Inorganic pyrophosphate generation and disposition in pathophysiology

Inorganic pyrophosphate (PP(i)) regulates certain intracellular functions and extracellular crystal deposition. PP(i) is produced, degraded, and transported by specialized mechanisms. Moreover, dysregulated cellular PP(i) production, degradation, and transport all have been associated with disease, and PP(i) appears to directly mediate specific disease manifestations. In addition, natural and synthetic analogs of PP(i) are in use or currently under evaluation as prophylactic agents or therapies for disease. This review summarizes recent developments in the understanding of how PP(i) is made and disposed of by cells and assesses the body of evidence for potentially significant physiological functions of intracellular PP(i) in higher organisms. Major topics addressed are recent lines of molecular evidence that directly link decreased and increased extracellular PP(i) levels with diseases in which connective tissue matrix calcification is disordered. To illustrate in depth the effects of disordered PP(i) metabolism, this review weighs the roles in matrix calcification of the transmembrane protein ANK, which regulates intracellular to extracellular movement of PP(i), and the PP(i)-generating phosphodiesterase nucleotide pyrophosphatase family isoenzyme plasma cell membrane glycoprotein-1 (PC-1).

RNA-catalyzed amino acid activation

We have selected RNAs that perform a new reaction that chemically activates amino acids, paralleling mixed phosphate anhydride synthesis by protein aminoacyl-transfer RNA synthetases. Care with recovery of the unstable reaction product was apparently essential to this selection. The best characterized RNA, KK13, requires only Ca2+ for reaction and is optimally active at low pH with KM = 50 mM and kcat = 1.1 min(-1) for activation of leucine. In conjunction with previous RNA-catalyzed aminoacyl-RNA synthesis, peptide bond formation, and RNA-based coding, these amino acid-activating RNAs complete an experimental demonstration that the four fundamental reactions of protein biosynthesis can be RNA-mediated. The appearance of translation in an RNA world is therefore supported.

Influence of different dentinal substrates on the tensile bond strength of three adhesive systems

PURPOSE

To evaluate the influence of the method and duration of storage for different types of teeth prior to their use in dentin bonding tests with three adhesive systems.

MATERIALS AND METHODS

Recently extracted sound human molars, bovine incisors, and human caries-free molars obtained from exhumed bones 5 years postmortem were used. The latter group of teeth was kept dry for 6 months, and then rehydrated in distilled water over a period of 30 days. The adhesive systems used were Prime&Bond 2.1. Single Bond, and Etch&Prime 3.0. Human teeth were embedded longitudinally in PVC cylinders; bovine incisors were embedded leaving the buccal surface exposed. Flat dentin surfaces were cut with a diamond disk and ground with up to 600-grit SiC paper. Adhesives were applied following manufacturers' instructions. A silicone mold with a cone-shaped perforation (4.5 mm high and 2 mm diameter at the smallest) was fixed on the dentin surface and filled with TPH composite resin. The specimens were stored in distilled water for two weeks before testing.

RESULTS

ANOVA did not detect statistical differences either in the main factors (substrate and adhesive system) or in their interaction (p > 0.05). Tensile bond strength averages ranged from 11.6 to 14.2 MPa. The dentinal substrates showed similar performances, regardless of the adhesives tested.

CONCLUSION

The differences among the three dentin substrates do not appear to be critical for the tensile bond strength test for the three adhesive systems. The adhesive systems presented similar bond strengths.

Effect of composite resin placement techniques on the microleakage of two self-etching dentin-bonding agents

PURPOSE

To evaluate microleakage of Class V resin-based composites (RBC) bonded with two self-etching dentin adhesive systems. Class V cavities were restored with either one or three increments of RBC to determine whether the restorative method affected microleakage.

MATERIALS AND METHODS

60 extracted human premolars and molars were randomly assigned to 6 groups for bonding with Clearfil Liner Bond 2V or Etch & Prime 3.0 or Prime & Bond NT. The latter, using a total-etch technique, was used as a control. Cavities were cut in both the buccal and lingual surfaces. Half of each preparation was in enamel and half was in cementum/dentin. The teeth were thermocycled and the restorations examined microscopically for leakage using Procion Brilliant Red as a marker. SEM microphotographs were prepared from dye-labeled and non dye-labeled areas to illustrate the micromorphology of the systems.

RESULTS

None of the groups showed microleakage at the enamel margins. All groups showed microleakage at the gingival margins. At the gingival margin, there was no significant difference between the groups irrespective of the bonding material (Kruskal-Wallis: ANOVA P=0.2113). No significant difference was observed with each material when the bulk filling (one increment) technique was compared with the three-increment technique. SEM showed that the self-etching materials produced a shallower depth of etch, and a less abundant resin tag complex than the material using a separate phosphoric acid gel. In dye-labeled areas, debonding was predominantly cohesive in resin.

CLINICAL SIGNIFICANCE

Gingival margin microleakage is not prevented by either restoring cavities with self-etching materials of the control using a total-etch technique.

Clinical evaluation of packable composite resins in Class-II restorations

This study investigated the clinical performance of two packable composite resins in Class-II restorations. One hundred and four Class-II restorations were placed in 52 patients by five dentists (four in dental practices and one in a university clinic) in a controlled prospective multicentre clinical trial. Each patient received one Definite/Etch & Prime 3.0 (D-EP) and one Solitaire/Solid Bond (S-SB) restoration, which were examined clinically according to modified USPHS-criteria after 1 week (baseline) and after 1 year. Statistical analysis was performed using the Wilcoxon rank sum test and the error rates method. The significance level was set to 0.05. At baseline both materials performed equally according to the evaluated criteria. After 1 year D-EP showed significantly worse marginal adaptation compared to S-SB. Both materials displayed significant deterioration for the criteria marginal adaptation, marginal discolouration, approximal contact, and fracture of restoration after 1 year compared to baseline. With a failure rate of 9.6% after 1 year, D-EP did not fulfill ADA acceptance criteria for restorative materials. It is proposed that at least 1-year data of clinical testing should be available before a new material is broadly marketed.

Toward a quantum-mechanical description of metal-assisted phosphoryl transfer in pyrophosphatase

The wealth of kinetic and structural information makes inorganic pyrophosphatases (PPases) a good model system to study the details of enzymatic phosphoryl transfer. The enzyme accelerates metal-complexed phosphoryl transfer 10(10)-fold: but how? Our structures of the yeast PPase product complex at 1.15 A and fluoride-inhibited complex at 1.9 A visualize the active site in three different states: substrate-bound, immediate product bound, and relaxed product bound. These span the steps around chemical catalysis and provide strong evidence that a water molecule (O(nu)) directly attacks PPi with a pK(a) vastly lowered by coordination to two metal ions and D117. They also suggest that a low-barrier hydrogen bond (LBHB) forms between D117 and O(nu), in part because of steric crowding by W100 and N116. Direct visualization of the double bonds on the phosphates appears possible. The flexible side chains at the top of the active site absorb the motion involved in the reaction, which may help accelerate catalysis. Relaxation of the product allows a new nucleophile to be generated and creates symmetry in the elementary catalytic steps on the enzyme. We are thus moving closer to understanding phosphoryl transfer in PPases at the quantum mechanical level. Ultra-high resolution structures can thus tease out overlapping complexes and so are as relevant to discussion of enzyme mechanism as structures produced by time-resolved crystallography.

Speciation and removal of zinc from composted municipal solid wastes

This paper presents composting of the organic fraction of municipal solid waste containing 50,000 mg/kg of cellucotton and 7980 mg/kg of zinc carried out under laboratory conditions. In the initial material as well as the compost obtained, zinc, cadmium, copper, nickel, and lead were analyzed, and their forms were determined by means of sequential extraction. It was found that 65% of zinc occurs in the organically bound form. Removal of zinc from the waste through leaching and subsequent electrochemical separation from the leaching solution was also examined. A double extraction of the waste with sodium diphosphate(V) enables a reduction of zinc content to 1240 mg/kg. As a result of electrolysis of the leaching solution, 90.2% of Zn is separated on the cathode. This paper suggests a method for processing municipal solid waste with high zinc content based on extraction of the waste with sodium diphosphate(V) and composting. The leaching solution is recovered electrochemically.

Inhibition of adenylyl and guanylyl cyclase isoforms by the antiviral drug foscarnet

The pyrophosphate (PP(i)) analog foscarnet inhibits viral DNA-polymerases and is used to treat cytomegalovirus and human immunodeficiency vius infections. Nucleotide cyclases and DNA-polymerases catalyze analogous reactions, i.e. a phosphodiester bond formation, and have similar topologies in their active sites. Inhibition by foscarnet of adenylyl cyclase isoforms was therefore tested with (i) purified catalytic domains C1 and C2 of types I and VII (IC1 and VIIC1) and of type II (IIC2) and (ii) membrane-bound holoenzymes (from mammalian tissues and types I, II, and V heterologously expressed in Sf9 cell membranes). Foscarnet was more potent than PP(i) in suppressing forskolin-stimulated catalysis by both, IC1/IIC2 and VIIC1/IIC2. Stimulation of VIIC1/IIC2 by Galpha(s) relieved the inhibition by foscarnet but not that by PP(i). The IC(50) of foscarnet on membrane-bound adenylyl cyclases also depended on their mode of regulation. These findings predict that receptor-dependent cAMP formation is sensitive to inhibition by foscarnet in some, but not all, cells. This was verified with two cell lines; foscarnet blocked cAMP accumulation after A(2A)-adenosine receptor stimulation in PC12 but not in HEK-A(2A) cells. Foscarnet also inhibited soluble and, to a lesser extent, particulate guanylyl cylase. Thus, foscarnet interferes with the generation of cyclic nucleotides, an effect which may give rise to clinical side effects. The extent of inhibition varies with the enzyme isoform and with the regulatory input.

Microleakage of hydrophilic adhesive systems in Class V composite restorations

PURPOSE

To investigate the microleakage of four hydrophilic adhesive systems: one "multiple-bottles" (Scotchbond Multi-Purpose Plus); two "one-bottle" (Single Bond, Stae); and one self-etching (Etch & Prime 3.0).

MATERIALS AND METHODS

120 bovine incisor teeth were divided into four groups (n = 30) and Class V cavities were prepared at the cemento-enamel junction. The cavities were restored with the adhesive systems and with Z100 composite. The teeth were thermocycled 1,000 times between 5+/-2 degrees C and 55+/-2 degrees C with a dwell time of 1 min, and then placed in a 2% methylene blue dye (pH 7.0) for 4 hrs, washed and sectioned vertically through the center of the restorations. The qualitative evaluation was made by three examiners who distributed pre-established scores (0-4) for each tooth using a stereomicroscope at x30 magnification.

RESULTS

In enamel margins little microleakage was observed and the Kruskal-Wallis analysis did not show differences. In dentin margins the Kruskal-Wallis and multiple comparison analyses were applied: microleakage was significantly greater with Stae (median 3) and Scotchbond MP Plus (median 4). Single Bond (median 1) and Etch & Prime 3.0 (median 2) showed the best results in dentin margins, and the statistical analysis did not demonstrate differences in microleakage among these groups.

Pyrosequencing sheds light on DNA sequencing

DNA sequencing is one of the most important platforms for the study of biological systems today. Sequence determination is most commonly performed using dideoxy chain termination technology. Recently, pyrosequencing has emerged as a new sequencing methodology. This technique is a widely applicable, alternative technology for the detailed characterization of nucleic acids. Pyrosequencing has the potential advantages of accuracy, flexibility, parallel processing, and can be easily automated. Furthermore, the technique dispenses with the need for labeled primers, labeled nucleotides, and gel-electrophoresis. This article considers key features regarding different aspects of pyrosequencing technology, including the general principles, enzyme properties, sequencing modes, instrumentation, and potential applications.

Agronomic use of biotechnologically processed grape wastes

Grape waste was composted by biodegradation and subsequently used as an organic fertilizer for 20 day-corn. Combinations of recently compressed grape waste and hen droppings (10% w/w) were prepared to study the activating effect of hen droppings and the effect of aeration on the composting process. The final hydrogen potential (pH), %C, %N and C/N ratio, indicated an adequate development of the bioprocess. Satisfactory results were observed when the products were applied at several doses (1,000-4,000 kg/ ha) as a soil conditioner for corn seed germination in greenhouses. Only the addition of hen droppings had a significant effect (P < 0.05) on corn dry matter (14% increase). A dose of 3000 kg/ha was considered as optimal and was used supplemented with triple superphosphate (TSP) in agronomic trials. All the treatments produced greater corn dry matter (P < 0.05) than the chemical industrial fertilizer used as a control (0.52-0.71 g/pot for the organic fertilizers vs 0.45 g/pot for the control). Anaerobic conditions and hen droppings addition significantly produced (P < 0.05) higher corn dry matter.

2-(Acyloxy)ethylphosphonate analogues of prenyl pyrophosphates: synthesis and biological characterization

2-(Acyloxy)ethylphosphonate analogues of geranyl, farnesyl, and geranylgeranyl pyrophosphate have been prepared. Horner-Wadsworth-Emmons condensation of different terpene aldehydes with an unsymmetrical bisphosphonate was the key step in syntheses of the phosphonates bearing alpha,beta-unsaturated acyloxy groups. After preparation of the respective phosphonic acids through reaction with TMSBr, both acids and esters were tested for their effects on DNA synthesis in human-derived myeloid and lymphoid leukemia cell lines. The phosphonate esters varied substantially in their ability to impair proliferation of the different cell lines, but testing against one possible target, farnesyl protein transferase (FPTase), revealed little impact at concentrations ranging up to 10 microM. Because the corresponding 2,3-dihydro compounds showed similar biological activity, conjugate addition would not appear to be involved in the toxicity.

Anticalculus effects of a novel, dual-phase polypyrophosphate dentifrice: chemical basis, mechanism, and clinical response

A primary patient motivation for oral hygiene is effective cleaning. Dentifrice serves this function by including ingredients such as abrasives, surfactants, and specialized cleaning ingredients such as anticalculus agents. This introductory article aims to introduce professionals, educators, and researchers on the rationale behind the development of an improved cleaning dentifrice formulation, Crest Multicare Advanced Cleaning. This new dentifrice is based upon the application of an improved tartar control/cleaning ingredient that is a polymeric adjunct of a pyrophosphate anion commonly applied in tartar control and stain control whitening dentifrices. The polypyrophosphate anion, also referred to as sodium hexametaphosphate, produces superior activity and substantivity on oral surfaces as compared to both pyrophosphate and some other commonly used dental cleaning ingredients and cleaning/conditioning adjuncts. The increased activity and substantivity translate into significant improvements in the prevention of dental stains and supragingival calculus and in the non-abrasive removal of dental stains. This article describes the structure of polypyrophosphate as compared to the parent pyrophosphate molecule, the rationale for its improved chemistry, and, in particular, its tartar control chemistry. In addition, the fundamental mechanisms of calculus formation and inhibition are reviewed. Lastly, a preliminary clinical study evaluating the improved efficacy of a polypyrophosphate dentifrice is described where the tartar control activity of the polypyrophosphate dentifrice is shown to be superior to that of a clinically established and marketed industry standard pyrophosphate dentifrice.

Catalytically important ionizations along the reaction pathway of yeast pyrophosphatase

Five catalytic functions of yeast inorganic pyrophosphatase were measured over wide pH ranges: steady-state PP(i) hydrolysis (pH 4. 8-10) and synthesis (6.3-9.3), phosphate-water oxygen exchange (pH 4. 8-9.3), equilibrium formation of enzyme-bound PP(i) (pH 4.8-9.3), and Mg(2+) binding (pH 5.5-9.3). These data confirmed that enzyme-PP(i) intermediate undergoes isomerization in the reaction cycle and allowed estimation of the microscopic rate constant for chemical bond breakage and the macroscopic rate constant for PP(i) release. The isomerization was found to decrease the pK(a) of the essential group in the enzyme-PP(i) intermediate, presumably nucleophilic water, from >7 to 5.85. Protonation of the isomerized enzyme-PP(i) intermediate decelerates PP(i) hydrolysis but accelerates PP(i) release by affecting the back isomerization. The binding of two Mg(2+) ions to free enzyme requires about five basic groups with a mean pK(a) of 6.3. An acidic group with a pK(a) approximately 9 is modulatory in PP(i) hydrolysis and metal ion binding, suggesting that this group maintains overall enzyme structure rather than being directly involved in catalysis.

A four-step enzymatic cascade for the one-pot synthesis of non-natural carbohydrates from glycerol

A total of four enzymatic steps were combined, in a one-pot reaction, to synthesize carbohydrates starting from glycerol. First, phosphorylation of glycerol by reaction with pyrophosphate in the presence of phytase at pH 4.0 in 95% glycerol afforded racemic glycerol-3-phosphate in 100% yield. The L-enantiomer of the latter underwent selective aerobic oxidation to dihydroxyacetone phosphate (DHAP) at pH 7.5 in the presence of glycerolphosphate oxidase (GPO) and catalase. Subsequently, fructose-1,6-bisphosphate aldolase catalyzed the aldol reaction of DHAP with butanal. Finally, dephosphorylation of the aldol adduct was mediated by phytase at pH 4 affording 5-deoxy-5-ethyl-D-xylulose in 57% yield from L-glycerol-3-phosphate. The phytase on/off-switch by pH was the key to controlling phosphorylation and dephosphorylation.

Fluoride effects along the reaction pathway of pyrophosphatase: evidence for a second enzyme.pyrophosphate intermediate

The fluoride ion is a potent and specific inhibitor of cytoplasmic pyrophosphatase (PPase). Fluoride action on yeast PPase during PP(i) hydrolysis involves rapid and slow phases, the latter being only slowly reversible [Smirnova, I. N., and Baykov, A. A. (1983) Biokhimiya 48, 1643-1653]. A similar behavior is observed during yeast PPase catalyzed PP(i) synthesis. The amount of enzyme.PP(i) complex formed from solution P(i) exhibits a rapid drop upon addition of fluoride, followed, at pH 7.2, by a slow increase to nearly 100% of the total enzyme. The slow reaction results in enzyme inactivation, which is not immediately reversed by dilution. These data show that fluoride binds to an enzyme.PP(i) intermediate during the slow phase and to an enzyme.P(i) intermediate during the rapid phase of the inhibition. In Escherichia coli PPase, the enzyme.PP(i) intermediate binds F(-) rapidly, explaining the lack of time dependence in the inhibition of this enzyme. The enzyme.PP(i) intermediate formed during PP(i) hydrolysis binds fluoride much faster (yeast PPase) or tighter (E. coli PPase) than the similar complex existing at equilibrium with P(i). It is concluded that PPase catalysis involves two enzyme.PP(i) intermediates, of which only one (immediately following PP(i) addition and predominating at acidic pH) can bind fluoride. Simulation experiments have indicated that interconversion of the enzyme.PP(i) intermediates is a partially rate-limiting step in the direction of hydrolysis and an exclusively rate-limiting step in the direction of synthesis.

Pyrophosphoryl derivatives of 1-(2-deoxy-3-O-phosphono-methyl-beta- and -alpha-D-erythro-pentofuranosyl)thymine: synthesis and substrate properties towards some DNA polymerases

The synthesis of 1-(2-deoxy-3-O-phosphonomethyl-beta-D-erythropentofuranosyl)thymine (17) and its alpha-anomer 18 is described. Attempts to prepare 1-[2-deoxy-3-O-(pyrophosphoryl)phosphonomethyl-beta-D-erythro-pentofuranosyl]thymine (19) by an activation of the respective phosphonate 17 with 1,1'-carbonyldiimidazole (Im2CO) resulted in the quantitative formation of the corresponding pyrophosphonate derivative 21 (Scheme 2). Activation of inorganic pyrophosphate with Im2CO followed by the condensation with the phosphonates 17 and 18 afforded the desired analogues of nucleoside triphosphate 19 (35%) and its alpha-anomer 20 (27%) along with the respective pyrophosphonate derivatives 21 (37%) and 24 (38%) (Scheme 3). It was found that compounds 19 and 20 display (i) no substrate properties toward calf thymus terminal deoxynucleotidyl transferase (TDT) and AMV reverse transcriptase, and (ii) moderate substrate activity with E. coli DNA polymerase I (Klenow fragment).

A pyrophosphate bridge links the pyruvate-containing secondary cell wall polymer of Paenibacillus alvei CCM 2051 to muramic acid

The peptidoglycan, the secondary cell wall polymer (SCWP), and the surface layer (S-layer) glycoprotein are the major glycosylated cell wall components of Paenibacillus alvei CCM 2051. In this report, the complete structure of the SCWP, its linkage to the peptidoglycan layer, and its physicochemical properties have been investigated. From the combined evidence of chemical and structural analyses together with one- and two-dimensional nuclear magnetic resonance spectroscopy, the following structure of the SCWP-peptidoglycan complex is proposed: [(Pyr4,6)-beta-D-ManpNAc-(1-->4)-beta-D-GlcpNAc-(1-->3)]n-11-(Pyr4,6)-beta-D-ManpNAc-(1-->4)-alpha-D-GlcpNAc-(1-->O)-PO2-O-PO2-(O-->6)-MurNAc- Each disaccharide unit is substituted by 4,6-linked pyruvic acid residues. Under mild acidic conditions, up to 50% of them are lost, leaving non-substituted ManNAc residues. The anionic glycan chains constituting the SCWP are randomly linked via pyrophosphate groups to C-6 of muramic acid residues of the peptidoglycan layer. 31P NMR reveals two signals that, as a consequence of micelle formation, experience different line broadening. Therefore, their integral ratio deviates significantly from 1:1. By treatment with ethylenediaminetetraacetic acid, sodium dodecyl sulfate, and sonication immediately prior to NMR measurement, this ratio approaches unity. The reversibility of this behavior corroborates the presence of a pyrophosphate linker in this SCWP-peptidoglycan complex. In addition to the determination of the structure and linkage of the SCWP, a possible scenario for its biological function is discussed.

The role of histidine-114 of Ssulfolobus acidocaldarius geranylgeranyl diphosphate synthase in chain-length determination

Sulfolobus acidocaldarius geranylgeranyl diphosphate synthase yields (all-E)-C(20) prenyl diphosphate as a final product. The three-dimensional model of the enzyme suggested that removing two bulky residues at 77 and 114 would allow additional prenyl-chain elongation. To test this, we examined several mutants with substitutions at 77 and/or 114. As a result, the mutants, F77G, F77G and H114A, F77G and H114G, H114A, and H114G gave C(30), C(45), C(50), C(30) and C(40) as the main long product, respectively. These observations indicate that histidine-114 plays a crucial role in chain-length determination along with phenylalanine-77.

Ab initio structure determination and Rietveld refinement of a high-temperature phase of zirconium hydrogen phosphate and a new polymorph of zirconium pyrophosphate from in situ temperature-resolved powder diffraction data

The collected in situ temperature-resolved synchrotron powder data revealed that the transformation of the recently reported three-dimensional tau-Zr(HPO4)2 to cubic ZrP2O7 goes through two intermediate phases. The first intermediate phase, rho-Zr(HPO4)2, is formed in a reversible phase transition at 598 K, which involves both rearrangement and disordering of the hydrogen phosphate groups of tau-Zr(HPO4)2. At 688 K condensation of the hydrogen phosphate groups leads to the formation of the second intermediate, a new polymorph of zirconium pyrophosphate (beta-ZrP2O7). Heating above 973 K results in the gradual transformation of beta-ZrP2O7 to cubic zirconium pyrophosphate (alpha-ZrP2O7). The crystal structures of the two intermediate phases were solved from the in situ powder diffraction data using direct methods and refined using the Rietveld method. Both phases are orthorhombic, space group Pnnm and Z = 2. The lattice parameters for the two phases are: p-Zr(HPO4)2: a = 8.1935 (2), b = 7.7090 (2), c = 5.4080 (1) A; beta-ZrP2O7: a = 8.3127 (5), b = 6.6389 (4), c = 5.3407 (3) A. The formation mechanism for the new zirconium pyrophosphate polymorph, beta-ZrP2O7, is discussed in relation to structurally restricted soft chemistry.

Synthesis of geranyl S-thiolodiphosphate. A new alternative substrate/inhibitor for prenyltransferases

The tris(tetra-n-butylammonium) salt of thiopyrophosphate 5 was prepared from trimethyl phosphate in four steps. Treatment of geranyl bromide with 5 gave an 80% yield of geranyl S-thiolodiphosphate (6). Thiolodiphosphate 6 is substantially less reactive than geranyl diphosphate (7) in the prenyl transfer reaction catalyzed by farnesyl diphosphate synthase and is a good inhibitor of the enzyme.

Antineoplastic agents. 443. Synthesis of the cancer cell growth inhibitor hydroxyphenstatin and its sodium diphosphate prodrug

A structure-activity relationship (SAR) study of the South African willow tree (Combretum caffrum) antineoplastic constituent combretastatin A-4 (3b) led to the discovery of a potent cancer cell growth inhibitor designated phenstatin (5a). This benzophenone derivative of combretastatin A-4 showed remarkable antineoplastic activity, and the benzophenone derivative of combretastatin A-1 was therefore synthesized. The benzophenone, designated hydroxyphenstatin (6a), was synthesized by coupling of a protected bromobenzene and a benzaldehyde to give the benzhydrol with subsequent oxidation to the ketone. Hydroxyphenstatin was converted to the sodium phosphate prodrug (6e) by a dibenzyl phosphite phosphorylation and subsequent benzyl cleavage (6a --> 6d --> 6e). While hydroxyphenstatin (6a) was a potent inhibitor of tubulin polymerization with activity comparable to that of combretastatin A-1 (3a), the phosphorylated derivative (6e) was inactive.

[Raman spectrometry applied to calcified tissue and calcium-phosphorus biomaterials]

The rigid part of the human body consists essentially of carbonated apatite (calcium phosphate). Biologists don't have any tools to study this "mineral" phase, though its origin is organic. A new approach of some compounds like enamel or bone is obtained with the Raman micro-characterisation by a very fine analysis of chemical bonds in a micrometric scale. This method allows the characterisation, the analysis and the dosage of ions, like carbonate, acid phosphates, proteins and fatty acids. The identification of other organic or mineral compounds (e.g. calcium carbonate, calcium oxide, substitutant ions...) is also possible. The Raman microspectrometry can also be used to study the chemical and physical properties of biomaterials and their evolution after implantation in a dental or bone site. On synthetical calcium phosphate, beta-TCP, brushite and hydroxyapatite can be distinguished and the impurities found in plasma spray deposits can be measured. The detection of alpha-, beta-, or gamma-pyrophosphates could be obtained in some commercial beta-TCP. The Raman microspectrometry is the only non-destructive method which allows the identification of the chemical bonds in a micrometric scale and gives the "fingerprint" of the studied component.

Capping DNA with DNA

Twelve classes of deoxyribozymes that promote an ATP-dependent "self-capping" reaction were isolated by in vitro selection from a random-sequence pool of DNA. Each deoxyribozyme catalyzes the transfer of the AMP moiety of ATP to its 5'-terminal phosphate group, thereby forming a 5',5'-pyrophosphate linkage. An identical DNA adenylate structure is generated by the T4 DNA ligase during enzymatic DNA ligation. A 41-nucleotide class 1 deoxyribozyme requires Cu(2+) as a cofactor and adopts a structure that recognizes both the adenine and triphosphate moieties of ATP or dATP. The catalytic efficiency for this DNA, measured at 10(4) M(-1) x min(-1) using either ATP or dATP as substrate, is similar to other catalytic nucleic acids that use small substrates. Chemical probing and site-directed mutagenesis implicate the formation of guanine quartets as critical components of the active structure. The observation of ATP-dependent "self-charging" by DNA suggests that DNA could be made to perform the reactions typically associated with DNA cloning, but without the assistance of protein enzymes.