J. Christian Mason

Binding constant determination of drugs toward subdomain IIIA of human serum albumin by near-infrared dye-displacement capillary electrophoresis.

Drug binding to serum albumin influences several important pharmacological properties such as toxicity, solubility, activity, distribution, and excretion. It is therefore of interest to have methodologies that allow for the determination of drug‐albumin affinity constants while simultaneously providing information on the location of the drug binding site. In the present work we describe a method for the determination of binding constants of drugs known to bind to subdomain IIIA of serum albumin. Drugs used in the study were ketoprofen, ibuprofen, quinidine, naproxen, imipramine, and clofibrate. Binding constants of the drugs were determined by near‐infrared dye‐displacement capillary electrophoresis. The dye‐displacement technique uses a competitive‐type interaction between the drug of interest and a dye probe to arrive at a binding constant. A heptamethine cyanine dye was used as a probe for drug binding at subdomain IIIA of serum albumin. The utility of the dye as a noncovalent label for serum albumin was investigated. Additionally, the ability of the method to illustrate enantioselective binding is shown. The dye displacement technique has advantages over current electrophoresis‐based techniques in that it is faster and uses less reagent.

Use of non-covalent labeling in illustrating ligand binding to human serum albumin via affinity capillary electrophoresis with near-infrared laser induced fluorescence detection

This paper demonstrates the use of a near-infrared (NIR) dye as a non-covalent label for human serum albumin (HSA). The dye is a water soluble, heptamethine cyanine dye. The utility of the dye as a tracer illustrating the binding of various drugs to HSA is demonstrated via affinity capillary electrophoresis with near-infrared laser-induced fluorescence detection (ACE-NIR-LIF). Additionally, the factors affecting the separation of relevant species were investigated. The change in quantum yield of the dye upon complexation with HSA was calculated. Spectrophotometric measurements were conducted to study the stoichiometry of the dye albumin complex.

SYNTHESIS OF 4-PERFLUOROALKYLQUINOLINES

Abstract 4-(Cn−1F2n−1)-Substituted quinolines (n = 2–4) are obtained by the reaction of 2-(CnF2n+1)-substituted anilines 1 with lithium enolate of acetaldehyde. A similar treatment of 1 with lithium enolates of methyl ketones, the treatment of 1 with lithium phenylacetylide or cyclization of ketimines derived from 1 and aryl methyl ketones furnish the corresponding 2-aryl-4-perfluoroalkylquinolines. The reaction of 1 with lithiated carbonitriles RCH(Li)CN (R = H, alkyl) provides an easy access to 2-amino-4-perfluoroalkyl-3-R-quinolines.

Base-mediated reactions of ortho- and para-perfluoroalkylanilines

Abstract The title chemistry involves regioselectively a benzylic position of the perfluoroalkyl group and provides an easy access to substituted quinolines and methanes.

Design, synthesis, and characterization of a calcium-sensitive near infrared dye.

Intracellular calcium concentration in biological cells varies from 0.1 to 10 muM depending upon cell signaling and disease states. A direct estimate of calcium concentration in cell tissues within this range is possible with a novel calcium-selective reagent 15C5-774. The molecule of 15C5-774 consists of a near-infrared (NIR) chromophore (lambda(max)=774 nm) and a metal complexing moiety of benzo-15-crown-5. The reagent shows a strong calcium binding affinity in a 1:1 ratio and metal selectivity in the order Ca(2+)>Mg(2+)>Sr(2+) approximately K(+) approximately Na(+)>Zn(2+)>Li(+). The high sensitivity is achieved by conducting absorption measurements in the NIR region where background interference from the biological matrix is low.

The addition reaction of hydroxide or ethoxide ion with benzindolium heptamethine cyanine dyes

Abstract This paper pertains to a nucleophilic addition reaction at the C2 atom of a benz[c]indolium or 3,3-dimethyl-1H-benz[e]indolium subunit of the corresponding near-infrared heptamethine cyanine that contains a chlorine atom at the central meso position of the chromophore. An important finding is that the efficient S RN 1 replacement of the chloro substituent in such dyes is completely suppressed in the reactions (i) of hydroxide and ethoxide ions, both of which are poor single electron donors and (ii) conducted in aqueous alcohol, a medium that does not promote single electron transfer. The adducts produced were isolated and characterized by elemental analysis, 1 H NMR, and 13 C NMR. The NIR-absorbing parent dye is regenerated quantitatively upon treatment of the corresponding adduct with a weak acid, including silica gel.

Characterization of a novel crown ether-bearing near-infrared heptamethine cyanine dye. A study of fluorescence quenching by lithium

Abstract The spectral characteristics of a crown ether-bearing heptamethine cyanine dye (JCM-15C5) and its quenching by lithium ion are reported. The absorbance maximum of the dye is at 776 nm in acetonitrile. This value matches the output of a commercially available laser diode (780 nm), thus making use of such a source practical for excitation. The emission wavelength of the dye in acetonitrile is at 799 nm. It was found that Li + ion selectively quenches the fluorescence intensity of JCM-15C5 by the static quenching mechanism. The Stern–Volmer quenching constant ( K sv ) was calculated from the Stern–Volmer plot and found to be 1.17×10 7 M −1 at room temperature. The detection limit for Li + ion was found to be 7.43×10 −2 ppb. The stability constant ( K s ) of the metal–dye complex was determined by fluorometric titration and found to be 5.40×10 7 M −1 .

AN ANIONICALLY ACTIVATED TRIFLUOROMETHYL GROUP AS A NOVEL SYNTHON FOR ISOXAZOLES AND 1,3,5-TRIAZINES

A reaction of trifluoromethyl-substituted anilines 1-3 with dianions derived from oximes of 3-pentanon and cyclohexanone provides a facile entry into the corrresponding isoxazoles 4-7. Triazines 8,9 are obtained upon treatment of a monoanion derived from benzamidine with the respective substrates 1, 2. Anions derived from 4-(trifluoromethyl)aniline 1 s its ortho isomer 2, substituted derivatives such as 3 (Scheme 1) and analogs containing other ionizable groups at ortho or para position to the trifluoromethyl function undergo elimination of fluoride to generate the corresponding intermediate products illustrated by 11 in Scheme 2. The meta isomers are stable under basic conditions. The early chemistry of the anionically activated trifluoromethyl group has been reviewed (1) and another recent review describes synthetic applications of the chemistry of trifluoromethyl-substituted substrates (2). The most recent developments not yet reviewed include one-pot synthesis of 2-(1-alkenyl)anilines (3), naphthalenes (4), fluoro heteroaromatic compounds (5,6), benzothiazoles (7), benzoxazoles (7), and additional examples of 4-aminoquinolines (8) obtained by the chemistry already described (2). A strong selective stabilization of the triplex DNA structure in the presence of duplex DNA has been found for certain 4-aminoquinoline products (9-11) derived from 2. The synthetic importance of the chemistry of the activated trifluoromethyl group, thus, is growing rapidly. A large number of substrates including 1-3 are available commercially, and others can easily be prepared by a trifluoromethylation reaction of electron-rich aromatic and heteroaromatic amines (12). In this paper, as part of our fundamental studies on the chemistry ο the anionically activated trifluoromethyl group, we describe a novel one-pot preparation of isoxazoles (13) and 1,3,5triazines (14) (Scheme 1). Isoxazoles 4-6 are obtained by the reaction of dianton derived from 3-pentanone oxime with the respective trifluoromethyl-substituted anilines 1-3. The cyclization involves the C F 3 group, the carbon atom of which becomes C-5 01 the isoxazole system. In a typical experiment a solution of LDA (20 mmol) and n-BuLi (20 mmol) prepared by the addition of n-BuLi (40 mmol, 2 Μ in cyclohexane) to a solution of diisopropylamine (20 mmol) in THF (20 mL) is treated dropwise at -75 °C under a nitrogen atmosphere with 3-pentanone oxime (20 mmol) (15,16). The mixture is stirred at +23 °C for 30 mir cooled to -75 °C and then treated with a solution of 1-3 (4 mmol) in THF (2 mL). The mixture is stirred at -75 °C for 30 min and then at +23 °C for 2 h. A standard workup is followed by chromatography on silica gel with pentanes/ether (1:1) as an eluent to give the corresponding isoxazole 4-6. A similar treatment of dianion of cyclohexanone oxime with 2 gave the