and inhibit dopamine uptake in vitro. Since 1,2,4-oxadiazoles are excellent bioisosteres of ester groups, we have prepared several 3 beta-(substituted phenyl)-2 beta-(3-substituted 1',2',4'-oxadiazol-5'-yl)tropanes (5b-h) and all four stereoisomers of (1R,5S)-3 phenyl-2-(3-methyl-1',2',4'-oxadiazol-5'-yl)tropane (5a and 6-8). The 3 alpha-phenyl-2-alpha-(3'-methyl-1',2',4'-oxadiazole) isomer 7 was prepared from a stereoselective addition of phenyllithium to (1R,5S)-2-(3'-methyl-1',2',4'-oxadiazol-5-yl)-8-methyl-8- azabicyclo[3.2.1]oct-2-ene (11). The binding affinities for 5a-h and 6-8 at the dopamine, serotonin, and norepinephrine transporters were obtained. In general these bioisosteres showed potencies for the dopamine transporter similar to those of their parent esters. 3 beta-(4'-Chlorophenyl)-2 beta-(3'-phenyl-1',2',4'-oxadiazol-5'-yl)tropane (5d) was the most potent analogue with an IC50 of 1.62nM. However, 3 beta-(4'-chlorophenyl)-2 beta-(3'-methoxyphenyl-1',2'4'- oxadiazol-5'-yl)tropane (5e) with an IC50 of 1.81 nM was the most selective analogue for the dopamine transporter showing NE/DA and 5-HT/DA ratios of 461 and 186, respectively. The cis- and trans-3 alpha-phenyl-2-(3'-methyl-1',2',4'-oxadiazol-5'-yl)tropanes (7 and 8), which exist in a boat conformation, have IC50 values only slightly greater than that of the 3 beta,2 beta-isomer (5a) which possesses the cocaine stereochemistry.