Coumarin Nucleus Research Articles

Structure-anti-leukemic activity relationship study of ortho-dihydroxycoumarins in U-937 cells: Key role of the δ-lactone ring in determining differentiation-inducing potency and selective pro-apoptotic action

Previous studies indicated the need of at least one phenolic hydroxyl group in the coumarin core for induction of cytotoxicity in different cell lines. Herein, we present an exhaustive structure-activity relationship study including ortho-dihydroxycoumarins (o-DHC) derivatives, cinnamic acid derivatives (as open-chain coumarin analogues) and 1,2-pyrones (representative of the δ-lactone ring of the coumarin core), carried out to further identify the structural features of o-DHC required to induce leukemic cell differentiation and apoptosis in U-937 cells. Our results show for the first time that the δ-lactone ring positively influences the aforementioned biological effects, by conferring greater potency to compounds with an intact coumarin nucleus. Most tellingly, we reveal herein the crucial role of this molecular portion in determining the selective toxicity that o-DHC show for leukemic cells over normal blood cells. From a pharmacological perspective, our findings point out that o-DHC may be useful prototypes for the development of novel chemotherapeutic agents.

A New Strategy for the One Pot Synthesis of (Aryloxyimino)Ethylcoumarins Promoted by CuCl2

Cupric chloride showed efficient catalytic activity for the cross coupling reaction of arylboronic acids and (hydroxyi mino)ethylcoumarins at room temperature in the presence of NEt3 as base. A simple and convenient protocol for the synthesis of O-aryloxime ethers having the highly base sensitive coumarin nucleus is reported. O-Aryloxime ethers are important as they provide access to scaffolds for the generation of various biologically active compounds. They are potential precursors to benzofurans and benzisoxazoles.

De novo design of 7-aminocoumarin derivatives as novel falcipain-3 inhibitors

The availability of the crystal structure of falcipain-3, knowledge of the peptides carrying the 7-aminocoumarin moiety as falcipain-3 ligands/substrates, and a need for new antimalarial agents stimulated us to look at the possibility of finding some novel falcipain-3 inhibitors. In this paper, we report the effect of substitution at the 7-amino position of the coumarin nucleus on the inhibition of falcipain-3, which is a well-validated antimalarial target. The de novo drug design was assisted by QSAR studies that shed light on the binding patterns of known and the newly designed inhibitors, thus taking this discovery process to the next level.

Synthesis and selective human monoamine oxidase inhibition of 3-carbonyl, 3-acyl, and 3-carboxyhydrazido coumarin derivatives

Several 3-carbonyl ( 1– 26), 3-acyl ( 27– 52), and 3-carboxyhydrazido ( 53– 58) coumarins have been synthesized in high yields (72–99%) and tested in vitro for their human monoamine oxidase A and B (hMAO-A and hMAO-B) inhibitory activity. Different substituents on the coumarin nucleus were evaluated for their effect on biological activity and isoform selectivity. Substitution at position C7 of the 3-ethyl ester coumarin ring, or the introduction of a hydrazido substituent at C3, were important to obtain highly potent and selective hMAO-B inhibitors with IC 50 values in the nanomolar range. Some derivatives were also submitted to a stability test and showed no chemical cleavage in vitro.

Abstract 3262: Pharmaco-modulation of dihydroxy coumarins towards more selective antileukemic agents

Abstract Background: We described that 7,8-dihydroxy-4-methylcoumarin (DHMC) induces apoptosis in human leukemic U-937 cells, mediated by its pro-oxidant activity and activation of JNK. We also reported that DHMC shows selective toxicity for leukemic cells over normal peripheral blood monocytes. The aim of the present work is to establish the structural requirements for DHMC to display pro-apoptotic activity performing a structure activity relationship study of DHMC derivatives, cinnamic acid derivatives (as open-chain coumarin analogues) and a-pyrones (as representative of the d-lactone ring of the coumarin nucleus). Further, in an attempt to explain its selective toxicity, the mechanism of DHMC action through the JNK pathway will be characterized. Materials and Methods: DHMC analogues, cinnamic acid derivatives and a-pyrones were tested for their ability to induce biological effects in U-937 cells. Growth inhibition was determined through 3H-thymidine incorporation. Cellular viability was tested by trypan blue exclusion assays. Pro-apoptotic activity was evaluated by flow cytometry (annexin V), determination of caspase-3 activity and Western Blot analysis of caspase-3 and cleaved PARP levels. The oxidation potential and the capacity to generate free radicals were evaluated by cyclic voltammetry and electron paramagnetic resonance, respectively. To evaluate the role of cytoplasmic p21 (Cip1/WAF1) in the mechanism of DHMC selective action, we used U-937 cells transfected with a zinc-inducible p21 deletion mutant lacking the nuclear localization signal. Results: Only DHMC derivatives bearing two adjacent aromatic hydroxyl groups (catechol moiety) showed proliferation inhibition and pro-apoptotic activity in U-937 cells. a-pyrones had no effect on cellular viability, and cinnamic acid derivatives bearing the catechol moiety exhibited proliferation inhibition but no cytotoxic activity. Although ortho-dihydroxy coumarins and ortho-dihydroxy cinnamic acid derivatives showed a similar oxidation potential, only the former could generate stable free radicals in medium-like conditions, suggesting this capacity would be critical for their pro-apoptotic activity in U-937 cells. Finally, the pro-apoptotic effect of DHMC via JNK activation was abolished in U-937 cells expressing cytoplasmic p21, indicating this protein would be involved in the resistance that normal lymphocytes and monocytes, which normally express p21 in their cytoplasm, show for DHMC. Conclusions: DHMC-derived compounds carrying a catechol moiety can only induce apoptosis in U-937 cells if the integrity of the coumarinic nucleus is preserved. Selective toxicity of DHMC for leukemic cells would involve activation of JNK in the absence of cytoplasmic p21 expression. Collectively, our results point to ortho-dihydroxy coumarins as promising prototypes for the design of more selective antileukemic drugs. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3262. doi:10.1158/1538-7445.AM2011-3262

ChemInform Abstract: Preparation and Optical Properties of Novel 3‐Alkoxycarbonyl Aza‐ and Diazacoumarins.

A series of 14 new 3-alkoxycarbonyl 6-aza-, 7-aza-, and 6,8-diaza-coumarins was prepared using various strategies involving either a Knoevenagel or a Pechmann condensation reaction. The coumarin nucleus displays different reactive functional groups allowing straightforward derivatization. The optical properties of the new azacoumarins were measured in methanol.

Preparation and Optical Properties of Novel 3-Alkoxycarbonyl Aza- and Diazacoumarins

A series of 14 new 3-alkoxycarbonyl 6-aza-, 7-aza-, and 6,8-diaza-coumarins was prepared using various strategies involving either a Knoevenagel or a Pechmann condensation reaction. The coumarin nucleus displays different reactive functional groups allowing straightforward derivatization. The optical properties of the new azacoumarins were measured in methanol.

Coumarins: Old Compounds with Novel Promising Therapeutic Perspectives

Natural as well as synthetic coumarins have recently drawn much attention due to its broad pharmacological activities. Many coumarins and their derivatives exert anti-coagulant, anti-tumor, anti-viral, anti-inflammatory and anti-oxidant effects, as well as anti-microbial and enzyme inhibition properties. The recognition of key structural features within coumarin family is crucial for the design and development of new analogues with improved activity and for the characterization of their mechanism of action and potential side effects. The different substituents in the coumarin nucleus strongly influence the biological activity of the resulting derivatives. Although some coumarins have been already characterized to evoke a particular biological activity, the challenge would be the design and synthesis of new derivatives with high specific activity for other pharmacological targets and define their mechanism of action to achieve new therapeutic drugs. The present review highlights the current progress in the development of coumarin scaffolds for drug discovery as novel anti-cancer agents. The major challenges about coumarins include the translation of current knowledge into new potential lead compounds and the repositioning of known compounds for the treatment of cancer.

Synthesis and characterization of new 3‐acyl‐7‐hydroxy‐6,8‐substituted‐coumarin and 3‐acyl‐7‐benzyloxy‐6,8‐substituted‐coumarin derivatives

Abstract magnified image A new series of 3‐acyl‐6,7,8‐substituted coumarin derivatives has been synthesized in high yields (79–99%) and characterized by means of elemental analysis, mass spectrometry, IR, and 1H NMR spectroscopy. We examined with particular attention the presence of an acyl group at position 3 (ethyl ester, carboxylic acid, and acyl chloride), and of a hydroxyl group at position 7 or a functionalized one like benzyloxy or phthalimido. The hydroxyl group has been modified by an etherification in presence of crown ether with substituted benzyl bromide or chloride to evaluate the influence on chemical characteristics and lipophilicity of coumarin nucleus. Halogens (Cl, Br) and methyl group were introduced in position 6 and 8 of the coumarin ring, respectively, in order to study their effect on reaction feasibility. Some of these 3‐acyl derivatives have been recently assayed as MAO inhibitors and as intermediates (i.e. reactive chloride derivative) to design new anti‐Helicobacter pylori agents. J. Heterocyclic Chem., (2010).

Design and synthesis of coumarin substituted oxathiadiazolone derivatives having anti-inflammatory activity possibly through p38 MAP kinase inhibition

Compounds containing oxathiadiazolone nucleus bearing substituted coumarin ring were designed and synthesized while retaining the pharmacophores required for binding with p38 MAP kinase. A four-step synthetic scheme was employed for the synthesis of 7-methoxy-4-(3t?-substituted-2t?-oxo-1t?,2t?,3t?,5t?-oxathiadiazol-4t?-yl)-coumarin. The reactions were monitored by TLC and structures of the intermediates and the target compounds were ascertained by IR, NMR, Mass spectral data. The compounds were found to possess anti-inflammatory activity comparable to indomethacin. Superimposition studies of the target compounds with the lead p38 kinase inhibitors suggested that anti-inflammatory activity of the target compounds may be due to p38 MAP kinase inhibition. It was also suggested that methoxy group on coumarin nucleus may improve the binding profile with p38 MAP kinase.

Improved separation of furocoumarins of essential oils by supercritical fluid chromatography

Separation of furocoumarins has become of a great interest for cosmetic industry and human health, since the recent directive of the European Union. Furocoumarins are a class of compounds presenting varied substituents linked mainly in two positions to an identical skeleton made by a furan ring bonded to a coumarin nucleus (Psoralen). The substituents are mainly methoxy, or alkyl chains, which can contain double bonds, hydroxyl or epoxy groups. Due to the variety of compounds, and their subtle structure differences, their separation requires high-performance methods. Multi-gradient high-performance liquid chromatography (HPLC) and two-dimensional chromatography are usually applied. This paper describes a new approach, by using super/subcritical fluid chromatography (SFC), with a green mobile phase: CO 2–ethanol. The choice of the stationary phase from varied types of phases, and the effects of numerous analytical parameters (flow rate, modifier percentage, temperature and outlet pressure) are studied, described and discussed, on the basis of the separation of a complex sample: lemon residue. From these studies, isocratic conditions are determined to obtain a satisfactory separation in 10 min. A two-dimensional analysis was also investigated, by performing first a class fractionation of compounds on an ethylpyridine (EP) phase, then by separating each class on a pentafluorophenyl phase (Discovery HS F5) with the selected isocratic mobile phase. A gradient elution is also studied to improve separation of some minor compounds. Structure of the eluted compounds was determined by comparison with standards, HPLC-DAD, HPLC–MS analysis, and NMR analysis of collected fractions. All these approaches allow relating structure of compounds to retention behaviour, which is unusual due to the selected pentafluorophenyl stationary phase.

SYNTHESIS AND ANTIMICROBIAL ACTIVITY OF SOME NITROGEN HETEROCYCLES INCORPORATION INTO COUMARIN

3-Carbethoxycoumarin derivatives were reacted with some neucleophilic reagents such as amines, hydrazines, urea derivatives and amino acids in order to study their effect on coumarin nucleus especially carbonyl coumarin and synthesis of new derivatives which have biological effects on microorganisms such as bacteria and fungi. The structural assignments of the new compounds were based on analytical and spectral data.

Synthesis, Molecular Modeling, and Selective Inhibitory Activity against Human Monoamine Oxidases of 3-Carboxamido-7-Substituted Coumarins

A large series of 3-carboxamido-7-substituted coumarins have been synthesized and tested in vitro for their human monoamine oxidase A and B (hMAO-A and hMAO-B) inhibitory activity. Taking into account all the relevant structural information on MAOs reported in the literature, we made some changes in the coumarin nucleus and examined with particular attention the effect on activity and selectivity of substituting at position 3 with N-aryl or N-alkyl carboxamide and at position 7 with a benzyloxy or a 4'-F-benzyloxy group. Some of the assayed compounds proved to be potent, selective inhibitors of hMAO-B with IC(50) values in the micromolar range. To better understand the enzyme-inhibitor interaction and to explain the selectivity of the most active compounds toward hMAOs, molecular modeling studies were carried out on new, high resolution, hMAO-A and hMAO-B crystallographic structures.

Specificities of Calreticulin Transacetylase to acetoxy derivatives of 3-alkyl-4-methylcoumarins: Effect on the activation of nitric oxide synthase

Calreticulin Transacetylase (CRTAase) catalyzes the transfer of acetyl groups from polyphenolic acetates (PAs) to the receptor proteins and modulates their biological activities. CRTAase was conveniently assayed by the irreversible inhibition of cytosolic glutathione S-transferase (GST) by the model acetoxycoumarin, 7,8-diacetoxy-4-methylcoumarin (DAMC). We have studied earlier, the influence of acetoxy groups on the benzenoid ring, the effect of reduction of double bond at C-3 and C-4 position, the effect of methyl/phenyl group at C-4, and the influence of position of carbonyl group with respect to oxygen heteroatom in the benzopyran nucleus, for the catalytic activity of CRTAase. In this communication, we have extended our previous work; wherein we studied the influence of an alkyl group (ethyl, hexyl and decyl) at the C-3 position of the acetoxy coumarins on the CRTAase activity. The substitution at C-3 position of coumarin nucleus resulted in the reduction of CRTAase activity and related effects. Accordingly the formation of NO in platelets by C-3 alkyl substituted acetoxy coumarins was found to be much less compared to the unsubstituted analogs. In addition the alkyl substitution at C-3 position exhibited the tendency to form radicals other than NO.

Synthesis and characterization of coumarin-based europium complexes and luminescence measurements in aqueous media

A series of new ligands suitable for the formation of luminescent lanthanide complexes in water is described. The chelates are designed for analyte labeling and play the role of fluorescent donor in homogeneous time-resolved fluorescence assays using LEDs as a light source for excitation at 370 nm. Ligands are constructed from a coumarin nucleus, for lanthanide sensitization, and different aminomethylenecarboxy moieties are introduced in positions 7 and 5, 6, or 8 of the sensitizer. A reactive spacer arm under biocompatible conditions (maleimide, azide) is introduced at position 3 for ultimate bioconjugation purposes. The synthesis and characterization of the ligands are described, together with the preparation of their corresponding europium complexes. Photophysical properties of the complexes are investigated in water by means of UV-vis and luminescence spectroscopy.

Antiproliferative and apoptotic activities of tosylcyclonovobiocic acids as potent heat shock protein 90 inhibitors in human cancer cells

We evaluated whether inhibition of heat shock protein 90 (hsp90) function by novobiocin derivatives could induce the degradation of signal transducers that drive cancer cell growth and thereby promote apoptosis. Removal of the noviose moiety in novobiocin and introduction of a tosyl substituent at C-4 or C-7 coumarin nucleus provided derivatives 4TCNA and 7TCNA which compared favourably with novobiocin in MCF-7 breast cancer cells. Here we extend the antiproliferative and apoptotic properties of these analogues to a panel of cancer cell lines. Destabilization of hsp90 client proteins Raf-1, HER2, and cdk4 suggests inhibition of hsp90 chaperoning function. In HT29 colon and IGROV1 ovarian cancer cells, the growth inhibiting effect of 4TCNA and 7TCNA was consistent with the stimulation of cell death as assessed by the processing and activation of caspase 9, 8, 7 and 3 and the subsequent cleavage of poly(ADP-ribose) polymerase (PARP). In Ishikawa endometrial adenocarcinoma cells, 4TCNA also promoted apoptosis and the processing of PARP. These derivatives impacting multiple pathways involved in the neoplastic process may represent promising drugs for cancer therapy.

Neuroprotective effect of prenyloxycoumarins from edible vegetables

The present study is designed to investigate the effect of some natural prenyloxyphenylpropanoids as neuroprotective agents against NMDA-induced toxicity in mixed cortical cell cultures containing both neurons and astrocytes. Excitotoxicity was induced by exposure of cultures to NMDA (100microM) at room temperature in a HEPES-buffered salt solution followed by incubation at 37 degrees C for the following 24h in MEM-Eagle's supplemented with 15.8mM NaHCO(3) and 25mM glucose. Tested compounds were mixed with NMDA. Neuronal injury was measured in all experiments by examination of cultures with phase-contrast microscopy at 20x, 18-20h after the insult while neuronal damage was quantitatively assessed by counting dead neurons stained with trypan blue and by measuring lactate dehydrogenase (LDH) released in the medium. Results showed that only natural prenyloxyphenylpropanoids containing a coumarin nucleus, namely 7-isopentenyloxycoumarin and auraptene, both found in nature from plants belonging to the genus Citrus and other of the family of Rutaceae, including edible ones, exerted a good dose-dependent manner protective effect against NMDA-induced neurotoxicity in particular at concentrations ranging from 1 to 10microM.

Selinidin: Crystal structure generated by C–H···O, C–H···π and π-π interactions

The title compound, 9,10-dihydro-8,8-dimethyl-2-oxo-2H,8H-benzo[1,2-b:3,4-b']dipyran-9-yl-2-methyl-2-butenoate, C19H20O5, was isolated from the roots of Selinum vaginatum. The compound crystallizes into monoclinic space group P2 1 with unit cell parameters: a = 12.830(2) A, b = 9.041(1) A, c = 14.983(1) A, β = 95.09(1)°, Z = 4. The crystal structure has been determined using direct methods and refined by full-matrix least-squares to a final R value of 0.0529 for 3142 observed reflections. There are two independent molecules, A and B, per asymmetric unit. In both the molecules, the coumarin nucleus is planar. However pronounced differences are observed in the conformation of dihydropyran ring which has a half-chair conformation with an 8β-9α orientation in molecule A and is intermediate between half-chair and sofa in molecule B. Differences also occur in the conformation of the 2-methylbutenoyloxy side chain at C9 due to the different geometry of C–H···π interactions in molecules A and B. Molecules A and B are connected by π–π interactions between their coumarin fragments forming dimers. The dimers interact through C–H···O and C–H···πhydrogen bonds.

Synthesis, X-ray structure determination and analysis of packing interactions in 9-(1,2-propenyl)-6-carboethoxy-2-methyl-2,3-dihydrofuro[2,3-h]-benzopyran-5H-one

Claisen rearrangement of ethyl-2,4-diallyloxy-α-carbethoxycinnamate (1) in refluxing DMA afforded ethyl-9-allyl-2-methyl-2,3-dihydrofuro(2,3-h)benzopyran-5H-one-6-carboxylate (2) in a single step. Dehydrogenation with Pd/C (10%) in DPE furnished an unexpected isomeric compound, 9-(1,2-propenyl)-6-carbethoxy-2-methyl-2,3-dihydrofuro[2,3-h]-benzopyran-5H-one (3). This compound, C18H18O5, crystallizes in the monoclinic space group P21/n with unit cell parameters, a = 7.346(1), b = 16.482(3), c = 12.653(2),A, and β = 92.71(1)°. The structure has been solved by direct methods and refined to R = 0.056 for 1719 observed reflections. The coumarin nucleus is planar. The five-membered ring is in envelope-conformation. The crystal structure is stabilized by intra- and intermolecular C―H⋯O hydrogen bonds.

Selectivity of 7-alkoxycoumarins as probe substrates for rat hepatic cytochrome P450 forms is influenced by the substitution pattern on the coumarin nucleus

The O-dealkylation of 7-alkoxycoumarins is widely used as an assay to characterize cytochrome P450 (CYP) activity. These substrates can also undergo oxidative attack at additional sites on the coumarin nucleus, which may influence their apparent selectivity for particular CYP forms.Accordingly, the effect of blockade of these additional sites was investigated on the selectivity towards rat hepatic CYP forms, with emphasis on the CYP1A and 2B forms.Blockade of the 3-/4- and 6-positions resulted in substrates for which the CYP1A1/2 selectivity of the unsubstituted 7-alkoxycoumarins was altered to a CYP2B selectivity; this was achieved with little overall change in the molecular dimensions of the substrate. Limited analysis of other inducible CYP forms indicated at most only small effects of structure modification on activity.The findings suggest that the sensitivity of probe substrates for CYP forms may be limited by the occurrence of competing side reactions of the substrate, and that better probes may be derived by blocking the sites of these side reactions.