Wet and Dry Processes for the Selective Transformation of Phosphonates to Phosphonic Acids Catalyzed by Brønsted Acids

Microwave-Accelerated McKenna Synthesis of Phosphonic Acids: An Investigation

Phosphonic acids represent one of the most important categories of organophosphorus compounds, with myriad examples found in chemical biology, medicine, materials, and other domains. Phosphonic acids are rapidly and conveniently prepared from their simple dialkyl esters by silyldealkylation with bromotrimethylsilane (BTMS), followed by desilylation upon contact with water or methanol. Introduced originally by McKenna, the BTMS route to phosphonic acids has long been a favored method due to its convenience, high yields, very mild conditions, and chemoselectivity. We systematically investigated microwave irradiation as a means to accelerate the BTMS silyldealkylations (MW-BTMS) of a series of dialkyl methylphosphonates with respect to solvent polarity (ACN, dioxane, neat BTMS, DMF, and sulfolane), alkyl group (Me, Et, and iPr), electron-withdrawing P-substitution, and phosphonate-carboxylate triester chemoselectivity. Control reactions were performed using conventional heating. We also applied MW-BTMS to the preparation of three acyclic nucleoside phosphonates (ANPs, an important class of antiviral and anticancer drugs), which were reported to undergo partial nucleoside degradation under MW hydrolysis with HCl at 130-140 °C (MW-HCl, a proposed alternative to BTMS). In all cases, MW-BTMS dramatically accelerated quantitative silyldealkylation compared to BTMS with conventional heating and was highly chemoselective, confirming it to be an important enhancement of the conventional BTMS method with significant advantages over the MW-HCl method.

Targeted Metabolomics of Organophosphate Pesticides and Chemical Warfare Nerve Agent Simulants Using High- and Low-Dose Exposure in Human Liver Microsomes

Our current understanding of organophosphorus agent (pesticides and chemical warfare nerve agents) metabolism in humans is limited to the general transformation by cytochrome P450 enzymes and, to some extent, by esterases and paraoxonases. The role of compound concentrations on the rate of clearance is not well established and is further explored in the current study. We discuss the metabolism of 56 diverse organophosphorus compounds (both pesticides and chemical warfare nerve agent simulants), many of which were explored at two variable dose regimens (high and low), determining their clearance rates (Clint) in human liver microsomes. For compounds that were soluble at high concentrations, 1D-NMR, 31P, and MRM LC-MS/MS were used to calculate the Clint and the identity of certain metabolites. The determined Clint rates ranged from 0.001 to 2245.52 µL/min/mg of protein in the lower dose regimen and from 0.002 to 98.57 µL/min/mg of protein in the high dose regimen. Though direct equivalency between the two regimens was absent, we observed (1) both mono- and bi-phasic metabolism of the OPs and simulants in the microsomes. Compounds such as aspon and formothion exhibited biphasic decay at both high and low doses, suggesting either the involvement of multiple enzymes with different KM or substrate/metabolite effects on the metabolism. (2) A second observation was that while some compounds, such as dibrom and merphos, demonstrated a biphasic decay curve at the lower concentrations, they exhibited only monophasic metabolism at the higher concentration, likely indicative of saturation of some metabolic enzymes. (3) Isomeric differences in metabolism (between Z- and E- isomers) were also observed. (4) Lastly, structural comparisons using examples of the oxon group over the original phosphorothioate OP are also discussed, along with the identification of some metabolites. This study provides initial data for the development of in silico metabolism models for OPs with broad applications.

Design, Synthesis and Actual Applications of the Polymers Containing Acidic P-OH Fragments: Part 2-Sidechain Phosphorus-Containing Polyacids

Macromolecules containing acidic fragments in side-groups—polyacids—occupy a special place among synthetic polymers. Properties and applications of polyacids are directly related to the chemical structure of macromolecules: the nature of the acidic groups, polymer backbone, and spacers between the main chain and acidic groups. The chemical nature of the phosphorus results in the diversity of acidic >P(O)OH fragments in sidechain phosphorus-containing polyacids (PCPAs) that can be derivatives of phosphoric or phosphinic acids. Sidechain PCPAs have many similarities with other polyacids. However, due to the relatively high acidity of −P(O)(OH)2 fragment, bone and mineral affinity, and biocompatibility, sidechain PCPAs have immense potential for diverse applications. Synthetic approaches to sidechain PCPAs also have their own specifics. All these issues are discussed in the present review.

Substituted Poly(Vinylphosphonate) Coatings of Magnetite Nanoparticles and Clusters

Magnetite nanoparticles and clusters of nanoparticles have been of Increasing scientific interest in the past decades. In order to prepare nanoparticles and clusters that are stable in suspension, different coatings have been used. Phosphates and phosphonates are a preferred anchoring group for the coating of magnetite nanomaterials. However, poly(vinylphosphonates) have rarely been used as a coating agent for any nanoparticles. Here, poly(methylvinylphosphonate) and other substituted polyvinylphosphonates are described as new coatings for magnetite nanoparticles and clusters. They show great stability in aqueous suspension. This is also the first time phosphonate-coated magnetite clusters have been synthesized in a one-pot polyol reaction. The coated magnetite nanoparticles and clusters have been characterized by TEM, EDX, FTIR, magnetization measurement, XRD as well as XPS. It has been shown that substituted vinylphosphonates can be easily synthesized in one-step procedures and as a polymeric coating can imbue important properties such as stability in suspension, tight binding to the particle surface, the ability to be further functionalized or to tightly adsorb metal ions. For the synthesis of magnetite clusters the cluster formation, polymerization and coating are done in a one-pot reaction and the resulting magnetite clusters show a higher amount of phosphonate coating than with a three-step procedure including a ligand exchange.

P-Chloride-Free Synthesis of Phosphoric Esters: Microwave-Assisted Esterification of Alkyl- and Dialkyl Phosphoric Ester-Acids Obtained from Phosphorus Pentoxide

It is a reasonable endeavour to replace P-chloride starting materials (e.g., POCl3) with greener and cheaper reagents. Our purpose was to start from phosphorus pentoxide, i.e. to utilize its reaction with alcohols in the preparation of (HO)2P(O)(OR) and HOP(O)(OR)2, and to convert the mixtures of the corresponding monoester and diester, so obtained, into the target trialkyl esters. Separate experiments showed that the monobutylphosphate undergo microwave (MW)-assisted esterification with butanol in the presence of [bmim][BF4] catalyst at 200 °C to afford dibutylphosphate in a selective manner (ca. 95%) that, in turn, may be converted into tributylphosphate by alkylation under MW irradiation. In this way, the mixtures of (HO)2P(O)(OR) and HOP(O)(OR)2 obtained by the practical reaction of phosphorus pentoxide and alcohol (ROH) could also be converted in two additional steps into the corresponding trialkyl esters. The three-step synthesis of trialkylphosphates starting from phosphorus pentoxide was also transformed in a one-pot (step 1: preparation of the monoester diester mixture, step 2: diesterification) and telescoping (step 3: triesterification) variation, avoiding the isolation and purification of the intermediates, and affording the triesters­ in 86–93% yields. The three- and two-step P-chloride-free methods developed are ‘green’ and of more general value.

Selective hydrolysis of phosphorus(V) compounds to form organophosphorus monoacids

An azide and transition metal-free method for the synthesis of elusive phosphonic, phosphinic, and phosphoric monoacids has been developed. Inert pentavalent P(v)-compounds (phosphonate, phosphinate, and phosphate) are activated by triflate anhydride (Tf2O)/pyridine system to form a highly reactive phosphoryl pyridinium intermediate that undergoes nucleophilic substitution with H2O to selectively deprotect one alkoxy group and form organophosphorus monoacids.