Recent advances in the synthesis of 4'-truncated nucleoside phosphonic acid analogues.

The synthesis of five series of 4'-truncated nucleoside phosphonic acid analogues is discussed in this review: (1) 4'-truncated furanose nucleoside phosphonic acid analogues; (2) 4'-truncated pyrrolidine nucleoside phosphonic acid analogues; (3) 4'-truncated carbocyclic nucleoside phosphonic acid analogues; (4) 4'-truncated isoxazole nucleoside phosphonic acid analogues; (5) 4'-truncated miscellaneous nucleoside phosphonic acid analogues. Five different ways are used to make the phosphonate moiety: (i) Michaelis-Arbuzov reaction of RX (X = Br, I, OTf) with trialkyl phosphate; (ii) Lewis acid catalyzed Michaelis-Arbuzov reaction of glycoside with trialkyl phosphite; (iii) nucleophilic addition of a dialkyl phosphite to a carbonyl group; (iv) direct coupling reaction with amino alkyl phosphonate; (v) de novo synthesis of phosphonated-isoxazole and 1,3-dioxolane heterocycles from phosphonated starting materials. Their biological activity results are briefly discussed.

Synthesis of hybrid phosphorated indenoquinolines and biological evaluation as topoisomerase I inhibitors and antiproliferative agents.

This work describes the first synthesis of diethyl 6,6a,7,11b-tetrahydro-5H-indeno[2,1-c]quinolinylphosphonates 5, diethyl 7H-indeno[2,1-c]quinolinylphosphonates 6 and diethyl 7-oxo-7H-indeno[2,1-c]quinolinylphosphonates 7, which were prepared in good to high overall yields. The synthetic route involves a multicomponent reaction of 2-phosphonateaniline, aldehydes and indene as olefin and allows the selective generation of three stereogenic centres in a short, efficient and reliable manner. The selective dehydrogenation of 1,2,3,4-tetrahydroindenoquinolines leads to the formation of corresponding indenoquinolines, and subsequent oxidation of methylene group of the indenoquinolines allows the access to indenoquinolinones.

Comparison of phosphonate, hydroxypropyl and carboxylate pendants in Fe(III) macrocyclic complexes as MRI contrast agents.

Fe(III) macrocyclic complexes containing a macrocycle and three pendant groups including phosphonate (NOTP =1,4,7-triazacyclononane-1,4,7-triyl-tris(methylenephosphonic acid), carboxylate (NOTA = 1,4,7 - triazacyclononane - N,N',N″ - triacetate) or hydroxypropyl (NOHP =(2S,2'S,2"S)-1,1',1″-(1,4,7-triazonane-1,4,7-triyl)tris(propan-2-ol)) were studied in order to compare the effect of these donor groups on solution chemistry and water proton relaxivity. All three complexes, Fe(NOTP), Fe(NOHP) and Fe(NOTA), display a large degree of kinetic inertness to dissociation in the presence of phosphate and carbonate, under acidic conditions of 100 mM HCl or 1 M HCl or to trans-metalation with Zn(II). The r1 proton relaxivity of the complexes at 1.4 T, 33 °C is compared over the pH range of 1 to 10. At pH 7.4, 33 °C, 1.4 T, Fe(NOHP) has the largest relaxivity (1.5 mM-1 s-1), Fe(NOTP) is second at 1.0 mM-1 s-1, whereas Fe(NOTA) is the lowest at 0.61 mM-1 s-1. Fe(NOTP), Fe(NOHP) and Fe(NOTA) all show an increase in relaxivity at very acidic pH values (< 3) that is consistent with an acid-catalyzed process. Variable temperature 17O NMR studies at near neutral pH are consistent with the absence of an inner-sphere water molecule for Fe(NOTP) and Fe(NOHP), supporting second-sphere or outer-sphere water contributions to proton relaxation. Fe(NOTP) shows contrast enhancement in T1 weighted MRI studies in mice and clears through a renal pathway.

Asymmetric Synthesis of Tetrasubstituted α-Aminophosphonic Acid Derivatives.

Due to their structural similarity with natural α-amino acids, α-aminophosphonic acid derivatives are known biologically active molecules. In view of the relevance of tetrasubstituted carbons in nature and medicine and the strong dependence of the biological activity of chiral molecules into their absolute configuration, the synthesis of α-aminophosphonates bearing tetrasubstituted carbons in an asymmetric fashion has grown in interest in the past few decades. In the following lines, the existing literatures for the synthesis of optically active tetrasubstituted α-aminophosphonates are summarized, comprising diastereoselective and enantioselective approaches.

New approaches towards the synthesis of 1,2,3,4-tetrahydro isoquinoline-3-phosphonic acid (TicP).

Two new strategies for the efficient synthesis of racemic 1,2,3,4-tetrahydroisoquinoline-3-phosphonic acid (TicP) (±)-2 have been developed. The first strategy involves the electron-transfer reduction of the easily obtained α,ß-dehydro phosphonophenylalanine followed by a Pictet-Spengler cyclization. The second strategy involves a radical decarboxylation-phosphorylation reaction on 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid (Tic). In both strategies, the highly electrophilic N-acyliminium ion is formed as a key intermediate, and the target compound is obtained in good yield using mild reaction conditions and readily available starting materials, complementing existing methodologies and contributing to the easy accessibility of (±)-2 for further research.

Synthesis of Axially Chiral 2,2'-Bisphosphobiarenes via a Nickel-Catalyzed Asymmetric Ullmann Coupling: General Access to Privileged Chiral Ligands without Optical Resolution.

We report an asymmetric homocoupling of ortho-(iodo)arylphosphine oxides and ortho-(iodo)arylphosphonates resulting in highly enantioenriched axially chiral bisphosphine oxides and bisphosphonates. These products are readily converted to enantioenriched biaryl bisphosphines without need for chiral auxiliaries or optical resolution. This provides a practical route for the development of previously uninvestigated atroposelective biaryl bisphosphine ligands. The conditions have also proven effective for asymmetric dimerization of other, non-phosphorus-containing aryl halides.

Excellency of pyrimidinyl moieties containing α-aminophosphonates over benzthiazolyl moieties for thermal and structural stability of stem bromelain.

An efficient approach has been made for the synthesis of a series of novel di α-aminophosphonates by the reaction of terephthalaldehyde with various pyrimidine/benzthiazole amines and diethyl phosphite using sulfonated graphitic carbon nitride - SA@g-C3N4 as catalyst under room temperature and solvent free conditions. Later, the different effects of these newly synthesized α-aminophosphonates as a function of concentration gradient has been scrutinized on the thermal and structural stability of stem bromelain (SBM) through combining the results of various spectroscopic techniques like UV-vis, steady state fluorescence and circular dichroism (CD). Lastly the competitive and distinctive behaviour of α-aminophosphonates towards the stability of SBM has been envisaged using molecular docking simulations which suggest that nature of α-aminophosphonates plays a crucial role for their interactions with SBM. Molecular docking results clearly show that α-aminophosphonates with pyrimidine ring are having more number of hydrogen bonding interaction with amino acid residues of SBM than α-aminophosphonates with benzthiazolyl ring. Sequentially for thermal and structure stability of SBM, concentration of α-aminophosphonates plays an inexorable role and through these results it must be concluded that most of the α-aminophosphonates are stabilizing the SBM upto the 0. 1 mM concentration.

Synthesis of a Bolaamphiphilic Alkenyl Phosphonic Acid by Ru-catalyzed Olefin Cross Metathesis Reaction.

We report the synthesis of bolaamphiphilic alkenyl phosphonic acid (BPC12) through the olefin crossmetathesis reaction of vinylphosphonic acid with 1,11-dodecadiene in the presence of a Ru-carbene catalyst. BPC12 possesses two trans-P-C=C moieties and is thus readily soluble in water up to 3.4 g L-1, as confirmed by 1H nuclear magnetic resonance (NMR) measurements. Surface tension measurements revealed that BPC12 reduced the surface tension of water from 72.0 to 47.0 mN m‒1. The occupied area per molecule at the air/water interface (A) of BPC12 (216 Å2) was ten times larger than that of dodecenyl phosphonic acid PC12 (23 Å2). Moreover, dynamic light scattering measurement of an aqueous BPC12 solution (5 mM) revealed the formation of large aggregates with an average diameter of 81.8±27.0 nm.

Synthesis and Inhibitory Studies of Phosphonic Acid Analogues of Homophenylalanine and Phenylalanine towards Alanyl Aminopeptidases.

A library of novel phosphonic acid analogues of homophenylalanine and phenylalanine, containing fluorine and bromine atoms in the phenyl ring, have been synthesized. Their inhibitory properties against two important alanine aminopeptidases, of human (hAPN, CD13) and porcine (pAPN) origin, were evaluated. Enzymatic studies and comparison with literature data indicated the higher inhibitory potential of the homophenylalanine over phenylalanine derivatives towards both enzymes. Their inhibition constants were in the submicromolar range for hAPN and the micromolar range for pAPN, with 1-amino-3-(3-fluorophenyl) propylphosphonic acid (compound 15c) being one of the best low-molecular inhibitors of both enzymes. To the best of our knowledge, P1 homophenylalanine analogues are the most active inhibitors of the APN among phosphonic and phosphinic derivatives described in the literature. Therefore, they constitute interesting building blocks for the further design of chemically more complex inhibitors. Based on molecular modeling simulations and SAR (structure-activity relationship) analysis, the optimal architecture of enzyme-inhibitor complexes for hAPN and pAPN were determined.

Synthesis of α-Aminophosphonic Acid Derivatives Through the Addition of O- and S-Nucleophiles to 2H-Azirines and Their Antiproliferative Effect on A549 Human Lung Adenocarcinoma Cells.

This work reports a straightforward regioselective synthetic methodology to prepare α-aminophosphine oxides and phosphonates through the addition of oxygen and sulfur nucleophiles to the C-N double bond of 2H-azirine derivatives. Determined by the nature of the nucleophile, different α-aminophosphorus compounds may be obtained. For instance, aliphatic alcohols such as methanol or ethanol afford α-aminophosphine oxide and phosphonate acetals after N-C3 ring opening of the intermediate aziridine. However, addition of 2,2,2-trifluoroethanol, phenols, substituted benzenthiols or ethanethiol to 2H-azirine phosphine oxides or phosphonates yields allylic α-aminophosphine oxides and phosphonates in good to high general yields. In some cases, the intermediate aziridine attained by the nucleophilic addition of O- or S-nucleophiles to the starting 2H-azirine may be isolated and characterized before ring opening. Additionally, the cytotoxic effect on cell lines derived from human lung adenocarcinoma (A549) and non-malignant cells (MCR-5) was also screened. Some α-aminophosphorus derivatives exhibited very good activity against the A549 cell line in vitro. Furthermore, selectivity towards cancer cell (A549) over non-malignant cells (MCR-5) has been detected in almost all compounds tested.

Rational design of some substituted phenyl azanediyl (bis) methylene phosphonic acid derivatives as potential anticancer agents and imaging probes: Computational inputs, chemical synthesis, radiolabeling, biodistribution and gamma scintigraphy.

Bisphosphonates are widely used for treatment of osteoporosis. Recently, they have been reported to be effective anticancer agents. In this work, we designed some substituted phenyl (azanediyl) bis (methylene phosphonic acid) to be tested for their anticancer effect. Both molecular docking and dynamics studies were used to select the top ranked highly scored compounds. The selected hits showed potential in vitro anticancer effect against some cell lines. Biodistribution pattern and gamma scintigraphy were conducted to the most effective derivative (BMBP) after radiolabeling with 99mTc. Results of biodistribution and scintigraphic imaging of 99mTc-BMBP in tumor bearing mice showed a notable tumor affinity, and confirmed the targeting affinity of BMBP to the tumor tissues. As a conclusion, BMBP could act as potential anticancer agent and imaging probe.

Synthesis, Characterization and Evaluation of Cytotoxic Activities of Novel Aziridinyl Phosphonic Acid Derivatives.

New aziridine 2-phosphonic acids were prepared by monohydrolysis of the aziridine 2-phosphonates that were obtained by the modified Gabriel-Cromwell reaction of vinyl phosphonate or α-tosylvinyl phosphonate with a primary amine or a chiral amine. The cellular cytotoxicity of these compounds was tested against the HCT-116 colorectal cancer cell lines and the CCD-18Co normal colon fibroblast lines using the MTT assay. Three of the synthesized phosphonic acid derivatives 2e (ethyl hydrogen {(2S)-1-[(1S)-1-(naphthalen-2-yl)ethyl]aziridin-2-yl}phosphonate), 2h (ethyl hydrogen (1-benzylaziridin-2-yl)phosphonate), and 2i (ethyl hydrogen (1-cyclohexylaziridin-2-yl)phosphonate) showed higher cytotoxicity than the reference cancer treatment agent etoposide. Cell death was through a robust induction of apoptosis even more effectively than etoposide, a well-known apoptosis inducing agent.

Structural exploration of cinnamate-based phosphonic acids as inhibitors of bacterial ureases.

The conjugated system of cinnamic acid, α-substituted with a phosphonoalkyl residue, was previously validated as a scaffold that provided one of the most potent organophosphorus inhibitors of bacterial urease. Following the idea of using Morita-Baylis-Hillman adducts to introduce the terminal phosphonic side chain functionality to the α,ß-unsaturated system, we currently report the synthesis and activity of an extended series of compounds. Cinnamates modified with 3-phosphonopropyl and 4-phosphonobutyl side chains were obtained in a convenient two-step procedure, which involved Pd-mediated transformations of the Morita-Baylis-Hillman bromides as the key substrates. The introduction of a terminal alkenyl fragment, which was achieved by Stille coupling with stannanes, was followed by a tandem C-P bond formation/oxidation process. A submicromolar ligand of Sporosarcina pasteurii urease (Ki = 0.509 µM) was identified among the active molecules. In addition, inhibitors of Proteus mirabilis urease affected bacterial growth at the micromolar level. Based on the structure-activity relationship and the mechanism of inhibition, we suggest a nontypical mixed mode of action for the slow binding compounds. We presume that the molecular distance between the phosphonic group and the backbone double bond allows a dual activity: complexation of the acidic group with nickel ions and Michael addition of a cysteine forming the active site lid.

Multiple-step, one-pot synthesis of 2-substituted-3-phosphono-1-thia-4-aza-2-cyclohexene-5-carboxylates and their corresponding ethyl esters.

The multiple-step, one-pot procedure for a series of 2-substituted-3-phosphono-1-thia-4-aza-2-cyclohexene-5-carboxylates, analogues of the natural, sulfur amino acid metabolite lanthionine ketimine (LK), its 5-ethyl ester (LKE) and 2-substituted LKEs is described. Initiating the synthesis with the Michaelis-Arbuzov preparation of α-ketophosphonates allows for a wide range of functional variation at the 2-position of the products. Nine new compounds were synthesized with overall yields range from 40 to 62%. In addition, the newly prepared 2-isopropyl-LK-P, 2-n-hexyl-LKE-P and 2-ethyl-LKE were shown to stimulate autophagy in cultured cells better than that of the parent compound, LKE.

Development of Biologically Active Compounds on the Basis of Phosphonic and Phosphinic Acid Functionalities.

Phosphonic and phosphinic acids, especially α-heteroatom-substituted ones, possess unique structural and physical features which enable them to act as hydrotically stable analogs to biological phosphates in biological processes. They also act as mimetics in the transition state of the protease-induced hydrolysis of dipeptides. The first half of this review focuses on selected new synthetic methods developed by our research group for the stereoselective synthesis of α-heteroatom-substituted phosphonic and phosphinic acid derivatives, including modified nucleotide analogs and phosphinyl dipeptide isosteres. In the latter half, this review summarizes the utility of difluoromethylenephosphonic acids and phosphonic acid esters in the development of enzyme inhibitors against protein tyrosine phosphatases, sphingomyelinases, purine nucleoside phosphorylases and thrombin. The enzyme inhibitors developed were used as probes to elucidate signal transductions and the mechanisms of enzyme actions. The findings of the studies are briefly described.

Dual targeting of cancer-related human matrix metalloproteinases and carbonic anhydrases by chiral N-(biarylsulfonyl)-phosphonic acids.

A series of nanomolar phosphonate matrix metalloproteinase (MPP) inhibitors was tested for inhibitory activity against a panel of selected human carbonic anhydrase (CA, EC 4.2.1.1) isozymes, covering the cancer-associated CA IX and XII. None of the reported sulfonyl and sulfonylamino-derivatives sensitively affected the catalytic activity of the cytosolic isoforms CA I and II, which are considered off-target isoforms in view of their physiological role. The most active inhibitors were in the series of chiral N-(sulfonyl)phosphovaline derivatives, which showed good to excellent inhibitory activity over target CAs, with compound 15 presenting the best isoform-selectivity toward CA IX. We suggest here that the phosphonates have the potential as dual inhibitors of MMPs and CAs, both involved in tumor formation, invasion and metastasis.

Highly selective enrichment of phosphopeptides by titanium (IV) attached monodisperse-porous poly(vinylphosphonic acid-co-ethylene dimethacrylate) microspheres.

A seeded polymerization protocol was developed for the synthesis of monodisperse-porous poly(vinylphosphonic acid-co-ethylene dimethacrylate), [poly(VPA-co-EDMA)] microspheres with superior porous properties. The protocol allowed the direct synthesis of phosphonic acid functionalized porous microspheres with the mean size of ∼4µm and the specific surface area of 420m2g-1 without applying any complicated post-derivatization protocol for the attachment of phosphonic acid group. The phosphonic acid content of poly(VPA-co-EDMA) microspheres was determined as 1.5mmol H2PO3g-1 microspheres. Ti(IV) ions were attached onto the microspheres via metal-chelate complex formation by phosphonate-groups and Ti(IV) carrying monodisperse-porous poly(vinylphosphonic acid-co-ethylene dimethacrylate), [Ti(IV)@poly(VPA-co-EDMA)] microspheres were obtained as a new sorbent for phosphopeptide enrichment via immobilized metal affinity chromatography. The phosphopeptides in the enriched samples were identified by matrix-assited laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). Four different phosphopeptides were detected with extremely high intensity by the treatment of ß-casein digest prepared with the concentration of 10 fmol/mL with Ti(IV)@poly(VPA-co-EDMA) microspheres. Highly selective enrichment of phosphopeptides was also successfully carried out even at trace amounts in a complex mixture of digested proteins (molar ratio of ß-casein to BSA, 1:1000) and eight different phosphorylated peptides from BSA digest were successfully identified. Moreover, four highly intense signals of the phosphopeptides in human serum were observed with high S/N ratio and clear background after enrichment by using Ti(IV)@poly(VPA-co-EDMA) microspheres.

1-Aminobenzocyclobutene-1-phosphonic Acid and Related Compounds as Inhibitors of Phenylalanine Ammonia-Lyase.

Five new geminal aminocycloalkanephosphonic acids (4 - 8) containing both an aromatic ring and a cycloalkane ring were synthesized and evaluated as potential inhibitors of buckwheat phenylalanine ammonia-lyase (PAL). Within the set of compounds which are related to 2-aminoindane-2-phosphonic acid (AIP, 3), a known powerful inhibitor of PAL, racemic 1-aminobenzocyclobutene-1-phosphonic acid (4), was six times weaker than AIP as an in vitro inhibitor of buckwheat PAL, but six times stronger than AIP as an in vivo inhibitor of phenylalanine-derived anthocyanin synthesis in buckwheat.

Diethylalkylsulfonamido(4-methoxyphenyl)methyl)phosphonate/phosphonic acid derivatives act as acid phosphatase inhibitors: synthesis accompanied by experimental and molecular modeling assessments.

Purple acid phosphatases (PAPs) are binuclear metallo-hydrolases that have been isolated from various mammals, plants, fungi and bacteria. In mammals, PAP activity is associated with bone resorption and can lead to bone metabolic disorders such as osteoporosis; thus human PAP is an attractive target to develop anti-osteoporotic drugs. The aim of the present study was to investigate inhibitory effect of synthesized diethylalkylsulfonamido(4-methoxyphenyl)methyl)phosphonate/phosphonic acid derivatives as potential red kidney bean PAP (rkbPAP) inhibitors accompanied by experimental and molecular modeling assessments. Enzyme kinetic data showed that they are good rkbPAP inhibitors whose potencies improve with increasing alkyl chain length. Hexadecyl derivatives, as most potent compounds (Ki = 1.1 µM), inhibit rkbPAP in the mixed manner, while dodecyl derivatives act as efficient noncompetitive inhibitor. Also, analysis by molecular modeling of the structure of the rkbPAP-inhibitor complexes reveals factors, which may be important for the determination of inhibition specificity.

Synthesis of Hydroxymethylenebisphosphonic Acid Derivatives in Different Solvents.

The syntheses of hydroxymethylenebisphosphonic acid derivatives (dronic acid derivatives) starting from the corresponding substituted acetic acids and P-reagents, mainly phosphorus trichloride and phosphorous acid are surveyed according to the solvents applied. The nature of the solvent is a critical point due to the heterogeneity of the reaction mixtures. This review sheds light on the optimum choice and ratio of the P-reactants, and on the optimum conditions.