Dopamine/serotonin receptor ligands. Part IV [1]: synthesis and pharmacology of novel 3-benzazecines and 3-benzazonines as potential 5-HT2A and dopamine receptor ligands

Advances in synthesis of novel annulated azecines and their unique pharmacological properties

Annulated azecines, mostly partially saturated benzo[d]azecine and dibenzo[c,g]azecine fusion isomers, constitute a unique class of alkaloids and nature-inspired azaheterocyclic compounds with interesting reactivity, physicochemical and biological properties. Due to difficulties associated with the synthesis of the benzazecine (or bioisosteric) scaffold they are not the focus of organic and medicinal chemists' consideration, whereas it is worth noting the range of their pharmacological activities and their potential application in medicinal chemistry. Herein, we reviewed the synthetic methodologies of arene-fused azecine derivatives known up to date and reported about the progress in disclosing their potential in drug discovery. Indeed, their conformational restriction or liberation drives their selectivity towards diverse biological targets, making them versatile scaffolds for developing drugs, including antipsychotic and anticancer drugs, but also small molecules with potential for anti-neurodegenerative treatments, as the recent literature shows.

P4O10/TfOH mediated domino condensation-cyclization of amines with diacids: a route to indolizidine alkaloids under catalyst- and solvent-free conditions

A domino condensation–cyclization method is developed to synthesize indolizidine alkaloids using a P₄O₁₀/TfOH reagent system without the employment of either a catalyst or solvent. The use of a few aliphatic and aromatic dicarboxylic acids is shown along with various primary amines. This method is suitable for synthesizing pyrrolo[2,1-a]isoquinolines, pyrido[2,1-a]isoquinolines, and isoindolo[1,2-a]isoquinolinones in excellent yields. When phthalic acid is used, a workup with either NaBH₄ or a saturated NaHCO₃ solution provided 12b-H or 12b-OH isoindolo[1,2-a]isoquinolinones, respectively.

A highly efficient and direct methodology for the construction of pyrrolo[2,1-a]isoquinoline, pyrido[2,1-a]isoquinoline, and 12b-H and 12b-OH isoindolo[2,1-a]isoquinolinone alkaloids from commercially available synthons is devised.

Frequency-dependency of the involvement of dopamine D1/D5 and beta-adrenergic receptors in hippocampal LTD triggered by locus coeruleus stimulation

Patterned stimulation of the locus coeruleus (LC, 100 Hz), in conjunction with test-pulse stimulation of hippocampal afferents, results in input-specific long-term depression (LTD) of synaptic plasticity in the hippocampus. Effects are long-lasting and have been described in Schaffer-collateral-CA1 and perforant path-dentate gyrus synapses in behaving rats. To what extent LC-mediated hippocampal LTD (LC-LTD) is frequency-dependent is unclear. Here, we report that LC-LTD can be triggered by LC stimulation with 2 and 5 Hz akin to tonic activity, 10 Hz equivalent to phasic activity, and 100 Hz akin to high-phasic activity in the dentate gyrus (DG) of freely behaving rats. LC-LTD at both 2 and 100 Hz can be significantly prevented by an NMDA receptor antagonist. The LC releases both noradrenaline (NA) and dopamine (DA) from its hippocampal terminals and may also trigger hippocampal DA release by activating the ventral tegmental area (VTA). Unclear is whether both neurotransmitters contribute equally to hippocampal LTD triggered by LC stimulation (LC-LTD). Both DA D1/D5 receptors (D1/D5R) and beta-adrenergic receptors (β-AR) are critically required for hippocampal LTD that is induced by patterned stimulation of hippocampal afferents, or is facilitated by spatial learning. We, therefore, explored to what extent these receptor subtypes mediate frequency-dependent hippocampal LC-LTD. LC-LTD elicited by 2, 5, and 10 Hz stimulation was unaffected by antagonism of β-AR with propranolol, whereas LC-LTD induced by these frequencies was prevented by D1/D5R-antagonism using SCH23390. By contrast, LC-LTD evoked at 100 Hz was prevented by β-AR-antagonism and only mildly affected by D1/D5R-antagonism. Taken together, these findings support that LC-LTD can be triggered by LC activity at a wide range of frequencies. Furthermore, the contribution of D1/D5R and β-AR to hippocampal LTD that is triggered by LC activity is frequency-dependent and suggests that D1/D5R may be involved in LC-mediated hippocampal tonus.

A concise synthesis of (E)-3-aryl-2,3,4,5-tetrahydro-1H-3-benzazonines by aryne induced [2,3] Stevens rearrangement of 1,2,3,4-tetrahydroisoquinolines

(E)-3-Aryl-2,3,4,5-tetrahydro-1H-3-benzazonines were prepared in moderate to good yields with excellent diastereoselectivity via aryne induced [2,3] Stevens rearrangement.

Synthetic cannabinoids: the multi-organ failure and metabolic derangements associated with getting high

Synthetic cannabinoids (SC), though not detected with routine urine toxicology screening, can cause severe metabolic derangements and widespread deleterious effects in multiple organ systems. The diversity of effects is related to the wide distribution of cannabinoid receptors in multiple organ systems. Both cannabinoid-receptor-mediated and non-receptor-mediated effects can result in severe cardiovascular, renal, and neurologic manifestations. We report the case of a 45-year-old African American male with ST-elevation myocardial infarction, subarachnoid hemorrhage, reversible cardiomyopathy, acute rhabdomyolysis, and severe metabolic derangement associated with the use of K2, an SC. Though each of these complications has been independently associated with SCs, the combination of these effects in a single patient has not been heretofore reported. This case demonstrates the range and severity of complications associated with the recreational use of SCs. Though now banned in the United States, use of systemic cannabinoids is still prevalent, especially among adolescents. Clinicians should be aware of their continued use and the potential for harm. To prevent delay in diagnosis, tests to screen for these substances should be made more readily available.

Synthesis and X-ray structural studies of a substituted 2,3,4,5-tetrahydro-1H-3-benzazonine and a 1,2,3,5-tetrahydro-4,3-benzoxazonine

Using a common 1-(1-phenylethenyl)-1,2,3,4-tetrahydroisoquinoline precursor to the required ylide or N-oxide intermediate, the Stevens [2,3] and analogous Meisenheimer [2,3] sigmatropic rearrangements have been applied to afford concise syntheses of phenyl -substituted representatives of each of the reduced 1H-3-benzazonine and 4,3-benzoxazonine systems, respectively. Single crystal X-ray structure determinations were employed to define the conformational characteristics for each ring type.

Novel 2,4-Diarylaminopyrimidine Analogues (DAAPalogues) Showing Potent c-Met/ALK Multikinase Inhibitory Activities

By repurposing a typical dopamine D1/D5 receptor agonist motif, C1-substituted-N3-benzazepine or benzazecine, into the classical RTK inhibitor 2,4-diaminopyrimidine skeleton, a series of new 2,4-diarylaminopyrimidine analogues (DAAPalogues) were developed. Compounds 7 and 8a were identified possessing high potency against both c-Met and ALK kinases. Compound 8a displayed appreciable antitumor efficacy at the dose of 1 mg/kg in the ALK-driven BF3/EML4-ALK xenograft mice model.

Inhibitory effects of dopamine on spinal synaptic transmission via dopamine D1-like receptors in neonatal rats

BACKGROUND AND PURPOSE

Dopamine released from the endings of descending dopaminergic nerve fibres in the spinal cord may be involved in modulating functions such as locomotion and nociception. Here, we examined the effects of dopamine on spinal synaptic transmissions in rats.

EXPERIMENTAL APPROACH

Spinal reflex potentials, monosynaptic reflex potential (MSR) and slow ventral root potential (sVRP), were measured in the isolated spinal cord of the neonatal rat. Dopamine release was measured by HPLC.

KEY RESULTS

Dopamine at lower concentrations (<1 µM) depressed sVRP, which is a C fibre-evoked polysynaptic response and believed to reflect nociceptive transmission. At higher concentrations (>1 µM), in addition to a potent sVRP depression, dopamine depolarized baseline potential and slightly depressed MSR. Depression of sVRP by dopamine was partially reversed by dopamine D(1) -like but not by D(2) -like receptor antagonists. SKF83959 and SKF81297, D(1) -like receptor agonists, and methamphetamine, an endogenous dopamine releaser, also caused the inhibition of sVRP. Methamphetamine also depressed MSR, which was inhibited by ketanserin, a 5-HT(2A/2C) receptor antagonist. Methamphetamine induced the release of dopamine and 5-HT from spinal cords, indicating that the release of endogenous dopamine and 5-HT depresses sVRP and MSR respectively.

CONCLUSION AND IMPLICATIONS

These results suggested that dopamine at lower concentrations preferentially inhibited sVRP, which is mediated via dopamine D(1) -like and other unidentified receptors. The dopamine-evoked depression is involved in modulating the spinal functions by the descending dopaminergic pathways.

Here today, gone tomorrow…and back again? A review of herbal marijuana alternatives (K2, Spice), synthetic cathinones (bath salts), kratom, Salvia divinorum, methoxetamine, and piperazines

Despite their widespread Internet availability and use, many of the new drugs of abuse remain unfamiliar to health care providers. The herbal marijuana alternatives, like K2 or Spice, are a group of herbal blends that contain a mixture of plant matter in addition to chemical grade synthetic cannabinoids. The synthetic cathinones, commonly called "bath salts," have resulted in nationwide emergency department visits for severe agitation, sympathomimetic toxicity, and death. Kratom, a plant product derived from Mitragyna speciosa Korth, has opioid-like effects, and has been used for the treatment of chronic pain and amelioration of opioid-withdrawal symptoms. Salvia divinorum is a hallucinogen with unique pharmacology that has therapeutic potential but has been banned in many states due to concerns regarding its psychiatric effects. Methoxetamine has recently become available via the Internet and is marked as "legal ketamine." Moreover, the piperazine derivatives, a class of amphetamine-like compounds that includes BZP and TMFPP, are making a resurgence as "legal Ecstasy." These psychoactives are available via the Internet, frequently legal, and often perceived as safe by the public. Unfortunately, these drugs often have adverse effects, which range from minimal to life-threatening. Health care providers must be familiar with these important new classes of drugs. This paper discusses the background, pharmacology, clinical effects, detection, and management of synthetic cannabinoid, synthetic cathinone, methoxetamine, and piperazine exposures.

The “New” Marijuana

Synthetic cannabinoid-induced toxicity is increasing in frequency across the US, with more than 1057 reported cases as of August 2010. There is a paucity of literature on synthetic cannabinoid toxicity; however, there are various reports of adverse effects including tachycardia, hypertension, tachypnea, chest pain, heart palpitations, hallucinations, racing thoughts, and seizures. While reports suggest that toxic symptoms last no longer than 3-4 hours, with no residual adverse effects in many cases, there is concern about serious acute and long-term toxicities. This article reviews the development, abuse, toxicity, treatment, and legal status of synthetic cannabinoids. It is important for health-care professionals to recognize and appropriately treat synthetic cannabinoid-induced toxicity.

The pyrrolo[2,1-a]isoquinoline alkaloids

The present chapter describes isolation, biogenetic proposals, and syntheses of the natural products 1-4 and 10-11 with a pyrrolo[2,1-a]-isoquinoline framework. Moreover, the syntheses of some structural analogs are discussed. The pyrrolo[2,1-a]isoquinolines are of interest due to their promising biological activities. For crispine A (1), many total syntheses have been reported and for trolline (3), only three. Only one total synthesis has been reported for each of the following natural products: peyoglutam (10), mescalotam (11), and the antitumor active crispine B (2). Some of the pyrrolo[2,1-a]isoquinoline alkaloids have not been synthesized yet. The following three tables summarize the synthetic efforts toward crispine A (1) (Table 1: racemic syntheses; Table 2: enantioselective syntheses) and trolline (3) (Table 3).

Novel fused pyrrole heterocyclic ring systems as structure analogs of LE 300: Synthesis and pharmacological evaluation as serotonin 5-HT(2A), dopamine and histamine H(1) receptor ligands

LE 300 represents a structurally novel type of antagonists acting preferentially at the dopamine D(1)/D(5 )receptors and the serotonin 5-HT(2A )receptor. This compound consists of a ten-membered central azecine ring fused to an indole ring on one side and a benzene moiety on the other side. To estimate the importance of the indole and / or phenyl moieties in this highly active benz-indolo-azecine, both rings were removed and replaced with a 1H-pyrrole counterpart. Accordingly, some new analogs of LE 300 namely, pyrrolo[2,3-g]indolizine, pyrrolo[3,2-a]quinolizine rings and their corresponding dimethylpyrrolo[2,3-d]azonine, and dimethylpyrrolo[2,3-d]azecine were synthesized to be evaluated for their activity at the 5-HT(2A) and dopamine D(1), D(2L), D(4), D(5) receptors in relation to LE 300. In addition, their activity at the H(1)-histamine receptors was also determined. The results suggested that the rigid pyrrolo[2,3-g]indolizine 7 and pyrrolo[3,2-a]quinolizine 8 analogs lacked biological activity in the adopted three bioassays. However, their corresponding flexible pyrrolo[2,3-d]azonine 11 and pyrrolo[2,3-d]azecine 12 derivatives revealed weak partial agonistic activity and weak antagonistic potency at the serotonin 5-HT(2A )and histamine H(1 )receptors, respectively. Meanwhile, they showed no affinity to any of the four utilized dopamine receptors. Variation in ring size did not contribute to a significant influence on the three tested bioactivities. Removal of the hydrophobic moiety (phenyl ring) and replacement of the indole moiety with a 1H-pyrrole counterpart led to a dramatic alteration in the profile of activity of such azecine-type compounds.

Attempts to Mimic Key Bond-Forming Events Associated with the Proposed Biogenesis of the Pentacyclic Lamellarins

The pyrrole-tethered veratroles 16 and 27 each engage in PIFA-induced oxidative cyclization reactions to give compounds 22 and 29, respectively, which incorporate a key tricyclic fragment associated with the title natural products. In contrast, the corresponding catechols 11 and 12 only produce polymeric materials on subjection to analogous reaction conditions. Efforts to study lactone ring formation by the oxidative cyclization of catechol 30 and veratrole 38 have been thwarted by an inability to prepare the former substrate and decomposition of the latter. The reported conversions 44 → 45 and 46 → 47 suggest that a C2-carboxy group attached to the pyrrole ring can ‘direct’ the oxidative cyclization of N-tethered aryl groups. The acquisition of compound 22 by the means described herein provides an adventitious and concise route to the racemic modification of the pyrrolo[2,1-a]isoquinoline alkaloid crispine A (52).

Dopamine/Serotonin Receptor Ligands. 10: SAR Studies on Azecine-type Dopamine Receptor Ligands by Functional Screening at Human Cloned D1, D2L, and D5 Receptors with a Microplate Reader Based Calcium Assay Lead to a Novel Potent D1/D5 Selective Antagonist

On the basis of the benz[d]indolo[2,3-g]azecine derivative 1 (LE300), structure-activity relations were investigated in order to identify the pharmacophore in this new class of ligands. Various structural modifications were performed and the inhibitory activities at human cloned D(1), D(2L), and D(5) receptors were measured by using a simple fluorescence microplate reader based calcium assay. Subsequently, the affinities of active compounds were estimated by radioligand binding experiments. Deleting one of the aromatic rings as well as replacing it by a phenyl moiety abolishes the inhibitory activities almost completely. Contraction of the 10-membered central ring decreases them significantly. The replacement of indole by thiophene or N-methylpyrrole reduces the inhibitory activity, whereas replacing the indole by benzene increases it. Finally, the hydroxylated dibenz[d,g]azecine derivative 11d (LE404) was found to be more active than the lead 1 in the functional calcium assay as well as in radioligand displacement experiments.

Dopamine/serotonin receptor ligands. Part VIII: the dopamine receptor antagonist LE300 - modelled and X-ray structure plus further pharmacological characterization, including serotonin receptor binding, biogenic amine transporter testing and in vivo testings

-LE300, a benz[d]indolo[2,3-g]azecine with nanomolar affinities to the hD(1) receptor family, has been further pharmacologically characterized and its modelled structure was compared to its X-ray structure in order to explain NMR data, that was not in accordance to the X-ray structure. Moderate affinity at the hD(3) receptor was determined, nanomolar affinities were found at the 5-HT(2A) and 5-HT(2C) receptors, micromolar affinity at the 5-HT(1A) receptor using binding assays. Functional studies indicate moderate antagonist activity at the 5-HT(2A) site. No activity was found at dopamine, serotonin and norepinephrine transporters. These results suggested the use of LE300 for cocaine addiction treatment. High activities were found using in vivo testing: LE300 suppressed spontaneous locomotor activity with an ID(50) of 1.24 mg/kg and attenuated locomotor activity induced by 20 mg/kg cocaine with an AD(50) of 1.50 mg/kg. It failed to substitute for the discriminative stimulus effects produced by cocaine.

A New Entry of Nucleophiles in Rhodium-Catalyzed Asymmetric 1,4-Addition Reactions: Addition of Organozinc Reagents for the Synthesis of 2-Aryl-4-piperidones

A rhodium-catalyzed asymmetric 1,4-addition reaction has been applied to the synthesis of 2-aryl-4-piperidones. While other conventional nucleophiles fail, organozinc reagents have been successfully utilized for the construction of these useful compounds in very good yield and enantiomeric excess.