Helicobacter pylori Xanthine-Guanine-Hypoxanthine Phosphoribosyltransferase-A Putative Target for Drug Discovery against Gastrointestinal Tract Infections.

Helicobacter pylori (Hp) is a human pathogen that lives in the gastric mucosa of approximately 50% of the world's population causing gastritis, peptic ulcers, and gastric cancer. An increase in resistance to current drugs has sparked the search for new Hp drug targets and therapeutics. One target is the disruption of nucleic acid production, which can be achieved by impeding the synthesis of 6-oxopurine nucleoside monophosphates, the precursors of DNA and RNA. These metabolites are synthesized by Hp xanthine-guanine-hypoxanthine phosphoribosyltransferase (XGHPRT). Here, nucleoside phosphonates have been evaluated, which inhibit the activity of this enzyme with Ki values as low as 200 nM. The prodrugs of these compounds arrest the growth of Hp at a concentration of 50 µM in cell-based assays. The kinetic properties of HpXGHPRT have been determined together with its X-ray crystal structure in the absence and presence of 9-[(N-3-phosphonopropyl)-aminomethyl-9-deazahypoxanthine, providing a basis for new antibiotic development.

Biosynthesis of the Fairy Chemicals, 2-Azahypoxanthine and Imidazole-4-carboxamide, in the Fairy Ring-Forming Fungus Lepista sordida.

Fairy rings resulting from a fungus-plant interaction appear worldwide. 2-Azahypoxanthine (AHX) and imidazole-4-carboxamide (ICA) were first isolated from the culture broth of one of the fairy ring-forming fungi, Lepista sordida. Afterward, a common metabolite of AHX in plants, 2-aza-8-oxohypoxanthine (AOH), was found in AHX-treated rice. The biosynthetic pathway of the three compounds that are named as fairy chemicals (FCs) in plants has been partially elucidated; however, that in mushrooms remains unknown. In this study, it was revealed that the carbon skeletons of AHX and ICA were constructed from Gly in L. sordida mycelia and the fungus metabolized 5-aminoimidazole-4-carboxamide (AICA) to both of the compounds. These results indicated that FCs were biosynthesized by a diversion of the purine metabolic pathway in L. sordida mycelia, similar to that in plants. Furthermore, we showed that recombinant adenine phosphoribosyltransferase (APRT) catalyzed reversible interconversion not only between 5-aminoimidazole-4-carboxamide-1-ß-d-ribofuranosyl 5'-monophosphate (AICAR) and AICA but also between ICA-ribotide (ICAR) and ICA. Furthermore, the presence of ICAR in L. sordida mycelia was proven for the first time by LC-MS/MS detection, and this study provided the first report that there was a novel metabolic pathway of ICA in which its ribotide was an intermediate in the fungus.

Acyclic Nucleoside Phosphonates Containing 9-Deazahypoxanthine and a Five-Membered Heterocycle as Selective Inhibitors of Plasmodial 6-Oxopurine Phosphoribosyltransferases.

Acyclic nucleoside phosphonates (ANPs) are an important class of therapeutic drugs that act as antiviral agents by inhibiting viral DNA polymerases and reverse transcriptases. ANPs containing a 6-oxopurine unit instead of a 6-aminopurine or pyrimidine base are inhibitors of the purine salvage enzyme, hypoxanthine-guanine-[xanthine] phosphoribosyltransferase (HG[X]PRT). Such compounds, and their prodrugs, are able to arrest the growth of Plasmodium falciparum (Pf) in cell culture. A new series of ANPs were synthesized and tested as inhibitors of human HGPRT, PfHGXPRT, and Plasmodium vivax (Pv) HGPRT. The novelty of these compounds is that they contain a five-membered heterocycle (imidazoline, imidazole, or triazole) inserted between the acyclic linker(s) and the nucleobase, namely, 9-deazahypoxanthine. Five of the compounds were found to be micromolar inhibitors of PfHGXPRT and PvHGPRT, but no inhibition of human HGPRT was observed under the same assay conditions. This demonstrates selectivity of these types of compounds for the two parasitic enzymes compared to the human counterpart and confirms the importance of the chemical nature of the acyclic moiety in conferring affinity/selectivity for these three enzymes.

Molecular, cellular and pharmacological effects of platinum(II) diiodido complexes containing 9-deazahypoxanthine derivatives: A group of broad-spectrum anticancer active agents.

The platinum(II) iodido complexes 1-5 of the general formula cis-[PtI2(Ln)2], where Ln stands for O-substituted 9-deazahypoxanthine derivatives, were prepared and thoroughly characterized by various techniques, including multinuclear 1D and 2D NMR spectroscopy. The complexes were screened for their anticancer potential in vitro on ten human cancer cell lines, concretely breast adenocarcinoma (MCF7), osteosarcoma (HOS), lung carcinoma (A549), cervix epithelioid carcinoma (HeLa), malignant melanoma (G-361), prostate carcinoma (22Rv1, PC-3), hepatocellular carcinoma (HepG2), ovarian carcinoma (A2780) and cisplatin-resistant ovarian carcinoma (A2780R). The complexes exhibited significant wide-spectrum anticancer activity in vitro against all the employed cell lines, with IC50≈0.5-24.0µM. Very good correlation between the lipophilicity parameter log P and IC50 values of anticancer activity in vitro were obtained by simple QSAR analysis. The most lipophilic complexes 2, 4 and 5 showed the best results, as they reached the sub-micromolar IC50 values against the A2780 and A2780R sub-lines, with the best result equal 0.5±0.1µM on A2780 for complex 5. The in vivo testing of the representative complexes 1, 4 and 5 (applied at the same dose of Pt as 2mg/kg dose of cisplatin) on a L1210 leukaemia model revealed their positive effect on the prolongation of the mean survival time, even if it was lower than that of cisplatin. The 1H NMR interaction study revealed the ability of complexes to interact with glutathione (GSH) and 5'-guanosine monophosphate (GMP) and overall higher stability of the complexes 1-5 as compared to cisplatin. The electrospray-ionization mass spectrometry experiments with complex 1 identified the formation of a rich collection of hydrolytic species in water-containing media after 24h and the interaction intermediates with sulfur-containing biomolecule l-cysteine, but not with the reduced glutathione at physiologically relevant concentration levels.

Design and synthesis of novel, potent and selective hypoxanthine analogs as adenosine A1 receptor antagonists and their biological evaluation.

Multipronged approach was used to synthesize a library of diverse C-8 cyclopentyl hypoxanthine analogs from a common intermediate III. Several potent and selective compounds were identified and evaluated for pharmacokinetic (PK) properties in Wistar rats. One of the compounds 14 with acceptable PK parameters was selected for testing in in vivo primary acute diuresis model. The compound demonstrated significant diuretic activity in this model.

The first example of palladium-catalyzed cascade amidine arylation-intramolecular ester amidation for the synthesis of hypoxanthines: application to the synthesis of 8-azanebularine analogues.

8-Azanebularine analogues display interesting antiviral, antitumour and biochemical activities. However, typical glycosylation of 8-azapurines always resulted in the desired products in low yields due to the lack of stereo- and regioselectivity of the glycosylation reaction. Herein, a concise synthetic route toward 8-azanebularine analogues has been developed. Key steps involve a copper-catalyzed 1,3-dipolar cycloaddition of a 1-ß-azido sugar moiety with ethyl 3-bromopropiolate and a palladium-catalyzed cascade amidine arylation-intramolecular ester amidation reaction to build the hypoxanthine structural motif. This protocol affords a facile methodology for the synthesis of a series of novel 8-azanebularine analogues from the readily accessible 1-ß-azido sugar moiety under mild conditions.

The biosynthetic pathway of 2-azahypoxanthine in fairy-ring forming fungus.

"Fairy rings" resulting from fungus-stimulated plant growth occur all over the world. In 2010, 2-azahypoxanthine (AHX) from a fungus Lepista sordida was identified as the "fairy" that stimulates plant growth. Furthermore, 2-aza-8-oxohypoxanthine (AOH) was isolated as a common metabolite of AHX in plants, and the endogenous existence of AHX and AOH in plants was proved. The structure of AHX allowed us to hypothesize that AHX was derived from 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR). Thus, we performed a feeding experiment that supplied AICAR to L. sordida. Consumption of AICAR and accumulation of AHX were observed after feeding. The mycelia extract had enzymatic activity of adenine/5-aminoimidazole-4-carboxamide phosphoribosyltransferase (APRT). APRT gene of L. sordida revealed its structural characteristics in homology modeling and showed transcriptional enhancement after feeding. These results support that AHX was synthesized from AICAR and AHX biosynthesis was transcriptionally controlled by AICAR, indicating the presence of novel purine metabolic pathway in L. sordida.

Ultrafast excited-state deactivation of 9-methylhypoxanthine in aqueous solution: A QM/MM MD study.

Photoinduced ultrafast non-adiabatic decay of 9-methylhypoxanthine (9MHPX) in aqueous solution was investigated by ab initio surface-hopping dynamics calculations using a combined quantum mechanical/molecular mechanical approach. The absorption spectra of 9MHPX in aqueous solution were also explored by the hybrid cluster-continuum model at the level of time-dependent density functional theory along with the polarizable continuum model (PCM). The static electronic-structure calculations indicate that the absorption spectra of 9MHPX simulated by TD-B3LYP/PCM and TD-X3LYP/PCM can reproduce very well the experimental findings, with the accuracy of about 0.20 eV. According to dynamics simulations, irradiation of 9MHPX populates the bright excited singlet S1 state, which may undergo an ultrafast non-radiative deactivation to the S0 state. The lifetime of the S1 state of 9MHPX in aqueous solution is predicted to be 115.6 fs, slightly longer than that in the gas phase (88.8 fs), suggesting that the solventwater has no significant influence on the excited-state lifetime of 9MHPX. Such a behavior in 9MHPX is distinctly different from its parent hypoxanthine keto-N9H tautomer in which the excited-state lifetime of the latter in watersolution was remarkably enhanced as compared to the gas phase. The significant difference of the photodynamical behaviors between 9MHPX and keto-N9H can be ascribed to their different hydrogen bond environment in aqueous solution.

Pleiotropic effects of gold(I) mixed-ligand complexes of 9-deazahypoxanthine on transcriptional activity of receptors for steroid hormones, nuclear receptors and xenoreceptors in human hepatocytes and cell lines.

Development of metal-based compounds is an important research avenue in anti-cancer and anti-inflammatory drug discovery. Here we examined the effects of three gold (I) mixed-ligand complexes with the general formula [Au(Ln)(PPh3)] (1, 2, 3) involving triphenylphosphine (PPh3) and a deprotonated form of O-substituted derivatives of 9-deazahypoxanthine (Ln) on the transcriptional activity of aryl hydrocarbon receptor (AhR), androgen receptor (AR), glucocorticoid receptor (GR), thyroid receptor (TR), pregnane X receptor (PXR) and vitamin D receptor (VDR), employing gene reporter assays. In addition, we measured mRNA (RT-PCR) and protein (western blot) expression of target genes for those receptors, including drug-metabolizing P450s, in primary human hepatocytes and cancer cell lines LS180 and HepG2. The tested compounds displayed anti-glucocorticoid effects, as revealed by inhibition of dexamethasone-inducible transcriptional activity of GR and down-regulation of tyrosine aminotransferase. All the compounds slightly and dose-dependently activated PXR and AhR, and moderately induced CYP3A4 and CYP1A1/2 genes in human hepatocytes and LS180 cells. The complexes antagonized basal and ligand-activated AR and VDR, indicating inverse agonist behaviour. Both basal and thyroid hormone-inducible transcriptional activity of TR was dose-dependently increased by all tested compounds. In contrast, the expression of SPOT14 mRNA was decreased by tested compounds in human hepatocytes and HepG2 cells. In conclusion, if intended for human pharmacotherapy, the potential of the complexes 1-3 to influence studied receptors should be taken in account.

Solution structures of purine base analogues 9-deazaguanine and 9-deazahypoxanthine.

Deaza analogues of nucleobases are potential drugs against infectious diseases caused by parasites. A caveat is that apart from binding their target parasite enzymes, they also bind and inhibit enzymes of the host. In order to design derivatives of deaza analogues which specifically bind target enzymes, knowledge of their molecular structure, protonation state, and predominant tautomers at physiological conditions is essential. We have employed resonance Raman spectroscopy at an excitation wavelength of 260 nm, to decipher solution structure of 9-deazaguanine (9DAG) and 9-deazahypoxanthine (9DAH). These are analogues of guanine and hypoxanthine, respectively, and have been exploited to study static complexes of nucleobase binding enzymes. Such enzymes are known to perturb pKa of their ligands, and thus, we also determined solution structures of these analogues at two, acidic and alkaline, pH. Structure of each possible protonation state and tautomer was computed using density functional theoretical calculations. Species at various pHs were identified based on isotopic shifts in experimental wavenumbers and by comparing these shifts with corresponding computed isotopic shifts. Our results show that at physiological pH, N1 of pyrimidine ring in 9DAG and 9DAH bears a proton. At lower pH, N3 is place of protonation, and at higher pH, deprotonation occurs at N1 position. The proton at N7 of purine ring remains intact even at pH 12.5. We have further compared these results with naturally occurring nucleotides. Our results identify key vibrational modes which can report on hydrogen bonding interactions, protonation and deprotonation in purine rings upon binding to the active site of enzymes.

Structural Diversity of Copper(II) Complexes with 9-Deazahypoxanthine and Their in Vitro SOD-Like Activity.

Two structurally different copper(II) complexes of the compositions [{Cu(9dhx)(H2O)3}2(µ-SO4)2] (1) and [Cu(9dhx)2(H2O)2(NO3)2]·H2O (2), involving 9-deazahypoxanthine (9dhx; 6-oxo-9-deazapurine; 9-deazahypoxanthine), have been prepared and characterized by elemental analysis, infrared and electronic spectroscopy, electrospray ionisation (ESI) mass spectrometry, thermogravimetric (TG) and differential thermal (DTA) analyses, and cyclic voltammetry. The X-ray structures of complexes 1 and [Cu(9dhx)2(H2O)2(NO3)2] (2a) revealed the distorted octahedral geometry in the vicinity of the copper(II) atoms, with the NO5 and N2O4 donor set, respectively. In the dimeric compound 1, the {Cu(9dhx)(H2O)3}2 units are bridged by sulfate groups with the Cu···Cu separation being 5.3446(2) Å. In both structures the 9dhx ligands are coordinated through the N3 atoms of the pyrimidine moieties. The SOD-like activity of complexes 1 and 2 was evaluated in vitro showing moderate effect, with the IC50 values equal to 18.20, and 53.33 µM, respectively.

2,4-Diamino-6-Hydroxypyrimidine Based Poly(azomethine-Urethane): Synthesis and Application as a Fluorescent Probe for Detection of Cu(2+) in Aqueous Solution.

A novel poly(azomethine-urethane)-based 2,4-diamino-6-hydroxyprimidine was synthesized with chemical reaction and it designed as fluorescence probe for determination of Cu(2+) in aqueous solution. The photoluminescence (PL) characteristic of the prepared Schiff base (HPAMP) and its poly(azomethine-urethane) (P-HPAMP) derivative were investigated in different polarity solvents suh as MeOH, THF and DMF. PL measurements showed that both HPAMP and P-HPAMP have higher emission intensity and Stoke's shift value (ΔλST) in THF than the other solvents. Also, the proposed probe exhibited a specific fluorescent on response to Cu(2+) over the other tested transition metal ions in aqueous solution. The sensor gave highly selective and sensetive response against Cu(2+) as increasing a new emission peak at 341 nm, and possible interference and quenching effect of the other tested transition metal ions were found too low. Detection limit of Cu(2+) sensor was also calculated as 7.87 × 10(-6) mol L(-1) in THF/deionized water (1:2, v:v).

Gold(I) complexes of 9-deazahypoxanthine as selective antitumor and anti-inflammatory agents.

The gold(I) mixed-ligand complexes involving O-substituted derivatives of 9-deazahypoxanthine (HLn) and triphenylphosphine (PPh3) with the general formula [Au(Ln)(PPh3)] (1-5) were prepared and thoroughly characterized by elemental analysis, FT-IR and multinuclear NMR spectroscopy, ESI+ mass spectrometry, single crystal X-ray (HL5 and complex 2) and TG/DTA analyses. Complexes 1-5 were evaluated for their in vitro antitumor activity against nine human cancer lines, i.e. MCF7 (breast carcinoma), HOS (osteosarcoma), A549 (adenocarcinoma), G361 (melanoma), HeLa (cervical cancer), A2780 (ovarian carcinoma), A2780R (ovarian carcinoma resistant to cisplatin), 22Rv1 (prostate cancer) and THP-1 (monocytic leukaemia), for their in vitro anti-inflammatory activity using a model of LPS-activated macrophages, and for their in vivo antiedematous activity by λ-carrageenan-induced hind paw edema model on rats. The results showed that the complexes 1-5 exhibit selective in vitro cytotoxicity against MCF7, HOS, 22Rv1, A2780 and A2780R, with submicromolar IC50 values for 2 against the MCF7 (0.6 µM) and HOS (0.9 µM). The results of in vitro cytotoxicity screening on primary culture of human hepatocytes (HEP220) revealed up to 30-times lower toxicity of compounds against healthy cells as compared with cancer cells. Additionally, the complexes 1-5 significantly influence the secretion and expression of pro-inflammatory cytokines TNF-α and IL-1ß by a similar manner as a commercially used anti-arthritic drug Auranofin. The tested complexes also significantly influence the rate and overall volume of the edema, caused by the intraplantar application of λ-carrageenan polysaccharide to rats. Based on these promising results, the presented compounds could qualify to become feasible candidates for advanced testing as potential antitumor and anti-inflammatory drug-like compounds.

Metal-ion-mediated base pairing between natural nucleobases and bidentate 3,5-dimethylpyrazolyl-substituted purine ligands.

The potential of three modified purine bases, namely, 6-(3,5-dimethylpyrazol-1-yl)purine, 2-(3,5-dimethylpyrazol-1-yl)hypoxanthine, and 2-(3,5-dimethylpyrazol-1-yl)adenine, for metal-ion-mediated base pairing within an oligonucleotide environment has been investigated. The respective modified nucleosides were incorporated in the middle of 9-mer 2'-O-methyl oligonucleotides and the hybridization of these modified oligonucleotides with their unmodified counterparts studied by UV and CD spectrometry in the absence and presence of Cu(2+) or Zn(2+). All of the modified oligonucleotides formed more stable duplexes in the presence of divalent metal ions than in the absence thereof, but with different preferences for the complementary oligonucleotide. The oligonucleotide incorporating 2-(3,5-dimethylpyrazol-1-yl)hypoxanthine readily accepted any of the natural nucleobases opposite to this modified base regardless of whether Cu(2+) or Zn(2+) was used as the bridging metal ion. The other two oligonucleotides, on the other hand, were much more discriminating, exhibiting markedly elevated Tm values only in the presence of Cu(2+) and only when certain natural nucleobases were paired with the modified one. The origin of the selectivity (or promiscuity) of the metal-ion-mediated base pairing is discussed in terms of the ability of the modified nucleobases, as well as their natural counterparts, to serve as anionic ligands.

Inosine octamer stabilized by alkali earth metal cations - as studied by electrospray ionization mass spectrometry.

By using electrospray ionization mass spectrometry, inosine was found to be able to form an octamer stabilized by alkali earth metal cation, namely Ca(2+), Sr(2+) and Ba(2+), of which the most stable is that stabilized by Ca(2+) (ion [I8+Ca](2+)). It was established that 9-methylhypoxanthine (M) did not form an analogical octamer, since ion [M8+Ca](2+) was not detected. On the other hand, 9-methylhypoxanthine can form "mixed" octamers together with inosine (ions [InMm+Ca](2+), n + m = 8, were detected).

Practical synthesis of natural plant-growth regulator 2-azahypoxanthine, its derivatives, and biotin-labeled probes.

We describe a practical, large-scale synthesis of the "fairy-ring" plant-growth regulator 2-azahypoxanthine (AHX), and its biologically active hydroxyl metabolite (AOH) and riboside derivative (AHXr). AHXr, a biosynthetic intermediate, was synthesized from inosine via a biomimetic route. Biotinylated derivatives of AHX and AHXr were also synthesized as probes for mechanistic studies.

Synthetic and biological studies of tubulin targeting c2-substituted 7-deazahypoxanthines derived from marine alkaloid rigidins.

C2-aryl- and C2-alkyl-7-deazahypoxanthines as analogues of marine alkaloid rigidins were prepared utilizing novel synthetic methods developed for the construction of the pyrrolo[2,3-d]pyrimidine ring system. The new compounds exhibited sub-micromolar to nanomolar antiproliferative potencies against a panel of cell lines including in vitro models for drug-resistant tumors, such as glioblastoma, melanoma and non-small-cell lung cancer. A selected representative C2-methyl-7-deazahypoxanthine was found to inhibit microtubule dynamics in cancer cells, lending evidence for tubulin targeting as a mode of action for these compounds in cancer cells. The results of the docking studies utilizing the colchicine site on ß-tubulin were consistent with the observed structure-activity relationship data, including an important finding that derivatization at C2 with linear alkyl groups leads to the retention of activity, thus permitting the attachment of a biotin-containing linker for the subsequent proteomics assays. Because many microtubule-targeting compounds are successfully used to fight cancer in the clinic, the reported antitubulin rigidin analogues have significant potential as new anticancer agents.

The source of "fairy rings": 2-azahypoxanthine and its metabolite found in a novel purine metabolic pathway in plants.

Rings or arcs of fungus-stimulated plant growth occur worldwide; these are commonly referred to as "fairy rings". In 2010, we discovered 2-azahypoxanthine (AHX), a compound responsible for the fairy-ring phenomenon caused by fungus; AHX stimulated the growth of all the plants tested. Herein, we reveal the isolation and structure determination of a common metabolite of AHX in plants, 2-aza-8-oxohypoxanthine (AOH). AHX is chemically synthesized from 5-aminoimidazole-4-carboxamide (AICA), and AHX can be converted into AOH by xanthine oxidase. AICA is one of the members of the purine metabolic pathway in animals, plants, and microorganisms. However, further metabolism of AICA remains elusive. Based on these results and facts, we hypothesized that plants themselves produce AHX and AOH through a pathway similar to the chemical synthesis. Herein, we demonstrate the existence of endogenous AHX and AOH and a novel purine pathway to produce them in plants.

Exceptionally strong sorption of infochemicals to activated carbon reduces their bioavailability to fish.

The addition of activated carbon (AC) to sediments is a relatively new approach to remediate contaminated sites. Activated carbon strongly sorbs hydrophobic organic contaminants, thereby reducing their bioavailability and uptake in organisms. Because of its high sorption capacity, AC might, however, also sorb other chemicals that are not contaminants but instead have ecological functions. Examples of such compounds are infochemicals or pheromones (i.e., compounds serving as chemical inter- and intraspecies information vectors). The present study investigated the sorption of 2 known infochemicals, hypoxanthine-3-N-oxide (H3NO) and pyridine-N-oxide (PNO), to 5 different powdered ACs. Sorption isotherms of these low-molecular-weight, polar fish kairomone substances appeared highly nonlinear, with logarithmic Freundlich sorption coefficients of up to 7.6. At physiologically relevant concentrations, sorption was up to 7 to 9 orders of magnitude stronger than expected on the basis of hydrophobic forces only (i.e., the compounds' log octanol-water partition coefficient, being approximately -1), indicating exceptionally strong binding to specific sites. This binding effectively reduced the bioavailability of H3NO to Sarasa goldfish, as was shown in a behavioral assay. The present study demonstrates the previously unrecognized potential of AC to sorb ecologically relevant chemicals. Whether this potential may lead to subtle, unwanted ecological effects in the field will have to be investigated in more detail during future research.

7-aminobutynyl-8-aza-7-deazahypoxanthine as a quasi-universal nucleobase.

Several 7-(hydroxy, amino, methylureido, and guanidino)alkynyl-substituted 8-aza-7-deaza- hypoxanthine analogues were investigated as potential universal nucleobases. 7-Aminobutynyl-8-aza-7-deazahypoxanthine was found to be the most promising quasi-universal nucleobase with improved hybridization and polymerase chain reaction (PCR) enhancing properties as compared to commonly used hypoxanthine (the nucleobase of inosine). It demonstrated improved ambiguity for pairing with A, T, and C bases and its base pairing properties can be summarized as follows: X:C∼X:A∼X:T > X:G. The improvement in PCR performance directly correlated with primer's Tm. Primers containing multiple 7-aminobutynyl-8-aza-7-deazahypoxanthines were successfully used without noticeable inhibition of Taq polymerase activity provided the modifications are positioned more than two bases away from the 3' end.