Fused Tetracyclic Quinoxalines from Reactions of o-Phenylenediamines in Polyphosphoric Acid

The condensation of 2,3-diaminobenzoic acid and the 5-chloro derivative with o-hydroxyphenylglyoxylic acid, isatin and benzothiophen-2,3-dione in polyphosphoric acid leads to the appropriate tetracycles. Isomeric products are formed from these unsymmetrical diamines, and methods of assigning particular structures are described.

Photoaffinity labeling of mefloquine-binding proteins in human serum, uninfected erythrocytes and Plasmodium falciparum-infected erythrocytes

A photoreactive quinolinemethanol analog, N-[4-[1-hydroxy-2-(dibutylamino)ethyl]quinolin-8yl]-4- azido-2-salicylamide (ASA-MQ) has been synthesized which closely mimics the action of mefloquine. ASA-MQ possesses potent antimalarial activity against a mefloquine-sensitive strain of Plasmodium falciparum and shows decreased activity against a mefloquine-resistant parasite strain. Radioiodinated ASA-MQ has been used in photoaffinity labeling studies to identify mefloquine-interacting proteins in serum, uninfected erythrocytes and Plasmodium falciparum-infected erythrocytes. We have shown that mefloquine interacts specifically with apo-A1, the major protein of serum high density lipoproteins. In addition, mefloquine was shown to interact specifically with the erythrocyte membrane protein, band 7.2b (stomatin). A further two high affinity mefloquine-binding proteins with apparent molecular masses of 22 and 36 kDa were identified in three different strains of Plasmodium falciparum. We suggest that these two mefloquine-binding parasite proteins may be involved in the uptake of mefloquine or may represent macromolecular targets of mefloquine action in malaria parasites.

Novel bisquinoline antimalarials. Synthesis, antimalarial activity, and inhibition of haem polymerisation

We report the synthesis of two series of novel bisquinoline compounds that inhibit the growth of both chloroquine-sensitive and chloroquine-resistant strains of Plasmodium falciparum. To study the molecular basis of the action of these novel antimalarial drugs, we examined their ability to inhibit haem polymerisation in the presence and absence of parasite extracts. The level of antimalarial potency was correlated with the level of inhibition of haem polymerisation, suggesting that these bisquinolines exert their antimalarial activity by antagonising the sequestration of toxic haem moieties.

Selective inhibition of cyclic AMP-dependent protein kinase by isoquinoline derivatives

A large series of isoquinoline derivatives was synthesised including derivatives of isoquinoline, isoquinolino[3,4-c]furazan, 1,2-dihydro-1-oxoisoquinoline, 6-oxopyrimido[1,2-d]isoquinoline, benzo[c][1,8]-naphthyridine, pyrazino[2,3-c]isoquinoline and benzimidazo[2,1-a]isoquinoline as well as further structurally related isoquinoline derivatives and pyrido-2,3-furazans. Representatives of all of these classes of isoquinolines are potent and selective inhibitors of the cyclic AMP-dependent protein kinase (PKA) catalytic subunit (cAK) from rat liver. The most effective cAK inhibitors are a series of 1,3-di-substituted and 1,3,4-tri-substituted isoquinolines (IC50 values 30-50 nM) (compounds A1, A2, A3, A4 and A5) and 2-ethylcarboxy-3-amino-5,6-dihydro-6-oxobenzo[c] [1,8]naphthyridine (E1) (IC50 0.08 microM). Compounds A1-A5 inhibit cAK in a fashion that is competitive with respect to ATP as substrate. The isoquinoline inhibitors A1-A5 are ineffective or very poor inhibitors of wheat embryo Ca(2+)-dependent protein kinase (CDPK) and rat brain Ca(2+)-dependent protein kinase C (PKC), chicken gizzard myosin light chain kinase (MLCK) and potato tuber cyclic nucleotide-binding phosphatase (Pase). E1 is a moderately effective inhibitor of CDPK and PKC (IC50 values 30 and 61 microM, respectively). The bisisoquinoline-1(2H)-one compound B7 inhibits cAK, CDPK, PKC and MLCK (IC50 values 8, 95, 24 and 7 microM, respectively) as does J1 [2-(p-bromophenyl)pyrrolo-[2,3-c]isoquinoline-5(4H)-one] (IC50 values 2, 50, 44 and 7 microM, respectively). The very potent isoquinoline-derived cAK inhibitors found here involve substitution of the N-containing isoquinoline ring system and these inhibitors show high specificity for cAK.

Fused Isoquinoline Systems From Reactions of an Iminoisocoumarin With Nitrogen Nucleophiles

Some reactions of 1-acetylimino-3-methyl-1H-2-benzopyran-4-carbonitrile with nitrogen nucleophiles are reported. This is a versatile intermediate and leads to isoquino [1,2-b] quinazoline (with methyl anthranilate ), [1,2,4] triazolo [5,1-a] isoquinoline (with hydrazine), imidazo [2,1-a] isoquinoline (with glycine ethyl ester), benzimidazo [2,1-a] isoqinoline (with o-phenylenediamine) and 1,3,5-triacine (with acetamidine ) systems.

Synthesis and Antibacterial Activity of Some 'Bisquinolones'

Ten ' bisquinolones' were prepared by joining two molecules of norfloxacin, or 1,8-naphthyridine and benzo [c][1,8] naphthyridine derivatives, with various aliphatic linkers. These were tested against 17 bacteria strains but none showed more than slight activity (MIC ≥ 10 mg/l). However, a 'monoquinolone' derived from benzo [c][1,8] naphthyridine showed greater activity than norfloxacin against a strain of Acinetobacter.

Synthesis and activity of some antimalarial bisquinolines

A new type of bisquinoline antimalarial, in which the basic side chain of chloroquine is retained, has been evaluated. Nine bisamides were prepared from aliphatic diacids with 6-amino- and 8-amino-((4-(diethylamino)-1-methylbutyl)amino)quinoline, and screened against chloroquine-sensitive and -resistant strains of Plasmodium falciparum in vitro. The resistance indices for all compounds were lower than for chloroquine. The position of attachment and length of the linker chain markedly affected activity. The most active (IC50 = 120 nM against the chloroquine-resistant FAC8 strain) was the -(O)C(CH2)4C(O)- linked 8-amino compound.

Cellulose Acetate-Based pH Indicator Optodes

Some pH indicators for use in optode membranes based on cellulose acetate have been prepared, and applications of membranes containing octyl bis (2,4-dinitrophenyl)acetate in static and flowing systems are discussed.

Inhibition of wheat embryo calcium-dependent protein kinase by acridines and azaacridines

The inhibition of wheat Ca(2+)-dependent protein kinase (CDPK) by substituted acridines and substituted 5-, 6-, 7- and 8-azaacridines (5-AA, 6-AA, 7-AA and 8-AA) was examined. Of a total of 71 substituted acridines and azaacridines examined, only 20 have IC50 values for wheat CDPK of less than 200 microM. Of these, effective compounds all have neutral or basic 4-substituents, except for 2,7-dibromo-4-carboxy-5-AAO (IC50 73 microM), the carboxymethyl ester of which is a much better inhibitor (IC50 20 microM). There is a large aza position effect so that various 4-substituted azaacridines can be either very active or very poor inhibitors depending upon the azaacridine nucleus substituted. One of the most potent inhibitors found is the 8-AA 4-N-(2-dimethylaminoethyl)carboxamide (4-P) derivative (IC50 1.5 microM), but the corresponding 4-substituted acridine analogue is a very poor inhibitor. Other potent inhibitors found include 1-nitro-4-P-8-AA (IC50 4 microM) and 7-bromo-4-methyl-5-AA (IC50 0.7 microM). These potent and relatively specific CDPK inhibitors may be useful in obtaining evidence for CDPK involvement in plant cell responses to specific signals.

Differential inhibition of cyclic AMP-dependent protein kinase, myosin light chain kinase and protein kinase C by azaacridine and acridine derivatives

A series of 72 acridine and azaacridine derivatives have been tested as inhibitors of Ca(2+)- and phospholipid-activated protein kinase C (PKC), the catalytic subunit of cyclic AMP-dependent protein kinase (cAK) and Ca(2+)-calmodulin-dependent myosin light chain kinase (MLCK). A series of monomethyl derivatives of N-(2-dimethylaminoethyl)-acridine-4-carboxamide that have anti-tumour activity are good inhibitors of MLCK (IC50 values ranging from 4-138 microM) but these same compounds are ineffective or relatively poor inhibitors of PKC or cAK. With only several exceptions, the effective azaacridine inhibitors of PKC and MLCK (IC50 values < 200 microM) have basic or neutral 4-substituents whereas the effective azaacridine inhibitors of cAK have either neutral or acidic 4-substituents. The four exceptions found to this generality are effective inhibitors of all three protein kinases with IC50 values of about 100 microM or less. With several exceptions azaacridine inhibitors of PKC are also inhibitors of MLCK but effective inhibitors of cAK are relatively poor inhibitors of MLCK and PKC and vice versa. 4-N-(2-dimethylaminoethyl)-6-azaacridone-4-carboxamide is a competitive inhibitor of MLCK with respect to both the peptide substrate and ATP. All other acridines and azaacridines examined are non-competitive inhibitors of both MLCK and cAK with respect to both ATP and peptide substrate. All azaacridine PKC inhibitors examined are competitive with respect to ATP and noncompetitive with respect to peptide substrate suggesting that binding of these inhibitors is at or near the enzyme active site. The inhibition of MLCK (but not cAK or PKC) by anti-tumour acridine carboxamides suggests a novel site of in vivo biological action and a useful criterion for the detection of potential antitumour compounds.

Photoaffinity labeling of chloroquine-binding proteins in Plasmodium falciparum

A photoreactive analog of chloroquine, N-(4-(4-diethylamino-1-methylbutylamino)quinolin-6-yl)-4- azi do-2- hydroxybenzamide (referred to as ASA-Q), has been synthesized and shown to mimic the action of chloroquine in possessing substantial antimalarial activity against a chloroquine-sensitive strain of Plasmodium falciparum. As for chloroquine, ASA-Q is less effective at killing drug-resistant strains of malaria, and the resistance can be modulated using the reagent verapamil. ASA-Q has been radiolabeled with Na125I and used as a photoaffinity probe for labeling chloroquine-binding proteins in malaria-infected erythrocytes. Two proteins have been identified with apparent molecular masses of 42 and 33 kDa in both chloroquine-sensitive and chloroquine-resistant strains of malaria. Photoaffinity labeling of the two proteins by iodo-ASA-Q was competitively inhibited by an excess of unlabeled chloroquine. The structurally related antimalarials amodiaquine and quinine also inhibited labeling of the two proteins, while verapamil and doxycycline had no effect. We suggest that the two labeled proteins are the macromolecular targets of chloroquine action in malaria parasites.

Electron-deficient DNA-intercalating agents as antitumor drugs: aza analogues of the experimental clinical agent N-[2-(dimethylamino)ethyl]acridine-4-carboxamide

A series of azaacridine (benzonaphthyridine) analogues of the drug N-[2-(dimethylamino)ethyl]-acridine-4-carboxamide (DACA) (currently in clinical trial) were synthesized. These compounds showed DNA binding affinities similar to that of DACA, as determined by the fluorometric ethidium displacement assay, but were generally less potent cytotoxins against P388 leukemia in vitro. The only compounds showing higher cytotoxicity than DACA were analogues with nitro substituents at the (acridine) 1-position; by analogy with the 1-nitroacridine nitracrine, these compounds probably undergo reductive metabolism. The only azaacridine to show significant in vivo antileukemic activity was benzo[b][1,5]naphthyridine-6-carboxamide. A possible reason for the unexpectedly low activity of these compounds (given the wide acceptability of substituents in DACA) may be their much lower lipophilicities, which are likely to result in lower rates of cell uptake.

Synthesis and biological evaluation of phenanthrene-derived carboxamides as cytotoxic agents

A series of phenanthrene-based tricyclic carboxamides has been synthesized as angular analogues of the clinical acridine carboxamide DACA, and their DNA binding, in vitro cytotoxicities and in vivo antitumour activities have been investigated. The compounds fall into two broad topological classes, where the carboxamide side chain is appended either to one of the terminal rings or to the central ring. In general, compounds of the first class showed stronger DNA binding than those of the second, and were the more potent in vitro cytotoxins. However, they were considerably less effective than DACA, both as DNA binders and cytotoxins. A 1,10-phenanthrolinecarboxamide derivative showed significant in vivo activity. As a class, these fused angular tricyclic carboxamides do not show sufficiently interesting activity to warrant further studies.

A Comparison of Chemical Reactivity in Some Benzo[b]Naphthyridines (Azaacridines)

Some comparisons between four series of benzo [b][1,x] naphthyridines (x=5-8) have been made. Bromination in acetic acid gave almost exclusive reaction β to the nitrogen in the outer pyrido ring. Basic silver oxide oxidation of the centre ring occurred in the order x = 6 > 8 > 7 > 5. Methylation occurred on the pyrido nitrogen, the relative nucleophilicities paralleling those of the corresponding naphthyridines . One methiodide (x = 6) underwent an interesting dimerization in solution and the structure of the product was determined by X-ray crystallography.

Chemistry of Some [1,2,5]Oxadiazolo[3,4-c]isoquinolines and N-Oxides

The reaction of some 4-nitroisoquinolin-3-amines with iodosobenzene diacetate [ PhI ( OAc )2] is a convenient preparation of the title compound N-oxides. Attempts to convert these into quinoxaline N,N′-dioxides were not successful, but reactions of some 5-substituents are described, along with deoxygenation to the corresponding furazan derivatives.

Synthesis of Some Benzo[b][1,6]naphthyridines and Benzo[b][1,7]naphthyridines

Pfitzinger (1-benzylpiperidin-4-one with 7-methylisatin) and Friedlander (3-aminopyridine-4-carbaldehyde with 2-methylcyclohexanone) syntheses, respectively, were used to prepare the title 'azaacridines' containing a methyl substituent peri to the central nitrogen. Oxidation of this group gave the corresponding aldehyde and carboxylic acid. In the [1,6] case, especially, the 10-position was also easily oxidized to give acridone analogues. Nitration occurred exclusively in the benzenoid rings.

Cytotoxic and DNA binding properties of aminoalkyl derivatives of di- and triazaphenanthrenes

A series of mono- and dicationic derivatives of various di- and triazaphenanthrenes were synthesized and evaluated against both wild-type and amsacrine-resistant P388 leukemia in vitro. Monocationic derivatives of the fully-aromatic benzo[c][1,8]naphthyridine chromophore showed moderate and equal cytotoxicity in both cell lines, suggestive of efficacy against both the alpha and beta isozymes of mammalian DNA topoisomerase II. Derivatives of both the benzo[c][1,8]naphthyridine and benzo[c][1,8]naphthyridine-3(4H)-one chromophores also showed significant in vivo activity against wild-type P388 leukemia.

Investigation of the Range of a Plastic pH Sensor Based on a Dibasic Ionophore

A study is reported of the use of a neutral carrier reagent containing two nitrogen atoms with very different basicities in a pH-sensitive membrane electrode with a view to obtaining a broad response range. This electrode responds well in the pH region of 6-12 but suffers anion interference in the region of pH 2-6. A study is included of the effect of adding various amounts of potassium tetrakis(4-chloropheny1)borate as an anion suppressing reagent to the membrane in order to reduce the anion interference at low pH values. The conclusion is drawn that an extension to the working pH range is not possible with this approach unless controlled amounts of anion suppressing reagent can be provided to approximately balance the positive charge of the carrier in each region of the pH scale.

Synthesis of Pyrazino[2,3-c]isoquinolinecarboxylic Acids and Related Compounds

1-Methylisoquinoline-3,4-diamine has been synthesized and condensed with α-dicarbonyl compounds to give the fused pyrazine ring. Oxidation of methyl groups gives the 3- and 6-carboxylic acids. Nitration occurs in the benzenoid ring to give the single 10-nitro product, and formation of an unusual 6-trinitromethyl compound is also reported.

Potentiometric Sensors Based on Macrocyclic Ligands: 1,8-Naphthyridine and 1,10-Phenanthroline Derivatives

The synthesis of some macrocyclic compounds based on 1,8-naphthyridine and 1,10-phenanthroline with rings containing four and five oxygen atoms is reported. These compounds were tested for cation selectivity in poly(vinyl chloride)-based potentiometric sensors. Nernstian esponse was observed towards the potassium ion but with low discrimination for potassium in the presence of other cations. Dimethyl 4-octyloxy-1,10-phenanthroline-2,9-dicarboxylate, a precursor to one of the macrocyclic series, showed a high preference for divalent cations such as Zn2+, Ba2+, Cu2+ and Co2+. .