Novel, Highly Potent Adenosine Deaminase Inhibitors Containing the Pyrazolo[3,4-d]pyrimidine Ring System. Synthesis, Structure−Activity Relationships, and Molecular Modeling Studies

Development of pyrazolo[3,4-d]pyrimidin-4-one scaffold as novel CDK2 inhibitors: Design, synthesis, and biological evaluation

A series of pyrazolo[3,4-d]pyrimidin-4-one scaffold were designed and synthesized as novel CDK2 inhibitors. By analyzing the common motifs of various known inhibitors, the designed compounds 1 were virtually screen for their inhibitory activity by docking into the active pocket of CDK2. The influence of different substitutes on the docking results was investigated. A total of 15 pyrazolo[3,4-d]pyrimidin-4-ones 1 were synthesized by Paal-Knorr reaction, pyrimidine ring closure, bromination, Suzuki coupling reaction, amide formation and Knoevenagel condensation. The Cell Counting Kit-8 (CCK-8) was used to evaluate the inhibitory activity of pyrazolo[3,4-d]pyrimidin-4-ones 1 in the breast cancer cell line MCF-7 in vitro using Etoposide as a reference control substance. The screening results demonstrated that the designed compounds have significant antiproliferative activity, and compounds 1e and 1j were the most active compounds with IC₅₀ values of 10.79 μM and 10.88 μM, respectively, being better than that of Etoposide (IC₅₀ = 18.75 μM). The enzyme inhibition assay was carried out against CDK2, the results indicated that the compounds 1e and 1j significantly inhibited CDK2 with IC₅₀ values of 1.71 μM and 1.60 μM.

Floro-pyrazolo[3,4-d]pyrimidine derivative as a novel plant activator induces two-pathway immune system

Plants are known to develop a multi-faceted innate immune system for pathogenic defense. Systemic acquired resistance (SAR) and induced systemic resistance (ISR) are the two main pathways. Many chemical inducers known as plant activators that activate innate immunity to defend against pathogens have been discovered. Currently, the exploitation of new plant activators is mainly done to develop analogs of salicylic acid as SAR-signaling molecules; however, the ISR pathway is hardly investigated for new plant activators. Based on recent studies on 1-methyl pyrazolo [3,4-d]pyrimidine bioactivity and ATP-induced resistance to biotrophic and necrotrophic pathogens, a new lead compound, 1-methyl-4-amino-pyrazolo [3,4-d]pyrimidine, was obtained as a new scaffold of plant activators for possible inducing ISR immunity system. Additionally, fluorine atom plays an important role in the design and development of new pesticides due to the unique physical chemistry effect, a series of pyrazolo [3,4-d]pyrimidine derivatives were designed and synthesized. Several compounds showed good broad-spectrum induced resistance in vivo, but there was no direct antibacterial activity in vitro. Notably, the introduction of fluorine atom at the para-position of the benzene ring greatly enhanced the induction activity of P1d both involved in SAR and ISR pathways, which implied the inducing resistance both in defending pathogens and insects.

Identification of Adenosine Deaminase Inhibitors by Metal-binding Pharmacophore Screening

Adenosine deaminase (ADA) is a human mononuclear Zn²⁺ metalloenzyme that converts adenosine to inosine. ADA is a validated drug target for cancer, but there has been little recent work on the development of new therapeutics against this enzyme. The lack of new advancements can be partially attributed to an absence of suitable assays for high-throughput screening (HTS) against ADA. To facilitate more rapid drug discovery efforts for this target, an in vitro assay was developed that utilizes the enzymatic conversion of a visibly emitting adenosine analogue to the corresponding fluorescent inosine analogue by ADA, which can be monitored via fluorescence intensity changes. Utilizing this assay, a library of ∼350 small molecules containing metal-binding pharmacophores (MBPs) was screened in an HTS format to identify new inhibitor scaffolds against ADA. This approach yielded a new metal-binding scaffold with a K_i value of 26±1 μM.

Ascertaining the activity and inhibition of adenosine deaminase via fluorescence-based assays

A fluorescence-based assay for adenosine deaminase (ADA) activity and inhibition, which may also be formatted as an inhibitor discovery assay, is described. It relies on differences in fluorescence between an isothiazolo-based adenosine analogs (^tzA) and its deaminated product, the corresponding inosine derivative (^tzI), which facilitates a real-time monitoring of enzymatic activity. Inhibitors are added to the enzyme-substrate reaction mixture at various concentrations and the fluorescence signal is recorded over 10min. The percent inhibition is calculated from the signal change at 10min relative to the uninhibited reaction. The percent inhibition is plotted against inhibitor concentration and fitted to a Hill curve. IC₅₀ values are then calculated.

Computational and experimental validation of morin as adenosine deaminase inhibitor

Adenosine deaminase (ADA) is one of the major enzymes involved in purin metabolism, it has a significant role in cell growth and differentiation. Over-activity of ADA has been noticed in some pathology, like malignancy and inflammation and makes it an attractive target for the development of drugs for such diseases. In the present study, ADA inhibitory activity of morin, a bioactive flavonoid, was assessed through computational and biophysical methods. The enzyme kinetics data showed that morin is a competitive inhibitor of ADA. Binding energy calculated from ITC analysis was -7.11 kcal/mol. Interaction of morin with ADA was also studied using fluorescence quenching method. Molecular docking studies revealed the structural details of the interaction. Molecular dynamics study in explicit solvent was also conducted to assess the structural stability of protein ligand complex.

Role of Copper in the Onset of Alzheimer's Disease Compared to Other Metals

Alzheimer's disease (AD) is a neurodegenerative disorder that is characterized by amyloid plaques in patients' brain tissue. The plaques are mainly made of β-amyloid peptides and trace elements including Zn2+, Cu2+, and Fe2+. Some studies have shown that AD can be considered a type of metal dyshomeostasis. Among metal ions involved in plaques, numerous studies have focused on copper ions, which seem to be one of the main cationic elements in plaque formation. The involvement of copper in AD is controversial, as some studies show a copper deficiency in AD, and consequently a need to enhance copper levels, while other data point to copper overload and therefore a need to reduce copper levels. In this paper, the role of copper ions in AD and some contradictory reports are reviewed and discussed.

A multicomponent reaction of 2-aminoimidazoles: microwave-assisted synthesis of novel 5-aza-7-deaza-adenines

An efficient and highly selective multicomponent synthesis of 4-aminoimidazo[1,2-a]triazines, which are 5-aza-7-deaza-isosteres of adenine, was developed.

Microwave-assisted synthesis and antibacterial evaluation of new derivatives of 1,2-dihydro-3H-pyrazolo[3,4-d]pyrimidin-3-one

Synthesis of new 1,2-dihydro-3H-pyrazolo[3,4-d] pyrimidin-3-ones4–6starting with ethyl 4-hydroxy-2-methylthio-pyrimidine-5-carboxylate (1) under classical heating and microwave-induced conditions is reported. The antibacterial activities of the synthesized compounds were evaluated using chloramphenicol and streptomycin as reference drugs.

A convenient four-component one-pot strategy toward the synthesis of pyrazolo[3,4-d]pyrimidines

An efficient one-pot synthesis of pyrazolo[3,4-d]pyrimidine derivatives by the four-component condensation of hydrazines, methylenemalononitriles, aldehydes and alcohols has been developed via two different reaction pathways. The structures of target products were characterized by IR spectroscopy, NMR (¹H and ¹³C) spectroscopy and HRMS (ESI) spectrometry. The crystal structure of 4-ethoxy-6-(2-nitrophenyl)-1-phenyl-1H-pyrazolo[3,4-d]pyrimidine was determined by single crystal X-ray diffraction.

PMMA/polysaccharides nanofilm loaded with adenosine deaminase inhibitor for targeted anti-inflammatory drug delivery

A novel drug delivery vector, a free-standing polymeric ultrathin film (nanofilm) composed of PMMA and a polysaccharides multilayer, is presented. Chitosan and sodium alginate are alternatively deposited by spin-assisted LbL assembly onto a plasma-treated PMMA thin film. Hydrophobic anti-inflammatory drugs, an adenosine deaminase inhibitor (APP) and its fluorescent dansyl derivate (APP-Dns), are encapsulated inside the LbL multilayer using a simple casting deposition procedure. The resulting drug loaded nanofilm can be suspended in water upon dissolution of a PVA sacrificial layer. Morphological characterization of the nanofilm shows that PMMA/LbL nanofilms possess nanometric thickness (<200 nm) and very low surface roughness (1-2 nm for drug loaded nanofilms and <1 nm for blank nanofilm). Drug loaded films exhibit a diffusion controlled release mechanism following the Korsmayer-Peppas release model, confirmed by the fit of release data with a characteristic power law. Drug release is impaired through the PMMA layer, which acts effectively as a barrier for drug transport. This ultrathin polymer film can find application as a nanopatch for targeted inflammatory drug delivery to treat localized pathologies as inflammatory bowel disease.

Structural consequences of the N7 and C8 translocation on the metal binding behavior of adenine

7-Deaza-8-aza-adenine, namely 4-aminopyrazolo[3,4-d]pyrimidine (H4app), is a bioisoster of adenine (Hade) resulting from the translocation of N7 and C8 atoms on the purine moiety. With the aim of studying the influence of this translocation on the metal binding abilities of H4app, we have prepared and structurally characterized two ternary copper(II) complexes having H4app and one N-benzyl-iminodiacetate chelator (MEBIDA or FBIDA, with a methyl or fluoro group in para- of the benzyl aromatic ring): [Cu(2)(MEBIDA)(2)(μ(2)-N1,N8-H4app)(H(2)O)(2)]·4H(2)O (1) and [Cu(4)(FBIDA)(4)(μ(2)-N8,N9-H4app)(2)(H(2)O)]·3.5H(2)O (2). Furthermore, thermal, spectral, and magnetic properties have been also investigated. In 1, H(N9)4app is disordered over two equally pondered positions and the μ(2)-N1,N8 coordination mode is assisted by N6-H···O and N9-H···O intramolecular interactions, respectively. The acyclic nonlinear molecular topology of 2 is strongly influenced by two intramolecular H-bonding interactions (O-H···O-carboxylate) involving the apical aqua ligand of a terminal Cu(II) atom. Thus, both compounds have in common the Cu-N8 bond. In order to better understand our limited structural information, DFT calculations for the individual tautomers of H4app as well as mononuclear Cu(II) model systems have been carried out. According to previous results, we conclude that H(N9)4app is the most stable tautomer followed by H(N8)4app. When N9 and N8 are metalated, then the tautomer H(N1)4app can come into play as observed in compound 2. Likewise, the findings concerning compound 1 suggest that the formation of a Cu-N1 bond in H4app results was favored compared to neutral adenine, for which only one case has been reported with such coordination despite the large variety of related Cu(II)-Hade described in the literature.

Design, Synthesis, and Antitumor Evaluation of Novel Pyrazolo[3,4-d]pyrimidine Derivatives

A new series of pyrazolo[3,4-d]pyrimidines has been synthesized. The new compounds were tested for their antitumor activity on 60 different cell lines, and some of the compounds were found to have potent antitumor activity. In particular, 2-hydroxybenzaldehyde [1-(4-chlorophenyl)-3-methyl-1H-pyrazolo-[3,4-d]pyrimidin-4-yl]hydrazone (VIIa) was found to be the most effective among the other derivatives, showing IC50 values of 0.326 to 4.31 μM on 57 different cell lines.

Sampling protein motion and solvent effect during ligand binding

An exhaustive description of the molecular recognition mechanism between a ligand and its biological target is of great value because it provides the opportunity for an exogenous control of the related process. Very often this aim can be pursued using high resolution structures of the complex in combination with inexpensive computational protocols such as docking algorithms. Unfortunately, in many other cases a number of factors, like protein flexibility or solvent effects, increase the degree of complexity of ligand/protein interaction and these standard techniques are no longer sufficient to describe the binding event. We have experienced and tested these limits in the present study in which we have developed and revealed the mechanism of binding of a new series of potent inhibitors of Adenosine Deaminase. We have first performed a large number of docking calculations, which unfortunately failed to yield reliable results due to the dynamical character of the enzyme and the complex role of the solvent. Thus, we have stepped up the computational strategy using a protocol based on metadynamics. Our approach has allowed dealing with protein motion and solvation during ligand binding and finally identifying the lowest energy binding modes of the most potent compound of the series, 4-decyl-pyrazolo[1,5-a]pyrimidin-7-one.

Application of Ullmann and Ullmann-Finkelstein reactions for the synthesis of N-aryl-N-(1H-pyrazol-3-yl) acetamide or N-(1-aryl-1H-pyrazol-3-yl) acetamide derivatives and pharmacological evaluation

Ullmann-type reactions are becoming a major tool in medicinal chemistry. In this article, we describe the use of these Copper-catalyzed reactions with various precursors, acyl-heteroarylamines or pyrazoles of interest for pharmacomodulation. To the medicinal chemist they offer new, usually untapped disconnection approaches to compounds of interest. They thus open the way to new original analogues of bioactive compounds possibly not patented, from common building-blocks. They also allow C to N bioisosteric replacements, which sometimes are synthetically challenging. We report for the first time the critical effect of acetylamino substituents on the regioselective arylation of unsymmetrical pyrazoles that are useful for medicinal chemists. Finally, we have applied this strategy to the design of novel AT(1) receptor antagonists. Though this family has been extensively investigated in the past 30 years, N-arylation and C to N replacement made possible by Ullmann chemistry, can produce original antagonists.

Investigation of a novel molecular descriptor for the lead optimization of 4-aminoquinazolines as vascular endothelial growth factor receptor-2 inhibitors: application for quantitative structure-activity relationship analysis in lead optimization

We investigated the use of infrared vibrational frequency of ligands as a potential novel molecular descriptor in three different molecular target and chemical series. The vibrational energy of a ligand was approximated from the sum of infrared (IR) absorptions of each functional group within a molecule and normalized by its molecular weight (MDIR). Calculations were performed on a set of 4-aminoquinazolines with similar docking scores for the VEGFR2/KDR receptor. 4-Aminoquinazolines with MDIR values ranging 192-196 provided compounds with KDR inhibitory activity. The correlation of KDR inhibitory activity was similarly observed in a separate chemical series, the pyrazolo[1,5-a]pyrimidines. Initial exploration of this molecular descriptor supports a tool for rapid lead optimization in the 4-aminoquinazoline chemical series and a potential method for scaffold hopping in pursuit of new inhibitors.

Investigations into the origin of the molecular recognition of several adenosine deaminase inhibitors

Inhibitors of adenosine deaminase (ADA, EC 3.5.4.4) are potential therapeutic agents for the treatment of various health disorders. Several highly potent inhibitors were previously identified, yet they exhibit unacceptable toxicities. We performed a SAR study involving a series of C2 or C8 substituted purine-riboside analogues with a view to discover less potent inhibitors with a lesser toxicity. We found that any substitution at C8 position of nebularine resulted in total loss of activity toward calf intestinal ADA. However, several 2-substituted-adenosine, 8-aza-adenosine, and nebularine analogues exhibited inhibitory activity. Specifically, 2-Cl-purine riboside, 8-aza-2-thiohexyl adenosine, 2-thiohexyl adenosine, and 2-MeS-purine riboside were found to be competitive inhibitors of ADA with K(i) values of 25, 22, 6, and 3 μM, respectively. We concluded that electronic parameters are not major recognition determinants of ADA but rather steric parameters. A C2 substituent which fits ADA hydrophobic pocket and improves H-bonding with the enzyme makes a good inhibitor. In addition, a gg rotamer about C4'-C5' bond is apparently an important recognition determinant.

Erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA) blocks differentiation and maintains the expression of pluripotency markers in human embryonic stem cells

hESCs (human embryonic stem cells) have enormous potential for use in pharmaceutical development and therapeutics; however, to realize this potential, there is a requirement for simple and reproducible cell culture methods that provide adequate numbers of cells of suitable quality. We have discovered a novel way of blocking the spontaneous differentiation of hESCs in the absence of exogenous cytokines by supplementing feeder-free conditions with EHNA [erythro-9-(2-hydroxy-3-nonyl)adenine], an established inhibitor of ADA (adenosine deaminase) and cyclic nucleotide PDE2 (phosphodiesterase 2). hESCs maintained in feeder-free conditions with EHNA for more than ten passages showed no reduction in hESC-associated markers including NANOG, POU5F1 (POU domain class 5 transcription factor 1, also known as Oct-4) and SSEA4 (stage-specific embryonic antigen 4) compared with cells maintained in feeder-free conditions containing bFGF (basic fibroblast growth factor). Spontaneous differentiation was reversibly suppressed by the addition of EHNA, but, upon removing EHNA, hESC populations underwent efficient spontaneous, multi-lineage and directed differentiation. EHNA also acts as a strong blocker of directed neuronal differentiation. Chemically distinct inhibitors of ADA and PDE2 lacked the capacity of EHNA to suppress hESC differentiation, suggesting that the effect is not driven by inhibition of either ADA or PDE2. Preliminary structure–activity relationship analysis found the differentiation-blocking properties of EHNA to reside in a pharmacophore comprising a close adenine mimetic with an extended hydrophobic substituent in the 8- or 9-position. We conclude that EHNA and simple 9-alkyladenines can block directed neuronal and spontaneous differentiation in the absence of exogenous cytokine addition, and may provide a useful replacement for bFGF in large-scale or cGMP-compliant processes.

Expanding the diversity of allosteric bcr-abl inhibitors

Inhibition of Bcr-Abl kinase activity by imatinib for the treatment of chronic myeloid leukemia (CML) currently serves as the paradigm for targeting dominant oncogenes with small molecules. We recently reported the discovery of GNF-2 (1) and GNF-5 (2) as selective non-ATP competitive inhibitors of cellular Bcr-Abl kinase activity that target the myristate binding site. Here, we used cell-based structure-activity relationships to guide the optimization and diversification of ligands that are capable of binding to the myristate binding site and rationalize the findings based upon an Abl-compound 1 cocrystal. We elucidate the structure-activity relationships required to obtain potent antiproliferative activity against Bcr-Abl transformed cells and report the discovery of new compounds (5g, 5h, 6a, 14d, and 21j-I) that display improved potency or pharmacological properties. This work demonstrates that a variety of structures can effectively target the Bcr-Abl myristate binding site and provides new leads for developing drugs that can target this binding site.

The blockade of adenosine deaminase ameliorates chronic experimental colitis through the recruitment of adenosine A2A and A3 receptors

Adenosine modulates immune/inflammatory reactions. This study investigates the expression of adenosine deaminase in the inflamed colon, the effects of adenosine deaminase inhibitors on established colitis, and the recruitment of adenosine receptors by endogenous adenosine after adenosine deaminase blockade. Adenosine deaminase expression was determined by Western blot. The effects of 4-amino-2-(2-hydroxy-1-decyl)pyrazole[3,4-d]pyrimidine (APP; a novel adenosine deaminase inhibitor), erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA; a reference adenosine deaminase inhibitor), dexamethasone, and selective adenosine receptor antagonists were tested in rats with 2,4-dinitrobenzenesulfonic acid-induced colitis. Systemic (food intake, body and spleen weight) and colonic [macroscopic/microscopic damage, tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and malondialdehyde (MDA)] inflammatory parameters were assessed. Test drugs were administered intraperitoneally for 6 days, starting at day 5 from colitis induction. Adenosine deaminase was detected in normal colon, and its expression was increased in inflamed tissues. Colitis was associated with decreased food intake and body weight, augmented spleen weight, and increased levels of colonic TNF-α, IL-6, and MDA. APP or EHNA, but not dexamethasone, improved food intake and body weight. APP, EHNA, and dexamethasone counteracted the increments of spleen weight, ameliorated macroscopic and microscopic indexes of inflammation, and reduced TNF-α, IL-6, and MDA levels. The beneficial effects of APP and EHNA on inflammatory parameters were prevented by the pharmacological blockade of A(2A) or A(3) receptors, but not A(1) or A(2B). The present results show that: 1) bowel inflammation is associated with an enhanced adenosine deaminase expression; and 2) the anti-inflammatory actions of adenosine deaminase inhibitors against chronic established colitis depend on the sparing of endogenous adenosine, leading to enhanced A(2A) and A(3) receptor activation.

Preparation of (S)-1-Halo-2-octanols Using Ionic Liquids and Biocatalysts

Preparation of (S)-1-chloro-2-octanol and (S)-1-bromo-2-octanol was carried out by the enzymatic hydrolysis of halohydrin palmitates using biocatalysts. Halohydrin palmitates were prepared by various methods from palmitic acid and 1,2-octanediol. A tandem hydrolysis was carried out using lipases from Candida antarctica (Novozym^® 435⁾, Rhizomucor miehei (Lipozyme IM), and “resting cells” from a Rhizopus oryzae strain that was not mycotoxigenic. The influence of the enzyme and the reaction medium on the selective hydrolysis of isomeric mixtures of halohydrin esters is described. Novozym^® 435 allowed preparation of (S)-1-chloro-2-octanol and (S)-1-bromo-2-octanol after 1–3 h of reaction at 40 °C in [BMIM][PF₆].

Synthesis of some new pyrazolo[3,4-d]pyrimidine derivatives of expected anticancer and radioprotective activity

On the account of the reported anticancer activity of pyrazolo[3,4-d]pyrimidines, a new series of pyrazolo[3,4-d]pyrimidine derivatives were synthesized and tested for in-vitro anticancer activity against Ehrlich Ascites Carcinoma (EAC) cell line. Moreover, one of the target products was evaluated for in-vivo radioprotective activity. The reaction of o-aminoester 1 with benzylamine in presence of triethylorthoformate yielded the corresponding 5-benzylpyrazolopyrimidine derivative 2. The N-amino derivative 3 was used to synthesize new derivatives of pyrazolopyrimidines 4-7. The corresponding 1,3,4-oxadiazolopyrazolopyrimidine derivatives 12 and 14 were obtained via reaction of compound 9 with reagent 10 and/or triethylorthoformate. Thiophosgenation of compound 1 furnished the corresponding 5-isothiocyanate derivative 15, which was reacted with o-phenylenediamine, thiosemicarbazide and anthranilic acid to give benzimidazolopyrazolopyrimidine, 17, pyrazolotriazolopyrimidine, 19 and pyrazolopyrimidobenzoxazine, 20 respectively. The structures of the synthesized compounds were confirmed by microanalyses, IR, NMR, and mass spectral data. Compounds 2 and 9 showed intermediate anticancer activity compared to doxorubicin as positive control with IC50 values of 90 and 100 microg/ml, respectively. On the other hand, compound 5 showed significant radioprotective effect.

Syntheses of tricyclic pyrones and pyridinones and protection of Abeta-peptide induced MC65 neuronal cell death

The SbetaC gene is conditionally expressed a 99-residue carboxy terminal fragment, C99, of amyloid precursor protein in MC65 cells and causes cell death. Consequently, MC65 cell line was used to identify inhibitors of toxicity related to intracellular amyloid beta (Abeta) oligomers. Compounds that reduce the level of Abeta peptides, prevent Abeta aggregation, or eliminate existing Abeta aggregates may be used in the treatment of Alzheimer's disease (AD). Previously, we found that a tricyclic pyrone (TP) molecule, compound 1, prevents MC65 cell death and inhibits Abeta aggregation. Hence various TPs containing heterocycle at C7 side chain and a nitrogen at position 2 or 5 were synthesized and their MC65 cell protective activities evaluated. TPs containing N3'-adenine moiety such as compounds 1 and 11 are most active with EC(50) values of 0.31 and 0.35 microM, respectively. EC(50) values of tricyclic N5-analog, pyranoisoquinolinone 13, and N2-analog, pyranopyridinone 20, are 2.49 and 1.25 microM, respectively, despite the lack of adenine moiety. Further investigation of tricyclic N2- and N5-analogs is warranted.

Transition-state variation in human, bovine, and Plasmodium falciparum adenosine deaminases

Adenosine deaminases (ADAs) from human, bovine, and Plasmodium falciparum sources were analyzed by kinetic isotope effects (KIEs) and shown to have distinct but related transition states. Human adenosine deaminase (HsADA) is present in most mammalian cells and is involved in B- and T-cell development. The ADA from Plasmodium falciparum (PfADA) is essential in this purine auxotroph, and its inhibition is expected to have therapeutic effects for malaria. Therefore, ADA is of continuing interest for inhibitor design. Stable structural mimics of ADA transition states are powerful inhibitors. Here we report the transition-state structures of PfADA, HsADA, and bovine ADA (BtADA) solved using competitive kinetic isotope effects (KIE) and density functional calculations. Adenines labeled at [6-13C], [6-15N], [6-13C, 6-15N], and [1-15N] were synthesized and enzymatically coupled with [1'-14C] ribose to give isotopically labeled adenosines as ADA substrates for KIE analysis. [6-13C], [6-15N], and [1-15N]adenosines reported intrinsic KIE values of (1.010, 1.011, 1.009), (1.005, 1.005, 1.002), and (1.004, 1.001, 0.995) for PfADA, HsADA, and BtADA, respectively. The differences in intrinsic KIEs reflect structural alterations in the transition states. The [1-15N] KIEs and computational modeling results indicate that PfADA, HsADA, and BtADA adopt early SNAr transition states, where N1 protonation is partial and the bond order to the attacking hydroxyl nucleophile is nearly complete. The key structural variation among PfADA, HsADA, and BtADA transition states lies in the degree of N1 protonation with the decreased bond lengths of 1.92, 1.55, and 1.28 A, respectively. Thus, PfADA has the earliest and BtADA has the most developed transition state. This conclusion is consistent with the 20-36-fold increase of kcat in comparing PfADA with HsADA and BtADA.

Inhibition of Adenosine Deaminase Attenuates Inflammation in Experimental Colitis

Adenosine modulates the immune system and inhibits inflammation via reduction of cytokine biosynthesis and neutrophil functions. Drugs able to prevent adenosine catabolism could represent an innovative strategy to treat inflammatory bowel disorders. In this study, the effects of 4-amino-2-(2-hydroxy-1-decyl)pyrazole[3,4-d]pyrimidine (APP; novel adenosine deaminase inhibitor), erythro-9-(2-hydroxy-3-nonyl)adenine hydrochloride (EHNA; standard adenosine deaminase inhibitor), and dexamethasone were tested in rats with colitis induced by 2,4-dinitrobenzenesulfonic acid (DNBS). DNBS-treated animals received APP (5, 15, or 45 micromol/kg), EHNA (10, 30, or 90 micromol/kg), or dexamethasone (0.25 micromol/kg) i.p. for 7 days starting 1 day before colitis induction. DNBS caused bowel inflammation associated with decrease in food intake and body weight. Animals treated with APP or EHNA, but not dexamethasone, displayed greater food intake and weight gain than inflamed rats. Colitis induced increment in spleen weight, which was counteracted by all test drugs. DNBS administration was followed by macroscopic and microscopic inflammatory colonic alterations, which were ameliorated by APP, EHNA, or dexamethasone. In DNBS-treated rats, colonic myeloperoxidase, malondialdehyde, and tumor necrosis factor (TNF)-alpha levels as well as plasma TNF-alpha and interleukin-6 were increased. All test drugs lowered these phlogistic indexes. Inflamed colonic tissues displayed an increment of inducible nitric-oxide synthase mRNA, which was unaffected by APP or EHNA, but reduced by dexamethasone. Cyclooxygenase-2 expression was unaffected by DNBS or test drugs. These findings indicate that 1) inhibition of adenosine deaminase results in a significant attenuation of intestinal inflammation and 2) the novel compound APP is more effective than EHNA in reducing systemic and intestinal inflammatory alterations.

Flow and batch mode focused microwave synthesis of 5-amino-4-cyanopyrazoles and their further conversion to 4-aminopyrazolopyrimidines

A new approach to the synthesis of 5-amino-4-cyanopyrazoles has been developed, utilising a novel flow microwave device. These products are then converted by a batch mode microwave process to structurally more complex dimeric and 'mixed' pyrazolopyrimidine structures.