Benny Bang-Andersen

Discovery of 1-[2-(2,4-dimethylphenylsulfanyl)phenyl]piperazine (Lu AA21004): a novel multimodal compound for the treatment of major depressive disorder.

The synthesis and structure-activity relationship of a novel series of compounds with combined effects on 5-HT(3A) and 5-HT(1A) receptors and on the serotonin (5-HT) transporter (SERT) are described. Compound 5m (Lu AA21004) was the lead compound, displaying high affinity for recombinant human 5-HT(1A) (K(i) = 15 nM), 5-HT(1B) (K(i) = 33 nM), 5-HT(3A) (K(i) = 3.7 nM), 5-HT(7) (K(i) = 19 nM), and noradrenergic β(1) (K(i) = 46 nM) receptors, and SERT (K(i) = 1.6 nM). Compound 5m displayed antagonistic properties at 5-HT(3A) and 5-HT(7) receptors, partial agonist properties at 5-HT(1B) receptors, agonistic properties at 5-HT(1A) receptors, and potent inhibition of SERT. In conscious rats, 5m significantly increased extracellular 5-HT levels in the brain after acute and 3 days of treatment. Following the 3-day treatment (5 or 10 (mg/kg)/day) SERT occupancies were only 43% and 57%, respectively. These characteristics indicate that 5m is a novel multimodal serotonergic compound, and 5m is currently in clinical development for major depressive disorder.

Pharmacological effects of Lu AA21004: a novel multimodal compound for the treatment of major depressive disorder.

1-[2-(2,4-Dimethylphenyl-sulfanyl)-phenyl]-piperazine (Lu AA21004) is a human (h) serotonin (5-HT)3A receptor antagonist (Ki = 3.7 nM), h5-HT7 receptor antagonist (Ki = 19 nM), h5-HT1B receptor partial agonist (Ki = 33 nM), h5-HT1A receptor agonist (Ki = 15 nM), and a human 5-HT transporter (SERT) inhibitor (Ki = 1.6 nM) (J Med Chem 54:3206–3221, 2011). Here, we confirm that Lu AA21004 is a partial h5-HT1B receptor agonist [EC50 = 460 nM, intrinsic activity = 22%] using a whole-cell cAMP-based assay and demonstrate that Lu AA21004 is a rat (r) 5-HT7 receptor antagonist (Ki = 200 nM and IC50 = 2080 nM). In vivo, Lu AA21004 occupies the r5-HT1B receptor and rSERT (ED50 = 3.2 and 0.4 mg/kg, respectively) after subcutaneous administration and is a 5-HT3 receptor antagonist in the Bezold-Jarisch reflex assay (ED50 = 0.11 mg/kg s.c.). In rat microdialysis experiments, Lu AA21004 (2.5–10.0 mg/kg s.c.) increased extracellular 5-HT, dopamine, and noradrenaline in the medial prefrontal cortex and ventral hippocampus. Lu AA21004 (5 mg/kg per day for 3 days; minipump subcutaneously), corresponding to 41% rSERT occupancy, significantly increased extracellular 5-HT in the ventral hippocampus. Furthermore, the 5-HT3 receptor antagonist, ondansetron, potentiated the increase in extracellular levels of 5-HT induced by citalopram. Lu AA21004 has antidepressant- and anxiolytic-like effects in the rat forced swim (Flinders Sensitive Line) and social interaction and conditioned fear tests (minimal effective doses: 7.8, 2.0, and 3.9 mg/kg). In conclusion, Lu AA21004 mediates its pharmacological effects via two pharmacological modalities: SERT inhibition and 5-HT receptor modulation. In vivo, this results in enhanced release of several neurotransmitters and antidepressant- and anxiolytic-like profiles at doses for which targets in addition to the SERT are occupied. The multimodal activity profile of Lu AA21004 is distinct from that of current antidepressants.

Lu AE58054, a 5-HT6 antagonist, reverses cognitive impairment induced by subchronic phencyclidine in a novel object recognition test in rats.

The in-vitro potency and selectivity, in-vivo binding affinity and effect of the 5-HT(6)R antagonist Lu AE58054 ([2-(6-fluoro-1H-indol-3-yl)-ethyl]-[3-(2,2,3,3-tetrafluoropropoxy)-benzyl]-amine) on impaired cognition were evaluated. Lu AE58054 displayed high affinity to the human 5-HT(6) receptor (5-HT(6)R) with a Ki of 0.83 nm. In a 5-HT(6) GTPgammaS efficacy assay Lu AE58054 showed no agonist activity, but demonstrated potent inhibition of 5-HT-mediated activation. Besides medium affinity to adrenergic alpha(1A)- and alpha(1B)-adrenoreceptors, Lu AE58054 demonstrated >50-fold selectivity for more than 70 targets examined. Orally administered Lu AE58054 potently inhibited striatal in-vivo binding of the 5-HT(6) antagonist radioligand [(3)H]Lu AE60157 ([(3)H]8-(4-methylpiperazin-1-yl)-3-phenylsulfonylquinoline), with an ED(50) of 2.7 mg/kg. Steady-state modelling of an acute pharmacokinetic/5-HT(6)R occupancy time-course experiment indicated a plasma EC(50) value of 20 ng/ml. Administration of Lu AE58054 in a dose range (5-20 mg/kg p.o.) leading to above 65% striatal 5-HT(6)R binding occupancy in vivo, reversed cognitive impairment in a rat novel object recognition task induced after subchronic treatment for 7 d with phencyclidine (PCP 2 mg/kg b.i.d., i.p. for 7 d, followed by 7 d drug free). The results indicate that Lu AE58054 is a selective antagonist of 5-HT(6)Rs with good oral bioavailability and robust efficacy in a rat model of cognitive impairment in schizophrenia. Lu AE58054 may be useful for the pharmacotherapy of cognitive dysfunction in disease states such as schizophrenia and Alzheimers disease.

Palladium-Catalyzed Three-Component Approach to Promazine with Formation of One Carbon–Sulfur and Two Carbon–Nitrogen Bonds

The formation of aromatic carbon–heteroatom bonds has traditionally been achieved by nucleophilic aromatic substitution or by the copper-mediated Ullman reaction. The former type of chemistry is generally limited to activated substrates, whereas the latter often requires prolonged heating in the presence of excess copper salts. The palladium-catalyzed formation of aromatic C N bonds, extensively developed by the groups of Hartwig and Buchwald, has provided a powerful alternative. Whereas aryl amination has been optimized so that it is even applicable to aryl chlorides and activated phenols, the analogous formation of C O and C S bonds has attracted less attention. For a medicinal chemistry project, we have identified conditions that enable the formation of C S bonds from thiophenols and aryl iodides, and C N bonds from amines and aryl bromides using the same catalyst in a one-pot reaction. We now report the application of this discovery to the synthesis of the promazine class of antipsychotics. Our attention was drawn to the phenothiazine backbone of the promazine series 1a–e as a suitable model system for the controlled construction of three carbon–heteroatom bonds in a single synthetic operation (Scheme 1). This synthesis would require that either C S or C N bond formation occur initially with subsequent cyclization to the phenothiazine nucleus. This disconnection of the promazines leads to the precursors 2-bromothiophenol (2), primary amine 3, and an appropriately substituted 1-bromo-2-iodobenzene 4a–e. From reported literature and our experience with reactions involving dppf, binap, dpephos, and xantphos, the formation of the C S bond was expected to precede the amination steps. Indeed, clean formation of diaryl sulfide 6 was observed when a mixture of 2, 3, 4a, and NaOtBu was treated with [Pd2dba3] and dppf at 60 8C for 20 minutes, and 1a was formed in high yield after 2 hours at 160 8C under microwave (MW) irradiation. These conditions were mimicked in a ligand optimization study using oil-bath heating (Figure 1). Figure 1 summarizes results obtained with commercially available and easily handled ligands reported for C S and C N coupling reactions. Ferrocene ligands such as dppf gave mainly the desired product (1a) in addition to the noncyclized intermediate 7. Significant amounts of aniline 5 were observed with davephos, x-phos, and binap. Noncyclized promazine 7 was the major product with dpephos and xantphos. Trace amounts of the desired product were formed with PPh3, P(o-tol)3, P(tBu)3, [12,13] or the carbene ligand. Low conversion of 4a occurred with diaryl sulfide 6 as the only detectable product in the absence of palladium and ligand, whereas small amounts of 6 and bromobenzene were formed without the ligand. The reaction appears to proceed in a stepwise fashion from diaryl sulfide 6 (only product with one equivalent of NaOtBu), to aniline 7 (only product with two equivalents of NaOtBu), to 1a (74% yield; Table 1) under MW conditions. The three-component reaction worked well for the parent promazines 1a–e with yields of the isolated products ranging from 50% to 76%, and an average yield of greater than 75% for each of the three bonds formed (Table 1). The reaction with allyl amine gave a complex mixture of unidentified products. Benzyl amines were good substrates and the scope of the reaction was extended to include anilines; 2,6disubstituted anilines participated in the reaction, albeit with reduced yields as the steric hindrance around the nitrogen atom increased. Themicrowave method was relatively slow as the reagents had to be mixed immediately before starting the reactions to avoid catalyst deactivation. Conveniently, the reaction was performed with conventional heating, warming from room temperature to 160 8C over approximately 0.5 hours, with subsequent stirring at 160 8C overnight (reaction times have not been optimized). Scheme 1. Retrosynthetic analysis for the promazines.

Emerging mechanisms and treatments for depression beyond SSRIs and SNRIs

The monoamine hypothesis has been the prevailing hypothesis of depression over the last several decades. It states that depression is associated with reduced monoamine function. Hence efforts to increase monoamine transmission by inhibiting serotonin (5-HT) and norepinephrine (NE) transporters has been a central theme in depression research since the 1960s. The selective 5-HT reuptake inhibitors (SSRIs) and 5-HT and NE reuptake inhibitors (SNRIs) that have emerged from this line of research are currently first line treatment options for major depressive disorder (MDD). One of the recent trends in antidepressant research has been to refine monoaminergic mechanisms by targeting monoaminergic receptors and additional transporters (e.g. with multimodal drugs and triple re-uptake inhibitors) or by adding atypical antipsychotics to SSRI or SNRI treatment. In addition, several other hypotheses of depression have been brought forward in pre-clinical and clinical research based on biological hallmarks of the disease and efficacy of pharmacological interventions. A central strategy has been to target glutamate receptors (for example, with intravenous infusions of the N-methyl-d-aspartate (NMDA) receptor antagonist ketamine). Other strategies have been based on modulation of cholinergic and γ-aminobutyric acid (GABA)ergic transmission, neuronal plasticity, stress/hypothalamic pituitary adrenal(HPA)-axis, the reward system and neuroinflammation. Here we review the pharmacological profiles of compounds that derived from these strategies and have been recently tested in clinical trials with published results. In addition, we discuss putative treatments for depression that are being investigated at the preclinical level and outline future directions for antidepressant research.

Mutational Mapping and Modeling of the Binding Site for (S)-Citalopram in the Human Serotonin Transporter

The serotonin transporter (SERT) regulates extracellular levels of the neurotransmitter serotonin (5-hydroxytryptamine) in the brain by facilitating uptake of released 5-hydroxytryptamine into neuronal cells. SERT is the target for widely used antidepressant drugs, including imipramine, fluoxetine, and (S)-citalopram, which are competitive inhibitors of the transport function. Knowledge of the molecular details of the antidepressant binding sites in SERT has been limited due to lack of structural data on SERT. Here, we present a characterization of the (S)-citalopram binding pocket in human SERT (hSERT) using mutational and computational approaches. Comparative modeling and ligand docking reveal that (S)-citalopram fits into the hSERT substrate binding pocket, where (S)-citalopram can adopt a number of different binding orientations. We find, however, that only one of these binding modes is functionally relevant from studying the effects of 64 point mutations around the putative substrate binding site. The mutational mapping also identify novel hSERT residues that are crucial for (S)-citalopram binding. The model defines the molecular determinants for (S)-citalopram binding to hSERT and demonstrates that the antidepressant binding site overlaps with the substrate binding site.

Identification of the Cytochrome P450 and Other Enzymes Involved in the In Vitro Oxidative Metabolism of a Novel Antidepressant, Lu AA21004

1-[2-(2,4-Dimethyl-phenylsulfanyl)-phenyl]-piperazine (Lu AA21004) is a novel antidepressant that is currently in late-stage clinical development for major depressive disorder. In the present study, the metabolism of Lu AA21004 was investigated using human liver microsomes (HLM), human liver S9 fraction, and recombinant enzymes. Lu AA21004 was found in vitro to be oxidized to a 4-hydroxy-phenyl metabolite, a sulfoxide, an N-hydroxylated piperazine, and a benzylic alcohol, which was further oxidized to the corresponding benzoic acid [3-methyl-4-(2-piperazin-1-yl-phenysulfanyl)-benzoic acid (Lu AA34443)]. The formation of the 4-hydroxy-phenyl metabolite was catalyzed by CYP2D6 with some contribution from CYP2C9, whereas the formation of the sulfoxide was mediated by CYP3A4/5 and CYP2A6. CYP2C9 and CYP2C19 were the primary enzymes responsible for formation of the N-hydroxylated metabolite. The benzylic alcohol was formed by CYP2D6 only. The oxidation of the benzylic alcohol to the corresponding benzoic acid of Lu AA21004 was catalyzed by alcohol dehydrogenase and aldehyde dehydrogenase, with some contribution from aldehyde oxidase. CYP2D6 was also capable of catalyzing the formation of the benzoic acid of Lu AA21004; however, its overall contribution to this pathway was negligible. Enzyme kinetic parameters revealed that the rate-limiting step in the formation of the benzoic acid from Lu AA21004 is the formation of the corresponding alcohol. Thus, the intrinsic clearance (Vmax/Km) in HLM for metabolism of Lu AA21004 to the benzylic alcohol was 1.13 × 10−6 l · min−1 · mg−1, whereas the subsequent metabolism of the benzylic alcohol to the benzoic acid of Lu AA21004 is characterized by an intrinsic clearance (Vmax/Km) in S9 fraction of 922 × 10−6 l · min−1 · mg−1.

Palladium-Catalyzed Carbonylative Sonogashira Coupling of Aryl Bromides Using Near Stoichiometric Carbon Monoxide

A general procedure for the palladium-catalyzed carbonylative Sonogashira coupling of aryl bromides is reported, using near stoichiometric amounts of carbon monoxide. The method allows a broad substrate scope in moderate to excellent yields. The formed alkynone motive serves as a platform for synthesis of various heterocyclic structures, including pyrimidines. Furthermore, the presented strategy allows effective (13)C labeling.

From the selective serotonin transporter inhibitor citalopram to the selective norepinephrine transporter inhibitor talopram: synthesis and structure-activity relationship studies.

Citalopram and talopram are structurally closely related, but they have very distinct pharmacological profiles as selective inhibitors of the serotonin and norepinephrine transporters, respectively. A systematic structure-activity relationship study was performed, in which each of the four positions distinguishing the two compounds were varied. The inhibitory potencies of the resulting 16 compounds were tested at both serotonin and norepinephrine transporters. This showed that particularly two of the four positions are determinants for the biological activity.

Molecular determinants for selective recognition of antidepressants in the human serotonin and norepinephrine transporters

Inhibitors of the serotonin transporter (SERT) and norepinephrine transporter (NET) are widely used in the treatment of major depressive disorder. Although SERT/NET selectivity is a key determinant for the therapeutic properties of these drugs, the molecular determinants defining SERT/NET selectivity are poorly understood. In this study, the structural basis for selectivity of the SERT selective inhibitor citalopram and the structurally closely related NET selective inhibitor talopram is delineated. A systematic structure-activity relationship study allowed identification of the substituents that control activity and selectivity toward SERT and NET and revealed a common pattern showing that SERT and NET have opposite preference for the stereochemical configuration of these inhibitors. Mutational analysis of nonconserved SERT/NET residues within the central substrate binding site was performed to determine the molecular basis for inhibitor selectivity. Changing only five residues in NET to the complementary residues in SERT transferred a SERT-like affinity profile for R- and S-citalopram into NET, showing that the selectivity of these compounds is determined by amino acid differences in the central binding site of the transporters. In contrast, the activity of R- and S-talopram was largely unaffected by any mutations within the central substrate binding site of SERT and NET and in the outer vestibule of NET, suggesting that citalopram and talopram bind to distinct sites on SERT and NET. Together, these findings provide important insight into the molecular basis for SERT/NET selectivity of antidepressants, which can be used to guide rational development of unique transporter inhibitors with fine-tuned transporter selectivity.