Tuning the activity of known drugs via the introduction of halogen atoms, a case study of SERT ligands - Fluoxetine and fluvoxamine.

The selective serotonin reuptake inhibitors (SSRIs), acting at the serotonin transporter (SERT), are one of the most widely prescribed antidepressant medications. All five approved SSRIs possess either fluorine or chlorine atoms, and there is a limited number of reports describing their analogs with heavier halogens, i.e., bromine and iodine. To elucidate the role of halogen atoms in the binding of SSRIs to SERT, we designed a series of 22 fluoxetine and fluvoxamine analogs substituted with fluorine, chlorine, bromine, and iodine atoms, differently arranged on the phenyl ring. The obtained biological activity data, supported by a thorough in silico binding mode analysis, allowed the identification of two partners for halogen bond interactions: the backbone carbonyl oxygen atoms of E493 and T497. Additionally, compounds with heavier halogen atoms were found to bind with the SERT via a distinctly different binding mode, a result not presented elsewhere. The subsequent analysis of the prepared XSAR sets showed that E493 and T497 participated in the largest number of formed halogen bonds. The XSAR library analysis led to the synthesis of two of the most active compounds (3,4-diCl-fluoxetine 42, SERT Ki = 5 nM and 3,4-diCl-fluvoxamine 46, SERT Ki = 9 nM, fluoxetine SERT Ki = 31 nM, fluvoxamine SERT Ki = 458 nM). We present an example of the successful use of a rational methodology to analyze binding and design more active compounds by halogen atom introduction. 'XSAR library analysis', a new tool in medicinal chemistry, was instrumental in identifying optimal halogen atom substitution.

Synthesis of Some Novel Thiadiazole Derivative Compounds and Screening Their Antidepressant-Like Activities.

Novel thiadiazole derivatives were synthesized through the reaction of acetylated 2-aminothiadiazole and piperazine derivatives. The chemical structures of the compounds were clarified by Infrared Spectroscopy (IR), ¹H Nuclear Magnetic Resonance Spectroscopy (¹H-NMR), 13C Nuclear Magnetic Resonance Spectroscopy (13C-NMR) and Electronspray Ionisation Mass Spectroscopy (ESI-MS) spectroscopic methods. Antidepressant-like activities were evaluated by the tail-suspension (TST) and modified forced swimming (MFST) methods. Besides, possible influence of the test compounds on motor activities of the animals were examined by activity cage tests. In the TST, administration of the compounds 2c, 2d, 2e, 2f, 2g and 2h significantly decreased the immobility time of mice regarding the control values. Further, in the MFST, the same compounds reduced the total number of immobility behaviors while increasing swimming performance. However, no change was observed in the total number of climbing behaviors. These data suggested that compounds 2c, 2d, 2e, 2f, 2g and 2h possess notable antidepressant-like activities. Reference drug fluoxetine (10 mg/kg) was also exhibited its antidepressant activity, as expected. No significant difference was seen between the locomotor activity values of the test groups signifying that observed antidepressant-like activities are specific. Theoretical calculation of absorption, distribution, metabolism, excretion (ADME) properties for the obtained compounds were performed and obtained data supported the antidepressant-like potential of these novel thiadiazole derivatives.

Synthesis of (18) F-Difluoromethylarenes from Aryl (Pseudo) Halides.

A general method for the synthesis of [(18) F]difluoromethylarenes from [(18) F]fluoride for radiopharmaceutical discovery is reported. The method is practical, operationally simple, tolerates a wide scope of functional groups, and enables the labeling of a variety of arenes and heteroarenes with radiochemical yields (RCYs, not decay-corrected) from 10 to 60 %. The (18) F-fluorination precursors are readily prepared from aryl chlorides, bromides, iodides, and triflates. Seven (18) F-difluoromethylarene drug analogues and radiopharmaceuticals including Claritin, fluoxetine (Prozac), and [(18) F]DAA1106 were synthesized to show the potential of the method for applications in PET radiopharmaceutical design.

Remote Hydroxylation through Radical Translocation and Polar Crossover.

Mild conditions are reported for the hydroxylation of aliphatic C-H bonds through radical translocation, oxidation to carbocation, and nucleophilic trapping with H2O. This remote functionalization employs fac-[Ir(ppy)3] together with Tz(o) sulfonate esters and sulfonamides to facilitate the site-selective replacement of relatively inert C-H bonds with the more synthetically useful C-OH group. The hydroxylation of a range of substrates and the methoxylation of two substrates through 1,6- and 1,7-hydrogen-atom transfer are demonstrated. In addition, a synthesis of the antidepressant fluoxetine using remote hydroxylation as a key step is presented.

ZnCl2 -promoted asymmetric hydrogenation of ß-secondary-amino ketones catalyzed by a P-chiral Rh-bisphosphine complex.

A new catalytic system has been developed for the asymmetric hydrogenation of ß-secondary-amino ketones using a highly efficient P-chiral bisphosphine-rhodium complex in combination with ZnCl2 as the activator of the catalyst. The chiral γ-secondary-amino alcohols were obtained in 90-94 % yields, 90-99 % enantioselectivities, and with high turnover numbers (up to 2000 S/C; S/C=substrate/catalyst ratio). A mechanism for the promoting effect of ZnCl2 on the catalytic system has been proposed on the basis of NMR spectroscopy and HRMS studies. This method was successfully applied to the asymmetric syntheses of three important drugs, (S)-duloxetine, (R)-fluoxetine, and (R)-atomoxetine, in high yields and with excellent enantioselectivities.

Copper-catalysed selective hydroamination reactions of alkynes.

The development of selective reactions that utilize easily available and abundant precursors for the efficient synthesis of amines is a long-standing goal of chemical research. Despite the centrality of amines in a number of important research areas, including medicinal chemistry, total synthesis and materials science, a general, selective and step-efficient synthesis of amines is still needed. Here, we describe a set of mild catalytic conditions utilizing a single copper-based catalyst that enables the direct preparation of three distinct and important amine classes (enamines, α-chiral branched alkylamines and linear alkylamines) from readily available alkyne starting materials with high levels of chemo-, regio- and stereoselectivity. This methodology was applied to the asymmetric synthesis of rivastigmine and the formal synthesis of several other pharmaceutical agents, including duloxetine, atomoxetine, fluoxetine and tolterodine.

Total synthesis of fluoxetine and duloxetine through an in situ imine formation/borylation/transimination and reduction approach.

We report efficient, catalytic, asymmetric total syntheses of both (R)-fluoxetine and (S)-duloxetine from α,ß-unsaturated aldehydes conducting five sequential one-pot steps (imine formation/copper mediated ß-borylation/transimination/reduction/oxidation) followed by the specific ether group formation which deliver the desired products (R)-fluoxetine in 45% yield (96% ee) and (S)-duloxetine in 47% yield (94% ee).

Copper(II)-catalyzed enantioselective hydrosilylation of halo-substituted alkyl aryl and heteroaryl ketones: asymmetric synthesis of (R)-fluoxetine and (S)-duloxetine.

A set of reaction conditions has been established to facilitate the non-precious copper-catalyzed enantioselective hydrosilylation of a number of structurally diverse ß-, γ- or ε-halo-substituted alkyl aryl ketones and α-, ß- or γ-halo-substituted alkyl heteroaryl ketones under air to afford a broad spectrum of halo alcohols in high yields and good to excellent enantioselectivities (up to 99% ee). The developed procedure has been successfully applied to the asymmetric synthesis of antidepressant drugs (R)-fluoxetine and (S)-duloxetine, which highlighted its synthetic utility.

Candida tenuis xylose reductase catalyzed reduction of aryl ketones for enantioselective synthesis of active oxetine derivatives.

Candida tenuis xylose reductase shows high catalytic efficiencies in carbonyl reduction of acetophenone and 1-phenyl-1-propanone derivatives. The quite low substrate solubility in aqueous buffer systems is circumvented by addition of methanol or by two-phase solvent systems. In the latter, methanol improves the substrate phase transfer as solvent mediator and leads to reasonable space/time yields. Resulting enantiomerically pure chiral alcohols are key intermediates for synthesis of active pharmaceutical ingredients. (R)-Atomoxetine is exemplarily synthesized in four steps, and the further use for generation of other oxetine derivatives and a polo-like kinase 1 inhibitor are discussed.

Reversal of selectivity in acetate aldol reactions of N-acetyl-(S)-4-isopropyl-1-[(R)-1-phenylethyl]imidazolidin-2-one.

Synergistic effects of the exo- and endocyclic chiral centers of an imidazolidinone-based auxiliary were investigated in the perspective of acetate aldol reactions. The reversal in diastereoselectivity was accomplished by lithium and titanium enolate reactions, which proceed through proposed open and closed transitions states, respectively. The aldol adducts were used in the stereoselective synthesis of fluoxetine.

Preparation of fluoxetine by multiple flow processing steps.

Microflow technology is established as a modern and fashionable tool in synthetic organic chemistry, bringing great improvement and potential, on account of a series of advantages over flask methods. The study presented here focuses on the application of flow chemistry process in performing an efficient multiple step syntheses of (±)-fluoxetine as an alternative to conventional synthetic methods, and one of the few examples of total synthesis accomplished by flow technique.

Gamma-aminobutyric acid amides of nortriptyline and fluoxetine display improved pain suppressing activity.

The GABA amides of the antidepressants nortriptyline and fluoxetine, 1 and 2, were compared to their respective parent compounds in rodent models of pain. The amides significantly reduced early nociceptive and late inflammatory responses compared to nortriptyline or fluoxetine, where 1 exhibited overall better efficacy than 2. Amide 1 was most efficacious in lowering cytokine secretion, edema and hyperalgesia induced by formalin and lambda-carrageenan, respectively. Thus, 1 is a promising candidate for the treatment of pain.

Synthesis of some tropane derivatives of anticipated activity on the reuptake of norepinephrine and/or serotonin.

A variety of tropane derivatives 14a-g were prepared via the reaction of the alcohol analogs 12a and 12b with substituted fluorobenzenes 13a-f. The prepared compounds were tested for their activity and selectivity toward the norepinephrine transporter (NET) and serotonin transporter (SERT) using yohimbine-induced mortality and 5-hydroxytryptophan-induced neurotoxicity in mice, respectively. All the tested compounds were found to be NE and 5-HT reuptake inhibitors except 14d which exhibited selective 5-HT reuptake inhibition activity.

Synthesis and carbon-11 labeling of (R)- and (S)-thionisoxetine, norepinephrine reuptake inhibitors, potential radioligands for positron emission tomography.

Standards and des-methyl precursors of (R)- and (S)-thionisoxetine, potent and selective norepinephrine reuptake inhibitors, were synthesized and radiolabeled with carbon-11. Both enantiomers of the N-methyl-3-(2-thiomethylphenoxy)-3-phenylpropanamine and the 3-(2-thiomethylphenoxy)-3-phenylpropylamine were obtained via multi-step syntheses, while the radiosyntheses were carried out using [11C]CH3I. The radiochemical yields were 26%, decay corrected and the specific radioactivity ranging from 2 to 3 Ci/micromol. The HPLC analyses were performed using a chiral column: during the radiolabeling, no racemization occurred and the isomers were synthesized with high enantiomeric purity.

Vasoactive properties of antidepressant N-alkyl derivatives.

Hypotension is a principal side effect of antidepressant therapy. In addition to serotonin and noradrenalin reuptake inhibition, some antidepressants have shown ion channel interactions which are thought to be related to the vascular effects of these agents. Methylation of the pharmacophore has shown to change the pharmacological properties of a variety of compounds. The purpose of this work was to evaluate whether methylation of the amino group of imipramine (TCA's) and fluoxetine (SSRI) could change their vasodilator properties. N-methyl imipramine (NMI), N-methyl fluoxetine and (NMF) N-N dimethyl fluoxetine (NNDF) were synthesized and compared with desipramine (DES), imipramine (IMI) and fluoxetine (F) in their ability to relax rat aortic rings pre-contracted with 80mM KCl using an isolated bath preparation. Drugs were evaluated in thoracic aorta rings with and without endothelium. All compounds displayed a vasorelaxant effect. Endothelium-denuded aortic rings showed an increased relaxant response for IMI and derivatives compared with endothelium-intact vessels, while no endothelium-dependent effect was observed with F and its methyl derivatives. Maximal relaxant potency was displayed by dimethylated derivatives (IMI and NMF), while NMI in the TCA series and NNDF in the SSRI series (both with 3 methyl groups), had the least potency to relax either preparation. Endothelium plays an important role inhibiting the vasodilatation induced by IMI and its derivatives. Vascular relaxation is increased in the compounds tested with 2 methyl groups in their structure, while the presence of 3 methyl groups (positive charge) importantly reduced the relaxant potency.

Preparation of polymer-supported Ru-TsDPEN catalysts and use for enantioselective synthesis of (S)-fluoxetine.

Polymer-supported chiral ligands 9 and 17 were prepared based on Noyori's (1S,2S)- or (1R,2R)-N-(p-tolylsulfonyl)-1,2-diphenylethylenediamine. The combination with [RuCl2(p-cymene)]2 has been shown to exhibit high activities and enantioselectivities for heterogeneous asymmetric transfer hydrogenation of aromatic ketones (19a-c) with formic acid-triethylamine azeotrope as the hydrogen donor, whereby affording the respective optically active alcohols 20a-c, the key precursors of chiral fluoxetine. As exemplified by ligand 17 for substrate 19c, the catalysts can be recovered and reused in three consecutive runs with no significant decline in enantioselectivity. The procedure avoids the plausible contamination of fluoxetine by the toxic transition metal species.

Synthesis and C-11 labeling of three potent norepinephrine transporter selective ligands ((R)-nisoxetine, lortalamine, and oxaprotiline) for comparative PET studies in baboons.

Three potent antidepressants, (R)-nisoxetine, lortalamine, and oxaprotiline, with high affinity and high selectivity for the norepinephrine transporter (NET) were synthesized and radiolabeled with C-11 via [11C]methylation. The reference compounds and their corresponding normethyl precursors were synthesized via multi-step synthetic approaches. The radiochemical syntheses were performed by simple alkylation of the corresponding normethyl precursors with no-carrier-added [11C]CH3I in DMF. After HPLC purification, (R)-[N-11CH3]nisoxetine, [11C]lortalamine, and [11C]oxaprotiline were obtained in 63-97% radiochemical yields, whereas (R)-[O-11CH3]nisoxetine was obtained in 23-29% radiochemical yields due to substantial formation of the undesired N-[11C]methylated byproduct (64-70%). These C-11 labeled tracers allowed us to carry out comparative studies of NET in baboons with positron emission tomography (PET) and evaluate their potential as PET tracers for imaging brain NET.

Imidazole analogues of fluoxetine, a novel class of anti-Candida agents.

Imidazole analogues of fluoxetine have been obtained by replacing the methylamino terminus of aminopropane chain with the imidazole ring. The newly designed imidazoles showed potent anti-Candida activity, superior to those of miconazole and other antifungal agents of clinical interest. 1-(4-Chlorophenyl)-1-(2,4-dichlorophenoxy)-3-(1H-imidazol-1-yl)propane (16), the most active among test imidazoles, was about 2-fold more active and as much less cytotoxic than miconazole. High increase of activity was observed with methyl, nitro, fluorine, and chlorine (Cl > F > CH(3) > NO(2) > CF(3)).

Evaluation of radioiodinated (R)-N-methyl-3-(2-iodophenoxy)-3-phenylpropanamine as a ligand for brain norepinephrine transporter imaging.

(R)-N-methyl-3-(2-iodophenoxy)-3-phenylpropanamine (MIPP) was evaluated as a radiopharmaceutical for investigating brain norepinephrine transporters (NET) by single photon emission computed tomography (SPECT). (R)-[(125)I]MIPP was synthesized with high radiochemical yield (60%) and high radiochemical purity (> 98%). In biodistribution experiments, (R)-[(125)I]MIPP indicated that the brain uptake of (R)-[(125)I]MIPP was rapid and retained, and that the regional cerebral distribution was consistent with the density of NET. Moreover, the administration of desipramine decreased the accumulation of (R)-[(125)I]MIPP in the brain. HPLC analysis of brain radioactivity showed that more than 90% was intact (R)-MIPP. These results suggested that (R)-[(123)I]MIPP is a potential radiopharmaceutical for imaging brain NET.