[Synthesis and antitumour activities of some pteridine derivatives]

AIM

To study the synthesis and antitumour activities of some aryl-substituted pteridines.

METHODS

A series of aryl-substituted pteridines were synthesized from 4, 6-diamino-5-nitrosopyrimidines by cyclization with 4-aminophenylacetonitriles. The antitumour activities were tested by MTT method.

RESULTS

Nine new compounds (I-III) were synthesized and their structures were characterized by EA, IR, 1HNMR and MS spectra. Compounds I-III showed antitumour activities in vitro.

CONCLUSION

Compounds I-III showed remarkable antitumour activities in vitro. No interaction was determined between the title compounds and calf thymus DNA. It indicated that these compounds possibly inhibit dihydrofolate reductase (DHFR) or other enzymes on which folic acid depends.

Synthesis of 2,4-Diamino-6-[2‘-O-(ω-carboxyalkyl)oxydibenz[b,f]azepin-5-yl]methylpteridines as Potent and Selective Inhibitors of Pneumocystis carinii, Toxoplasma gondii, and Mycobacterium avium Dihydrofolate Reductase

Six previously undescribed N-(2,4-diaminopteridin-6-yl)methyldibenz[b,f]azepines with water-solubilizing O-carboxyalkyloxy or O-carboxybenzyloxy side chains at the 2'-position were synthesized and compared with trimethoprim (TMP) and piritrexim (PTX) as inhibitors of dihydrofolate reductase (DHFR) from Pneumocystis carinii (Pc), Toxoplasma gondii (Tg), and Mycobacterium avium (Ma), three of the opportunistic organisms known to cause significant morbidity and mortality in patients with AIDS and other disorders of the immune system. The ability of the new analogues to inhibit reduction of dihydrofolate to tetrahydrofolate by Pc, Tg, Ma, and rat DHFR was determined, and the selectivity index (SI) was calculated from the ratio IC(50)(rat DHFR)/IC(50)(Pc, Tg, or Ma DHFR). The IC(50) values of the 2'-O-carboxypropyl analogue (10), with SI values in parentheses, were 1.1 nM (1300) against Pc DHFR, 9.9 nM (120) against Tg DHFR, and 2.0 nM (600) against Ma DHFR. The corresponding values for the 2'-O-(4-carboxybenzyloxy) analogue (12) were 1.0 nM (560), 22 nM (21), and 0.75 nM (630). By comparison, the IC(50) and SI values for TMP were Pc, 13 000 nM (14); Tg, 2800 nM (65); and Ma, 300 nM (610). For the prototypical potent but nonselective inhibitors PTX and TMX, respectively, these values were Pc, 13 nM (0.26) and 47 nM (0.17); Tg, 4.3 nM (0.76) and 16 nM (0.50); Ma, 0.61 nM (5.4) and 1.5 nM (5.3). Thus 10 and 12 met the criterion for DHFR inhibitors that combine the high selectivity of TMP with the high potency of PTX and TMX.

A prototype solid phase synthesis of pteridines and related heterocyclic compounds

The development of a versatile solid phase synthesis of bicyclic polyaza heterocycles including pteridines, purines, and deazapurines is described. The strategy comprises the linking of a pre-formed pyrimidine through a thioether at the 2 or 4 position to a polystyrene resin, the cyclisation of the second ring, and the direct or oxidative cleavage of the product from the resin by nucleophilic substitution. This provides not only for substituent variation in the second ring, but also for variation at the site of cleavage. Limitations in the scope of the methodology are set by the intrinsic reactivity of pyrimidinyl 2- or 4-thioethers which, whilst undergoing ready nitration at C5, are surprisingly difficult to alkylate and acylate.

Syntheses of highly functionalised 6-substituted pteridines

Methods for the synthesis of polyfunctional 6-substituted pteridines from the corresponding 6-aldehydes are described. Alkene, ester, ketone, amide, cyano, oxime, bromo, methoxy and dihydroxy functional groups have all been introduced principally through improved methodologies for Wittig reactions using 2-thioalkyl-6-formylpteridines as substrates. Further modification of the alkenes derived from the Wittig reactions was difficult but selective conversion to the vic-diol was possible using ligand assisted catalysis with osmium tetraoxide. These methods are a component of an extensive methodology for the preparation of compounds that might serve as modulators of tetrahydrobiopterin activity or as inhibitors of dihydroneopterin aldolase.

Design, synthesis, and evaluation of 6-carboxyalkyl and 6-phosphonoxyalkyl derivatives of 7-oxo-8-ribitylaminolumazines as inhibitors of riboflavin synthase and lumazine synthase

A series of 6-carboxyalkyl and 6-phosphonoxyalkyl derivatives of 7-oxo-8-D-ribityllumazine were synthesized as inhibitors of both Escherichia coli riboflavin synthase and Bacillus subtilis lumazine synthase. The compounds were designed to bind to both the ribitylpurine binding site and the phosphate binding site of lumazine synthase. In the carboxyalkyl series, maximum activity against both enzymes was observed with the 3'-carboxypropyl compound 22. Lengthening or shortening the chain linking the carboxyl group to the lumazine by one carbon resulted in decreased activity. In the phosphonoxyalkyl series, the 3'-phosphonoxypropyl compound 33 was more potent than the 4'-phosphonoxybutyl derivative 39 against lumazine synthase, but it was less potent against riboflavin synthase. Molecular modeling suggested that the terminal carboxyl group of 6-(3'-carboxypropyl)-7-oxo-8-D-ribityllumazine (22) may bind to the side chains of Arg127 and Lys135 of the enzyme. A hypothetical molecular model was also constructed for the binding of 6-(2'-carboxyethyl)-7-oxolumazine (15) in the active site of E. coli riboflavin synthase, which demonstrated that the active site could readily accommodate two molecules of the inhibitor.

Structural requirements for inhibition of the neuronal nitric oxide synthase (NOS-I): 3D-QSAR analysis of 4-oxo- and 4-amino-pteridine-based inhibitors

The family of homodimeric nitric oxide synthases (NOS I-III) catalyzes the generation of the cellular messenger nitric oxide (NO) by oxidation of the substrate L-arginine. The rational design of specific NOS inhibitors is of therapeutic interest in regulating pathological NO levels associated with sepsis, inflammatory, and neurodegenerative diseases. The cofactor (6R)-5,6,7,8-tetrahydrobiopterin (H(4)Bip) maximally activates all NOSs and stabilizes enzyme quaternary structure by promoting and stabilizing dimerization. Here, we describe the synthesis and three-dimensional (3D) quantitative structure-activity relationship (QSAR) analysis of 65 novel 4-amino- and 4-oxo-pteridines (antipterins) as inhibitors targeting the H(4)Bip binding site of the neuronal NOS isoform (NOS-I). The experimental binding modes for two inhibitors complexed with the related endothelial NO synthase (NOS-III) reveal requirements of biological affinity and form the basis for ligand alignment. Different alignment rules were derived by building other compounds accordingly using manual superposition or a genetic algorithm for flexible superposition. Those alignments led to 3D-QSAR models (comparative molecular field analysis (CoMFA) and comparative molecular similarity index analysis (CoMSIA)), which were validated using leave-one-out cross-validation, multiple analyses with two and five randomly chosen cross-validation groups, perturbation of biological activities by randomization or progressive scrambling, and external prediction. An iterative realignment procedure based on rigid field fit was used to improve the consistency of the resulting partial least squares models. This led to consistent and highly predictive 3D-QSAR models with good correlation coefficients for both CoMFA and CoMSIA, which correspond to experimentally determined NOS-II and -III H(4)Bip binding site topologies as well as to the NOS-I homology model binding site in terms of steric, electrostatic, and hydrophobic complementarity. These models provide clear guidelines and accurate activity predictions for novel NOS-I inhibitors.

Recent advances in the chemistry and biology of folypoly-gamma-glutamate synthetase substrates and inhibitors

The importance of folylpoly-gamma-glutamate synthetase (FPGS) in cancer chemotherapy arises from its function of adding gamma-L-glutamate moieties to classical antifolates which contain an L-glutamate. Polyglutamylation of classical antifolates used in cancer chemotherapy have certain advantages. The polyglutamylated antifolates are trapped within the cell and hence are retained for a longer duration. In addition some polyglutamylated forms of classical antifolates also inhibit the target folate-dependent enzyme to a greater extent than those monoglumate form. There are however certain drawbacks to this enzymatic transformation of classical antifolates. For those analogs which need polyglutamylation for activation either for retention within tumor cells or to increase inhibitory activity against the target folate-dependent enzyme(s) (both of which could contribute to the antitumor activity of the analog), resistance to the antifolates can be manifested by reduction in the level of FPGS activity. In addition retention of polyglutamate forms of antifolates within normal cells may be a cause of toxicity. Thus the structural requirements for substrate activity for FPGS are of critical importance in the design of classical antifolates as cancer chemotherapeutic agents. In addition classical antifolates which lack the necessity of polyglutamation could circumvent the resistance due to a decrease in the level and activity of FPGS. FPGS activity on natural folate is essential to cell proliferation and survival. Thus inhibition of FPGS activity itself has been suggested as a chemotherapeutic strategy. Structural requirement for inhibition of FPGS have also been studied extensively. This review highlights the synthesis and the structural requirement for substrate and inhibitory activity of classical antifolates for FPGS and their relevance to cancer chemotherapy.

Synthesis and in vitro antitumor activity of new deaza analogues of the nonpolyglutamatable antifolate N(alpha)-(4-amino-4-deoxypteroyl)-N(delta)-hemiphthaloyl-L-ornithine (PT523)

Details are disclosed for the synthesis of N(alpha)-[4-[2-(2,4-diaminoquinazolin-6-yl)ethyl]benzoyl]-N(delta)-hemiphthaloyl-L-ornithine (2) and N(alpha)-[4-[5-(2,4-diaminoteridin-6-yl)pent-1-yn-4-yl]benzoyl]-N(delta)-hemiphthaloyl-L-ornithine (6) as analogues of N(alpha)-(4-amino-4-deoxypteroyl)-N(delta)-hemiphthaloyl-L-ornithine (1, PT523), a nonpolyglutamatable antifolate currently in advanced preclinical development. In a 72 h growth inhibition assay against cultures of CCRF-CEM human leukemic lymphoblasts, the IC(50) of 2 and 6 was 0.69 +/- 0.044 nM and 1.3 +/- 0.35 nM, respectively, as compared with previously reported values 4.4 +/- 0.10 nM for aminopterin (AMT) and 1.5 +/- 0.39 nM for PT523. In a spectrophotometric assay of dihydrofolate reductase (DHFR) inhibition using dihydrofolate and NADPH as the cosubstrates, the previously unreported compounds 2 and the mixed 10R and 10S diastereomers of 6 had K(i) values of 0.21 +/- 0.05 pM and 0.60 +/- 0.02 pM, respectively, as compared with previously reported values of 3.70 +/- 0.35 pM for AMT and 0.33 +/- 0.04 pM for PT523. Thus, while they were comparable to 1 and several of its previously studied analogues in their ability to bind to DHFR and inhibit the growth of CCRF-CEM cells, 2 and the mixed diastereomers of 6 were several times more active than AMT despite the fact that they cannot form gamma-polyglutamylated metabolites of the type formed in cells from AMT and other classical antifolates with a glutamate side chain.

Investigation of the binding of epimer A of the covalent hydrate of 6,7-bis(trifluoromethyl)-8-D-ribityllumazine to a recombinant F22W Bacillus subtilis lumazine synthase mutant by (15)N[(19)F] REDOR NMR

The two epimeric covalent hydrates A and B of 6,7-bis(trifluoromethyl)-8-D-ribityllumazine are metabolically stable analogues of hypothetical intermediates proposed in the reactions catalyzed by riboflavin synthase and lumazine synthase. To confirm the stereochemical assignments previously based solely on results for epimer B, a (15)N[(19)F] REDOR NMR study was performed on the complex formed from epimer A and a recombinant, uniformly (15)N-labeled F22W mutant of Bacillus subtilis lumazine synthase. The results indicate that the fluorines of the ligands are closer to the side chain nitrogens of Arg127 and farther away from the side chain nitrogens of Lys135 in epimer B than in epimer A. These results are consistent with the assignment of the earlier 7R configuration of epimer A and the 7S configuration of epimer B.

Synthesis and fluorescence characterization of pteridine adenosine nucleoside analogs for DNA incorporation

Two fluorescent adenosine analogs, 4-amino-6-methyl-8-(2-deoxy-beta-d-ribofuranosyl)-7(8H)-pteridone (6MAP) and 4-amino-2,6-dimethyl-8-(2'-deoxy-beta-d-ribofuranosyl)-7(8H)-pteridone (DMAP), have been synthesized as phosphoramidites. These probes are site-selectively incorporated into oligonucleotides using automated DNA synthesis. Relative quantum yields are 0.39 for 6MAP and 0.48 for DMAP as monomers and range from >0.01 to 0.11 in oligonucleotides. Excitation maxima are 310 (6MAP) and 330 nm (DMAP) and the emission maximum for each is 430 nm. Fluorescence decay curves of each are monoexponential exhibiting lifetimes of 3.8 and 4.8 ns for 6MAP and DMAP, respectively. When these probes are incorporated into oligonucleotides they display quenching of fluorescence intensity, increases in the complexity of decay curves, and decreases in mean lifetimes. Because these changes are apparently mediated by interactions with neighboring bases, spectral changes that occur as probe-containing oligonucleotides meet and react with other molecules provide a means of monitoring these interactions in real time. These probes are minimally disruptive to DNA structure as evidenced by melting temperatures of probe-containing oligonucleotides that are very similar to those of controls. Digestion of probe-containing oligonucleotides with P1 nuclease confirms probe stability as fluorescence levels are restored to those expected for each monomer. These adenosine analog probes are capable of providing information on DNA structure as it responds to binding or catalysis through interaction with other molecules.

Synthesis, characterization and reactions of 2-deoxo-5-deazaalloxazines

5-Deazaflavins and their homologues have been known as potential riboflavin antagonists, bioreductives, and compounds with potent antitumor activity. 2-Amino-4-methylquinoline-3-carbonitrile (2) was prepared as unreported starting material for several interesting 2-deoxo-5-deazalloxazine derivatives. Cyclization of 2 using formamide afforded the 2,4-deoxo-5-deazaalloxazine derivative 7, which was subjected to deamination with nitrous acid to give the 2-deoxo-5-deazaalloxazine (8). The compound 8 was also obtained via 13 by treating the latter with refluxing formic acid or formamide and used as a precursor for synthesis of several 2-deoxo-5-deazaalloxazines 18, 19, 20, 21 and 22. The pharmacological and biological properties of these compounds are still under investigation.

Antimycobacterial activity of 1-deaza-7,8-dihydropteridine derivatives against Mycobacterium tuberculosis and Mycobacterium avium complex in vitro

Twenty-five 1-deaza-7,8-dihydropteridine derivatives were screened for antimycobacterial activity against Mycobacterium tuberculosis strain H37Ra and three Mycobacterium avium clinical isolates (serovar 1, 4 or 6). Antibacterial activity was determined with a colorimetric microdilution broth assay. Seventeen of the compounds inhibited growth in the range >1.28 to <or=12.8 mg/L against one or more of the test strains. The presence of an alkoxycarbonyl group on the amino nitrogen at position 2 was not required for activity. Activity was dependent upon the type and location of group substitutions on the 6-phenyl ring and, in some cases, the presence of a 7-alkyl group.

5,6-Diaminocytidine, a versatile synthon for pyrimidine-based bicyclic nucleosides

This communication describes a convenient, facile, and high-yield synthesis of 3-(beta-D-ribofuranosyl)isoguanine and its 8-methyl derivative, as well as nucleoside analogues of pteridines, from a common precursor, 5,6-diaminocytidine. 5,6-Diamino-2',3', 5'-tri-O-benzoylcytidine was synthesized from 4, 6-diamino-2-oxopyrimidine in three steps.

Antimycobacterial activities of 2,4-diamino-5-deazapteridine derivatives and effects on mycobacterial dihydrofolate reductase

Development of new antimycobacterial agents for Mycobacterium avium complex (MAC) infections is important particularly for persons coinfected with human immunodeficiency virus. The objectives of this study were to evaluate the in vitro activity of 2, 4-diamino-5-methyl-5-deazapteridines (DMDPs) against MAC and to assess their activities against MAC dihydrofolate reductase recombinant enzyme (rDHFR). Seventy-seven DMDP derivatives were evaluated initially for in vitro activity against one to three strains of MAC (NJ168, NJ211, and/or NJ3404). MICs were determined with 10-fold dilutions of drug and a colorimetric (Alamar Blue) microdilution broth assay. MAC rDHFR 50% inhibitory concentrations versus those of human rDHFR were also determined. Substitutions at position 5 of the pteridine moiety included -CH(3), -CH(2)CH(3), and -CH(2)OCH(3) groups. Additionally, different substituted and unsubstituted aryl groups were linked at position 6 through a two-atom bridge of either -CH(2)NH, -CH(2)N(CH(3)), -CH(2)CH(2), or -CH(2)S. All but 4 of the 77 derivatives were active against MAC NJ168 at concentrations of < or =13 microg/ml. Depending on the MAC strain used, 81 to 87% had MICs of < or =1.3 microg/ml. Twenty-one derivatives were >100-fold more active against MAC rDHFR than against human rDHFR. In general, selectivity was dependent on the composition of the two-atom bridge at position 6 and the attached aryl group with substitutions at the 2' and 5' positions on the phenyl ring. Using this assessment, a rational synthetic approach was implemented that resulted in a DMDP derivative that had significant intracellular activity against a MAC-infected Mono Mac 6 monocytic cell line. These results demonstrate that it is possible to synthesize pteridine derivatives that have selective activity against MAC.

New gamma-fluoromethotrexates modified in the pteridine ring: synthesis and in vitro immunosuppressive activity

Our continuing program to develop new antifolate drugs useful against rheumatoid arthritis led us to modify the pteridine ring of gamma-fluoromethotrexate. Pyrrolopyrimidine derivatives 1e and 1t were found to exhibit potent suppressive effects on the responses of both T and B cells to mitogens, although tetrahydropyridopyrimidine derivatives 2e and 2t and quinazoline derivatives 3e, 3t and 4e showed very weak suppressive activities. Thus, conversion of the pteridine ring of gamma-fluoromethotrexate to a pyrrolopyrimidine ring led to a new potential antirheumatic compound.

Effects of 6-formylpterin, a xanthine oxidase inhibitor and a superoxide scavenger, on production of nitric oxide in RAW 264.7 macrophages

As well as superoxide generated from neutrophils, nitric oxide (NO) produced by inducible nitric oxide synthase (iNOS) in macrophages plays an important role in inflammation. We previously showed that 6-formylpterin, a xanthine oxidase inhibitor, has a superoxide scavenging activity. In the present study, to elucidate other pharmacological activities of 6-formylpterin, we investigated the effects of 6-formylpterin on production of nitric oxide (NO) in the murine macrophage cell line RAW 264.7 stimulated by lipopolysaccharide (LPS) and interferon-gamma (INF-gamma). 6-Formylpterin suppressed the expression of iNOS, and it also inhibited the catalytic activity of iNOS, which collectively resulted in the inhibition of NO production in the stimulated macrophages. However, 6-formylpterin did not scavenge the released NO from an NO donor, S-nitroso-N-acetylpenicillamine (SNAP). These results indicate that 6-formylpterin inhibits pathological NO generation from macrophages during inflammation, but that it does not disturb the physiological action of NO released from other sources.

Structure-based design of selective inhibitors of dihydrofolate reductase: synthesis and antiparasitic activity of 2, 4-diaminopteridine analogues with a bridged diarylamine side chain

As part of a larger search for potent as well as selective inhibitors of dihydrofolate reductase (DHFR) enzymes from opportunistic pathogens found in patients with AIDS and other immune disorders, N-[(2,4-diaminopteridin-6-yl)methyl]dibenz[b,f]azepine (4a) and the corresponding dihydrodibenz[b,f]azepine, dihydroacridine, phenoxazine, phenothiazine, carbazole, and diphenylamine analogues were synthesized from 2, 4-diamino-6-(bromomethyl)pteridine in 50-75% yield by reaction with the sodium salts of the amines in dry tetrahydrofuran at room temperature. The products were tested for the ability to inhibit DHFR from Pneumocystis carinii (pcDHFR), Toxoplasma gondii (tgDHFR), Mycobacterium avium (maDHFR), and rat liver (rlDHFR). The member of the series with the best combination of potency and species selectivity was 4a, with IC(50) values against the four enzymes of 0. 21, 0.043, 0.012, and 4.4 microM, respectively. The dihydroacridine, phenothiazine, and carbazole analogues were also potent, but nonselective. Of the compounds tested, 4a was the only one to successfully combine the potency of trimetrexate with the selectivity of trimethoprim. Molecular docking simulations using published 3D structural coordinates for the crystalline ternary complexes of pcDHFR and hDHFR suggested a possible structural interpretation for the binding selectivity of 4a and the lack of selectivity of the other compounds. According to this model, 4a is selective because of a unique propensity of the seven-membered ring in the dibenz[b,f]azepine moiety to adopt a puckered orientation that allows it to fit more comfortably into the active site of the P. carinii enzyme than into the active site of the human enzyme. Compound 4a was also evaluated for the ability to be taken up into, and retard the growth of, P. carinii and T. gondii in culture. The IC(50) of 4a against P. carinii trophozoites after 7 days of continuous drug treatment was 1.9 microM as compared with previously observed IC(50) values of >340 microM for trimethoprim and 0.27 microM for trimetrexate. In an assay involving [(3)H]uracil incorporation into the nuclear DNA of T. gondii tachyzoites as the surrogate endpoint for growth, the IC(50) of 4a after 5 h of drug exposure was 0.077 microM. The favorable combination of potency and enzyme selectivity shown by 4a suggests that this novel structure may be an interesting lead for structure-activity optimization.

Inhibition of neuronal nitric oxide synthase by 4-amino pteridine derivatives: structure-activity relationship of antagonists of (6R)-5,6,7,8-tetrahydrobiopterin cofactor

The family of nitric oxide synthases (NOS) catalyzes the conversion of L-arginine to L-citrulline and nitric oxide (NO), an important cellular messenger molecule which has been implicated in the pathophysiology of septic shock and inflammatory and neurodegenerative disease states. NOS can be maximally activated by the ubiquitous cofactor, (6R)-5,6,7,8-tetrahydrobiopterin (H(4)Bip), and antagonists of H(4)Bip may be of therapeutic importance to inhibit pathologically high NO formation. The 4-amino substituted analogue of H(4)Bip was reported to be a potent NOS inhibitor. Therefore, we developed a series of novel 4-amino pteridine derivatives, anti-pterins, to pharmacologically target the neuronal isoform of nitric oxide synthase (NOS-I). To functionally characterize the pterin/anti-pterin interaction and establish a structure-activity relationship (SAR), we systematically altered the substituents in the 2-, 4-, 5-, 6-, and 7-position of the pteridine nucleus. Varying the substitution pattern in the 2-, 5-, and 7-position resulted in no significant inhibitory effect on enzyme activity. In contrast, bulky substituents in the 6-position, such as phenyl, markedly increased the inhibitory potency of the reduced 4-amino-5,6,7,8-tetrahydropteridines, possibly as a consequence of hydrophobic interactions within NOS-I. However, this was not the case for the aromatic 4-amino pteridines. Interestingly, chemical modification of the 4-amino substituent by dialkyl/diaralkylation together with 6-arylation of the aromatic 2,4-diamino pteridine resulted in potent and efficacious inhibitors of NOS-I, suggesting possible hydrophilic and hydrophobic interactions within NOS-I. This SAR agrees with (a) the recently published crystal structure of the oxygenase domain of the inducible NOS isoform (NOS-II) and (b) the comparative molecular field analysis of selected NOS-I inhibitors, which resulted in a 3D-QSAR model of the pterin binding site interactions. Further optimization should be possible when the full length structure of NOS-I becomes available.

Synthesis and pharmacological activity of pyrazolopyrrolopyrimidine derivatives having vasorelaxing activity

A new series of 5-substituted and 5-nonsubstituted pyrazolopyrrolopyrimidine derivatives were synthesized, and their vasorelaxing and hypotensive activities were evaluated. The syntheses were efficiently accomplished through the use of three key intermediates (7, 16, and 24), as shown in Schemes I-III. The desired pharmacological activities were confirmed on the basis of vasorelaxing activity in rat aorta (in vitro) and hypotensive activity in rats (in vivo). Specifically, compound 25 exhibited the strongest activity and appears to be a promising clinical lead for the development of a new antihypertensive agent.

Generation and biomimetic chemistry of tungsten-dithiolene complexes containing the hydrotris(3,5-dimethylpyrazol-1-yl)borate ligand

Reactions of bis(thio)-W(VI) complexes, LWS2X (L = hydrotris (3,5-dimethylpyrazol-1-yl)borate, X = monoanion), with alkynes produce dithiolene complexes, LWX(dithiolene). The synthesis and characterization of orange LW(OPh){S2C2(CO2Me)2} (1) and burgundyred LW(SePh) {S2C2(Ph)(2-quinoxalinyl)} (2) and the X-ray crystal structure of 1.0.5CH2Cl2, are described in detail. Crystals of 1.0.5CH2Cl2 are orthorhombic, space group Pbcn, with a = 29.826(6), b = 13.291(4), c = 16.078(4) A, V = 6373(5) A3, and Z = 8. The six-coordinate, distorted-octahedral complex features a tridentate L ligand, a monodentate phenoxide ligand, and a bidentate dithiolene ligand. The short W-S bonds (2.267(4) and 2.279(4) A) and the parameters associated with the phenoxide ligand (W-O = 1.850(8) A, W-O-C = 146(1) degree), point to a considerable degree of W-ligand multiple bonding in the [W(OPh)(dithiolene)]+ unit. For 2, W-Se and average W-S distances of 2.49(2) A and 2.30(2) A, respectively, have been obtained from EXAFS studies. The formation of yellow 3,3'-dithiobis[2-(phenyl)thieno[2,3-b]quinoxaline] (3) upon oxidation of 2 supports the likely generation of urothione upon oxidative degradation of molybdopterin-containing tungsten enzymes from hyperthermophilic organisms.

Synthesis of 7-benzylamino-6-chloro-2-piperazino-4-pyrrolidinopteridine and novel derivatives free of positional isomers. Potent inhibitors of cAMP-specific phosphodiesterase and of malignant tumor cell growth

7-Benzylamino-6-chloro-2-piperazino-4-pyrrolidinopteridine (7a) is a potent inhibitor of the cAMP-specific phosphodiesterase isoenzyme family PDE4 and induces growth inhibition in a panel of tumor cell lines. In this study, we describe a synthesis that yields 7a and novel derivatives free of positional isomers. The synthesis of alkylamino substituted pteridines is based on the successive nucleophilic aromatic substitution of the chlorine atoms of 2,4,6, 7-tetrachloropteridine. For the reaction with secondary amines, the positional order of reactivity was found to be C4 > C7 > C2 > C6. Final structural proof is given by X-ray crystallography. To unravel structural elements of 7a crucial for the interaction with the target enzyme, the compound was modified systematically. The impact of the modifications on activity was tested by evaluating the ability of the compounds to inhibit cAMP hydrolysis by cAMP-specific phosphodiesterase (PDE4) purified from the solid human large cell lung tumor xenograft LXFL529. Growth inhibitory properties were determined by in vitro treatment of the respective cell line LXFL529L using the sulforhodamine B assay (SRB). The results show that for high activity, the heterocyclic substituent in position 2 of the pteridine ring system requires the presence of a basic nitrogen in 4'-position, as represented by piperazine.

Anthelmintic activity of 6,7-diaryl-pteridines

In a search for new anthelmintic compounds, some 6,7-diaryl-pteridines were synthesized from the corresponding diaminopyrimidines and aromatic aldehydes. Their anthelmintic activity was tested in vitro against Caenorhabditis elegans and Heligmosomoides polygyrus and in vivo against Trichinella spiralis. Structure-activity relationships are discussed.

Guanine, pyrazolo[3,4-d]pyrimidine, and triazolo[4,5-d]pyrimidine (8-azaguanine) phosphonate acyclic derivatives as inhibitors of purine nucleoside phosphorylase

Phosphonate acyclic derivates of guanines, pyrazolo[3,4-d]pyrimidines, and triazolo[4,5-d]-pyrimidines (8-azaguanines) are inhibitors of the enzyme purine nucleoside phosphorylase (PNPase) with Ki' values ranging from 0.05 to 1.6 microM. These compounds are enzymatically stable congeners of the potent PNPase inhibitor acyclovir diphosphate (53).

Substituted xanthines, pteridinediones, and related compounds as potential antiinflammatory agents. Synthesis and biological evaluation of inhibitors of tumor necrosis factor alpha

A series of analogues of pentoxifylline metabolites were prepared in the purine, pteridine, [1,2,5]-thiadiazolo[3,4-d]pyrimidine, and quinazoline ring systems and evaluated for their ability to inhibit the production of tumor necrosis factor-alpha (TNF alpha) in human peripheral blood monocytes stimulated with bacterial lipopolysaccharide (LPS). The more active compounds were also tested for inhibition of cyclic AMP phosphodiesterase type IV (PDE IV) from human neutrophils in order to help determine their mechanism of action. Selected compounds which showed good activity in the in vitro TNF alpha assay were evaluated in an in vivo LPS-induced leukopenia model in mice. The most potent compounds in the TNF alpha assay, 6, 31, and 58, inhibited TNF alpha production at an IC50 of approximately 5 microM for each. Compound 58 was a very poor inhibitor of PDE IV but was the most active at preventing the leukopenia induced by TNF alpha in mice, providing more than 60% protection at 50 mg/kg. Thus, compounds such as 58, which are good inhibitors of TNF alpha production but are devoid of PDE IV inhibitory properties, may have potential as new antiinflammatory agents.

Chiral lumazines: preparation, properties, enantiomeric separation

Optically active lumazines (biolumazine, dictyolumazine, monalumazine, and neolumazine) are prepared from the corresponding pterins by enzymatic reaction, using pterin deaminase excreted by Dictyostelium discoideum. The fluorescence properties, circular dichroism spectra, and chromatographic behavior of these lumazines are studied. D- and L-enantiomers of biolumazine, dictyolumazine, and monalumazine are separated using a chiral flavoprotein column. This column also separates the enantiomeric pterins of the threo form: monapterin and dictyopterin. However, the column does not separate the enantiomeric pterins of the erythro form: neopterin and biopterin. By coupling a reverse-phase column to the flavoprotein column, the separation of pterins and lumazines in function of their hydrophobicity, as well as the separation of the diastereomers, is achieved. This coupled achiral/chiral high-performance liquid chromatography method enables determination of the stereoconfiguration of natural lumazines by comparison with optically pure compounds. A lumazine derivative, present in the extracellular medium of Dictyostelium discoideum, is identified as D-dictyolumazine, i.e., 6-(D-threo-1,2-dihydroxypropyl)-lumazine.