Preparation of cyclohexene isotopologues and stereoisotopomers from benzene.

The hydrogen isotopes deuterium (D) and tritium (T) have become essential tools in chemistry, biology and medicine1. Beyond their widespread use in spectroscopy, mass spectrometry and mechanistic and pharmacokinetic studies, there has been considerable interest in incorporating deuterium into drug molecules1. Deutetrabenazine, a deuterated drug that is promising for the treatment of Huntington's disease2, was recently approved by the United States' Food and Drug Administration. The deuterium kinetic isotope effect, which compares the rate of a chemical reaction for a compound with that for its deuterated counterpart, can be substantial1,3,4. The strategic replacement of hydrogen with deuterium can affect both the rate of metabolism and the distribution of metabolites for a compound5, improving the efficacy and safety of a drug. The pharmacokinetics of a deuterated compound depends on the location(s) of deuterium. Although methods are available for deuterium incorporation at both early and late stages of the synthesis of a drug6,7, these processes are often unselective and the stereoisotopic purity can be difficult to measure7,8. Here we describe the preparation of stereoselectively deuterated building blocks for pharmaceutical research. As a proof of concept, we demonstrate a four-step conversion of benzene to cyclohexene with varying degrees of deuterium incorporation, via binding to a tungsten complex. Using different combinations of deuterated and proteated acid and hydride reagents, the deuterated positions on the cyclohexene ring can be controlled precisely. In total, 52 unique stereoisotopomers of cyclohexene are available, in the form of ten different isotopologues. This concept can be extended to prepare discrete stereoisotopomers of functionalized cyclohexenes. Such systematic methods for the preparation of pharmacologically active compounds as discrete stereoisotopomers could improve the pharmacological and toxicological properties of drugs and provide mechanistic information related to their distribution and metabolism in the body.

Construction of Polycarbonates with Pendant Multifunctional Groups via a One-Step CO2/ Diepoxide Copolymerization Approach.

A "one-step" strategy has been demonstrated for the tunable synthesis of multifunctional aliphatic polycarbonates (APCs) with ethylene oxide (EO), ethylene carbonate (EC), and cyclohexene oxide (CHO) side groups by the copolymerization of 4-vinyl-1-cyclohexene diepoxide with carbon dioxide under an aminotriphenolate iron/PPNBz (PPN = bis(triphenylphosphine)-iminium, Bz = benzoate) binary catalyst. By adjusting the PPNBz-to-iron complex ratio and incorporating auxiliary solvents, the content of functional side groups can be tuned within the ranges of 53-75% for EO, 18-47% for EC, and <1-7% for CHO. The yield and molecular weight distribution of the resulting multifunctional APCs are affected by the viscosity of the polymerization system. The use of tetrahydrofuran as an auxiliary solvent enables the preparation of narrow-distribution polycarbonates at high conversion. This work presents a novel perspective for the preparation of tailorable multifunctional APCs.

HSPiP, Computational, and Thermodynamic Model-Based Optimized Solvents for Subcutaneous Delivery of Tolterodine Tartrate and GastroPlus­Based In Vivo Prediction in Humans: Part II.

In part I, we reported Hansen solubility parameters (HSP, HSPiP program), experimental solubility at varied temperatures for TOTA delivery. Here, we studied dose volume selection, stability, pH, osmolality, dispersion, clarity, and viscosity of the explored combinations (I-VI). Ex vivo permeation and deposition studies were performed to observe relative diffusion rate from the injected site in rat skin. Confocal laser scanning microscopy (CLSM) study was conducted to support ex vivo findings. Moreover, GastroPlus predicted in vivo parameters in humans and the impact of various critical factors on pharmacokinetic parameters (PK). Immediate release product (IR) contained 60% of PEG400 whereas controlled release formulation (CR) contained PEG400 (60%), water (10%) and d-limonene (30%) to deliver 2 mg of TOTA. GastroPlus predicted the plasma drug concentration of weakly basic TOTA as function of pH (from pH 2.0 to 9). The cumulative drug permeation and drug deposition were found to be in the order as B-VI˃ C-VI˃A-VI across rat skin. This finding was further supported with CLSM. Moreover, IR and CR were predicted to achieve Cmax of 0.0038 µg/ mL and 0.00023 µg/mL, respectively, after sub-Q delivery. Added limonene in CR extended the plasma drug concentration over period of 12 h as predicted in GastroPlus. Parameters sensitivity analysis (PSA) assessment predicted that sub-Q blood flow rate is the only factor affecting PK parameters in IR formulation whereas this was insignificant for CR. Thus, sub-Q delivery CR would be promising alternative with ease of delivery to children and aged patient.

Cooperative Activation of CO2 and Epoxide by a Heterobinuclear Al-Fe Complex via Radical Pair Mechanisms.

Activation of inert molecules like CO2 is often mediated by cooperative chemistry between two reactive sites within a catalytic assembly, the most common form of which is Lewis acid/base bifunctionality observed in both natural metalloenzymes and synthetic systems. Here, we disclose a heterobinuclear complex with an Al-Fe bond that instead activates CO2 and other substrates through cooperative behavior of two radical intermediates. The complex Ldipp(Me)AlFp (2, Ldipp = HC{(CMe)(2,6-iPr2C6H3N)}2, Fp = FeCp(CO)2, Cp = η5-C5H5) was found to insert CO2 and cyclohexene oxide, producing LdippAl(Me)(µ:κ2-O2C)Fp (3) and LdippAl(Me)(µ-OC6H10)Fp (4), respectively. Detailed mechanistic studies indicate unusual pathways in which (i) the Al-Fe bond dissociates homolytically to generate formally AlII and FeI metalloradicals, then (ii) the metalloradicals add to substrate in a pairwise fashion initiated by O-coordination to Al. The accessibility of this unusual mechanism is aided, in part, by the redox noninnocent nature of Ldipp that stabilizes the formally AlII intermediates, instead giving them predominantly AlIII-like physical character. The redox noninnocent nature of the radical intermediates was elucidated through direct observation of LdippAl(Me)(OCPh2) (22), a metalloradical species generated by addition of benzophenone to 2. Complex 22 was characterized by X-band EPR, Q-band EPR, and ENDOR spectroscopies as well as computational modeling. The "radical pair" pathway represents an unprecedented mechanism for CO2 activation.

Effective Isolation of Picrocrocin and Crocins from Saffron: From HPTLC to Working Standard Obtaining.

Saffron is widely cultivated and used as a spice. Recently published data on the chemical composition and pharmacological potential of saffron determine its use in pharmacy and medicine. The proposed high-performance thin-layer chromatography (HPTLC) method allows good separation of 11 analytes. The saffron quality (Iran, Ukraine, Spain, Morocco samples) assessment was based on the European Pharmacopoeia monograph and ISO 3632. The HPTLC method for the safranal, crocin, and picrocrocin quantification was proposed and validated. The crocins content in Ukrainian saffron was from 17.80% to 33.25%. Based on qualitative and quantitative assessment results, the saffron sample from Zaporizhzhia (Ukraine) had the highest compounds content and was chosen to obtain the working standards of picrocrocin and crocins (trans-4GG, trans-2G, trans-3Gg) by preparative chromatography. The compounds were isolated from lyophilized extract of saffron using a Symmetry Prep C18 column (300 × 19 mm × 7 µm), and identified by spectroscopic techniques (HPLC-DAD, UPLC-ESI-MS/MS). The purity of crocins and picrocrocin was more than 97%. A novel method proposed to obtain working standards is simple and reproducible for the routine analysis of saffron quality control.

Characterization of a 3-hydroxyanthranilic acid 6-hydroxylase involved in paulomycin biosynthesis.

Paulomycins (PAUs) refer to a group of glycosylated antibiotics with attractive antibacterial activities against Gram-positive bacteria. They contain a special ring A moiety that is prone to dehydrate between C-4 and C-5 to a quinone-type form at acidic condition, which will reduce the antibacterial activities of PAUs significantly. Elucidation of the biosynthetic mechanism of the ring A moiety may facilitate its structure modifications by combinatorial biosynthesis to generate PAU analogues with enhanced bioactivity or stability. Previous studies showed that the ring A moiety is derived from chorismate, which is converted to 3-hydroxyanthranilic acid (3-HAA) by a 2-amino-2-deoxyisochorismate (ADIC) synthase, a 2,3-dihydro-3-hydroxyanthranilic acid (DHHA) synthase, and a DHHA dehydrogenase. Unfortunately, little is known about the conversion process from 3-HAA to the highly decorated ring A moiety of PAUs. In this work, we characterized Pau17 as an unprecedented 3-HAA 6-hydroxylase responsible for the conversion of 3-HAA to 3,6-DHAA by in vivo and in vitro studies, pushing one step forward toward elucidating the biosynthetic mechanism of the ring A moiety of PAUs.

Artificial Enzymes for Diels-Alder Reactions.

The Diels-Alder (DA) reaction is a cycloaddition of a conjugated diene and an alkene (dienophile) leading to the formation of a cyclohexene derivative through a concerted mechanism. As DA reactions generally proceed with a high degree of regio- and stereoselectivity, they are widely used in synthetic organic chemistry. Considering eco-conscious public and governmental movements, efforts are now directed towards the development of synthetic processes that meet environmental concerns. Artificial enzymes, which can be developed to catalyze abiotic reactions, appear to be important synthetic tools in the synthetic biology field. This review describes the different strategies used to develop protein-based artificial enzymes for DA reactions, including for in cellulo approaches.

Oxygenated Cyclohexene Derivatives from the Stem and Root Barks of Uvaria pandensis.

Five new cyclohexene derivatives, dipandensin A and B (1 and 2) and pandensenols A-C (3-5), and 16 known secondary metabolites (6-21) were isolated from the methanol-soluble extracts of the stem and root barks of Uvaria pandensis. The structures were characterized by NMR spectroscopic and mass spectrometric analyses, and that of 6-methoxyzeylenol (6) was further confirmed by single-crystal X-ray crystallography, which also established its absolute configuration. The isolated metabolites were evaluated for antibacterial activity against the Gram-positive bacteria Bacillus subtilis and Staphylococcus epidermidis and the Gram-negative bacteria Enterococcus raffinosus, Escherichia coli, Paraburkholderia caledonica, Pectobacterium carotovorum, and Pseudomonas putida, as well as for cytotoxicity against the MCF-7 human breast cancer cell line. A mixture of uvaretin (20) and isouvaretin (21) exhibited significant antibacterial activity against B. subtilis (EC50 8.7 µM) and S. epidermidis (IC50 7.9 µM). (8'α,9'ß-Dihydroxy)-3-farnesylindole (12) showed strong inhibitory activity (EC50 9.8 µM) against B. subtilis, comparable to the clinical reference ampicillin (EC50 17.9 µM). None of the compounds showed relevant cytotoxicity against the MCF-7 human breast cancer cell line.

Semipinacol rearrangement of a bicyclo[7.2.0]undecane framework into a bicyclo[6.3.0]undecane skeleton: a model study on the biosynthesis of seiridiasteriscane A.

Seiridiasteriscane A is an asteriscane-type sesquiterpenoid bearing a trans-fused bicyclo[6.3.0]undecane skeleton. Although its biosynthesis has been proposed to involve a semipinacol rearrangement of a putative intermediary acetate bearing a bicyclo[7.2.0]undecane ring system (presumably derived from coisolated pestalotiopsin M) followed by epimerization of the resulting cis-fused seiridiasteriscane B, such a type of semipinacol rearrangement has never been reported so far. Our model study revealed that a 1-hydroxybicyclo[7.2.0]undecan-2-yl acetate underwent a smooth and stereospecific semipinacol rearrangement with the assistance of Et2AlCl to give the corresponding bicyclo[6.3.0]undecane-9-one. In addition, the resulting cis-fused 5,8-bicyclic ketone was partially epimerized to the corresponding trans-fused ketone by prolonged adsorption onto a silica gel plate. These results may support a recently proposed biosynthetic pathway of seiridiasteriscane A.

Effect of ZnSO4, MnSO4 and FeSO4 on the Partial Hydrogenation of Benzene over Nano Ru-Based Catalysts.

Nano Ru-based catalysts, including monometallic Ru and Ru-Zn nanoparticles, were synthesized via a precipitation method. The prepared catalysts were evaluated on partial hydrogenation of benzene towards cyclohexene generation, during which the effect of reaction modifiers, i.e., ZnSO4, MnSO4, and FeSO4, was investigated. The fresh and the spent catalysts were thoroughly characterized by XRD, TEM, SEM, XPS, XRF, and DFT studies. It was found that Zn2+ or Fe2+ could be adsorbed on the surface of a monometallic Ru catalyst, where a stabilized complex could be formed between the cations and the cyclohexene. This led to an enhancement of catalytic selectivity towards cyclohexene. Furthermore, electron transfer was observed from Zn2+ or Fe2+ to Ru, hindering the catalytic activity towards benzene hydrogenation. In comparison, very few Mn2+ cations were adsorbed on the Ru surface, for which no cyclohexene could be detected. On the other hand, for Ru-Zn catalyst, Zn existed as rodlike ZnO. The added ZnSO4 and FeSO4 could react with ZnO to generate (Zn(OH)2)5(ZnSO4)(H2O) and basic Fe sulfate, respectively. This further benefited the adsorption of Zn2+ or Fe2+, leading to the decrease of catalytic activity towards benzene conversion and the increase of selectivity towards cyclohexene synthesis. When 0.57 mol·L-1 of ZnSO4 was applied, the highest cyclohexene yield of 62.6% was achieved. When MnSO4 was used as a reaction modifier, H2SO4 could be generated in the slurry via its hydrolysis, which reacted with ZnO to form ZnSO4. The selectivity towards cyclohexene formation was then improved by the adsorbed Zn2+.

Crocus sativus L. Extracts and Its Constituents Crocins and Safranal; Potential Candidates for Schizophrenia Treatment?

Schizophrenia is a chronic mental devastating disease. Current therapy suffers from various limitations including low efficacy and serious side effects. Thus, there is an urgent necessity to develop new antipsychotics with higher efficacy and safety. The dried stigma of the plant Crocus sativus L., (CS) commonly known as saffron, are used in traditional medicine for various purposes. It has been demonstrated that saffron and its bioactive components crocins and safranal exert a beneficial action in different pathologies of the central nervous system such as anxiety, depression, epilepsy and memory problems. Recently, their role as potential antipsychotic agents is under investigation. In the present review, I intended to critically assess advances in research of these molecules for the treatment of schizophrenia, comment on their advantages over currently used neuroleptics as well-remaining challenges. Up to our days, few preclinical studies have been conducted to this end. In spite of it, results are encouraging and strongly corroborate that additional research is mandatory aiming to definitively establish a role for saffron and its bioactive components for the treatment of schizophrenia.

GABAA Receptor-Mediated Sleep-Promoting Effect of Saaz-Saphir Hops Mixture Containing Xanthohumol and Humulone.

Hops contain flavonoids that have sedative and sleep-promoting activities such as α-acid, ß-acid, and xanthohumol. In this study, the sleep-enhancing activity of a Saaz-Saphir hops mixture was measured. In the caffeine-induced insomnia model, the administration of a Saaz-Saphir mixture increased the sleep time compared to Saaz or Saphir administration alone, which was attributed to the increase in NREM sleep time by the δ-wave increase. Oral administration of the Saaz-Saphir mixture for 3 weeks increased the γ-amino butyric acid (GABA) content in the brain and increased the expression of the GABAA receptor. As the GABA antagonists picrotoxin and bicuculline showed a decrease in sleep activity, it was confirmed that the GABAA receptor was involved in the Saaz-Saphir mixture activity. In addition, the GABAA receptor antagonist also reduced the sleep activity induced by xanthohumol and humulone contained in the Saaz-Saphir mixture. Therefore, xanthohumol and humulone contained in the Saaz-Saphir mixture showed sleep-promoting activity mediated by the GABAA receptors. The mixture of the Saaz and Saphir hop varieties may thus help mitigate sleep disturbances compared to other hop varieties.

Origins of Endo Selectivity in Diels-Alder Reactions of Cyclic Allene Dienophiles.

Strained cyclic allenes, first discovered in 1966 by Wittig and co-workers, have recently emerged as valuable synthetic building blocks. Previous experimental investigations, and computations reported here, demonstrate that the Diels-Alder reactions of furans and pyrroles with 1,2-cyclohexadiene and oxa- and azaheterocyclic analogs proceed with endo selectivity. This endo selectivity gives the adduct with the allylic saturated carbon of the cyclic allene endo to the diene carbons. The selectivity is very general and useful in synthetic applications. Our computational study establishes the origins of this endo selectivity. We analyze the helical frontier molecular orbitals of strained cyclic allenes and show how secondary orbital and electrostatic effects influence stereoselectivity. The LUMO of carbon-3 of the allene (C-3 is not involved in primary orbital interactions) interacts in a stabilizing fashion with the HOMO of the diene in such a way that the carbon of the cyclic allene attached to C-1 favors the endo position in the transition state. The furan LUMO, allene HOMO interaction reinforces this preference. These mechanistic studies are expected to prompt the further use of long-avoided strained cyclic allenes in chemical synthesis.

Antidepressant mechanism and active compounds of saffron from network pharmacology study.

Saffron has been applied in depression treatment, but its antidepressant compounds and mechanisms are unclear. In this research, a network pharmacology-based method was proposed to screen the active compounds and the potential mechanisms of saffron for depression treatment. Firstly, the chemical compounds of saffron were collected from literature and filtered by drug-like prediction. Secondly, common targets, by comparing the targets of saffron predicted by Pharm Mapper server with targets associated with depression collected from Genecards, were regarded as the antidepressant targets of saffron. Thirdly, common targets were mapped to KEGG pathways, considered as the pathways related with the antidepressant effects of saffron. Finally, the network of compounds-targets-pathways was constructed and analyzed by cytoscape 3.4.0. Ten compounds including crocetin, picrocrocin, (1R, 5S, 6R)-5-(hydroxymethyl)- 4, 4, 6-trimethyl-7-Oxabicyclo[4.1.0]heptan-2-one and its glycoside were screened as the main antidepressant compounds, some of which were reported for the first time. They might have effective treatment for depression by acting on targets, such as MAP2K1, MAPK1, HRAS, PIK3R1, ALB and AKT1 and pathways related with immune system, signal transduction and so on. This study provided a new insight into the antidepressant mechanism and active compounds of saffron, which also had a guiding effect on later experiments.

Organocatalyzed Birch Reduction Driven by Visible Light.

The Birch reduction is a powerful synthetic methodology that uses solvated electrons to convert inert arenes to 1,4-cyclohexadienes-valuable intermediates for building molecular complexity. Birch reductions traditionally employ alkali metals dissolved in ammonia to produce a solvated electron for the reduction of unactivated arenes such as benzene (Ered < -3.42 V vs SCE). Photoredox catalysts have been gaining popularity in highly reducing applications, but none have been reported to demonstrate reduction potentials powerful enough to reduce benzene. Here, we introduce benzo[ghi]perylene imides as new organic photoredox catalysts for Birch reductions performed at ambient temperature and driven by visible light from commercially available LEDs. Using low catalyst loadings (<1 mol percent), benzene and other functionalized arenes were selectively transformed to 1,4-cyclohexadienes in moderate to good yields in a completely metal-free reaction. Mechanistic studies support that this unprecedented visible-light-induced reactivity is enabled by the ability of the organic photoredox catalyst to harness the energy from two visible-light photons to affect a single, high-energy chemical transformation.

Hydroarylation of Arenes via Reductive Radical-Polar Crossover.

A photocatalytic system for the dearomative hydroarylation of benzene derivatives has been developed. Using a combination of an organic photoredox catalyst and an amine reductant, this process operates through a reductive radical-polar crossover mechanism where aryl halide reduction triggers a regioselective radical cyclization event, followed by anion formation and quenching to produce a range of complex spirocyclic cyclohexadienes. This light-driven protocol functions at room temperature in a green solvent system (aq. MeCN) without the need for precious metal-based catalysts or reagents or the generation of stoichiometric metal byproducts.

Studies on the Catalytic Promiscuity of Limonene Epoxide Hydrolases in the Non-hydrolytic Ring Opening of 1,2-Epoxides.

The non-hydrolytic ring opening of 1,2-epoxides in the presence of limonene epoxide hydrolases (LEHs) and different nucleophiles has been investigated. Lyophilized, wild-type LEHs were tested in selected water-saturated organic solvents in the presence of cyclohexene oxide as substrate and different alcohols, thiols and primary amines as nucleophiles. Although the LEHs retained an appreciable catalytic activity under different reaction conditions, formation of the desired 1,2-substituted cyclohexanols was not observed. Alternatively, LEH variants incapable of performing the hydrolytic reaction were generated by site-directed mutagenesis and tested in aqueous media in the presence of different water-soluble nucleophiles and cyclohexene oxide. Under defined reaction conditions, an acceleration of up to about threefold of the spontaneous reaction rate was observed in the presence of sodium azide and potassium thiocyanate as nucleophiles.

Chemiluminescence-Induced Free Radical-Promoted Cationic Polymerization.

Chemiluminescence (CL) has recently been featured as a new external light source for various photoinduced reactions with attractive features such as eliminating continuous energy supply and advanced light source setups. In the present study, the free-radical-promoted cationic polymerization of cyclohexene oxide, n-butyl vinyl ether, and N-vinyl carbazole under CL irradiation is described. The method is based on the visible-light-induced generation of electron donor radicals from bis-(4-methoxybenzoyl)diethyl germane (BAG), bis(2,4,6-trimethylbenzoyl) phenyl phosphinate, and camphorquinone by CL illumination followed by electron transfer to diphenyl iodonium hexafluorophosphate (Ph2 I+ PF6 - ) to form corresponding cations capable of initiating cationic polymerization. The applicability of the process to network formation is also demonstrated by using a bifunctional monomer, tri(ethylene glycol) divinyl ether.

Oxygenated Cyclohexene Derivatives and Other Constituents from the Roots of Monanthotaxis trichocarpa.

Three new oxygenated cyclohexene derivatives, trichocarpeols A (1), B (2), and C (3), along with nine known secondary metabolites, were isolated from the methanolic root extract of Monanthotaxis trichocarpa. They were identified by NMR spectroscopic and mass spectrometric analyses, and the structure of trichocarpeol A (1) was confirmed by single-crystal X-ray diffraction. Out of the 12 isolated natural products, uvaretin (4) showed activity against the Gram-positive bacterium Bacillus subtilis with a MIC value of 18 µM. None of the isolated metabolites was active against the Gram-negative Escherichia coli at a ∼5 mM (2000 µg/mL) concentration. Whereas 4 showed cytotoxicity at EC50 10.2 µM against the MCF-7 human breast cancer cell line, the other compounds were inactive or not tested.

Efficacy of novel methylenecyclohexenone derivatives as TrxR inhibitors in suppressing the proliferation and metastasis of human cancer cells.

A series of mono- and di-methylenecyclohexenone derivatives, 3a-f and 4a-f, respectively, were designed and synthesized from piperlongumine (PL) and their in vitro and in vivo pharmacological properties were evaluated. A majority of the compounds exhibited a potent antiproliferative effect on five human cancer cell lines, especially those causing breast cancer. Compound 4f showed the highest antiproliferative potency among all of the compounds, almost a 10-fold higher inhibitory potency against thioredoxin reductase (TrxR) compared with PL in cells causing breast cancer. In addition, 4f was found to increase the levels of reactive oxygen species (ROS), thus leading to more potent antiproliferative effects. More importantly, the suppression assays of migration and invasion revealed that compound 4f could reverse the epithelial-mesenchymal transition induced by the transforming growth factor ß1, and exhibit prominent anti-metastasis effects. Compound 4f also showed strong inhibition potency toward solid tumors of breast cancer in vivo. Our findings show that compound 4f is a promising therapeutic candidate in the treatment of breast cancer, which, however, needs further research to be proved.