Search

Inhibitors of the enzyme NQO2 (NRH: quinone oxidoreductase 2) are of potential use in cancer chemotherapy and malaria. We have previously reported that non-symmetrical furan amidines are potent inhibitors of NQO2 and here novel analogues are evaluated. The furan ring has been changed to other heterocycles (imidazole, N-methylimidazole, oxazole, thiophene) and the amidine group has been replaced with imidate, reversed amidine, N-arylamide and amidoxime to probe NQO2 activity, improve solubility and decrease basicity of the lead furan amidine. All compounds were fully characterised spectroscopically and the structure of the unexpected product N-hydroxy-4-(5-methyl-4-phenylfuran-2-yl)benzamidine was established by X-ray crystallography. The analogues were evaluated for inhibition of NQO2, which showed lower activity than the lead furan amidine. The observed structure-activity relationship for the furanamidine series with NQO2 was rationalized by preliminary molecular docking and binding mode analysis. In addition, the oxazole-amidine analogue inhibited the growth of Plasmodium\ud falciparum with an IC50 value of 0.3 M.

(NRH):quinone oxidoreductase 2 (NQO2) is associated with various processes involved in cancer initiation and progression probably via the production of ROS during quinone metabolism. Thus, there is a need to develop inhibitors of NQO2 that are active in vitro and in vivo. As part of a strategy to achieve this we have used the 4-aminoquinoline backbone as a starting point and synthesized 21 novel analogues. The syntheses utilised p-anisidine with Meldrum's acid and trimethyl orthoacetate or trimethyl orthobenzoate to give the 4-hydrazin-quinoline scaffold, which was derivatised with aldehydes or acid chlorides to give hydrazone or hydrazide analogues, respectively. The hydrazones were the most potent inhibitors of NQO2 in cell free systems, some with low nano-molar IC50 values. Structure-activity analysis highlighted the importance of a small substituent at the 2-position of the 4-aminoquinoline ring, to reduce steric hindrance and improve engagement of the scaffold within the NQO2 active site. Cytotoxicity and NQO2–inhibitory activity in vitro was evaluated using ovarian cancer SKOV-3 and TOV-112 cells (expressing high and low levels of NQO2, respectively). Generally, the hydrazones were more toxic than hydrazide analogues and further, toxicity is unrelated to cellular NQO2 activity. Pharmacological inhibition of NQO2 in cells was measured using the toxicity of CB1954 as a surrogate end-point. Both the hydrazone and hydrazide derivatives are functionally active as inhibitors of NQO2 in the cells, but at different inhibitory potency levels. In particular, 4-((2-(6-methoxy-2-methylquinolin-4-yl)hydrazono)methyl)phenol has the greatest potency of any compound yet evaluated (53 nM), which is 50-fold lower than its toxicity IC50. This compound and some of its analogues could serve as useful pharmacological probes to determine the functional role of NQO2 in cancer development and response to therapy.

NRH:quinone oxidoreductase 2 enzyme (NQO2) is a potential therapeutic target in cancer and neurodegenerative diseases, with roles in either chemoprevention or chemotherapy. Here we report the design, synthesis and evaluation of non-symmetrical furan-amidines and their analogues as novel selective NQO2 inhibitors with reduced adverse off-target effects, such as binding to DNA. A pathway for the synthesis of the non-symmetrical furan-amidines was established from the corresponding 1,4-diketones. The synthesized non-symmetrical furan-amidines and their analogues showed potent NQO2 inhibition activity with nano-molar IC50 values. The most active compounds were non-symmetrical furan-amidines with meta- and para-nitro substitution on the aromatic ring, with IC50 values of 15 nM. In contrast to the symmetric furan-amidines, which showed potent intercalation in the minor grooves of DNA, the synthesized non-symmetrical furan-amidines showed no affinity towards DNA, as demonstrated by DNA melting temperature experiments. In addition, Plasmodium parasites, which possess their own quinone oxidoreductase PfNDH2, were inhibited by the non-symmetrical furan-amidines, the most active possessing a para-fluoro substituent (IC50 9.6 nM). The high NQO2 inhibition activity and nanomolar antimalarial effect of some of these analogues suggest the lead compounds are worthy of further development and optimization as potential drugs for novel anti-cancer and antimalarial strategies.

The diethyl ester of [(18)F]ML-10 is a small molecule apoptotic PET probe for cancer studies. Here we report a novel multi-step synthesis of the diethyl ester of ML-10 in excellent yields via fluorination using Xtal-Fluor-E. In addition, a one-pot radiosynthesis of the diethyl ester of [(18)F]ML-10 from nucleophilic [(18)F]fluoride was completed in 23% radiochemical yield (decay corrected). The radiochemical purity of the product was ≥99%. The diethyl ester of [(18)F]ML-10 was used in vivo to detect apoptosis in the testes of mice. In parallel studies, the dansyl-ML-10 diethyl ester was prepared and used to detect apoptotic cells in an in vitro cell based assay.

Sterically constrained probes 2,4- O -bisdansyl-6,7-diazabicyclo[3.2.1]oct-6-ene ( 8 ) and 2,4- O -bispyrenoyl-6,7-diazabicyclo[3.2.1]oct-6-ene ( 9 ) exhibit specific dimer fluorescent characteristics ( λ max 555 nm and 511 nm, respectively), attributed to the 2,4-diaxial arrangement of the dansyl or pyrene groups. Reduction of the azo-conformational locking group in ( 8 ) and ( 9 ) yielded 1,3-bisdansyl-4,6-diaminocyclohexane ( 16 ) and 1,3-bispyrenoyl-4,6-diaminocyclohexane ( 17 ) in the tetra-equatorial chair conformation, thus minimising interaction of the bisdansyl or bispyrenoyl groups. This induces a change in fluorescence from a cooperative green emission dimer band to a blue-shifted, monomer type fluorescence, with λ max 448 nm and 396 nm for the reduced forms ( 16 ) and ( 17 ), respectively. The azo-bond conformational lock can either be reduced under biomimetic conditions (using sodium dithionite) or with bacteria ( Clostridium perfringens or Escherichia coli ) utilising azo-reductase enzymes. These fluorescent probes have the potential to specifically detect azo-reductase expressing bacteria.

5-(2-Aminopropyl)indole (5-IT) and 3-(2-aminopropyl)indole (α-methyltryptamine, AMT) are isomeric substances and their differentiation can be a challenge under routine analytical conditions, especially when reference material is unavailable. 5-IT represents a very recent addition to the battery of new psychoactive substances that are commercially available from online retailers. This report illustrates how subtle differences observed under mass spectral and UV conditions can help to facilitate the differentiation between the two isomers. Analyses included 1 H and 13C NMR, GC-EI/CI ion trap MS, applications of several U/HPLC-DAD and HPLC-MS methods. Investigations currently underway also highlight the confirmation that AMT was detected in a number of fatal intoxications. These findings also demonstrate that there is a potential risk of misidentification when dealing with both substances. Copyright © 2012 John Wiley & Sons, Ltd.

Animal cells contain a pool of inositol phosphates whose biological function is still under current investigation. Ins(1,2,3)P3 is probably an important safe chelator of iron cations not strongly bound to proteins. In order to clarify its biological functions, Ins(1,2,3)P3 chemistry under physiological conditions must be completely elucidated. The protonation and complexation behaviour of Ins(1,2,3)P3 has been recently studied under these conditions by potentiometry. Under simulated physiological conditions it forms the protonated species H2L4− and H3L3−. The presence of high concentrations of potassium in intracellular compartments causes the formation of two predominant Ins(1,2,3)P3 complexes: [K(HL)]4− and [K(H2L)]3−, in the absence of iron. In this work we expand part of this macroscopic knowledge to the inframolecular level, by 31P NMR measurements and focusing on the protonation and complexation of this biologically relevant molecule to potassium. We complete this study with theoretical calculations which lead us to predict the geometries of every form of the ligand and their relative stabilities. The influence of the ring conformation in protonated and complexed forms is also discussed.

myo -Inositol 1,2,3-trisphosphate [Ins(1,2,3)P 3 ], a component in mammalian cells, possesses the correct chemical properties of an intracellular iron transit ligand. Here we have examined the conformation of the Ins(1,2,3)P 3 –Fe 3+ complex. The synthesis and antioxidant properties of 4,6-carbonate- myo -inositol 1,2,3,5-tetrakisphosphate [4,6-carbonate Ins(1,2,3,5)P 4 ], which is locked in the unstable penta-axial chair conformation and 1,2,3-trisphosphoglycerol, a flexible acyclic analogue of Ins(1,2,3)P 3 , are reported. 4,6-Carbonate Ins(1,2,3,5)P 4 caused complete inhibition of iron-catalysed hydroxyl radical (HO ) formation at 100 μM, thereby resembling Ins(1,2,3)P 3 and supporting a penta-axial chair binding conformation. In contrast, 1,2,3-trisphosphoglycerol was shown to have incomplete antioxidant properties. In support of experimental observations, we have applied high-level density functional calculations to the binding of Ins(1,2,3)P 3 to iron. This study provides evidence that Fe 3+ binds tightly to the less stable penta-axial conformation of Ins(1,2,3)P 3 using terminal and bridging phosphate oxygens, thought to also contain a tightly bound water molecule or hydroxyl ligand in the complex.

Naphyrone (naphthylpyrovalerone, O-2482) has been recently advertised for purchase on a number of websites. This compound has been viewed as a so-called ‘legal high’ and was classified as a controlled drug under the UK Misuse of Drugs Act 1971 in mid-July 2010. So far, naphyrone is commonly equated with 1-naphthalen-2-yl-2-pyrrolidin-1-yl-pentan-1-one (β-naphyrone) but analytical characterization of two naphyrone samples revealed the existence of a novel isomer consistent with 1naphthalen-1-yl-2-pyrrolidin-1-yl-pentan-1-one (α-naphyrone). Analyses of both α -a ndβ-naphyrone were carried out using gas chromatography ion trap (EI/CI) mass spectrometry and 1D/2D nuclear magnetic resonance spectroscopy. This provides the first report of α-naphyrone in the scientific literature and the ability to differentiate it from the β-isomer should be of interest to forensic and clinical communities. Copyright c � 2010 John Wiley & Sons, Ltd.

Restricted rotation in indol-3-yl-N-alkyl- and indol-3-yl-N,N-dialkyl-glyoxalylamides can in principle give the syn-periplanar and anti-periplanar rotamers. In asymmetrically disubstituted glyoxalylamides, steric effects lead to the occurrence of both rotamers, as observed by NMR spectroscopy. The predominant peak corresponds with the anti rotamer, in which the bulkier alkyl group is orientated trans to the amide carbonyl group. In monoalkylated glyoxalylamides, only one set of peaks is observed, consistent with the presence of only one rotamer. Crystal structures of 5-methoxyindole-3-yl-N-tert-butylglyoxalylamide, indole-3-yl-N-tert-butylglyoxalylamide, and indole-3-yl-N-isopropylglyoxalylamide reported here reveal a syn conformation held by an intramolecular N-HO hydrogen bond.

Mammalian cells contain a pool of iron that is not strongly bound to proteins, which can be detected with fluorescent chelating probes. The cellular ligands of this biologically important "chelatable", "labile" or "transit" iron are not known. Proposed ligands are problematic, because they are saturated by magnesium under cellular conditions and/or because they are not "safe", i.e. they allow iron to catalyse hydroxyl radical formation. Among small cellular molecules, certain inositol phosphates (InsPs) excel at complexing Fe(3+) in such a "safe" manner in vitro. However, we previously calculated that the most abundant InsP, inositol hexakisphosphate, cannot interact with Fe(3+) in the presence of cellular concentrations of Mg(2+). In this work, we study the metal complexation behaviour of inositol 1,2,3-trisphosphate [Ins(1,2,3)P(3)], a cellular constituent of unknown function and the simplest InsP to display high-affinity, "safe", iron complexation. We report thermodynamic constants for the interaction of Ins(1,2,3)P(3) with Na(+), K(+), Mg(2+), Ca(2+), Cu(2+), Fe(2+) and Fe(3+). Our calculations indicate that Ins(1,2,3)P(3) can be expected to complex all available Fe(3+) in a quantitative, 1:1 reaction, both in cytosol/nucleus and in acidic compartments, in which an important labile iron subpool is thought to exist. In addition, we calculate that the fluorescent iron probe calcein would strip Fe(3+) from Ins(1,2,3)P(3) under cellular conditions, and hence labile iron detected using this probe may include iron bound to Ins(1,2,3)P(3). Therefore Ins(1,2,3)P(3) is the first viable proposal for a transit iron ligand.

The aim of this study is to evaluate the potential use of first-generation (G1) polyamidoamine (PAMAM) dendrimers as drug carriers to enhance the permeability, hence oral absorption, of drugs that are substrates for P-glycoprotein (P-gp) efflux transporters. G1 PAMAM dendrimer-based prodrugs of the water-insoluble P-gp substrate terfenadine (Ter) were synthesized using succinic acid (suc) or succinyl-diethylene glycol (suc-deg) as a linker/spacer (to yield G1-suc-Ter and G1-suc-deg-Ter, respectively). In addition, the permeability of G1-suc-deg-Ter was enhanced by attaching two lauroyl chains (L) to the dendrimer surface (L2-G1-suc-deg-Ter). All of the G1 dendrimer-terfenadine prodrugs were more hydrophilic than the parent drug, as evaluated by drug partitioning between 1-octanol and phosphate buffer at pH 7.4 (log K(app)). The influence of the dendrimer prodrugs on the integrity and viability of human Caucasian colon adenocarcinoma cells (Caco-2) was determined by measuring the transepithelial electrical resistance (TEER) and leakage of lactate dehydrogenase (LDH) enzyme, respectively. The LDH assay indicated that the dendrimer prodrugs had no impact on the viability of Caco-2 cells up to a concentration of 1 mM. However, the IC(50) of the prodrugs was lower than that of G1 PAMAM dendrimer because of the high toxicity of terfenadine. Measurements of the transport of dendrimer prodrugs across monolayers of Caco-2 cells showed an increase of the apparent permeability coefficient (P(app)) of terfenadine in both apical-to-basolateral (A --> B) and basolateral-to-apical (B --> A) directions after its conjugation to G1 PAMAM dendrimer. The A --> B P(app) of the dendrimer prodrugs was significantly greater than B --> A P(app). The surface-modified dendrimer prodrug L2-G1-suc-deg-Ter showed the highest A --> B permeability among the conjugates.

Many tryptamine derivatives are known to induce altered states of consciousness and are increasingly of interest in forensic and neurobiological studies. The analytical chemistry of certain synthetic routes to the tryptamines is discussed and likely side products and impurities identified, where literature reports are available. Recent examples from the authors' laboratory are presented to highlight future prospects and implications for analytical procedures. The aim of this review is to provide the analytical chemist with the foundation chemistry and some analytical targets to be able to undertake direct characterisation of products and intermediates. These might become available from interdiction of clandestine operations in a forensic environment or during the synthesis of the tryptamines for investigative neurobiological and clinical procedures.

A series of water soluble N(1)- and C(6)-substituted uracil pyridinium compounds were prepared as potential inhibitors of thymidine phosphorylase (TP). The C(6)-uracil substituted derivatives were the most active. 1-[(5-Chloro-2,4-dihydroxypyrimidin-6-yl)methyl]pyridinium chloride, was identified as the best inhibitor being 5-fold more potent than the known inhibitor, 6-amino-5-bromouracil.

myo-Inositol monophosphatase (IMPase), the proposed target for lithium therapy for manic depression, is an important enzyme in the biosynthesis of second messengers. Earlier studies have shown that the IMPase-catalyzed hydrolysis of myo-inositol monophosphates to inorganic phosphate and myo-inositol proceeds by direct attack of water at phosphorus. However, research groups have independently proposed either an in-line displacement (with inversion of stereochemistry at phosphorus) or an adjacent attack with a pseudorotation (with retention of stereochemistry at phosphorus). Here, the elucidation of the stereochemical pathway is presented. The IMPase-catalyzed hydrolysis of D-1-S(p)-myo-inositol [(17)O]-thiophosphate in the presence of H(2)(18)O gave inorganic R(p)-[(16)O,(17)O,(18)O]-thiophosphate, with inversion of configuration at phosphorus. This is only consistent with an in-line displacement, and it rules out the controversial adjacent/pseudorotation mechanism. This result will assist in the design of alternative inhibitors of IMPase.

dl -3,4,5,6-Tetra-O-benzyl-1-deoxy-1-fluoro-scyllo-inositol was resolved using (−)-(1S, 4R)-camphanyl chloride. The diastereoisomers formed were separated and the structure of d -3,4,5,6-tetra-O-benzyl-2-(1S,4R)-camphanyl-1-deoxy-1-fluoro-scyllo-inositol was solved by X-ray crystallography to an R-factor of 4.2%. A series of manipulations led to the preparation of d -1,2-dideoxy-1,2-difluoro-myo-inositol 3,4,5,6-tetrakisphosphate and its enantiomer. The d -1,2-difluoro enantiomer stereospecifically inhibited CaMK II-activated Cl− current, but with low potency; however, efficacy of this compound was greatly enhanced by myo-inositol 3,4,5,6-tetrakisphosphate itself.

The crystal structure of (±)-1,2;4,5-di-O-cyclohexylidene myo-inositol, refined to R = 2.9%, shows interestingly disordered (flip-flop) hydrogen bonding. The higher reactivity of the 1/3 positions (rather than 4/6) has been evaluated using semi-empirical calculations. This diol has been phosphorylated with (2R,4S,5R)-2-chloro-3,4-dimethyl-5-phenyl-1,3,2-oxazaphospholidin-2-one and the diastereoisomer derived from phosphorylation at the 3-position was isolated by crystallisation. Deprotection with TFA/H2O then H2/Pd-C afforded myo-inositol 3-phosphate in only four steps from myo-inositol.

The inositol ring in C 40 H 44 O 6 is in a chair conformation with the O atom at C2 in the expected axial position and the other five O atoms in equatorial positions. The ring is twisted with one approximate twofold axis retained through the mid-points of the C2-C3 and C5-C6 bonds.

The first syntheses of the natural products myo-inositol 1,2,3-trisphosphate and (+/-)-myo-inositol 1,2-bisphosphate are described. The protected key intermediates 4,5,6-tri-O-benzoyl-myo-inositol and (+/-)-3,4,5,6-tetra-O-benzyl-myo-inositol were phosphorylated with dibenzyl N,N-di-isopropylphosphoramidite in the presence of 1H-tetrazole and subsequent oxidation of the phosphite. The crystal structures of the synthetic intermediates (+/-)-1-O-(tert-butyldiphenylsilyl)-2,3,O-cyclohexylidene-myo-inos itol and (+/-)-4,5,6-tri-O-benzoyl-1-O-(tert-butyldiphenylsilyl)-2,3-O-cycl ohexylidene- myo-inositol are reported. myo-Inositol 1,2,3-trisphosphate, (+/-)-myo-inositol 1,2-bisphosphate, and all isomeric myo-inositol tetrakisphosphates were evaluated for their ability to alter HO. production in the iron-catalysed Haber-Weiss reaction. The results demonstrated that a 1,2,3-grouping of phosphates in myo-inositol was necessary for inhibition, also that (+/-)-myo-inositol 1,2-bisphosphate potentiated HO. production. myo-Inositol 1,2,3-trisphosphate resembled myo-inositol hexakisphosphate (phytic acid) in its ability to act as a siderophore by promoting iron-uptake into Pseudomonas aeruginosa.

Summary The soft-drug 1 (R = Me, Et) and pro-soft-drug 3 have been prepared as models of topical anti-psoriatic β-adrenergic agonists. The chemical hydrolysis of 3 proceeded via the acid 18 with a maximum stability at apparent pH ∼ 4.0. In the presence of PLCE, the required metabolism of 3 to the soft-drug 1 (R = Et) was achieved, which slowly degraded to the dihydroxy acid 2 . Soft-drug 1 (R = Et) was poorly transported across a silicone membrane, whereas the pro-soft-drug 3 was more efficient and the rate increased over the donor apparent pH range 3–8. Soft-drug 1 (R = Et) was a full β-agonist on the guinea-pig tracheal preparation, whereas the pro-soft-drug 3 produced only slowly developing responses at high concentrations (>10 μM).

4-Acyloxybenzyl bis(nucleosid-5′-yl) phosphates 7a-c and 9a-c were prepared as potential prodrugs of the anti-HIV nucleosides 3′-azido-3′-deoxythymidine (AZT) and 2′,3′-dideoxyinosine (ddI) or their 5′-monophosphates. The anti-HIV activities of these triesters were determined in two T-cell lines. In a C8166 cell line they displayed activities comparable to and in some cases superior to AZT, but they also exhibited an increase in cytotoxicity. In a thymidine kinase deficient JM T-cell line the activity was reduced but was still superior to AZT. In the presence of porcine liver carboxyesterase (PLCE), triester 7b biodegrades to the diester 10 which, with phosphodiesterase, gives initially AZT monophosphate 3 and AZT.

The first syntheses of the natural products myo-inositol 1,2,3-trisphosphate and (+/-)-myo-inositol 1,2-bisphosphate are described. The protected key intermediates 4,5,6-tri-O-benzoyl-myo-inositol and (+/-)-3,4,5,6-tetra-O-benzyl-myo-inositol were phosphorylated with dibenzyl N,N-di-isopropylphosphoramidite in the presence of 1H-tetrazole and subsequent oxidation of the phosphite. The crystal structures of the synthetic intermediates (+/-)-1-O-(tert-butyldiphenylsilyl)-2,3,O-cyclohexylidene-myo-inos itol and (+/-)-4,5,6-tri-O-benzoyl-1-O-(tert-butyldiphenylsilyl)-2,3-O-cycl ohexylidene- myo-inositol are reported. myo-Inositol 1,2,3-trisphosphate (+/-)-myo-inositol 1,2-bisphosphate, and all isomeric myo-inositol tetrakisphosphates were evaluated for their ability to alter HO. production in the iron-catalysed Haber-Weiss reaction. The results demonstrated that a 1,2,3-grouping of phosphates in myo-inositol was necessary for inhibition also that (+/-)-myo-inositol 1,2-bisphosphate potentiated HO. production. myo-Inositol 1,2,3-trisphosphate resembled myo-inositol hexakisphosphate (phytic acid) in its ability to act as a siderophore by promoting iron-uptake into Pseudomonas aeruginosa.

DL-1,2-Dideoxy-1,2-difluoro-myo-inositol was prepared from DL-3,4,5,6-tetra-O-benzyl-myo-inositol in five steps in an overall yield of 36%. The fluoro substituents were introduced with DAST in separate steps by displacement of hydroxy substituents with inversion of stereochemistry. Difluorination could not be achieved in one step because of competing formation of a 1,4-anhydro derivative. DL-1,2-Dideoxy-1,2-difluoro-scyllo-inositol was prepared in 42% overall yield using similar chemistry, with the required inversion of one stereocentre being accomplished by displacement of a tosyl group with caesium propionate. Both difluoroinositol analogues increased the levels of phytic acid (InsP6) in a skeletal muscle cell line. Each compound was tetraphosphorylated with dibenzyl N,N-diisopropylphosphoramidite in the presence of 1H-tetrazole, with subsequent oxidation of the phosphite with MCPBA. The P–OBn groups were removed by H2/Pd–C, and the sodium salts of the tetrakisphosphates of the difluoroinositol analogues were obtained by cation exchange.

Novel non-nucleobase-derived inhibitors of the angiogenic enzyme, thymidine phosphorylase, have been identified using molecular modelling, synthesis and biological evaluation. These inhibitors are 2,4,5-trioxoimidazolidines bearing N-(substituted)phenylalkyl groups, together with, in most cases, N'-(CH(2))(n)-carboxylic acid, ester or amide side chains. The best compound from this series is 3-(2,4,5-trioxo-3-phenylethyl-imidazolodin-1-yl)propionamide, with an IC(50) of 40 μM against Escherichia coli TP. Molecular modelling suggests that this ligand, when complexed with closed-cleft human TP, would have the phenylalkyl group in the active site region normally occupied by a thymine-containing structure.

The autoinducer (4S)-4,5-dihydroxypentane-2,3-dione ((S)-DPD, AI-2) facilitates chemical communication, termed 'quorum sensing', amongst a wide range of bacteria, The synthesis of (S)-DPD is challenging in part due to its instability. Herein we report a novel synthesis of (S)-DPD via (2S)-2,3-O-isopropylidene glyceraldehyde, through Wittig, dihydroxylation and oxidation reactions, with a complimentary asymmetric synthesis to a key precursor. Its enantiomer (R)-DPD, was prepared from d-mannitol via (2R)-2,3-O-isopropylideneglyceraldehyde. The synthesized enantiomers of DPD have AI-2 bioluminescence-inducing properties in the Vibrio harveyi BB170 strain.

Natural myo-inositol phosphate antioxidants containing the 1,2,3-trisphosphate motif bind Fe(3+) in the unstable penta-axial conformation.

2-O-tert-Butyldimethylsilyl-4,6-bis-O-pyrenoyl-myo-inositol-1,3,5-orthoformate (6) and 2-O-tert-butyldimethylsilyl-4-O-[4-(dimethylamino)benzoyl]-6-O-pyrenoyl-myo-inositol-1,3,5-orthoacetate (10) adopt conformationally restricted unstable chairs with five axial substituents. In the symmetrical diester 6, the two pi-stacked pyrenoyl groups are electron acceptor-donor partners, giving a strong intramolecular excimer emission. In the mixed ester 10, the pyrenoyl group is the electron acceptor and the 4-(dimethylamino)benzoyl ester is the electron donor, giving a strong intramolecular exciplex emission. The conformation of the mixed ester 10 was assessed using 1H NMR spectroscopy (1H-NOESY) and computational studies. which showed the minimum inter-centroid distance between the two aromatic systems to be approximately 3.9 A. Upon addition of acid, the orthoformate/orthoacetate trigger in 6 and 10 was cleaved, which caused a switch of the conformation of the myo-inositol ring to the more stable penta-equatorial chair, leading to separation of the aromatic ester groups and loss of excimer and exciplex fluorescence, respectively. This study provides proof of principle for the development of novel fluorescent molecular probes.

Src signalling and transduction are directly involved in cell growth, cell cycle, malignant transformation and cell migration, providing therapeutic opportunities through inhibition of Src. Here we report virtual screening for novel compounds that inhibit the Src-SH3 protein–protein interaction with a proline-rich peptide ligand. Computational docking of the ZINC compound database was performed using GOLD. Top-scoring compounds were assayed using a fluorescence polarization-based assay. A benzoquinoline derivative showed micromolar inhibition of binding between Src-SH3 and the proline-rich peptide. Several analogues were subsequently assayed showing the requirement of a linker between the benzoquinoline and phenyl rings, and electron donating substituents on the phenyl ring.

A series of novel imidazolyluracil conjugates were rationally designed and synthesised to probe the active site constraints of the angiogenic enzyme, thymidine phosphorylase (TP, E.C. 2.4.2.4). The lead compound in the series, 15d, showed good binding in the active site of human TP with an inhibition in the low μM range. The absence of a methylene bridge between the uracil and the imidazolyl sub-units (series 16) decreased potency (up to 3-fold). Modelling suggested that active site residues Arg202, Ser217 and His116 are important for inhibitor binding.

Thymidine phosphorylase (EC 2.4.2.4) catalyses the reversible phosphorolysis of pyrimidine 2'-deoxynucleosides, forming 2-deoxyribose-1-phosphate and pyrimidine. 5-Chloro-6-(2-imino-pyrrolidin-1-yl)methyl-uracil hydrochloride (TPI, 1) and its 5-bromo analogue (2), 6-(2-amino-imidazol-1-yl)methyl-5-bromo-uracil (3) and its 5-chloro analogue (4) act as tight-binding stoichiometric inhibitors of recombinant E. coli thymidine phosphorylase, and thus can be used as the first active-site titrants for it using either thymidine or 5-nitro-2'-deoxyuridine as substrate.

Thymidine phosphorylase (TP) is an important target enzyme for cancer chemotherapy because it is expressed at high levels in the hypoxic regions of many tumors and inhibitors of TP have been shown in animal model studies to inhibit angiogenesis and metastasis, and to promote tumor cell apoptosis. The 5-halo-6-[(2'-aminoimidazol-1'-yl)methyl]uracils (3, X = Cl, Br) are very potent inhibitors of E. coli and human TP with IC(50) values of approximately 20 nM when the enzyme concentration is approximately 40 nM. Their 4'-aminoimidazol-1'-yl analogues (4, X = Cl, Br) are >350-fold less active with IC(50) values of approximately 7 microM. The 5-unsubstituted analogues (3 and 4, X = H) were both less active than their 5-halo derivatives. Determination of pK(a) values and molecular modeling studies of these compounds in the active site of human TP was used to rationalize their activities. The finding that 3, X = Br has a poor pharmacokinetic (PK) profile in mice, coupled with the desire for tumor selectivity, led us to design prodrugs. The corresponding 2'-nitroimidazol-1'-ylmethyluracils (5, X = Cl, Br) are >1000-fold less active (IC(50) 22-24 microM) than their 2'-amino analogues and are reduced to the 2'-amino inhibitors (3, X = Cl, Br) by xanthine oxidase (XO). As XO is also highly expressed in many tumors, the 2'-nitro prodrugs have the potential to selectively deliver the potent 2'-aminoimidazol-1'-yl TP inhibitors into hypoxic solid tumors.

3-Arsonopyruvate was prepared in four steps from glycine. The arsenic-carbon bond was formed by a Meyer reaction between alkaline arsenite and 2-bromo-3-hydroxy-2-(hydroxymethyl)propionic acid; the 3-arsono-2-hydroxy-2-(hydroxymethyl) propionic acid formed was oxidized with periodate to give 3-arsonopyruvate. This proves to be an alternative substrate for phosphoenolpyruvate mutase, giving pyruvate, which was assayed using lactate dehydrogenase. The K(m) is 20 microM, similar to that observed for the natural substrate phosphonopyruvate (17 microM), whereas the kcat. of 0.01 s-1 was much lower than that for phosphonopyruvate (58 s-1). Arsonopyruvate competitively inhibited the action of the mutase on phosphonopyruvate.

myo-Inositol phosphates possessing the 1,2,3-trisphosphate motif share the remarkable ability to completely inhibit iron-catalysed hydroxyl radical formation. The simplest derivative, myo-inositol 1,2,3-trisphosphate [Ins(1,2,3)P(3)], has been proposed as an intracellular iron chelator involved in iron transport. The binding conformation of Ins(1,2,3)P(3) is considered to be important to complex Fe(3+) in a 'safe' manner. Here, a pyrene-based fluorescent probe, 4,6-bispyrenoyl-myo-inositol 1,2,3,5-tetrakisphosphate [4,6-bispyrenoyl Ins(1,2,3,5)P(4)], has been synthesised and used to monitor the conformation of the 1,2,3-trisphosphate motif using excimer fluorescence emission. Ring-flip of the cyclohexane chair to the penta-axial conformation occurs upon association with Fe(3+), evident from excimer fluorescence induced by pi-pi stacking of the pyrene reporter groups, accompanied by excimer formation by excitation at 351 nm. This effect is unique amongst biologically relevant metal cations, except for Ca(2+) cations exceeding a 1 : 1 molar ratio. In addition, the thermodynamic constants for the interaction of the fluorescent probe with Fe(3+) have been determined. The complexes formed between Fe(3+) and 4,6-bispyrenoyl Ins(1,2,3,5)P(4) display similar stability to those formed with Ins(1,2,3)P(3), indicating that the fluorescent probe acts as a good model for the 1,2,3-trisphosphate motif. This is further supported by the antioxidant properties of 4,6-bispyrenoyl Ins(1,2,3,5)P(4), which closely resemble those obtained for Ins(1,2,3)P(3). The data presented confirms that Fe(3+) binds tightly to the unstable penta-axial conformation of myo-inositol phosphates possessing the 1,2,3-trisphosphate motif.

The degree of alkylation of the side chain nitrogen in tryptamines is one important factor that affects psychoactivity. The method of Speeter and Anthony is considered to be one of the most important synthetic preparative methods. The final step in this reaction is based on the reduction of a (substituted) indole-3-yl-glyoxalylamide to the desired tryptamine with metal hydride. Twelve symmetrically and 13 asymmetrically N,N-disubstituted glyoxalylamides and their corresponding tryptamine derivatives have been synthesised and characterised by gas chromatography EI-ion trap mass spectrometry, electrospray-triple quadrupole-tandem mass spectrometry and NMR spectroscopy. Mass spectral and NMR similarities and differences between the investigated compounds are discussed. A solvent dependency is observed that has to be taken into consideration for the unambiguous assignment of (1)H- and (13)C-NMR chemical shifts. The (1)H-NMR study demonstrated that one can evaluate the rotamer populations of the asymmetrical glyoxalylamides. In a forensic or clinical scenario where single or multiple reaction monitoring approaches are contemplated, the appropriate ion transitions of choice may then focus on the two main fragmentations, namely beta-cleavage ([M+H](+)-->CH(2)N(+)R(2)R(3)) and/or alpha-cleavage ([M+H](+)-->[3-vinylindole](+)), respectively. The synthesis, NMR and MS analytical data presented provide the forensic analyst and clinical biochemist with a detailed and self-consistent body of information and mechanisms for the spectral identification of the more likely psychoactive tryptamines that may be met.

DL-1,2-Dideoxy-1,2-difluoro-myo-inositol was prepared from DL-3,4,5,6-tetra-O-benzyl-myo-inositol in five steps in an overall yield of 36%. The fluoro substituents were introduced with DAST in separate steps by displacement of hydroxy substituents with inversion of stereochemistry. Difluorination could not be achieved in one step because of competing formation of a 1,4-anhydro derivative. DL-1,2-Dideoxy-1,2-difluoro-scyllo-inositol was prepared in 42% overall yield using similar chemistry, with the required inversion of one stereocentre being accomplished by displacement of a tosyl group with caesium propionate. Both difluoroinositol analogues increased the levels of phytic acid (InsP6) in a skeletal muscle cell line. Each compound was tetraphosphorylated with dibenzyl N,N-diisopropylphosphoramidite in the presence of 1H-tetrazole, with subsequent oxidation of the phosphite with MCPBA. The P–OBn groups were removed by H2/Pd–C, and the sodium salts of the tetrakisphosphates of the difluoroinositol analogues were obtained by cation exchange.

The di(4-acetoxybenzyl) ester of methylphosphonate 4(X = H, R = Me) and the di(4-acyloxybenzyl) esters of methoxycarbonylmethylphosphonate 4(X = MeO2C, R = Me, Et, Pr, Pri, Bu or But) were prepared from the appropriate benzyl alcohol and phosphonic dichloride. At pD 8.0 and 37 °C, both series of compounds hydrolyse with half-lives greater than 24 h to the corresponding mono(4-acyloxybenzyl) esters 5(X = H or MeO2C, R = Me, Et, Pr, Pri Bu or But) which were prepared by treatment of the di(4-acyloxybenzyl) esters 4 with sodium or lithium iodide. The mono(4-acyloxybenzyl) esters 5(X = H, R = Me) and 5(X = MeO2C, R = Me, Et, Pr, Pri or But) undergo chemical hydrolysis to methylphosphonate 6(X = H), and methoxycarbonylmethylphosphonate 6(X = MeO2C) respectively, together with 4-hydroxybenzyl alcohol and the appropriate acylate anion. The rates of hydrolysis of the mono(4-acyloxybenzyl) esters decrease as the length and steric bulk of the acyl group increases, with half-lives ranging from ∼ 150 h for the acetyl analogues to 2240 h for the pivaloyl derivative. The hydrolyses of the di- and mono-(4-acyloxybenzyl) esters were catalysed by porcine liver carboxyesterase (PLCE), and in all cases the acylate anion was formed. The rate of enzymatic hydrolysis was most rapid for the 4-butanoyloxybenzyl and 4-isobutanoyloxybenzyl analogues. The methoxycarbonyl ester of the phosphonoacetate analogues was not cleaved by PLCE. The methylphosphonate generated from the reaction of 4(X = H, R = Me) in the presence of esterase and H218O, did not contain 18O attached directly to phosphorus. These results suggest that both the chemical and enzymatic hydrolyses of the mono(4-acyloxybenzyl) esters and the PLCE-catalysed hydrolyses of the di(4-acyloxybenzyl) esters proceed via hydrolysis of the acyl group to give the acylate anion and the unstable 4-hydroxybenzyl esters. The electron-donating 4-hydroxy group facilitates the cleavage of the benzyl-oxygen bond with the formation of the 4-hydroxybenzyl carbonium ion 9, which readily reacts either with water or the phosphate buffer. The 4-acyloxybenzyl phosphoesters provide the first example of a protecting group which will enable the bioactivation of phosphonate prodrugs at rates appropriate to biological systems.

The para-substituted analogues of dibenzyl methoxycarbonylphosphonate (1; X = N3, NO2, CF3) have been prepared in ca. 60% yield and their product and kinetic profiles of hydrolysis have been evaluated. Relative to the unsubstituted analogue 1(X = H) which has a half-life of 64 min, the para-substituted triesters of phosphonoformate undergo rapid hydrolysis at pH 7.4 and 36.4°C with half-lives of 2.5 min (X = N3), 5.6 min (X = NO2) and 15 min (X = CF3). In contrast to 1(X = H), which on hydrolysis gives ca. 30% C–P bond cleavage with dibenzyl phosphite formation, the para-substituted analogues hydrolyse predominantly to the para-substituted benzyl methoxycarbonyl-phosphonate diesters (2). Triester 1(X = NO2) hydrolyses to the diester 2(X = NO2) with P–O bond cleavage, consistent with nucleophilic attack of water at phosphorus and identical to that observed for the unsubstitued analogue. In contrast, triester 1(X = N3) hydrolyses to the diester 2(X = N3) with C–O bond cleavage presumably via an intermediate with benzyl carbonium ion character.

In contrast to high chemical stability (t1/2 55.4 h at 36.4 °C), with porcine liver Carboxyesterase the title compound 1 spontaneously decomposes first to the monoester 2 then to methylphosphonate, both reactions proceeding via the 4-hydroxybenzyl intermediates 3 and 4.

The diastereoisomers of the title phosphonamidic chloride (8) have been separated and their substitution reactions with ButNH2 and PriNH2(MeCN solvent) have been examined. The reactions are entirely dissociative in nature, any contribution from SN2(P) being insignificant. At very low concentrations of amine, reaction occurs mainly by simple elimination-addition with a free monomeric metaphosphonimidate intermediate (13). This mechanism is first-order in amine (base) and gives the phosphoric diamide product (14) with complete non-stereospecificity. As the concentration of amine is increased, preassociation elimination–addition becomes increasingly important. This mechanism is second-order in amine (base and nucleophile) and has variable stereochemistry. The degree of stereospecificity is very small at first, but it increases with the concentration of the amine. Even with neat amine, however, the preassociation elimination–addition mechanism is still substantially non-stereospecific. For both elimination–addition mechanisms, there is only weak discrimination between PriNH2 and ButNH2 under competitive conditions.

The stereochemical course of the phospho group transfer catalyzed by mutant (S102C) alkaline phosphatase from Escherichia coli was investigated by using 31P nuclear magnetic resonance spectroscopy. Transphosphorylation from 4-nitrophenyl (Rp)-[16O, 17O, 18O]phosphate to (S)-propane-1,2-diol occurs with overall retention of configuration at phosphorus. This result is consistent with the view that the hydrolysis of substrates by this mutant enzyme proceeds by way of a covalent phosphoenzyme intermediate in the same manner as the wild-type alkaline phosphatase.

The crystal structure of the antiviral agent PMEA 1 has been determined to R= 0.032 and reveals a zwitterion whose side chain emerges in-plane from the adenine ring; the conformation is compared with that of crystal structures of acyclic nucleoside analogues and AMP 2.

Ester prodrugs have the potential to eliminate the gastrotoxicity associated with the carboxylic acid group of indomethacin. 4,6-Bis- O -2′-[1′-(4″-chlorobenzoyl)-5′-methoxy-2′-methyl-1′ H -indol-3′-acetyl]- myo -inositol-1,3,5-orthoacetate ( 2 ) was synthesised and evaluated as a COX-2 inhibitor. It adopts a conformationally restricted chair with two indomethacin groups in the sterically hindered 1,3-diaxial positions. Acid-induced cleavage of the orthoacetate lock of the prodrug leads to a ring flip of the myo -inositol ring with the two indomethacin groups now in 1,3-diequatorial positions. This increases the susceptibility of hydrolysis of the ester groups to release indomethacin under acidic conditions. The long half-life (152 min) of decomposition of ( 2 ) at ∼pH 1–2 suggests that it may bypass the stomach with minimal hydrolysis upon oral administration. Indomethacin ester ( 2 ) was completely stable at pH 4.0–8.5 over 24 h at 37 °C and showed comparable activity to indomethacin in a COX-2 assay (pH 8.0).

To investigate the design of prodrugs of antiviral nucleosides for targeting to the central nervous system, the bis(4-acyloxybenzyl) esters of the 5′-monophosphate of AZT 5(R = Me, Et, Pri or But) have been prepared. The reaction of the appropriate bis(4-acyloxybenzyl)N,N-diisopropylphosphoramidite 10(R = Me, Et, Pri or But) with AZT in the presence of 1H-tetrazole, followed by oxidation of the PIII intermediate with 3-chlcroperoxybenzoic acid gave the required triesters 5 in good yield. The lithium salts of the mono (4-acyloxybenzyl) esters of the 5′-phosphate of AZT 7(R = Me, Et, Pri or But) were prepared by treatment of the triesters 5 with lithium iodide. In the presence of porcine liver carboxyesterase the triesters 5 and diesters 7 decomposed readily to the 5′-monophosphate of AZT 9. The anti-HIV activities of the triesters 5 and diesters 7 were, with one exception, comparable to that of AZT, but the greater cytotoxicity of certain compounds in particular types of cell significantly reduced their selectivity indices.

The two types of phosphonamidic chloride ArP(O)(Cl)NMe2(5) and ArP(O)(Cl)NHBut(7) have been prepared with Ar = Ph, o-MeC6H4, 2,4,6-Me3C6H2, and 2,4,6-Pri3C6H2. Both types give the expected phosphonic diamide substitution products with PriNH2 and ButNH2 in MeCN, but the two types display contrasting reactivity. With ButNH2 the NMe2 substrates (5) become progressively less reactive as the degree of steric crowding increases, and although the decrease is quite small (70-fold overall) it seems consistent with an associative [SN2(P)] mechanism. These substrates react 100 times faster with PriNH2, than with ButNH2 and in PriNH2–ButNH2 competitive experiments they give almost exclusively (99%) the product derived from the less hindered PriNH2. For the NHBut substrates (7) with ButNH2, there is little difference in reactivity between the Ph and o-MeC6H4 compounds, and between the 2,4,6-Me3C6H2 and 2,4,6-Pri3C6H2 compounds, but remarkably the more crowded pair of substrates is the more reactive, by a factor of ca. 100. Also, in competitive experiments these substrates display relatively little preference for reaction with PriNH2. Here a dissociative eliminationaddition mechanism, with a metaphosphonimidate intermediate, is seen to be important. A possible explanation of the steric acceleration is advanced. The ability of (7; Ar = Ph) to undergo substitution by elimination–addition makes possible the phosphonylation of unreactive nucleophiles such as ButOH and Pri2NH under mild conditions.

The substitution reactions of N-t-butyl-P-phenylphosphonamidic chloride (4a) with isopropylamine and t-butylamine (or t-pentylamine in stereochemical experiments) in MeCN at O °C can apparently proceed by one associative and two dissociative mechanisms viz: SN2(P)[first-order in amine (nucleophile), high selectivity for PriNH2 in PriNH2–ButNH2 competitive experiments; complete stereospecificity]; simple elimination–addition with a free (symmetrically solvated) metaphosphonimidate intermediate [first-order in amine (base); low selectivity; practically complete racemisation]; preassociation elimination–addition [second-order in amine (nucleophile and base); low selectivity; extensive but not complete racemisation].