Identification of novel β-lactams and pyrrolidinone derivatives as selective Histamine-3 receptor (H3R) modulators as possible anti-obesity agents

Desymmetric [3+3] Cyclization of p-Quinamines for the Synthesis of 1,2,4-Oxadiazines and Hydroquinoxalines

General and efficient strategies for highly diastereoselective synthesis of divergent heterocyclic scaffolds through desymmetric [3+3] cycloaddition of p-quinamines with 1,3-dipole surrogates hydroximoyl halides and α-halohydroxamates have been developed. This synthetic protocol provided a variety of heterocyclic architectures containing 1,2,4-oxadiazine and hydroquinoxaline skeletons in good yields with a wide substrate scope.

Solvent-free synthesis and in-silico molecular docking study of (E)-3-(β-C-glycosylmethylidene)-N-aryl/alkyl succinimides

Globally, human papillomavirus (HPV) infection is the leading cause of mortality associated with cervical cancer, oral cancer (oropharyngeal), and head and neck squamous cell carcinoma (HNSCC). It is essential to explore anti-cancer drugs against life-threatening HPV infections. Aiming to search for potentially better anticancer agents, a small library of β-C-glycosylated methylidene succinimides have been synthesized under bulk and mechanical grinding conditions using the Wittig olefination reaction. Thus, the reaction of different 2,3,4,6-tetra-O-benzyl-C-glycosyl aldehydes with N-aryl/alkyl maleimides in the presence of PPh3 at 25 °C under bulk and mechanical grinding conditions results in the formation of stereochemically defined (E)-3-(2,3,4,6-tetra-O-benzyl-C-glycosylmethylidene)-N-alkyl/phenyl succinimides, which upon debenzylation with 1 M BCl3 in DCM at -78 °C lead to the synthesis of (E)-3-(C-glycosylmethylidene)-N-alkyl/phenyl succinimides in good to excellent yields. The developed methodology is efficient and environmentally benign because there is no use of organic solvents, and the products are obtained in a stereochemically defined form and in high yields. The aqueous solubility of all synthesized β-C-glycosylated methylidene succinimides makes them potential candidates for the evaluation of their different biological activities. In the present work, the synthesized glycosylated alkylidine succinimides were subjected to an in-silico molecular docking study against the E6 oncoprotein of high-risk type HPV16, which is responsible for the inactivation of the tumor suppressor p53 protein. Analysis of the molecular docking data revealed that the synthesized compounds are effective inhibitors of HPV infection, which is the cause of oral, head and neck, and cervical cancer. In comparison with the positive control 5-FU, an anti-cancer drug used in chemotherapy, more than fifteen compounds were found to be better E6 protein inhibitors.

Palladium(II)-Catalyzed Decarboxylative Difunctionalization of Alkynoic Acids To Access (E)-β-Sulfonylacrylamides and DFT Study

A palladium(II)-catalyzed regio- and stereoselective difunctionalization of alkynoic acids has been achieved using sodium sulfinates and isocyanides to synthesize (E)-β-sulfonylacrylamides. The reaction proceeds via decarboxylative isocyanide addition, followed by sulfonylation. This three-component process works well with aromatic, heteroaromatic, and aliphatic alkynoic acids with good functional group tolerance and excellent regio- and stereoselectivity. DFT calculations were carried out to explain the reaction mechanism and the stereoselective formation of (E)-β-sulfonylacrylamides.

Synthesis of sulfur-containing benzo[b]pyrrolo[2,1-c][1,4]oxazine-3,9-diones: blue light promoted radical cyclization process

The selective and controllable construction of spio-tricyclic skeletons through visible light promoted radical cyclization still remains challenging. Herein, a general and convenient protocol for the blue light-promoted radical-mediated cascade spiro-cyclization/Michael addition of N-arylpropiolamides with thiophenols under metal-free conditions was developed. In this protocol, commercially available hydrochloric acid was employed as the cheap promoter and air as the sustainable oxidant. In addition, many functional groups tolerate the reaction conditions and produce a series of sulfur-containing benzo[b]pyrrolo[2,1-c][1,4]oxazine-3,9-diones.

Rapid access to C2-quaternary 3-methyleneindolines via base-mediated post-Ugi Conia-ene cyclization

Highly efficient synthesis of diverse 2,2-disubstituted 3-methyleneindoline derivatives through a one-pot base-promoted post-Ugi 5-exo-dig "Conia-ene"-type cyclization has been disclosed. The mechanism study indicates that an intramolecular hydrogen bond may play a vital role in this process. The antiproliferative evaluation of cancer cell lines reveals that this protocol provides practical use in the green synthesis of bioactive compound libraries.

Tandem Synthesis of 2-Azaspiro[4.5]deca-1,6,9-trien-8-ones Based on Tf2O-Promoted Activation of N-(2-Propyn-1-yl) Amides

Structurally novel 2-azaspiro[4.5]deca-1,6,9-trien-8-ones were synthesized from N-(2-propyn-1-yl) amides and 1,3,5-trimethoxybenzenes by a tandem method consisting of a Tf₂O-promoted amide activation and a TfOH-promoted Friedel-Crafts ipso-cyclization. The method offered the first example of using N-(2-propyn-1-yl) amides as substrates in both Tf₂O-promoted secondary amide activation and the synthesis of azaspiro[4.5]deca-6,9-diene-8-ones.

SAR exploration of the non-imidazole histamine H3 receptor ligand ZEL-H16 reveals potent inverse agonism

Histamine H₃ receptor (H₃ R) agonists without an imidazole moiety remain very scarce. Of these, ZEL-H16 (1) has been reported previously as a high-affinity non-imidazole H₃ R (partial) agonist. Our structure-activity relationship analysis using derivatives of 1 identified both basic moieties as key interaction motifs and the distance of these from the central core as a determinant for H₃ R affinity. However, in spite of the reported H₃ R (partial) agonism, in our hands, 1 acts as an inverse agonist for Gα_i signaling in a CRE-luciferase reporter gene assay and using an H₃ R conformational sensor. Inverse agonism was also observed for all of the synthesized derivatives of 1. Docking studies and molecular dynamics simulations suggest ionic interactions/hydrogen bonds to H₃ R residues D114^3.32 and E206^5.46 as essential interaction points.

Synthesis of Spiro[5.5]trienones- and Spiro[4.5]trienones-Fused Selenocyanates via Electrophilic Selenocyanogen Cyclization and Dearomative Spirocyclization

A practical strategy for the synthesis of spiro[5.5]trienones-fused selenocyanates and spiro[4.5]trienones-fused selenocyanates through electrophilic selenocyanogen cyclization and dearomative spirocyclization is reported. This approach was conducted under mild conditions with broad substrate scope and good functional group tolerance. The utility of this procedure is exhibited in the late-stage functionalization of nature product and drug molecules.

Copper(II)-catalyzed oxidative ipso-annulation of N-arylpropiolamides and biaryl ynones with 1,3-diketones: construction of diketoalkyl spiro-trienones

An unprecedented copper-catalyzed ipso-annulation reaction of N-(p-methoxyaryl)propiolamides with 1,3-diketones has been developed, which enables the assembly of diketoalkylated spiro[4.5]trienones involving oxidative dearomatization in the presence of ammonium persulfate [(NH₄)₂S₂O₈] as the oxidant. This protocol was extended to biaryl ynones, efficiently affording the diketoalkylated spiro[5.5]trienones in good yields. The significance of the diketoalkyl functionality has been illustrated by further transformation into 3-pyrazoyl spiro-trienone, a structurally unique motif.

Discovery of 2,3-dihydro-1H-pyrrolo[3,4-b]quinolin-1-one derivatives as possible antileishmanial agents

A series of uniquely functionalized 2,3,-dihydro-1H-pyyrolo[3,4-b]quinolin-1-one derivatives were synthesized in one to two steps by utilizing a post-Ugi modification strategy and were evaluated for antileishmanial efficacy against visceral leishmaniasis (VL). Among the library compounds, compound 5m exhibited potential in vitro antileishmanial activity (CC50 = 65.11 μM, SI = 7.79, anti-amastigote IC50 = 8.36 μM). In vivo antileishmanial evaluation of 5m demonstrated 56.2% inhibition in liver and 61.1% inhibition in spleen parasite burden in infected Balb/c mice (12.5 mg kg-1, i.p.). In vitro pharmacokinetic study ascertained the stability of 5m in both simulated gastric fluid and simulated intestinal fluid. All the active compounds passed the PAINS filter and showed no toxicity in in silico predictions.

Metal-free dearomatization reactions of naphthol-ynamides for the divergent and enantioselective synthesis of azaspirocycles

An efficient Brønsted acid (BA) catalyzed intramolecular dearomatization cyclization of naphthol-ynamides has been developed, enabling the practical and divergent synthesis of two azaspirocycles in high yields.

Targeting Histamine and Histamine Receptors for the Precise Regulation of Feeding

Histamine has long been accepted as an anorexigenic agent. However, lines of evidence have suggested that the roles of histamine in feeding behaviors are much more complex than previously thought, being involved in satiety, satiation, feeding motivation, feeding circadian rhythm, and taste perception and memory. The functional diversity of histamine makes it a viable target for clinical management of obesity and other feeding-related disorders. Here, we update the current knowledge about the functions of histamine in feeding and summarize the underlying molecular and neural circuit mechanisms. Finally, we review the main clinical studies about the impacts of histamine-related compounds on weight control and discuss insights into future research on the roles of histamine in feeding. Despite the recent progress in histamine research, the histaminergic feeding circuits are poorly understood, and it is also worth verifying the functions of histamine receptors in a more spatiotemporally specific manner.

Palladium-catalyzed difunctionalization/dearomatization of N-benzylacrylamides with α-carbonyl alkyl bromides: facile access to azaspirocyclohexadienones

An efficient palladium-catalyzed difunctionalization/dearomatization of N-benzylacrylamides with α-carbonyl alkyl bromides as alkyl radical precursors has been described. Various α-carbonyl alkyl bromides, including α-bromoalkyl esters and ketones, reacted smoothly to provide important azaspirocyclohexadienones in moderate to excellent yields. In addition, mechanistic studies suggested that the reaction proceeded via a radical pathway.

Synthesis of Arylidene-β-lactams via exo-Selective Matsuda-Heck Arylation of Methylene-β-lactams

exo-Methylene-β-lactams were synthesized in two steps from commercially available 3-bromo-2-(bromomethyl)propionic acid and reacted with arene diazonium salts in a Heck-type arylation in the presence of catalytic amounts of Pd(OAc)₂ under ligand-free conditions. The products, arylidene-β-lactams, were obtained in high yields as single isomers. The β-hydride elimination step of the Pd-catalyzed coupling reaction proceeds with high exo-regioselectivity and E-stereoselectivity. With aryl iodides, triflates, or bromides, the coupling products were isolated only in low yields, due to extensive decomposition of the starting material at elevated temperatures. This underlines that arene diazonium salts can be superior arylating reagents in Heck-type reactions and yield coupling products in synthetically useful yields and selectivities when conventional conditions fail.

Structural modifications in the distal, regulatory region of histamine H3 receptor antagonists leading to the identification of a potent anti-obesity agent

A series of 4-pyridylpiperazine derivatives with varying regulatory region substituents proved to be potent histamine H3 receptor (H3R) ligands in the nanomolar concentration range. The most influential modification that affected the affinity toward the H3R appeared by introducing electron-withdrawing moieties into the distal aromatic ring. In order to finally discuss the influence of the characteristic 4-pyridylpiperazine moiety on H3R affinity, two Ciproxifan analogues 2 and 3 with a slight modification in their basic part were obtained. The replacement of piperazine in 3 with piperidine in compound 2, led to slightly reduced affinity towards the H3R (Ki = 3.17 and 7.70 nM, respectively). In fact, 3 showed the highest antagonistic properties among all compounds in this series, hence affirming our previous assumptions, that the 4-pyridylpiperazine moiety is the key element for suitable interaction with the human histamine H3 receptor. While its structural replacement to piperidine is also tolerated for H3R binding, the heteroaromatic 4-pyridyl moiety seems to be essential for proper ligand-receptor interaction. The putative protein-ligand interactions responsible for their high affinity were demonstrated using molecular modeling techniques. Furthermore, selectivity, intrinsic activity at the H3R, as well as drug-like properties of ligands were evaluated using in vitro methods. Moreover, pharmacological in vivo test results of compound 9 (structural analogue of Abbott's A-331440) clearly indicate that it may affect the amount of calories consumed, thus act as an anorectic compound.

Visible-light-induced metal-free cascade cyclization of N-arylpropiolamides to 3-phosphorylated, trifluoromethylated and thiocyanated azaspiro[4.5]trienones

Photocatalytic strategies for the preparation of 3-functionalized azaspiro[4.5]trienones via a radical-initiated cascade annulation reaction was developed.

Research progress in biological activities of succinimide derivatives

Succinimides are well recognized heterocyclic compounds in drug discovery which produce diverse therapeutically related applications in pharmacological practices. Researches in medicinal chemistry field have isolated and synthesized succinimide derivatives with multiple medicinal properties including anticonvulsant, anti-inflammatory, antitumor and antimicrobial agents, 5-HT receptor ligands and enzyme inhibitors. Simultaneously, SAR (Structure-Activity Relationship) analysis has been gradually possessed, along with a great deal of derivatives have been derived for potential targets. In this article, we comprehensively summarize the biological activities and SAR for succinimide derivatives, along with the featuring bioactive molecules reported in patents, wishing to provide an overall retrospect and prospect on the succinimide analogues.

[3 + 2]-Dipolar Cycloaddition of Aldehyde-Tethered Alkynamides and Trimethylsilyl Amino Esters: A Gateway to Uniquely Functionalized Polycyclic N-Heterocycles via Post-Ugi Functionalization

An efficient method for the generation of uniquely functionalized pyrrolo-pyrrolizinones, pyrido-pyrrolizinones, and azepino-pyrrolizinones via [3 + 2]-dipolar cycloaddition is described. The method involves the synthesis of tethered alkynamides using Ugi condensation and oxidation that were subsequently subjected to a dipolar cycloaddition reaction with trimethylsilyl amino esters. Further transformations to demonstrate the utility of these scaffolds were also investigated.

Synthesis of β- and γ-lactam fused dihydropyrazinones from Ugi adducts via a sequential ring construction strategy

A modular approach for the construction of β- and γ-lactam fused dihydropyrazinones from the readily available Ugi adducts has been described. The sequential construction of rings through base-mediated cycloisomerization followed by acid-mediated cyclization yielded β-lactam fused dihydropyrazinones. However, the Ugi-derived dihydropyrazinones afforded γ-lactam fused dihydropyrazinones under base-mediated cycloisomerization. The regioselectivity in the cycloisomerization reactions is explained on the basis of ring-strain. Substrate scope, limitations and mechanistic investigations through DFT-calculations have been explored.

Construction of Highly Functionalized Piperazinones via Post-Ugi Cyclization and Diastereoselective Nucleophilic Addition

A novel method for the generation of uniquely functionalized piperazinones by utilizing post-Ugi functionalization is described. The method involves an Ugi reaction with aminoacetaldehyde dimethyl acetal, followed by acid-mediated cyclization to generate the iminium precursor that was subjected to nucleophilic addition in a diastereoselective manner. The method was also employed to synthesize trans-dragmacidine C and praziquantel-like molecules.

Novel pyrrolidinone derivative lacks claimed histamine H3 receptor stimulation in receptor binding and functional studies

Since the discovery and early characterization of the histamine H₃ receptor (H₃R) in the 1980's, predominantly imidazole-based agonists were presented to the scientific community such as N^α-methylhistamine (N^α-MeHA) or (R)-α-methylhistamine ((R)α-MeHA). Whereas therapeutic applications have been prompted for H₃R agonists such as treatment of pain, asthma and obesity, several drawbacks associated with imidazole-containing ligands makes the search for new agonists for this receptor demanding. Accordingly, high interest arose after publication of several pyrrolidindione-based, highly affine H₃R agonists within this journal that avoid the imidazole moiety and thus, presenting a novel type of potential pharmacophores (Ghoshal, Anirban et al., 2018). In our present study performed in two independent laboratories, we further evaluated the exposed lead-compound (EC₅₀ = 0.1 nM) of the previous research project with regards to pharmacological behavior at H₃R. Thereby, no binding affinity was observed in neither [³H]N^α-MeHA nor bodilisant displacement assays that contradicts the previously published activity. Additional functional exploration employing GTPγ[³⁵S], cAMP-accumulation assay and cAMP response element (CRE)-driven reporter gene assays exhibited slight partial agonist properties of such pyrrolidindiones but acting apart from the reported concentration range. We conclude, that the previously reported actions of such pyrrolidindiones result from an overestimation based on the method of measurement and thus, we cast doubt on the new pharmacophores with H₃R agonist activity.

4-(3-Aminoazetidin-1-yl)pyrimidin-2-amines as High-Affinity Non-imidazole Histamine H3 Receptor Agonists with in Vivo Central Nervous System Activity

Despite the high diversity of histamine H3 receptor (H3R) antagonist/inverse agonist structures, partial or full H3R agonists have typically been imidazole derivatives. An in-house screening campaign intriguingly afforded the non-imidazole 4-(3-azetidin-1-yl)pyrimidin-2-amine 11b as a partial H3R agonist. Here, the design, synthesis, and structure-activity relationships of 11b analogues are described. This series yields several non-imidazole full agonists with potencies varying with the alkyl substitution pattern on the basic amine following the in vitro evaluation of H3R agonism using a cyclic adenosine monophosphate response element-luciferase reporter gene assay. The key compound VUF16839 (14d) combines nanomolar on-target activity (pKi = 8.5, pEC50 = 9.5) with weak activity on cytochrome P450 enzymes and good metabolic stability. The proposed H3R binding mode of 14d indicates key interactions similar to those attained by histamine. In vivo evaluation of 14d in a social recognition test in mice revealed an amnesic effect at 5 mg/kg intraperitoneally. The excellent in vitro and in vivo pharmacological profiles and the non-imidazole structure of 14d make it a promising tool compound in H3R research.

Novel Tetrahydroquinazolinamines as Selective Histamine 3 Receptor Antagonists for the Treatment of Obesity

The histamine 3 receptor (H3R) is a presynaptic receptor, which modulates several neurotransmitters including histamine and various essential physiological processes, such as feeding, arousal, cognition, and pain. The H3R is considered as a drug target for the treatment of several central nervous system disorders. We have synthesized and identified a novel series of 4-aryl-6-methyl-5,6,7,8-tetrahydroquinazolinamines that act as selective H3R antagonists. Among all the synthesized compounds, in vitro and docking studies suggested that the 4-methoxy-phenyl-substituted tetrahydroquinazolinamine compound 4c has potent and selective H3R antagonist activity (IC₅₀ < 0.04 μM). Compound 4c did not exhibit any activity on the hERG ion channel and pan-assay interference compounds liability. Pharmacokinetic studies showed that 4c crosses the blood brain barrier, and in vivo studies demonstrated that 4c induces anorexia and weight loss in obese, but not in lean mice. These data reveal the therapeutic potential of 4c as an anti-obesity candidate drug via antagonizing the H3R.