Coumarin Ester Research Articles

Preparation of Spiro[Benzopyran-Isoxazoles] from the Condensation–Cyclization of Oxime 1,4-Dianions with Select Coumarins

A representative spiro[benzopyran-isoxazole], 3′-(3,4-dimethoxyphenyl)-N,N-diethyl-4-methyl-4′H-spiro[2H-1-benzopyran-2,5′-isoxazol]-7-amine 3a, was submitted for single crystal X-ray analysis. It has been prepared by the condensation–cyclization of dilithiated C(α),O-3′,4′-dimethoxyacetophenone oxime with a substituted coumarin, 7-(diethylamino)-4-methyl-2H-1-benzopyran-2-one. This results from the 1,2-carbonyl addition, Claisen type, of the dilithiated oxime with this coumarin ester carbonyl to afford C-acylated intermediates that were not isolated, but were acid cyclized to the spiro[benzopyran-isoxazoles], a new spiro heterocyclic system. There was no evidence for Michael-type 1,4-addition found during this initial investigation. An indication that the experimental multiple anion procedure is general, has been the preparation of two additional spiro(benzopyran-isoxazoles) 3b and 3c. Crystals of C24H28N2O4 3a are triclinic, $$p\bar{1}$$ , a = 9.161(2) A, b = 9.716(2) A, c = 12.869(3) A, α = 75.84(3)°, β = 81.03(3)°, γ = 73.96(3)°, Z = 2, V = 1062.5(4) A3, R 1 = 0.0539 and wR 2 = 0.1366 for reflections with I > 2σ(I). X-ray crystal analysis confirmed the structure of 3′-(3,4-dimethoxyphenyl)-N,N-diethyl-4-methyl-4′H-spiro(2H-1-benzopyran-2,5′-isoxazol)-7-amine prepared by the condensation–cyclization of dilithiated C(α),O-3′,4′-dimethoxyacetophenone oxime with a substituted coumarin, 7-(diethylamino)-4-methyl-2H-1-benzopyran-2-one.

Analysis of hydrogen-bond patterns of a new coumarin ester

Analysis of hydrogen-bond patterns of a new coumarin ester

Mesoporous Borated Zirconia: A Solid Acid–Base Bifunctional Catalyst

AbstractThe development and use of reusable solid catalysts for the selective organic transformation in solvent‐free or environmentally benign solvent media is the key interest of modern frontier science. Herein a facile low temperature aqueous solution based chemical route for the synthesis of mesoporous borated zirconia, an acid–base bifunctional solid catalyst, using aqueous zirconium ammonium carbonate complex and borax in presence of cetyltrimethylammonium bromide is presented. The material has a very high surface area and acidity with weak basicity. The catalytic activity of the material was investigated for the solvent‐free Knoevenagel condensation reaction of benzaldehyde/substituted benzaldehyde and malononitrile/cyano ethylacetate to confirm the acid–base bifunctionality. High yield (>90 %) of the corresponding benzylidene was obtained within 15–30 min at room temperature. The evidence that the high catalytic activity is a result of acid–base bifunctionality of the synthesized borated zirconia material was further supported by performing Claisen–Schmidt condensation of benzaldehyde and acetophenone. The methodology was also extended for targeted synthesis of cinnamyl ethyl ester and coumarin or coumarin ester; and resulted in a good yield.

Dependence of the optical absorption and Na+ binding energies of coumarin-crown ethers on the size and attachment position of ether ring: density functional investigation

The crowned coumarin complexes are well known compounds for their ion recognition abilities. They undergo photophysical changes upon cation binding. On the basis of density functional theory calculations, we examined the sodium cation (Na+) binding energies of coumarin-crown ethers based on 15-Crown-5 (15 C5) and 18-Crown-6 (18 C6) as well as the optical absorptions of coumarin-crown ethers based on 12-Crown-4 (12 C4), 15 C5 and 18 C6. We explored why the attachment of crown ether ring to coumarin affects the Na+ binding energies of coumarin-crown ethers and also why the optical absorption of coumarin is modified by the crown ethers. Our study reveals that the Na+ ion binding energies of coumarin-crown ethers depend strongly on the size of the crown ether ring and also on the attachment position of the ether ring on coumarin. These factors affect the intramolecular charge transfer and overall stability of the complexes. The absorptions of the coumarin and ether ring parts of coumarin-crown ether are red shifted from those of isolated coumarin and crown ether, respectively. The red-shift of the coumarin ester group absorption is much stronger depending on the attachment position of the ether ring to coumarin. The absorption intensity of the coumarin part in coumarin-crown ethers is reduced for the benzene group absorption, but is enhanced for the ester group absorption.

ChemInform Abstract: Stereoselective Synthesis of Bio‐Hybrid Amphiphiles of Coumarin Derivatives by Ugi—Mannich Triazole Randomization Using Copper Catalyzed Alkyne Azide Click Chemistry.

An efficient synthesis of ester-triazole-amide amphiphiles of coumarin derivatives by triazole randomization based on click approach is described. Twenty-five small peptide azides were synthesized using Ugi or alternate Mannich-type multi-component reactions. The new azides were then used for the triazole randomization of alkyne functionalized coumarin ester under CuAAC conditions. Sixty-five new peptide bio-hybrids are obtained in near quantitative yield with high regio and stereoselectivity.

Stereoselective synthesis of bio-hybrid amphiphiles of coumarin derivatives by Ugi–Mannich triazole randomization using copper catalyzed alkyne azide click chemistry

An efficient synthesis of ester-triazole-amide amphiphiles of coumarin derivatives by triazole randomization based on click approach is described. Twenty-five small peptide azides were synthesized using Ugi or alternate Mannich-type multi-component reactions. The new azides were then used for the triazole randomization of alkyne functionalized coumarin ester under CuAAC conditions. Sixty-five new peptide bio-hybrids are obtained in near quantitative yield with high regio and stereoselectivity.

PH Effect on the Photochemistry of 4-Methylcoumarin Phosphate Esters: Caged-Phosphate Case Study

There are numerous reports of coumarin ester derivatives, in particular phosphate esters, as photocleavable cages in biological systems. Despite the comprehensive analysis of the photocleavage mechanism, studies of 4-methylcoumarin caged phosphates and/or nucleotides were always performed at constant pH. In this work, we present the study of the pH effect on the photochemistry of (7-diethylaminocoumarin-4-yl)methyl phosphate (DEACM-P). Fluorescence and photocleavage quantum yields, as well as the fluorescence decay times were measured as a function of the pH. It was found that the pH produces significant changes in the overall photochemical quantum yield of DEACM-P, and the observed changes are complementary to those obtained from the fluorescence quantum yield. Deprotonation of DEACM-HPO(4)(-) to yield DEACM-PO(4)(2-), produces a decrease in the photochemical quantum yield (from 0.0045 to 0.0003) and an increase in the fluorescence quantum yield (from 0.072 to 0.092). Moreover, from the analysis of the decay times, we have also found that hydroxyl ion is not only relevant, but it is mechanistically involved in the photoreaction of DEACM-HPO(4)(-).

Improved Nucleic Acid Triggered Probe Activation through the Use of a 5-Thiomethyluracil Peptide Nucleic Acid Building Block

To improve the efficiency of a nucleic acid triggered probe activation (NATPA) system a 5-thiomethyluracil peptide nucleic acid (PNA) building block has been synthesized. Attachment of imidazole and a coumarin ester to uracils at the ends of two PNAs resulted in a 550 000-fold acceleration of DNA-triggered coumarin release relative to imidazole and a 6-fold increase in k(cat) relative to a system which had these groups attached to the amino and carboxy ends of PNAs. [structure: see text]

PNA-based RNA-triggered drug-releasing system.

A three-component sequence-specific RNA-triggered drug-releasing system is described that consists of an 8-mer PNA linked to a coumarin ester (the prodrug component) and a 14-mer PNA linked to histidine (the catalytic component) that are complementary to the C loop of E. coli 5S rRNA (the triggering component). Binding of the catalytic component to the RNA creates a prodrug-metabolizing enzyme that catalyzes a 60,000-fold acceleration in the rate of coumarin release from the prodrug compared to the rate of coumarin release from the ester subunit catalyzed by imidazole alone. RNA-triggered release of hydroxycoumarin is only slightly less efficient than that triggered by a short unfolded DNA sequence corresponding to the PNA binding sites. The lower efficiency results from a decrease in k(cat) and an increase in K(M), presumably due to the bent nature of the RNA. The efficiency of DNA-triggered hydroxycoumarin release was found to depend on the distance between the catalytic and prodrug components.

Superoxide organic chemistry within the liposomal bilayer, part II: a correlation between location and chemistry

Coumarin ester derivatives 1, substituted at C-4 and/or C-12 with alkyl chains, were synthesized and intercalated within DMPC liposomal bilayers. By correlating the 13C chemical shift with medium polarity [ E T(30)], the relative location of these substrates within the liposomal bilayer was determined. The length of the alkyl chain substituents clearly influences the lipophilicity of the substrates and their location and orientation within the liposome: Superoxide readily saponifies the C-12 esteric linkage of 1, when this reaction site lies in a polar region of the liposome ( E T(30) > 45 kcal/mol), to give the corresponding 7-hydroxy coumarin derivatives 2. However, when C-12 lies deeper and is hence less available to O 2 − , the lactonic carbon C-2, which lies in a shallower region ( E T(30) = 43–49), is the preferred site for superoxide-mediated cleavage. When coumarin 1 is disubstituted with long chains at both C-12 and C-4, these derivatives lie deep within the bilayer and react only slowly with O 2 − . These results indicate there is indeed a correlation between location within the bilayer and substrate reactivity. Contrary to the suggestion of Dix and Aikens ( Chem. Res. Toxicol. 6:2–18; 1993) superoxide can penetrate deep within the liposomal bilayer. Nevertheless, its concentration drops precipitously (to ∼16% of what it is near the interface) below E T values of 38, thereby precluding substantial reaction with many highly lipophilic substrates. This work also confirms the findings of others that reactions of small oxy-radicals occur within cellular membranes and appear to be of significant biological importance.

HPLC Determination of Valproic Acid as Bromophenacyl Ester in Blood Plasma

Valproic acid (2-propylpentanoic acid) is an effective anticonvulsant widely used alone or in combination with other drugs (e.g., with carbamazepine, phenitoin, and phenobarbital) [1]. In the latter case, valproic acid (VA) decreases binding of other drugs (e.g., phenitoin and phenobarbital) to blood plasma proteins. On the other hand, phenitoin and phenobarbital also reduce the VA concentration in the blood plasma. VA is characterized by a high rate of absorption and elimination; for this reason the drug level in the plasma exhibits significant variations, especially if the interval between doses exceeds 8 h [2]. Therefore, monitoring of the VA level in the blood is very important both for successful therapy and for studying the VA pharmacokinetics and interactions with other drugs. Although numerous data have been reported on the determination of VA by various conventional methods [3 – 9], development of the new analytical procedures is still important for several reasons. First, VA, being a volatile compound, introduces large uncertainties as a result of losses in the sample concentration stage upon liquid extraction. Second, VA determination by HPLC with conventional UV detectors encounters problems related to weak optical absorption in this spectral range. For this reason, gas chromatography with a plasma-ionization detector was frequently preferred. However, being an acid, VA yields peaks with considerable tails on the GC chromatograms. This is usually eliminated by converting VA into derivatives (mostly by methylation) [3]. It should be noted that HPLC is still the most natural method for the analysis of biological samples, but VA has to be converted into derivatives exhibiting stronger absorption in the UV range, such as bromophenacyl, pentafluorobenzyl, or coumarin esters [4 – 9]. However, the release of VA in the course of derivatization (typically conducted in a micellar medium or upon precipitating proteins with acetonitrile [6, 9]) is incomplete because VA is strongly bound to proteins (80 – 90%) and is partly lost as a result of coprecipitation [6, 9]. Therefore, the total (bound plus free) VA concentration in the plasma is more reliably determined by methods involving the primary denaturation of proteins, followed by VA extraction with an appropriate organic solvent and, finally, derivatization [8]. The purpose of this study was to establish optimum conditions for VA extraction from blood plasma and conversion into bromophenacyl ester. We have also selected the optimum mobile and immobile phases for the HPLC analysis of bromophenacyl esters of VA (VABE) and nonanoic acid (NABE) and verified the method by determining VA in the blood plasma of experimental animals.

Porphyrin Core Star Polymers: Synthesis, Modification, and Implication for Site Isolation

Porphyrin Core Star Polymers: Synthesis, Modification, and Implication for Site Isolation

Identification of Essential Residues for the Catalytic Function of 85-kDa Cytosolic Phospholipase A2: PROBING THE ROLE OF HISTIDINE, ASPARTIC ACID, CYSTEINE, AND ARGININE

Cytosolic phospholipase A2 (cPLA2) hydrolyzes the sn-2-acyl ester bond of phospholipids and shows a preference for arachidonic acid-containing substrates. We found previously that Ser-228 is essential for enzyme activity and is likely to function as a nucleophile in the catalytic center of the enzyme (Sharp, J. D., White, D. L., Chiou, X. G., Goodson, T., Gamboa, G. C., McClure, D., Burgett, S., Hoskins, J., Skatrud, P. L., Sportsman, J. R., Becker, G. W., Kang, L. H., Roberts, E. F., and Kramer, R. M.(1991) J. Biol. Chem. 266, 14850-14853). cPLA2 contains a catalytic aspartic acid motif common to the subtilisin family of serine proteases. Substitution within this motif of Ala for Asp-549 completely inactivated the enzyme, and substitutions with either glutamic acid or asparagine reduced activity 2000- and 300-fold, respectively. Additionally, using mutants with cysteine replaced by alanine, we found that Cys-331 is responsible for the enzyme's sensitivity to N-ethylmaleimide. Surprisingly, substituting alanine for any of the 19 histidines did not produce inactive enzyme, demonstrating that a classical serine-histidine-aspartate mechanism does not operate in this hydrolase. We found that substituting alanine or histidine for Arg-200 did produce inactive enzyme, while substituting lysine reduced activity 200-fold. Results obtained with the lysine mutant (R200K) and a coumarin ester substrate suggest no specific interaction between Arg-200 and the phosphoryl group of the phospholipid substrate. Arg-200, Ser-228, and Asp-549 are conserved in cPLA2 from six species and also in four nonmammalian phospholipase B enzymes. Our results, supported by circular dichroism, provide evidence that Asp-549 and Arg-200 are critical to the enzyme's function and suggest that the cPLA2 catalytic center is novel.

5362627 Stabilization and reduction of background fluorescence of hydroxy coumarin ester enzyme substrates : Blumenthal Richard A; Lau Hon-Peng P; Yang Esther K - E I Du Pont de Nemours and Company

5362627 Stabilization and reduction of background fluorescence of hydroxy coumarin ester enzyme substrates : Blumenthal Richard A; Lau Hon-Peng P; Yang Esther K - E I Du Pont de Nemours and Company

Synthesis and Evaluation of Novel Crowned Coumarins as Self-Catalytic Fluorescence Reagents

Abstract Three coumarin reagents carrying crown-ether moieties as catalytic sites for the fluorescence derivatization of carboxylic acids were designed and synthesized. The catalytic abilities of these reagents were evaluated based on the stability constants (Ks) for complexation with metal acetates in methanol. The derivatization reactions of carboxylic acids with these reagents proceeded self-catalytically without crown-ether catalysts, and gave the corresponding coumarin esters in good yields. It was found that their reactivities significantly depended upon the metal-binding ability of the reagent molecules from kinetic treatments of the reactions. The derivatized products showed remarkably high fluorescence quantum yields of above 0.8 in methanol. These results suggested that the functionalization of reagents was a quite useful approach for the development of new-type analytical reagents.

Quantitative analysis of total resin acids by high-performance liquid chromatography of their coumarin ester derivatives

A method for the quantitative analysis of resin acids in effluent and water samples using high-performance liquid chromatography is described. Resin acids in aqueous samples are extracted by passage through C 18 solid-phase cartridges at pH 9. The (7-methoxycoumarin-4-yl) methyl (MMC) and (7-acetoxycoumarin-4-yl) methyl (MAC) esters are quantitatively formed at room temperature by the reaction of resin acids with 4-bromomethyl-7-methoxycoumarin and 4-bromomethyl-7-acetoxycoumarin respectively, in the presence of potassium carbonate. The effect of potassium carbonate particle size, exposure to light, presence of residual water, and derivatisation reagent: resin acid ratio on their formation are described. The MMC esters of resin acids may be detected by UV absorption at 318 nm at concentration > 20 μg 1 −1, while the (7-hydroxycoumarin-4-yl) methyl esters, obtained by post-column alkaline hydrolysis of the resin acid MAC (RAMAC) esters, enable the detection or resin acids by fluorescence spectrophotometry to levels below 1 μg 1 −1. The method has been compared to gas chromatogrpahic analysis of the carboxylic acid methyl esters and shows no evidence of any interferences by other carboxylic acids. The method is routinely used by two newsprint mills for environmental monitoring of resin acids in effluent.

Photophysical behavior of ester-substituted aminocoumarins: a new twist

Abstract : The fluorescent behavior of two amino-substituted coumarin esters was examined in solvents of different polarity. Coumarin 3, a simple ester derivative, behaves conventionally. Its fluorescence emission shifts to lower energy as the solvent polarity increases and the efficiency of the emission is essentially unaffected by solvent change. This behavior is characteristic of a rotation-inhibited intramolecular charge transfer (ICT) state. Coumarin 4, substituted with an alpha-keto ester function at the 3-position, also shows emission characteristic of an ICT state. However, in this case, the fluorescence efficiency and lifetime of the excited state decrease markedly as the solvent polarity increases. This behavior is characteristic of formation of a non- emissive twisted intramolecular charge transfer (TICT) state. Since rotation of 4 about the carbon-nitrogen bond is inhibited, twisting must occur around another group in the molecule. Consideration of the structure leads to identification of a rotation around the bond connecting the carbonyl group of 4 as leading to a TICT state. Keywords: Twisted charge transfer, Amino compounds.

A one-vial method for routine extraction and quantification of free fatty acids in blood and tissue by HPLC

A one-vial procedure has been developed to quantify free fatty acids in human blood serum and rat heart tissue. To allow routine analysis the system has been constructed to allow simultaneous processing of nine samples (Praechromat). The free fatty acids are extracted with Freon 11 and then derivatized to coumarin esters prior to HPLC. The Freon 11 extraction of the free fatty acids is rapid and complete. Neither hydrolytic degradation of natural fatty acid esters nor oxidative damage of unsaturated fatty acids was observed. Fifteen free fatty acids (FFA) were routinely quantified by isocratic elution with high reproducibility (SD < 4%) and good recovery (0.1 m m FFA: 98–100%, 0.02 m m: 91–105%). The free fatty acids could be determined in the range from 20 pmol to 20 nmol.

Coumarin Derivatives fromEryngium campestre1

Aegelinol benzoate, a new dihydroxanthyletin ester and the known coumarin esters agasyllin and grandivittin, as well as, aegelinol have been isolated from ERYNGIUM CAMPESTRE roots using column chromatography and subsequent semipreparative HPLC. The structures of the compounds have been elucidated by a combination of spectroscopic methods.

The acute toxicity of dichloroalkyl aryl phosphates in relation to chemical structure

The acute toxicity of di-alkyl 3-chloro-2-methyl coumarin-7-yl phosphates varies with basic group structure in the order (EtO) 2P(O) > (EtO) 2P(S) > (Bu n O) 2P(O) > (PR n O) 2P(O) > (4-chlorobutyl- O) 2P(O) > (3-chloropropyl- O) 2P(O) > (2-chloropropyl) 2P(O) > (2-chloroethyl) 2P(O) > (2, 3-dichloropropyl- O) 2P(O). A similar order was obtained with p-nitrophenyl esters. Poor correlation between rates of hydrolysis and inhibition of acetylcholinesterase suggests that the electronic effects of these structural variations on affinity for cholinesterase are outweighed by other considerations. Increased susceptibility to hydrolysis consequent upon chlorine substitution did not completely account for the low toxicity of the di-(2-chloroethyl) coumarin ester, which hydrolysed faster than the other members of the series. Chlorine substitution increases the reactivation rate of phosphorylated calf erythrocyte acetylcholinesterase. This effect is greatest when the substitution is close to the phosphorus atom. The conversion of unstable phosphorylated enzyme to a stable form is also accelerated in the propyl compounds, particularly when the substitution is terminal. However, ageing rates following inhibition by butyl and 4-chlorobutyl compounds are essentially similar. These properties are shown to be relevant in vitro by comparing the recovery of brain acetylcholinesterase activity in poisoned chicks with the success of 2PAM therapy. The potencies of the coumarin phosphates were assessed by incubating them with acetylcholinesterase under standard conditions. The order of potencies corresponded well with the order of toxicity with the exception of ethyl and 2-chloroethyl compounds.