Studies on Cation Selectivities of Some Pyridine-Based Ionophores for Use in Polymer Membrane Chemical Sensors

The synthesis of some macrocyclic compounds based on 4-octyloxypyridine-2,6-dicarboxylic acid, containing sulfur and/or oxygen atoms in the 2 to 6-bridging unit, along with some non-cyclic analogues is reported. These were tested for cation selectivity in poly(vinyl chloride)-based membrane electrodes. Little selectivity was found for any ion with the oxygen-containing compounds, and none approached the selectivity for potassium reported previously for a related compound. High bonding affinities for class b acceptors, particularly Ag+ and Hg2+, were found for sulfur-containing compounds. The complexation with Hg2+ was so strong that the electrodes showed behaviour characteristic of an anion response.

Synthesis and Further Ring-Forming Reactions of a New 3-Amino-isoquinoline-4-carbaldehyde

The synthesis of 3-amino-6-(p- methylphenoxy )isoquinoline-4-carbaldehyde in two steps from the corresponding ethyl ester is reported. Further ring annulations by Friedlander synthesis are described to give, for example, new tetra- and penta -cyclic systems ( benzo [f] pyrimido [4,5-b][1,8] naphthyridine and benz [f] indolo [3,2-b][1,8] naphthyridine ).

Nucleophilic Substitution Reactions in Benzo[C][1,8]naphthyridines. II

3-Chloro-1-methyl-6-(p- methylphenoxy ) benzo [c][1,8] naphthyridine has been prepared, the reactions with various nitrogen, oxygen and sulfur nucleophiles studied, and the results compared with those for the 1- chloro-3-methyl isomer. The 6-position was more reactive for oxygen and nitrogen nucleophiles, so much so that an initially added 6-NHR group was displaced by a second R′NH2 nucleophile at least as readily as was the 3-chloro group. With p- chloro ( thiophenol ), however, the 3-chloro group was preferentially displaced.

A New Synthesis of Pyrazino[2,3-c]isoquinolines

A convenient synthesis of 1-(p-chlorophenoxy )isoquinoline-3,4-diame is described. Condensation with ethyl pyruvate gave entry to the tricyclic title system, and some further nucleophilic displacement reactions of substituent groups are described. The direction of ring closure in the tricycle formation was proved by determining the crystal structure of one of the derivatives; rhombohedral crystals of (3b) belong to the space group R3 with a 21.822(5)Ǻ, α 116.81(2)° and Z 12. Full-matrix refinement using 3093 reflections converged at R 0.085.

Ethoxycarbonylation of α-Cyano-o-toluonitrile and Cyclization to Isoquinolines and Pyrimido[4,5-c]isoquinolines

α -Cyano-o-toluonitrile is a-ethoxycarbonylated with ethyl chloroformate and 4-dimethylamino- pyridine, and cyclized to ethyl 3-amino-1-bromoisoquinoline-4-carboxylate. This is further functionalized, and examples of third-ring annulation to pyrimido [4,5-c] isoquinolines are reported.

Cation-Binding Properties of Macrocyclic Polyether and Polythioether Diesters and Dithioesters From 1,10-Phenanthrolines and 1,8-Naphthyridines

The cation-binding properties of the title compounds (1)-(7) with the alkali, alkaline-earth, silver, ammonium and copper(II) picrates have been determined from host/guest complexation experiments. The association constants depend on the ligand cavity diameter, the nature of the heterocycle , the type and number of donor atoms and charge on the complexed cation. Dynamic 1H n.m.r . spectroscopy has also been employed, to demonstrate the comparable stability of a 21-membered 1,10-phenanthrolino ligand to its pyridine analogue in binding a benzylammonium salt. From this study, information on both the complex and ligand conformations was obtained.

Nucleophilic-Substitution Reactions in Benzo[C][1,8]Naphthyridines

The reactions of 1-chloro-3-methyl-6-(p- methylphenoxy ) benzo [c][1,8] naphthyridine with a variety of nucleophiles are reported. The relative reactivity of the 1- and 6-positions depends on the nucleophile and reaction conditions. Anilines, and alkyl and aryl thioxides react at position 1, alkylamines and alkoxide at position 6, and acidified alcohol at both 1 and 6. Some possible reasons for these positional reactivities are discussed.

A Synthesis of 1-Methoxyisoquinoline-3,4-Diamine and Some Derived Imidazo[4,5-C]Isoquinolines

A convenient synthesis of 1-methoxyisoquinoline-3,4-diamine is described. From this, one-carbon bridging units were used to prepare the angular imidazo [4,5-c] isoquinoline system containing 2-aryl, 2-thio and 2-amino substituents . From the latter two, further ring formation between substituent and imidazo nitrogen was investigated.

Kinetics of inhibition and hysteresis of sheep liver cytoplasmic aldehyde dehydrogenase with glyoxylic acid: further evidence relating to the two-site model for aldehyde oxidation

Despite the fact that it is an aldehyde, glyoxylic acid is not a substrate for sheep liver cytoplasmic aldehyde dehydrogenase; instead it functions as an inhibitor of both the esterase and dehydrogenase activities. From a consideration of the inhibition patterns it is concluded that glyoxylic acid does not bind in the catalytic propionaldehyde-binding domain, thus confirming the two-site model as proposed previously. Since the corresponding neutral methyl ester is a substrate it is suggested that the catalytic binding domain must contain a negatively charged group which prevents the binding of glyoxylic acid. Steady-state and pre-steady-state kinetic studies indicate that glyoxylic acid inhibits the dehydrogenase activity by converting the enzyme into a dead-end form which cannot undergo the catalytically essential conformational change. Incubation of the enzyme with NAD+ and glyoxylic acid for 10 min before the addition of propionaldehyde gave rise to hysteresis effects which can be explained on the basis of a slow isomerization of the enzyme X NAD+ X glyoxylic acid complex.

An Intramolecular Rearrangement in the Acetylation of Pyridin-4-amine

The surprisingly rapid formation of 4-( acetylamino )pyridine from reaction of pyridin-4-amine with various acetylating agents seems explicable by a mechanism which involves rate-determining intramolecular rearrangement of a first-formed ring N-acetyl intermediate.

Substitutent Effects in Non-Aromatic Nitrogen Heterocycles: Alkaline Hydrolysis of Methyl N-Methyl (oxo)dihydropyridinecarboxylates and Diaza Analogues

Ester hydrolysis studies on some isomeric methoxycarbonyl derivatives of N-methylpyridin-2- and 4-ones show that reaction rates are affected by the relative positions of CO2Me, =O and NMe functions in ways which could not be predicted. However, from limited result for analogous pyrimidine derivatives, it seems that reactivity in these polyfunctional compounds can be predicted from the pyridine data by assuming additivity of effects.

Reaction with acetic anhydride as a method for estimating the basicity of exocyclic amino groups in nitrogen heterocycles

Relative rates for acetylation of various anilines and amino heterocycles with acetic anhydride in pyridine were determined by a competition method. From a Bronsted plot of reactivity against basicity for the anilines, and by considering the heterocycles as substituted anilines, pKa values for the amino group in a variety of heterocycles have been obtained.

A synthesis of Benzo[c][1,8]naphthyridinones: an exception to the Knorr reaction

The reaction of 1-methoxyisoquinolin-3-amine with ethyl acetoacetate, and subsequent ring closure, is reported. Conrad-Limpach synthesis leads to the expected 4(1H)-one. The same isomer is formed under Knorr conditions (hot polyphosphoric acid), while a less acidic medium (hot acetic acid) gives the 2(1H)-one.

The effect of acid concentration on the pyridine nitramine rearrangement: an N.M.R. study

The rearrangement of 2-and 4-nitraminopyridines in 70-95% sulfuric acid has been investigated by n.m.r. Ring nitration is favoured by conditions leading to initial dissociation of the nitramine, and the results provide no support for an intramolecular rearrangement mechanism. 2-Nitraminopyridines react to give the analogous pyridin-2-one at the low and, surprisingly, high ends of the concentration range. The 4-nitraminopyridine rearrangement is slower because of the greater basicity of pyridin-4-amine, and also because of the formation of an unidentified species which required heat to give the rearrangement product.

A two-site model for the esterase and dehydrogenase activities of sheep liver aldehyde dehydrogenase

Although aldehyde dehydrogenase (ALDH) from sheep liver cytosol has a broad specificity, it will not oxidize the aldehyde group of glyoxylic acid which is in fact an inhibitor of the enzyme. The inhibition pattern is non-linear but competitive at high propionaldehyde concentrations (2-20 mM); however, a simple non-competitive pattern is observed at low (less than 100 microM) propionaldehyde concentrations (Ki = 1.6 mM). The esterase activity was unaffected by glyoxylic acid in the absence of NAD+ but a simple competitive inhibition pattern (Ki = 2.5 mM) was observed with respect to 4-nitrophenyl acetate in the presence of NAD+. The data require a two-site model in which ester and aldehyde binding sites are distinct but with a second propionaldehyde molecule, and glyoxylic acid, binding at or near the ester binding site. Consistent with this model is the fact that chloral hydrate was a non-competitive inhibitor of the esterase activity in the presence of NAD+ but a competitive inhibitor in its absence. The enzyme exhibited hysteretic behavior governed by the protonated form of an ionizable group with an apparent pKa of 7.55.

A synthesis of 6- and 4-hydroxymethyl derivatives of pyridin-3-ols

Studies are reported of dimethylaminomethylation of pyridin-3-ols-in which a bromo substituent is used as a temporary block to control orientation-and subsequent conversion into hydroxymethyl analogues.

Catalysis by α-substituted pyridines in the hydrolysis of aryl acetates and acetic anhydride

Results for the hydrolysis of p-nitrophenyl acetate, 2,4-dinitrophenyl acetate and acetic anhydride, catalysed by various substituted 2-amino- and 2-methyl-pyridines, are reported. The results seem consistent with nucleophilic catalysis throughout, contrary to some literature reports.

Substituent effects on the isomer ratios in the rearrangement of some 2- and 4-nitraminopyridines

The preparation, and rearrangement in 92% sulfuric acid, of 4-X-2-nitramino- (1), 2-X-4-nitramino-(2), and 6-X-2-nitramino-pyridines (3) is reported (X = H, Me, MeO, Br, Cl, CO2H). The product isomer ratios can be explained by differential electronic stabilization of the appropriate a complexes for aromatic nitration and steric effects seem relatively unimportant. Deuteration [3-D in series (1), X = Me] had no effect on the product distribution.

Kinetic studies on the mechanism of the nitraminopyridine rearrangement

Rate data are reported for the rearrangement, in 92% sulfuric acid at 30�, of a series of 4-X-2-nitra-minopyridines (X = H, Me, Br, CI, MeO, CO2H) and of 4-methyl-2-nitramino(3-D)pyridine. Values of pKa for second protonation of the corresponding pyridin-2-amines were also measured and rate constants for nitration of the monoprotonated pyridinamines were thereby calculated. The results suggest that the rate-determining step occurs prior to formation of the appropriate 3-and 5-nitro σ complexes. The nature of this step is not clear, however, and a key role for the nitramine itself is not proven by the current evidence.