Flexible and biomimetic analogs of triple uptake inhibitor 4-((((3S,6S)-6-benzhydryltetrahydro-2H-pyran-3-yl)amino)methyl)phenol: Synthesis, biological characterization, and development of a pharmacophore model

In this study we have generated a pharmacophore model of triple uptake inhibitor compounds based on novel asymmetric pyran derivatives and the newly developed asymmetric furan derivatives. The model revealed features important for inhibitors to exhibit a balanced activity against dopamine transporter (DAT), serotonin transporter (SERT), and norepinephrine transporter (NET). In particular, a 'folded' conformation was found common to the active pyran compounds in the training set and was crucial to triple uptake inhibitory activity. Furthermore, the distances between the benzhydryl moiety and the N-benzyl group as well as the orientation of the secondary nitrogen were also important for TUI activity. We have validated our findings by synthesizing and testing novel asymmetric pyran analogs. The present work has also resulted in the discovery of a new series of asymmetric tetrahydrofuran derivatives as novel TUIs. Lead compounds 41 and 42 exhibited moderate TUI activity. Interestingly, the highest TUI activity by lead tetrahydrofuran compounds for example, 41 and 42, was exhibited in a stereochemical preference similar to pyran TUI for example, D-161.

Synthesis and structure-activity studies of benzyl ester meperidine and normeperidine derivatives as selective serotonin transporter ligands

A series of benzyl esters of meperidine and normeperidine were synthesized and evaluated for binding affinity at serotonin, dopamine and norepinephrine transporters. The 4-methoxybenzyl ester 8b and 4-nitrobenzyl ester 8c in the meperidine series and 4-methoxybenzyl ester 14a in the normeperidine series exhibited low nanomolar binding affinities at the SERT (K(i) values <2nM) and high SERT selectivity (DAT/SERT >1500 and NET/SERT >1500).

Reduced levels of norepinephrine transporters in the locus coeruleus in major depression

The norepinephrine transporter (NET) is a membrane protein responsible for termination of the action of synaptic norepinephrine and is a site of action of many drugs used to treat major depression. The present study determined whether the binding of [3H]nisoxetine to the NET is altered in the locus coeruleus (LC) in major depression, using brain tissue collected postmortem from subjects diagnosed with major depression and from age-matched normal control subjects. Thirteen of the 15 major depressive subjects studied died by suicide. The distribution of [3H]nisoxetine binding along the rostro-caudal axis of the nucleus was uneven and was paralleled by a similar uneven distribution of neuromelanin-containing cells in both major depressives and psychiatrically normal control subjects. The binding of [3H]nisoxetine to NETs in the midcaudal portion of the LC from major depressive subjects was significantly lower than that from age-matched, normal control subjects. The binding of [3H]nisoxetine to NETs in other regions of the LC was similar in major depressives and control subjects. In contrast to reductions in binding to NETs, there were no significant differences in the number of noradrenergic cells at any particular level of the LC between major depressives and normal control subjects. The decreased binding of [3H]nisoxetine to NETs in the LC in major depression may reflect a compensatory downregulation of this transporter protein in response to an insufficient availability of its substrate (norepinephrine) at the synapse.

Pharmacology and distribution of norepinephrine transporters in the human locus coeruleus and raphe nuclei

The norepinephrine transporter (NET) is a site of action for tricyclic antidepressant drugs and for drugs of abuse such as amphetamine and cocaine. In this study, the binding of [3H]nisoxetine to NETs in the noradrenergic cell group, the locus coeruleus, and the serotonergic cell groups, the dorsal raphe nuclei, was measured autoradiographically in postmortem human brain. [3H]nisoxetine binding was unevenly distributed along the rostral-caudal axis of the locus coeruleus and correlated positively with numbers of neuromelanin-containing (noradrenergic) cells along the axis of the locus coeruleus within individuals. Binding densities of [3H]nisoxetine in dorsal raphe nuclei were similar to that in the locus coeruleus. [3H]nisoxetine binding was unevenly distributed along the entire rostral-caudal extent of the dorsal raphe, with the highest binding occurring in the interfascicular and ventral nuclei. A moderate amount of [3H]nisoxetine binding was also observed in the median raphe nucleus. The specificity of [3H]nisoxetine binding to NETs in monoaminergic nuclei was assessed by measuring the inhibition of its binding by desipramine, imipramine, or citalopram. The order of affinities of these drugs was identical in the locus coeruleus and dorsal and median raphe and was characteristic of binding to NETs (desipramine > imipramine > citalopram). Thus, high levels of NETs and an uneven distribution of NETs occur in the locus coeruleus as well as in the dorsal raphe nuclei of the human.