526
D. J. Lapinsky et al. / Bioorg. Med. Chem. Lett. 22 (2012) 523–526
bupropion-binding site lies within the nAChR ion channel and not at
the agonist-binding site8,16; thus, probe ( )-3 is pharmacologically
distinct from nAChR agonist photoprobes such as 5-azidoepibati-
dine. Furthermore, the modest nAChR binding affinity of ( )-3 does
not preclude identification of the bupropion-binding site within
neuronal nAChR ion channels.25 Iodine-125-labeled ( )-3 was
shown to bind covalently to hDAT expressed in cultured cells and
References and notes
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affinity-purified, lipid-reincorporated human
a4b2 neuronal nAC-
hRs. Successful adduction of ( )-[125I]-3 to these proteins suggests
that this non-tropane ligand tolerates direct substitution of a photo-
reactive azido group on the aromatic ring of the inhibitor scaffold.
This contrasts with the design of tropane-based DAT photoaffinity li-
gands, wherein the azide is placed at a distance (usually via a linker)
from the inhibitor pharmacophore in order to achieve successful
DAT labeling.26 As a result, compact photoaffinity ligands based on
bupropion offer the advantage of a shorter tether between probe
functional groups and protein amino acid residues in or near the
inhibitor-binding site. Given the evidence that both DAT and nAChR
inhibitors bind to non-identical sites or conformations,8–12,16 this
suggests that novel irreversible ligands based on bupropion may
yield new nAChR and monoamine transporter structure–function
information. Future directions include additional photoprobes
based on bupropion and its major active metabolite, (2S,3S)-hydrox-
ybupropion, their pharmacological characterization, binding site
prediction via docking within DAT and nAChR computational mod-
els, and detailed elucidation of the binding domains within the DAT
and selected nAChRs.
16. Arias, H. R.; Gumilar, F.; Rosenberg, A.; Targowska-Duda, K. M.; Feuerbach, D.;
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Acknowledgments
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This work was funded by a Hunkele Dreaded Disease Award
(D.J.L.), the Mylan School of Pharmacy at Duquesne University
(D.J.L.), the Center of Membrane Protein Research (M.P.B.), Texas
Tech University Health Sciences Center School of Medicine
(M.P.B.), and NIH Grants DA27081 (D.J.L.), DA16604 (C.K.S.), and
DA15175 (R.A.V.).
20. Perrine, D. M.; Ross, J. T.; Nervi, S. J.; Zimmerman, R. H. J. Chem. Ed. 2000, 77, 1479.
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Supplementary data
25. Experimental observation;
a
manuscript detailing mapping of ( )-[125I]-3
within the Torpedo nAChR ion channel is currently in preparation.
26. Newman, A. H.; Cha, J. H.; Cao, J.; Kopajtic, T.; Katz, J. L.; Parnas, M. L.; Vaughan,
R.; Lever, J. R. J. Med. Chem. 2006, 49, 6621.
Supplementary data (Experimental section and spectral data.)
associated with this article can be found, in the online version, at