Synthesis of Mixed Phosphonate Esters and Amino Acid-Based Phosphonamidates, and Their Screening as Herbicides.

While organophosphorus chemistry is gaining attention in a variety of fields, the synthesis of the phosphorus derivatives of amino acids remains a challenging task. Previously reported methods require the deprotonation of the nucleophile, complex reagents or hydrolysis of the phosphonate ester. In this paper, we demonstrate how to avoid these issues by employing phosphonylaminium salts for the synthesis of novel mixed n-alkylphosphonate diesters or amino acid-derived n-alkylphosphonamidates. We successfully applied this methodology for the synthesis of novel N-acyl homoserine lactone analogues with varying alkyl chains and ester groups in the phosphorus moiety. Finally, we developed a rapid, quantitative and high-throughput bioassay to screen a selection of these compounds for their herbicidal activity. Together, these results will aid future research in phosphorus chemistry, agrochemistry and the synthesis of bioactive targets.

Synthesis of LAVR-289, a new [(Z)-3-(acetoxymethyl)-4-(2,4-diaminopyrimidin-6-yl)oxy-but-2-enyl]phosphonic acid prodrug with pronounced antiviral activity against DNA viruses.

New acyclic pyrimidine nucleoside phosphonate prodrugs with a 4-(2,4-diaminopyrimidin-6-yl)oxy-but-2-enyl]phosphonic acid skeleton (O-DAPy nucleobase) were prepared through a convergent synthesis by olefin cross-metathesis as the key step. Several acyclic nucleoside 4-(2,4-diaminopyrimidin-6-yl)oxy-but-2-enyl]phosphonic acid prodrug exhibited in vitro antiviral activity in submicromolar or nanomolar range against varicella zoster virus (VZV), human cytomegalovirus (HCMV), human herpes virus type 1 (HSV-1) and type 2 (HSV-2), and vaccinia virus (VV), with good selective index (SI). Among them, the analogue 9c (LAVR-289) proved markedly inhibitory against VZV wild-type (TK+) (EC50 0.0035 µM, SI 740) and for thymidine kinase VZV deficient strains (EC50 0.018 µM, SI 145), with a low morphological toxicity in cell culture at 100 µM and acceptable cytostatic activity resulting in excellent selectivity. Compound 9c exhibited antiviral activity against HCMV (EC50 0.021 µM) and VV (EC50 0.050 µM), as well as against HSV-1 (TK-) (EC50 0.0085 µM). Finally, LAVR-289 (9c) deserves further (pre)clinical investigations as a potent candidate broad-spectrum anti-herpesvirus drug.

N-Functionalization of ß-aminophosphonates: cytotoxic effects of the new derivatives.

ß-Aminophosphonates obtained by the Michael addition of primary amines to the double bond of diethyl vinylphosphonate proved to be suitable starting materials (amine components) in the Kabachnik-Fields reaction with formaldehyde and dialkyl phosphites or secondary phosphine oxides to afford N-phosphonylmethyl- and N-phosphinoylmethyl-ß-aminophosphonates. On the other hand, the starting aminophosphonates were modified by N-acylation using acid chlorides. The N-acyl products were found to exist in a dynamic equilibrium of two conformers as suggested by the broad NMR signals. At 26 °C, there may be rotation around the N-C axis of the acylamide function. At the same time, low-temperature NMR measurements at -5 °C revealed the presence of two distinct rotamers that could be characterized by 31P, 13C and 1H NMR data. The modified ß-aminophosphonic derivatives were subjected to a comparative structure-activity analysis on MDA-MB-231, PC-3, A431 and Ebc-1 tumor cell lines, and in a few cases, significant activity was detected.

Novel electrocatalytic capacitive deionization with catalytic electrodes for selective phosphonate degradation: Performance and mechanism.

Phosphonate is becoming a global interest and concern owing to its environment risk and potential value. Degradation of phosphonate into phosphate followed by the recovery is regarded as a promising strategy to control phosphonate pollution, relieve phosphorus crisis, and promote phosphorus cycle. Given these objectives, an anion-membrane-coated-electrode (A-MCE) doped with Fe-Co based carbon catalyst and cation-membrane-coated-electrode (C-MCE) doped with carbon-based catalyst were prepared as catalytic electrodes, and a novel electrocatalytic capacitive deionization (E-CDI) was developed. During charging process, phosphonate was enriched around A-MCE surface based on electrostatic attraction, ligand exchange, and hydrogen bond. Meanwhile, Fe2+ and Co2+ were self-oxidized into Fe3+ and Co3+, forming a complex with enriched phosphonate and enabling an intramolecular electron transfer process for phosphonate degradation. Additionally, benefiting from the stable dissolved oxygen and high oxygen reduction reaction activity of C-MCE, hydrogen peroxide accumulated in E-CDI (158 µM) and thus hydroxyl radicals (·OH) were generated by activation. E-CDI provided an ideal platform for the effective reaction between ·OH and phosphonate, avoiding the loss of ·OH and triggering selective degradation of most phosphonate. After charging for 70 min, approximately 89.9% of phosphonate was degraded into phosphate, and phosphate was subsequently adsorbed by A-MCE. Results also showed that phosphonate degradation was highly dependent on solution pH and voltage, and was insignificantly affected by electrolyte concentration. Compared to traditional advanced oxidation processes, E-CDI exhibited a higher degradation efficiency, lower cost, and less sensitive to co-existed ions in treating simulated wastewaters. Self-enhanced and selective degradation of phosphonate, and in-situ phosphate adsorption were simultaneously achieved for the first time by a E-CDI system, showing high promise in treating organic-containing saline wastewaters.

A Comparative Study of New Fluorescent Anthraquinone and Benzanthrone α-Aminophosphonates: Synthesis, Spectroscopy, Toxicology, X-ray Crystallography, and Microscopy of Opisthorchis felineus.

In this research, we explore the synthesis of and characterize α-aminophosphonates derived from anthraquinone and benzanthrone, focusing on their fluorescence properties and potential applications in confocal laser scanning microscopy (CLSM). The synthesized compounds exhibit notable solvatochromic behavior, emitting fluorescence from green to red across various solvents. Spectroscopic analysis, including 1H-, 13C-, and 31P-NMR, FTIR, and mass spectrometry, confirms the chemical structures. The compounds' toxicity is evaluated using etiolated wheat sprouts, revealing varying degrees of impact on growth and oxidative damage. Furthermore, the study introduces these α-aminophosphonates for CLSM imaging of the parasitic flatworm Opisthorchis felineus, demonstrating their potential in visualizing biological specimens. Additionally, an X-ray crystallographic study of an anthraquinone α-aminophosphonate provides valuable structural insights.

Membrane-permeable tenofovir-di- and monophosphate analogues.

The development of new antiviral agents such as nucleoside analogues or acyclic nucleotide analogues (ANPs) and prodrugs thereof is an ongoing task. We report on the synthesis of three types of lipophilic triphosphate analogues of (R)-PMPA and dialkylated diphosphate analogues of (R)-PMPA. A highly selective release of the different nucleotide analogues ((R)-PMPA-DP, (R)-PMPA-MP, and (R)-PMPA) from these compounds was achieved. All dialkylated (R)-PMPA-prodrugs proved to be very stable in PBS as well as in CEM/0 cell extracts and human plasma. In primer extension assays, both the monoalkylated and the dialkylated (R)-PMPA-DP derivatives acted as (R)-PMPA-DP as a substrate for HIV-RT. In contrast, no incorporation events were observed using human polymerase γ. The dialkylated (R)-PMPA-compounds exhibited significant anti-HIV efficacy in HIV-1/2 infected cells (CEM/0 and CEM/TK-). Remarkably, the dialkylated (R)-PMPA-MP derivative 9a showed a 326-fold improved activity as compared to (R)-PMPA in HIV-2 infected CEM/TK- cells as well as a very high SI of 14,000. We are convinced that this study may significantly contribute to advancing antiviral agents developed based on nucleotide analogues in the future.

Kinetics of glyphosate and aminomethylphosphonic acid sorption onto montmorillonite clays in soil and their translocation to genetically modified corn.

The co-occurrence of glyphosate (GLP) and aminomethylphosphonic acid (AMPA) in contaminated water, soil, sediment and plants is a cause for concern due to potential threats to the ecosystem and human health. A major route of exposure is through contact with contaminated soil and consumption of crops containing GLP and AMPA residues. However, clay-based sorption strategies for mixtures of GLP and AMPA in soil, plants and garden produce have been very limited. In this study, in vitro soil and in vivo genetically modified corn models were used to establish the proof of concept that the inclusion of clay sorbents in contaminated soils will reduce the bioavailability of GLP and AMPA in soils and their adverse effects on plant growth. Effects of chemical concentration (1-10 mg/kg), sorbent dose (0.5%-3% in soil and 0.5%-1% in plants) and duration (up to 28 days) on sorption kinetics were studied. The time course results showed a continuous GLP degradation to AMPA. The inclusion of calcium montmorillonite (CM) and acid processed montmorillonite (APM) clays at all doses significantly and consistently reduced the bioavailability of both chemicals from soils to plant roots and leaves in a dose- and time-dependent manner without detectable dissociation. Plants treated with 0.5% and 1% APM inclusion showed the highest growth rate (p ≤ 0.05) and lowest chemical bioavailability with up to 76% reduction in roots and 57% reduction in leaves. Results indicated that montmorillonite clays could be added as soil supplements to reduce hazardous mixtures of GLP and AMPA in soils and plants.

Harvesting phosphorus-containing moieties for their antibacterial effects.

Clinically manifested resistance of bacteria to antibiotics has emerged as a global threat to society and there is an urgent need for the development of novel classes of antibacterial agents. Recently, the use of phosphorus in antibacterial agents has been explored in quite an unprecedent manner. In this comprehensive review, we summarize the use of phosphorus-containing moieties (phosphonates, phosphonamidates, phosphonopeptides, phosphates, phosphoramidates, phosphinates, phosphine oxides, and phosphoniums) in compounds with antibacterial effect, including their use as ß-lactamase inhibitors and antibacterial disinfectants. We show that phosphorus-containing moieties can serve as novel pharmacophores, bioisosteres, and prodrugs to modify pharmacodynamic and pharmacokinetic properties. We further discuss the mechanisms of action, biological activities, clinical use and highlight possible future prospects.

The Microbial Degradation of Natural and Anthropogenic Phosphonates.

Phosphonates are compounds containing a direct carbon-phosphorus (C-P) bond, which is particularly resistant to chemical and enzymatic degradation. They are environmentally ubiquitous: some of them are produced by microorganisms and invertebrates, whereas others derive from anthropogenic activities. Because of their chemical stability and potential toxicity, man-made phosphonates pose pollution problems, and many studies have tried to identify biocompatible systems for their elimination. On the other hand, phosphonates are a resource for microorganisms living in environments where the availability of phosphate is limited; thus, bacteria in particular have evolved systems to uptake and catabolize phosphonates. Such systems can be either selective for a narrow subset of compounds or show a broader specificity. The role, distribution, and evolution of microbial genes and enzymes dedicated to phosphonate degradation, as well as their regulation, have been the subjects of substantial studies. At least three enzyme systems have been identified so far, schematically distinguished based on the mechanism by which the C-P bond is ultimately cleaved-i.e., through either a hydrolytic, radical, or oxidative reaction. This review summarizes our current understanding of the molecular systems and pathways that serve to catabolize phosphonates, as well as the regulatory mechanisms that govern their activity.

Asymmetric Transfer Hydrogenation as a Key Step in the Synthesis of the Phosphonic Acid Analogs of Aminocarboxylic Acids.

α-Aminophosphonic acids have a remarkably broad bioactivity spectrum. They can function as highly efficient transition state mimics for a variety of hydrolytic and angiotensin-converting enzymes, which makes them interesting target structures for synthetic chemists. In particular, the phosphonic acid analogs to α-aminocarboxylic acids (Pa AAs) are potent enzyme inhibitors, but many of them are only available by chiral or enzymatic resolution; sometimes only one enantiomer is accessible, and several have never been prepared in enantiopure form at all. Today, a variety of methods to access enantiopure α-aminophosphonic acids is known but none of the reported approaches can be generally applied for the synthesis of Pa AAs. Here we show that the phosphonic acid analogs of many (proteinogenic) α-amino acids become accessible by the catalytic, stereoselective asymmetric transfer hydrogenation (ATH) of α-oxo-phosphonates. The highly enantioenriched (enantiomeric excess (ee) ≥ 98 %) α-hydroxyphosphonates obtained are important pharmaceutical building blocks in themselves and could be easily converted to α-aminophosphonic acids in most studied cases. Even stereoselectively deuterated analogs became easily accessible from the same α-oxo-phosphonates using deuterated formic acid (DCO2 H).

N2'-Branched Acyclic Nucleoside Phosphonates Containing 9-Deazahypoxanthine as Inhibitors of Plasmodium falciparum 6-Oxopurine Phosphoribosyltransferase.

Twelve N2'-branched acyclic nucleoside phosphonates and bisphosphonates were synthesized as potential inhibitors of Plasmodium falciparum hypoxanthine-guanine-xanthine phosphoribosyltransferase (PfHGXPRT), the key enzyme in the purine salvage pathway for production of purine nucleotides. The chemical structures were designed with the aim to study selectivity of the inhibitors for PfHGXPRT over human HGPRT. The newly prepared compounds contain 9-deazahypoxanthine connected to a phosphonate group via a five-atom-linker bearing a nitrogen atom (N2') as a branching point. All compounds, with the additional phosphonate group(s) in the second aliphatic linker attached to N2' atom, were low micromolar inhibitors of PfHGXPRT with low to modest selectivity for the parasite enzyme over human HGPRT. The effect of the addition of different chemical groups/linkers to N2' atom on the inhibition constants and selectivity is discussed.

A Novel Pathway for Biosynthesis of the Herbicidal Phosphonate Natural Product Phosphonothrixin Is Widespread in Actinobacteria.

Phosphonothrixin is an herbicidal phosphonate natural product with an unusual, branched carbon skeleton. Bioinformatic analyses of the ftx gene cluster, which is responsible for synthesis of the compound, suggest that early steps of the biosynthetic pathway, up to production of the intermediate 2,3-dihydroxypropylphosphonic acid (DHPPA) are identical to those of the unrelated phosphonate natural product valinophos. This conclusion was strongly supported by the observation of biosynthetic intermediates from the shared pathway in spent media from two phosphonothrixin producing strains. Biochemical characterization of ftx-encoded proteins confirmed these early steps, as well as subsequent steps involving the oxidation of DHPPA to 3-hydroxy-2-oxopropylphosphonate and its conversion to phosphonothrixin by the combined action of an unusual heterodimeric, thiamine-pyrophosphate (TPP)-dependent ketotransferase and a TPP-dependent acetolactate synthase. The frequent observation of ftx-like gene clusters within actinobacteria suggests that production of compounds related to phosphonothrixin is common within these bacteria. IMPORTANCE Phosphonic acid natural products, such as phosphonothrixin, have great potential for biomedical and agricultural applications; however, discovery and development of these compounds requires detailed knowledge of the metabolism involved in their biosynthesis. The studies reported here reveal the biochemical pathway phosphonothrixin production, which enhances our ability to design strains that overproduce this potentially useful herbicide. This knowledge also improves our ability to predict the products of related biosynthetic gene clusters and the functions of homologous enzymes.

Enzymatic Synthesis of a Novel Coumarin Aminophosphonates: Antibacterial Effects and Oxidative Stress Modulation on Selected E. coli Strains.

The objective of the present study was to evaluate the synergistic effect of two important pharmacophores, coumarin and α-amino dimethyl phosphonate moieties, on antimicrobial activity toward selected LPS-varied E. coli strains. Studied antimicrobial agents were prepared via a Kabachnik-Fields reaction promoted by lipases. The products were provided with an excellent yield (up to 92%) under mild, solvent- and metal-free conditions. A preliminary exploration of coumarin α-amino dimethyl phosphonate analogs as novel antimicrobial agents was carried out to determine the basic features of the structure responsible for the observed biological activity. The structure-activity relationship revealed that an inhibitory activity of the synthesized compounds is strongly related to the type of the substituents located in the phenyl ring. The collected data demonstrated that coumarin-based α-aminophosphonates can be potential antimicrobial drug candidates, which is particularly crucial due to the constantly increasing resistance of bacteria to commonly used antibiotics.

Synthesis, antiviral activity, and computational study of ß-d-xylofuranosyl nucleoside phosphonates.

Molecular dynamics (MD) simulations provided insights into the favorable interactions between xylose nucleosides bearing a phosphonate moiety at their 3'-position and specific residues at the active site of the archetypal RNA-dependent RNA-polymerase (RdRp) of Enterovirus 71. Therefore, a series of xylosyl nucleoside phosphonates with adenine, uracil, cytosine, guanosine, and hypoxanthine as nucleobases were synthesized through multistep sequences starting from a single common precursor. Following antiviral activity evaluation, the adenine containing analogue was found to possess good antiviral activity against RNA viruses displaying an EC50 of 12 and 16 µM against measles virus (MeV) and enterovirus-68 (EV-68), respectively, whereas lacking cytotoxicity.

The functional importance of bacterial oxidative phosphonate pathways.

Organophosphonates (Pns) are a unique class of natural products characterized by a highly stable C-P bond. Pns exhibit a wide array of interesting structures as well as useful bioactivities ranging from antibacterial to herbicidal. More structurally simple Pns are scavenged and catabolized by bacteria as a source of phosphorus. Despite their environmental and industrial importance, the pathways involved in the metabolism of Pns are far from being fully elucidated. Pathways that have been characterized often reveal unusual chemical transformations and new enzyme mechanisms. Among these, oxidative enzymes play an outstanding role during the biosynthesis and degradation of Pns. They are to a high extent responsible for the structural diversity of Pn secondary metabolites and for the break-down of both man-made and biogenic Pns. Here, we review our current understanding of the importance of oxidative enzymes for microbial Pn metabolism, discuss the underlying mechanistic principles, similarities, and differences between pathways. This review illustrates Pn biochemistry to involve a mix of classical redox biochemistry and unique oxidative reactions, including ring formations, rearrangements, and desaturations. Many of these reactions are mediated by specialized iron-dependent oxygenases and oxidases. Such enzymes are the key to both early pathway diversification and late-stage functionalization of complex Pns.

Initial Steps of the Acid-Catalyzed Polyoxometalate-Functionalization with Phosphonic Acid Esters.

The organo-functionalization of metal oxides is a key strategy to introduce new functionalities. Often, phosphonates are used to anchor organic moieties to a range of metal oxides. Despite their widespread use, there is a lack of understanding of the parameters which enable selective and efficient formation of organophosphonate-metal oxide hybrids. Here, we report fundamental insights into the mechanism of phosphonate anchoring to a molecular metal oxide model. Specifically, we use in situ 31P NMR spectroscopy to follow the acid-catalyzed deprotection of a model phosphonate and its subsequent condensation to form a phosphonate-functionalized Dawson-polyoxometalate. Our study shows that the nucleophilicity of the acid anion is a key parameter which controls the clean and selective deprotection and polyoxometalate attachment of phosphonates. This insight will allow researchers to expand the scope of phosphonate anchoring to metal oxides by enabling the development of mild and scalable syntheses.

Enantioselective total syntheses of (S)-phosphonothrixin and unexpected cyclic derivative (S)-cyclic phosphonothrixin via enzymatic resolution.

(S)-Phosphonothrixin is a phosphonate natural product produced by Saccharothrix sp. ST-888 that exhibits herbicidal activity. The previously reported asymmetric synthesis of (S)-phosphonothrixin is laborious and difficult to reproduce. In this study, we developed a scalable and concise enantioselective total synthesis of (S)-phosphonothrixin via two different synthetic routes by the enzymatic resolution of a known racemic epoxy alcohol. The second-generation synthesis was more efficient in terms of the overall yield (15%) and the number of steps (7) and afforded a unique cyclic phosphonate (phostone) as the product of the C-P bond formation reaction, which was converted to (S)-cyclic phosphonothrixin. Both (S)-phosphonothrixin and (S)-cyclic phosphonothrixin induced chlorosis in the plant Arabidopsis thaliana. However, (S)-cyclic phosphonothrixin exhibited lower activity than (S)-phosphonothrixin owing to its fixed conformation, as evidenced by a structure-activity relationship study. This study paves the way for the elucidation of the detailed mode of action of (S)-phosphonothrixin.

Novel coumarin aminophosphonates as potential multitargeting antibacterial agents against Staphylococcus aureus.

Unique coumarin aminophosphonates as new antibacterial agents were designed and synthesized to combat severely bacterial resistance. Bioactivity assessment identified that 3-hydroxylphenyl aminophosphonate 6f with low hemolytic activity not only exhibited excellent inhibition potency against Staphylococcus aureus at low concentration (0.5 µg/mL) in vitro but also showed considerable antibacterial potency in vivo. Meanwhile, the active compound 6f was capable of eradicating the S. aureus biofilm, thus alleviating the development of S. aureus resistance. Furthermore, the drug combination of compound 6f with norfloxacin could enhance the antibacterial efficacy. Mechanistic explorations manifested that molecule 6f was able to destroy the integrity of cell membrane, which resulted in the leakage of protein and metabolism inhibition. The cellular redox homeostasis was interfered through inducing the generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS), leading to the reduction of glutathione (GSH) activity and lipid peroxidation. Furthermore, compound 6f could intercalate into DNA base pair to hinder normal biological function. The above results provided powerful information for the further development of coumarin aminophosphonates as antibacterial agents.

Rh-catalyzed asymmetric hydrogenation of α- and ß-enamido phosphonates: highly enantioselective access to amino phosphonic acids.

Catalytic asymmetric hydrogenation of α- and ß-enamido phosphonates was developed using a complex formed in situ through a chiral hybrid phosphine-bicyclic bridgehead phosphoramidite ligand and rhodium metal precursor as the catalyst. This strategy afforded a wide variety of substrates in excellent yield (96-99%) and enantiomeric excess (≤99%) with very low catalyst loading (S/C up to 10 000) and relatively mild reaction conditions. Further investigations suggested that the hydrogenation reaction occurred only at the CC bond of the enamido phosphate stage without tautomerization to the imine form. Tandem hydrolysis reactions of hydrogenated products gave the corresponding α- and ß-amino phosphonic acids in fairly high yield, which could be multipurpose building blocks for bioorganic chemistry, medicinal chemistry and organic synthesis.

Design and Synthesis of New α-hydroxy ß-fluoro/ß-trifluoromethyl and Unsaturated Phosphonates from Carbohydrate-Derived Building Blocks via Pudovik and Horner-Wadsworth-Emmons Reactions.

Herein, we present the application of fluorinated carbohydrate-derived building blocks for α-hydroxy ß-fluoro/ß-trifluoromethyl and unsaturated phosphonates synthesis. Pudovik and Horner-Wadsworth-Emmons reactions were applied to achieve this goal. The proposed pathway of the key reactions is supported by the experimental results, as well as quantum chemical calculations. The structure of the products was established by spectroscopic (1D, 2D NMR) and spectrometric (MS) techniques. Based on our data received, we claim that the progress of the Pudovik and HWE reactions is significantly influenced by the acidic protons present in the molecules as assessed by pKa values of the reagent.