(+)-CPCA - DAT Arylpiperidine CoMFA Study

DAT Arylpiperidine CoMFA Study

(Hongbin Yuan, et al. 2004)

A generally recognized pharmacophore model for cocaine and phenyltropanes comprises two electrostatic interactions of the basic nitrogen and the ester group of the C-2 substituent, and one hydrophobic interaction of the C-3 aryl group. This model has been disputed because of the finding that in certain compounds neither the basic N nor the ester group was necessary for high binding affinity and inhibition of MAR. Instead, a hydrophobic pocket was proposed to exist in the vicinity of the C-2 carbon. Carroll et al., however, provided further evidence for an electrostatic interaction at the C-2β-position in a later study.

Other models proposed for the DAT binding site include a linear fashion binding pocket for the 3β-substituted phenyltropane analogs, and a prohibited conical region about 5.5–10 Å distant from the 3α-substituted piperidine ring. Noticeably, high potency at the DAT of dimeric piperidine-based esters and amides suggested that the flexible linker combining the two piperidine units was able to adjust its orientation and to avoid unfavorable interactions with the binding site. All these lines of evidence suggest that the DAT binding site is much more complicated than the proposed pharmacophore models.

In an attempt to uncover the details of the DAT binding site, a number of 3D-QSAR studies were performed. Several QSAR/CoMFA studies focused on phenyltropanes concluded that an increased negative electrostatic potential in the regions around the 3β-substituent of the tropane ring and the para-position of the phenyl ring favored high potency in inhibiting the MATs. Wright et al. studied the role of the 3β-substituent of tropanes in binding to the DAT and blocking DA re-uptake. Their CoMFA model indicated that the 3β-substituent binding site is barrel-shaped and hydrophobic interactions make a dominant contribution to the binding, which is consistent with the studies of 3α-substituted tropane analogs reported by Newman et al. Newman and co-authors also studied N-substituted tropanes and concluded that the steric interaction of the N-substituent with the DAT is a principal factor for the binding affinity.