| Abstract
| - 3α-(Diphenylmethoxy)tropane (benztropine) and its analogues are tropane ring-containingdopamine uptake inhibitors that display binding and behavioral profiles that are distinct fromcocaine. We previously prepared a benztropine-based photoaffinity label [125I]-(N-[4-(4‘-azido-3‘-iodophenyl)butyl]-3α-[bis(4‘-fluorophenyl)methoxy]tropane, [125I]1, that covalently attachedto the 1−2 transmembrane spanning region of the dopamine transporter (DAT). This was incontrast to the 4−7 transmembrane spanning region labeled by a cocaine-based photoaffinitylabel, [125I] 2 (RTI 82). To characterize further these different binding domains, photoaffinityligands that had the 4‘-azido-3‘-iodophenyl substituent extended from the same position onthe tropane ring were desirable. Thus, identification of the optimal alkyl linker between thissubstituent and the tropane nitrogen in the benztropine series was investigated to ultimatelyprepare the identical N-substituted analogue of 2. In this pursuit, the N-[4-(4‘-azido-3‘-iodophenyl)propyl] analogue of 3α-[bis(4‘-fluorophenyl)methoxy]tropane (9a) was synthesizedas well as two isothiocyanate analogues that do not require photoactivation (10a,b) forirreversible binding. The synthesis of these target compounds was achieved using a modificationof the strategy developed for 1. Evaluation of these compounds for displacing [3H]WIN 35 428binding at DAT in rat caudate putamen revealed that the 4‘-azido-3‘-iodophenylbutylsubstituent, found in 1, provided optimal binding affinity and was chosen to replace the N−CH3group on 2. Both the 4‘-azido-3‘-iodophenyl- and the 4‘-isothiocyanatophenylbutyl analoguesof 2 (25 and 26, respectively) were synthesized. Both products bound to DAT with comparablepotency (IC50 = 30 nM) to RTI 82 (2). In addition, compound 26 demonstrated wash-resistantdisplacement of [3H]WIN 35 428 in HEK 293 cells stably transfected with hDAT. These ligandswill provide important tools for further characterizing the binding domains for tropane-baseddopamine uptake inhibitors at the DAT.
|
