Synthesis of coumarin-3-O-acylisoureas by dicyclohexylcarbodiimide

Synthesis and Photophysical Properties of Fluorescent 6-Aryl-D-π-A Coumarin Derivatives

A series of 6-aryl coumarin dyes were synthesized in satisfactory yields by Pd-catalyzed Suzuki cross-coupling reactions with a panel of boronic acids and coumarin bromides. Photophysical studies highlighted a large Stoke shift and interesting fluorescence quantum yield for these compounds. Optical properties were also investigated with the aid of quantum chemical calculations. The treatment of selected coumarin dyes with increasing amounts of trifluoroacetic acid showed that their fluorescence can be strongly influenced by pH (fluorescence quenching at high acid concentrations), while the addition of Fe³⁺ and Al³⁺ metal ions allowed to highlight dichotomous behavior with the corresponding reduction in fluorescence with the increase of [Fe³⁺] or [Al³⁺]. Finally, biological assays and fluorescence microscopy imaging investigations indicated that these compounds can be used as potential biomarkers in living and fixed cells.

Structure–property relationship of novel supramolecular gels based on coumarins

LMWGs based on coumarins could form supramolecular gels with unusual mechanical properties explained by its interactions at theoretical level.

Samarium (III) triiodide catalysed reaction of salicylaldehydes with active methylene compounds

The unambiguous synthesis and isolation of 2-oxo-2H-1-benzopyran derivatives are described. The Knoevenagel condensation of 2-hydroxy benzaldehydes with active methylene compounds catalysed by samarium triiodide resulted in coumarium derivatives in fair yields under refluxing conditions.

Coumarin Synthesis via Knoevenagel Condensation in Moisture Stable Room Temperature Ionic Liquids

Several coumarins have been synthesised by Knoevenagel condensation in the piperidine/HOAc/moisture stable room temperature ionic liquid ([Emim]+BF4- referring to structure) system at room temperature; the yield of the reaction is good and the reaction medium can be recycled.

Synthesis and in vitro antioxidant activity evaluation of 3-carboxycoumarin derivatives and QSAR study of their DPPH• radical scavenging activity

The in vitro antioxidant activities of eight 3-carboxycoumarin derivatives were assayed by the quantitative 1,1-diphenyl-2-picrylhydrazil (DPPH•) radical scavenging activity method. 3-Acetyl-6-hydroxy-2H-1-benzopyran-2-one (C1) and ethyl 6-hydroxy-2-oxo-2H-1-benzopyran-3-carboxylate (C2) presented the best radical-scavenging activity. A quantitative structure-activity relationship (QSAR) study was performed and correlated with the experimental DPPH• scavenging data. We used structural, geometrical, topological and quantum-chemical descriptors selected with Genetic Algorithms in order to determine which of these parameters are responsible of the observed DPPH• radical scavenging activity. We constructed a back propagation neural network with the hydrophilic factor (Hy) descriptor to generate an adequate architecture of neurons for the system description. The mathematical model showed a multiple determination coefficient of 0.9196 and a root mean squared error of 0.0851. Our results shows that the presence of hydroxyl groups on the ring structure of 3-carboxy-coumarins are correlated with the observed DPPH• radical scavenging activity effects.

Synthesis and characterization of new diiodocoumarin derivatives with promising antimicrobial activities

A series of 6,8-diiodocoumarin-3-N-carboxamides (4-11) were prepared. Treatment of ethyl 6,8-diiodocoumarin-3-carboxylate (1) with ethyl cyanoacetate/NH(4)OAc gave ethyl 2-(3-carbamoyl-6,8-diiodocoumarin-4-yl)-2-cyanoacetate (12) and 2-amino-4-hydroxy-7,9-diiodocoumarino[3,4-c]pyridine-1-carbonitrile (13), and treatment with acetone in the presence of NH(4)OAc or methylamine gave the ethyl 4-oxo-2,6-methano-2-methyl-3,4,5,6-tetrahydro-8,10-diiodobenzo[2,1-g]-2H-1,3-oxazocine-5-carboxylate derivatives 14a,b. All compounds were evaluated for their antimicrobial activity and the compounds 12-14a,b exhibited a pronounced effect on all tested microorganisms.

Thermal [4 + 2] cycloadditions of 3-acetyl-, 3-carbamoyl-, and 3-ethoxycarbonyl-coumarins with 2,3-dimethyl-1,3-butadiene under solventless conditions: a structural study

The thermal [4+2] cycloadditions of 3-acetyl-, 3-carbamoyl, and 3-ethoxycarbonylcoumarins with 2,3-dimethyl-1,3-butadiene under solvent free conditions are reported, as well as the epoxidation reactions of some adducts. Discussion is focused on the structural features of the Diels-Alder adducts and their epoxides, based upon NMR, X-ray, and mass spectral data, and supported by ab initio theoretical calculations.

Chemistry and catalysis in functional cavitands

Biological macromolecules use binding forces to access unfavorable chemical equilibria and stabilize reactive intermediates by temporarily isolating them from the surrounding medium. Certain synthetic receptors, functional cavitands, share these abilities and allow for the direct observation of labile intermediates by conventional spectroscopy. The cavitands feature inwardly directed functional groups that form reversible, covalent bonds with small molecules held inside. Tetrahedral intermediates of carbonyl addition reactions--hemiaminals, hemiacetals, and hemiketals--show amplified concentrations and lifetimes of minutes under ambient conditions. Labile intermediates in addition reactions of carboxylic acids to isonitriles are also stabilized by isolation in the space of the cavitands. The restricted environments channel the reactions of intermediates in cavitands along a specific path and strengthen the parallels between functional synthetic cavitands and enzymes.

New novobiocin analogues as antiproliferative agents in breast cancer cells and potential inhibitors of heat shock protein 90

Selective hsp90 inhibitors simultaneously destabilize and deplete key signaling proteins involved in cell proliferation and survival, angiogenesis, and metastasis. Investigation of novobiocin analogues lacking the noviose moiety as novel inhibitors of hsp90 was carried out. A novel series of 3-aminocoumarin analogues has been produced and screened in cell proliferation, and the molecular signature of hsp90 inhibition was assessed by depletion of estrogen receptor, HER2, Raf-1, and cdk4 in human breast cancer cells. This structure-activity relationship study highlights the crucial role of the C-4 and/or C-7 positions of coumarin which appeared to be essential for degradation of hsp90 client proteins. Removal of the noviose moiety in novobiocin together with introduction of a tosyl substituent at C-4 or C-7 coumarins provides 6e and 6f as lead structures which compared favorably with novobiocin as demonstrated by enhanced rates of cell death. The processing and activation of caspases 7 and 8 and the subsequent cleavage of PARP by 6e suggest stimulation of the extrinsic apoptosis pathway.

Ethyl-2-amino-6-bromo-4-(1-cyano-2-ethoxy-2-oxoethyl)-4H- chromene-3-carboxylate (HA 14-1), a Prototype Small-Molecule Antagonist against Antiapoptotic Bcl-2 Proteins, Decomposes To Generate Reactive Oxygen Species That Induce Apoptosis

Overexpressing antiapoptotic Bcl-2 proteins to suppress apoptosis is one major mechanism via which cancer cells acquire drug resistance against cancer therapy. Ethyl-2-amino-6-bromo-4-(1-cyano-2-ethoxy-2-oxoethyl)-4 H-chromene-3-carboxylate (HA 14-1) is one of the earliest small-molecule antagonists against antiapoptotic Bcl-2 proteins. Since its discovery, HA 14-1 has been shown to be able to synergize a variety of anticancer agents. HA 14-1 also could selectively eliminate tumor cells with elevated level of Bcl-2 protein. HA 14-1, therefore, is being intensely investigated as a potential anticancer agent. Previous reports of HA 14-1 implied that it may not be stable, raising the question of whether HA 14-1 is a suitable drug candidate. The potential stability also raised the concern about whether HA 14-1 is the bioactive species. In this report, we confirm that HA 14-1 is not stable under physiological conditions: it rapidly decomposes in RPMI cell culture medium with a half-life of 15 min. This decomposition process also generates reactive oxygen species (ROS). To identify the actual candidate(s) for the observed bioactivity of HA 14-1, we characterized the structures, quantified the amount, and evaluated the bioactivities of the decomposed products. We also used ROS scavengers to explore the function of ROS. From these studies, we established that none of the decomposition products could account for the bioactivity of HA 14-1. ROS generated during the decomposition process, however, are critical for the in vitro cytotoxicity and the apoptosis induced by HA 14-1. This study demonstrates that HA 14-1 is not stable under physiological conditions and that HA 14-1 can generate ROS through its decomposition, independent of Bcl-2 antagonism. Because of its intrinsic tendency to decompose and to generate ROS, caution should be taken in using HA 14-1 as a qualified antagonist against antiapoptotic Bcl-2 proteins.

Reaction of an Introverted Carboxylic Acid with Carbodiimide

The reaction of carboxylic acids with carbodiimides is reviewed, and an "introverted" carboxylic acid is proposed as a means of trapping reactive intermediates along the reaction pathway. The introverted acid is a cavitand with the carboxylic function directed toward the floor of the cavity. Its reaction with diisopropyl carboodiimide gives a covalent adduct that is either the elusive O-acylisourea or the commonly encountered N-acylurea.

Asymmetric Total Synthesis of (−)-Linderol A

The first asymmetric total synthesis of (-)-Linderol A, a potent inhibitor of melanin biosynthesis of cultured B-16 melanoma cells, has been achieved via two key reactions: a diastereoselective [2+2] photocycloaddition of a coumarin-3-carboxylate bearing a chiral auxiliary with 3-methyl-1-butene and a subsequent stereoconvergent transformation of the photoadducts with use of dimethylsulfoxonium methylide to afford a tetrahydrodibenzofuran derivative.

Benzopyrans as selective estrogen receptor beta agonists (SERBAs). Part 3: synthesis of cyclopentanone and cyclohexanone intermediates for C-ring modification

Benzopyrans are selective estrogen receptor (ER) beta agonists (SERBAs), which bind the ER subtypes alpha and beta in opposite orientations. Here we describe the syntheses of cyclopentanone and cyclohexanone intermediates for SAR studies of the C-ring on the benzopyran scaffold. Modification of the C-ring disrupts binding to ERalpha, thus improving ERbeta selectivity up to 100-fold. X-ray cocrystal structures confirm previously observed binding modes.

N-Acylureido functionality as acceptor substituent in solvatochromic fluorescence probes: detection of carboxylic acids, alcohols, and fluoride ions

N,N'-Dicyclohexyl-N-(6'-methoxyanthryl-2-carbonyl)urea (1a) exhibits a strong solvatochromism with respect to its fluorescence properties. The emission maxima of 1a correlate well with the anion-stabilizing properties of the solvent. This feature allows the detection of analytes with high acceptor numbers, such as alcohols and carboxylic acids, and the detection of analytes such as fluoride ions which form strong hydrogen bonds with the amido hydrogen atom.

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.

Novel stereoconvergent transformation of 1,2a-disubstituted 1,2,2a,8b-tetrahydro-3H-benzo[b]cyclobuta[d]pyran-3-ones to 1,3-disubstituted 1,2,4a,9b-tetrahydrodibenzofuran-4-ols and its application to the second-generation synthesis of (+/-)-linderol A

1,2a-Disubstituted 1,2,2a,8b-tetrahydro-3H-benzo[b]cyclobuta[d]pyran-3-ones bearing an electron-withdrawing group at the 2a-position were treated with two equivalents of dimethylsulfoxonium methylide to give r-1,t-4a,t-9b-1,3-disubstituted 1,2,4a,9b-tetrahydrodibenzofuran-4-ols stereoconvergently regardless of the stereochemistry of the 1-position on the benzocyclobutapyran ring. This methodology was applied to the second-generation synthesis of (+/-)-linderol A, a melanin biosynthesis inhibitory natural product.

An Efficient Solid–Phase Synthesis of 3-Carboxycoumarins Based on a Scaffold–Polymer-Bound Cyclic Malonic Ester

The condensation of substituted o-methoxybenzaldehydes or o-hydroxybenzaldehydes with a resin-bound cyclic malonic ester 3 afforded the resin 4 without catalyst. Cyclisation of the resin 4 in sulfuric acid formed 3-carboxycoumarins in good yield and excellent purity.