Structure-activity studies on phosphonoacetate

The Biological Impact of Some Phosphonic and Phosphinic Acid Derivatives on Human Osteosarcoma

Osteosarcoma malignancy currently represents a major health problem; therefore, the need for new therapy approaches is of great interest. In this regard, the current study aims to evaluate the anti-neoplastic potential of a newly developed phosphinic acid derivative (2-carboxyethylphenylphosphinic acid) and, subsequently, to outline its pharmaco-toxicological profile by employing two different in vitro human cell cultures (keratinocytes-HaCaT-and osteosarcoma SAOS-2 cells), employing different techniques (MTT assay, cell morphology assessment, LDH assay, Hoechst staining and RT-PCR). Additionally, the results obtained are compared with three commercially available phosphorus-containing compounds (P1, P2, P3). The results recorded for the newly developed compound (P4) revealed good biocompatibility (cell viability of 77%) when concentrations up to 5 mM were used on HaCaT cells for 24 h. Also, the HaCaT cultures showed no significant morphological alterations or gene modulation, thus achieving a biosafety profile even superior to some of the commercial products tested herein. Moreover, in terms of anti-osteosarcoma activity, 2-carboxyethylphenylphosphinic acid expressed promising activity on SAOS-2 monolayers, the cells showing viability of only 55%, as well as apoptosis features and important gene expression modulation, especially Bid downregulation. Therefore, the newly developed compound should be considered a promising candidate for further in vitro and in vivo research related to osteosarcoma therapy.

Pd-Catalysed Suzuki coupling of α-bromoethenylphosphonates with organotrifluoroborates: a general protocol for the synthesis of terminal α-substituted vinylphosphonates

No concern will arise in the preparation of terminal α-substituted vinylphosphonates employing our general and practical protocol.

Route to α-Aryl Phosphonoacetates: Useful Synthetic Precursors in the Horner-Wadsworth-Emmons Olefination

A versatile and general catalytic strategy has been developed for the α-arylation of phosphonoacetates utilizing parallel microscale experimentation. These α-substituted phosphonoacetates are widely useful, notably as substrates in the Horner–Wadsworth–Emmons-type olefinations. However, the current routes to these products involve harsh conditions, limiting the variety of functionality. The reported method can be used with a variety of aryl chlorides and aryl bromides, including several heterocyclic examples.

Phosphonate- and carboxylate-based chelating agents that solubilize (hydr)oxide-bound MnIII

Recent field studies suggest that dissolved MnIII should be ubiquitous at oxic/anoxic interfaces in all natural waters and may play important roles in biogeochemical redox processes. Here, we uncovered environmentally relevant synthetic phosphonate-based chelators that solubilize (hydr)oxide-bound MnIII via ligand-promoted dissolution at circum-neutral pHs and that their ability to release aqueous MnIII can be predicted based on the chemical structure. For two (hydr)oxides (manganite and birnessite) reacting with excess concentrations of pyrophosphoric acid (PP), methylenediphosphonic acid (MDP), and phosphonoacetic acid (PAA), ligand-promoted dissolution is predominant from pH 6--8, initial dissolution rates and plateau concentrations for dissolved MnIII decrease in the order PP > MDP > PAA, and at pH 5, MDP reacts equally well (with birnessite) or more efficiently (with manganite) than PP, and PAA remains the least reactive chelator. For manganite reacting with an excess concentration of aminophosphonate/carboxylate-based chelators, the aminophosphonate-containing iminodimethylenephosphonic acid and glyphosate yield appreciable amounts of dissolved MnIII, but the aminocarboxylate-based methyliminodiacetic acid yields solely dissolved MnII via MnIII reduction.

Use of phosphonocarboxylic acids as inhibitors of sodium-phosphate cotransport

Phosphonocarboxylic acids, initially developed as antiviral agents, are found to be specific inhibitors of phosphate (P(i)) transport across cell membranes. Foscarnet (PFA), the most potent and the most widely used compound, can induce phosphaturia both after parenteral and oral administration. Furthermore, it can inhibit intestinal phosphate absorption when administered orally. PFA absorption and bioavailability are increased in animals on phosphate-restricted diets. PFA also blunts the adaptive increase in intestinal and renal Na(+)-P(i) cotransport which accompanies dietary phosphorus restriction. Finally, PFA is shown to inhibit hydroxyapatite crystal formation and calcium-phosphate precipitation when tested in in vitro systems. These properties, and the low toxicity of PFA, point to potential new applications for PFA and some of its analogs in clinical conditions such as chronic renal insufficiency, where phosphate retention may lead to progression of renal failure and to other serious complications.

Synthesis and applications of phosphonoacetic derivatives

In this paper, the synthesis of new phosphonoacetic acid derivatives and their applications in fields of biotechnological interest are discussed. Phosphonoacetic acids are competitive inhibitors of alkaline phosphatase, an enzyme widely used in diagnostics, as colorimetric detection tool. The phosphonoacetic acid's inhibition activity has been exploited by us for the obtainment of an innovative technique for non-radioactive DNA probes detection, the last being based on DNA labeling with the enzyme inhibitor, followed by detection by means of the chromogenic enzyme and substrate. Moreover, we have found a further application of phosphonoacetic acids, by the preparation of an affinity chromatography support that has been revealed to be very effective in the purification of alkaline phosphatase. Finally, phosphonoacetic acid derivatives have been tested also for their antiviral activity. Some of them, examined in preliminary in vitro experiments, have been found very active against Herpes simplex virus.

Phosphonato complexes of platinum(II): kinetics of formation and phosphorus-31 NMR characterization studies

Reactions of cis-diamminedichloroplatinum(II) with phosphonoformic acid (PFA), phosphonoacetic acid (PAA), and methylenediphosphonic acid (MDP) yield various phosphonatoplatinum(II) chelates which were characterized by phosphorus-31 NMR spectroscopy. The P-31 resonances for the chelates appear at 6-12 ppm downfield as compared to the uncomplexed ligands. All complexes exhibit monoprotic acidic behavior in the pH range 2-10. The chemical shift-pH profiles yielded acidity constants, 1.0 x 10(-4), 1.5 x 10(-4), and 1.3 x 10(-6) M-1, for the PFA, PAA, and MDP chelates. In addition to the monomeric chelate, MDP formed a bridged diplatinum(II,II) complex when it reacted with cis-Pt (NH3)2(H2O)2(2)+. The P-31 resonance for this binuclear complex appears at 22 ppm downfield from the unreacted ligand. Rate data for the complexation reactions of the phosphonate ligands with the dichloroplatinum complex are consistent with a mechanism in which a monodentate complex is formed initially through rate-limiting aquation process of the platinum complex, followed by a rapid chelation. For the PFA and PAA complexes, initial binding sites are the carboxylato oxygens. Implications of the various binding modes of the phosphonates in relationship to their antiviral activities are discussed.

Irreversible inhibition of renal Na(+)-Pi cotransporter by alpha-bromophosphonoacetic acid

We investigated the suitability of alpha-bromophosphonoacetic acid (alpha-BrPAA) to act as a possible irreversible inhibitor of Na(+)-dependent transport of Pi across renal brush-border membrane (BBM). When added directly into the Pi uptake medium, alpha-BrPAA causes specific, competitive [apparent inhibition constant (Ki) = 0.33 mM; no change in maximum velocity (Vmax)], and reversible (by washing) inhibition of Na+ gradient [Na+o greater than Na+i]-dependent uptake of Pi by BBM vesicles (BBMV). Next, BBMV were preincubated with 5 mM alpha-BrPAA in alkaline (pH 9) medium for 30 min, then twice washed by 1:100 dilution and recentrifugation, and tested for transport and other properties. This preincubation of BBMV with alpha-BrPAA in alkaline medium resulted in a different type of inhibition [lower Vmax; no change in Michaelis constant (Km)] of the Na+ gradient-dependent uptake of 32Pi, whereas the uptakes of D-[3H]glucose and other solutes were not altered. This inhibition of Pi transport was not reversed by dilution and washing of BBMV. The BBMV Na(+)-dependent binding of [14C]phosphonoformic acid, but not of [3H]phlorizin, was decreased; activities of BBM marker enzymes were not changed. Results suggest that alpha-BrPAA binds onto the same locus on luminal surface of BBM on which Pi and Na+ bind and inhibits Na(+)-Pi cotransporter similar to phosphonoformic acid. Furthermore, after a 30-min incubation in alkaline medium, alpha-BrPAA apparently forms a more stable association with BBM in the vicinity of the Na(+)-Pi cotransporter. We thus suggest that alpha-BrPAA acts under these conditions as an apparently irreversible inhibitor of Na(+)-Pi cotransporter in BBM.(ABSTRACT TRUNCATED AT 250 WORDS)

Structural requirement of monophosphates for inhibition of Na+-Pi cotransport in renal brush border membrane

Using the chemical structural analogs of phosphonoacetic acid (PAA) and related phosphonate compounds, we investigated which structural features are required for competitive inhibition of Na+-Pi cotransport in rat renal cortical brush border membrane (BBM) vesicles (BBMV). The effects of compounds on [Nao+ greater than Nai+]-gradient-dependent 32Pi uptake by BBMV were examined using various inhibitor-to-32Pi concentration ratios in the transport assay medium. The replacement of a phosphono-group with an arsono-group in PAA, or the substitution of a carboxylic group in PAA by an amino or hydroxyl group, totally abolished the inhibitory action on Na+-Pi cotransport. Decreased electronegativity of carboxyl in PAA by coupling with hydrazine or hydroxylamine lowered the inhibitory potenty of PAA. Substitution of H at the alpha-carbon of PAA with ethyl or p-Cl-phenyl groups completely abolished the inhibitory activity, whereas alpha-halogenation with Br greatly increased the inhibitory potency of PAA, close to that of phosphonoformic acid (PFA). The inhibition by all the active tested monophosphates was strictly competitive. The tested compounds displaced [14C]PFA pre-bound onto BBMV in the presence of 100 mM NaCl. The ability of monophosphates to inhibit Na+-Pi cotransport across BBM and the binding of [14C]PFA were closely correlated (r = 0.925; P greater than 0.001). These results show that: (a) strong electronegativity at both ends of the PAA molecule is needed for inhibitory action, (b) an alpha-aliphatic or aromatic substituent at the alpha-carbon probably hinders the access of the inhibitor to the Pi-binding site of the Na+-Pi cotransporter in BBM, whereas (c) an alpha-electrophilic substituent--Br--enhances the inhibitory potency of PAA. The tested compounds inhibited Na+-Pi cotransport by binding, in the presence of Na+, on the same site on the luminal surface of BBM as did PFA and, by extension, Pi.

Antiviral effects of phosphonoformate (PFA, foscarnet sodium)

This article describes the antiviral properties of foscarnet (trisodium phosphonoformate) at the enzyme level as well as in cell cultures and in vivo. The mechanism of action against herpesvirus DNA polymerases and reverse transcriptases is outlined. Clinical studies using topical foscarnet against mucocutaneous herpes simplex virus infections are presented. The clinical use of intravenous foscarnet against severe viral infections caused by cytomegalovirus, hepatitis B virus and human immunodeficiency virus is discussed.

alpha-Cl-alpha-Br-phosphonoacetic acid is a potent and selective inhibitor of Na+/Pi cotransport across renal cortical brush border membrane

We found that alpha-Cl-alpha-Br-phosphonoacetate (ClBrPAA) is a competitive, solute-specific inhibitor of Na+/Pi cotransport across renal cortical brush border membrane. Inhibition by ClBrPAA (Ki = 62 microM) is more than three times more effective than inhibition by phosphonoformate (PFA), the most potent Na+/Pi cotransport inhibitor known to date, and 26 times more effective than the parent compound, phosphonoacetate (PAA). These observations indicate that substitution of bromine and chlorine atoms at the alpha-carbon of PAA greatly enhances its efficacy as a competitive inhibitor of Na+/Pi cotransport. As ClBrPAA is much less inhibitory than PAA and PFA towards viral DNA polymerases and did not inhibit human alpha-DNA polymerase (ref. 10), the results also demonstrate that Na+/Pi cotransport inhibition can be dissociated from inhibition of DNA polymerases by phosphonocarboxylate compounds.

Increased efficacy of phosphonoformate and phosphonoacetate inhibition of herpes simplex virus type 2 replication by encapsulation in liposomes

Phosphonoformate and phosphonoacetate encapsulated in liposomes have substantially greater activity against herpes simplex virus type 2 in Vero cell tissue culture than the nonencapsulated compounds at the same dose. Encapsulation of phosphonoformate in liposomes resulted in a 30-fold increase of the antiviral effect with no increase in cytotoxicity measured by inhibition of thymidine incorporation into normal Vero cells. Thus, the selectivity of the liposomal drug increased 27-fold compared with the nonencapsulated compound. Liposome encapsulation of phosphonoacetate at a ratio of 0.3 mumol/mumol of lipid resulted in a 150-fold increase of antiviral activity with a concomitant 250-fold increase in cytotoxicity. However, the selectivity of phosphonoacetate could be increased by reducing the drug-to-lipid ratio. Liposome uptake by Vero cells, measured by the cell association of a nonexchangeable radiolabeled lipid, plateaued after 24 h of incubation and saturated at 60 nmol of lipid per mg of cellular protein at a lipid concentration of 300 microM. The saturation of liposome uptake on the Vero cells may account for the 27-fold increase in selectivity observed with the liposomal phosphonoformate. The greater activity of the encapsulated phosphono compounds is most likely due to their increased transport into the cytoplasm; this occurs subsequent to the uptake and processing of the liposome in the lysosomes of the cell. Liposome encapsulation of these agents may result in superior efficacy against viral infections residing in endocytotically and phagocytically active cells such as macrophages.