Toxicity, bioactivity, release of H2S in vivo and pharmaco-kinetics of H2S-donors with thiophosphamide structure.

H2S donors are substitutes of H2S with various biological activities like inhibiting the inflammatory response and protecting myocardial cells from injury. In order to confirm whether the H2S donors have drug-like properties, two series thiophosphamide H2S donors were evaluated including toxicity, bioactivity and pharmacokinetic properties in vivo and in vitro. The following results were obtained. Firstly, all the compounds released H2S under measuring condition; with the increase of pH value, the H2S release rate of all the compounds decreased and the amount reduced, but pH value had little effect on the maximum release of H2S. Secondly, in the organs and tissues of rats, the compounds released H2S in the same way as in PBS. In plasma, compound 1 reached the Cmax after administration 55 min, and no compound 1 was detected after 12 h; for compound 18, the Cmax reached only after administration 100 min, and after 6 h, compound 18 was not detected; in organs and tissues, the H2S-release rates were different from those in PBS, but the mechanism of H2S release was the same. Thirdly, in the test of toxicity, all the compounds displayed low toxicities to 5 cancer cells and W138 cell lines; compounds 1 and 18 had slight effect on the physiological tissue and function of rat liver at low concentration; the compounds had almost no effect on the hatching rate, survival rate of zebrafish embryos, and the spontaneous movement of zebrafish embryos at below 0.5 µM, but when they were over 1 µM, the compounds displayed inhibitory effect in the manner of concentration dependence. Fourthly, in the course of anti-inflammatory test, all the tested compounds significantly reduced the level of TNF-α and increased the level of IL-10; when they were 100 µM, the levels of IL-10 were three times as high as those in the control group. Among them, compounds 10 and 18 displayed stronger activities than the others. In addition, the compounds protected H9c2 cells from injure and improved myocardial injury through anti-oxidation pathway. In summary, the compounds have druglike properties due to low toxicity, better activity and good pharmacokinetic property. Therefore, they have potential to be as candidates to investigate further.

Discovery of New H2S Releasing Phosphordithioates and 2,3-Dihydro-2-phenyl-2-sulfanylenebenzo[d][1,3,2]oxazaphospholes with Improved Antiproliferative Activity.

Hydrogen sulfide (H2S) is now recognized as a physiologically important gasotransmitter. Compounds which release H2S slowly are sought after for their potential in therapy. Herein the synthesis of a series of phosphordithioates based on 1 (GYY4137) are described. Their H2S release profiles are characterized using 2,6-dansyl azide (2), an H2S specific fluorescent probe. Most compounds have anticancer activity in several solid tumor cell lines and are less toxic in a normal human lung fibroblast, WI38. A preferred compound, 14, with 10-fold greater anticancer activity than 1, was shown to release H2S in MCF7 cells using a cell active probe, 21. Both permeability and intracellular pH (pHi) were found to be significantly improved for 14 compared to 1. Furthermore, 14 was also negative in the AMES test for genotoxicity. Cyclization of these initial structures gave a series of 2,3-dihydro-2-phenyl-2-sulfanylenebenzo[d][1,3,2]oxazaphospholes, of which the simplest member, compound 22 (FW1256), was significantly more potent in cells. The improved therapeutic window of 22 in WI38 cells was compared with three other cell types. Potency of 22 was superior to 1 in MCF7 tumor spheroids and the mechanism of cell death was shown to be via apoptosis with an increase in cleaved PARP and activated caspase-7. Evidence of H2S release in cells is also presented. This work provides a "toolbox" of slow-release H2S donors useful for studies of H2S in biology and as potential therapeutics in cancer, inflammation, and cardiovascular disease.

Medicinal Chemistry: Insights into the Development of Novel H2S Donors.

Hydrogen sulfide (H2S) was traditionally considered as a toxic gas. However, recent studies have demonstrated H2S is an endogenously generated gaseous signaling molecule (gasotransmitter) with importance on par with that of two other well-known endogenous gasotransmitters, nitric oxide (NO) and carbon monoxide (CO). Although H2S's exact mechanisms of action are still under investigation, the production of endogenous H2S and the exogenous administration of H2S have been demonstrated to elicit a wide range of physiological responses including modulation of blood pressure and protection of ischemia reperfusion injury, exertion of anti-inflammatory effects, and reduction of metabolic rate. These results strongly suggest that modulation of H2S levels could have potential therapeutic values. In this regard, synthetic H2S-releasing agents (i.e., H2S donors) are not only important research tools, but also potential therapeutic agents. This chapter summarizes the knowledge of currently available H2S donors. Their preparation, H2S releasing mechanisms, and biological applications are discussed.

Solventless synthesis of acyl phosphonamidates, precursors to masked bisphosphonates.

A series of acyl phosphonamidates, the synthetic precursors to bisphosphonates, have been readily prepared from phosphoramidite type reagents and a range of acid chlorides. These reactions were performed using solventless conditions, where purification was easily achieved using column chromatography with yields ranging from 71-90%. Furthermore, we have demonstrated that these acyl phosphonamidates could be used for the preparation of unsymmetrical bisphosphonates, which do date are scarcely reported in the literature.

Hydrolysis of 2'3'-cGAMP by ENPP1 and design of nonhydrolyzable analogs.

Agonists of mouse STING (TMEM173) shrink and even cure solid tumors by activating innate immunity; human STING (hSTING) agonists are needed to test this therapeutic hypothesis in humans. The endogenous STING agonist is 2'3'-cGAMP, a second messenger that signals the presence of cytosolic double-stranded DNA. We report activity-guided partial purification and identification of ecto-nucleotide pyrophosphatase/phosphodiesterase (ENPP1) to be the dominant 2'3'-cGAMP hydrolyzing activity in cultured cells. The hydrolysis activity of ENPP1 was confirmed using recombinant protein and was depleted in tissue extracts and plasma from Enpp1(-/-) mice. We synthesized a hydrolysis-resistant bisphosphothioate analog of 2'3'-cGAMP (2'3'-cG(s)A(s)MP) that has similar affinity for hSTING in vitro and is ten times more potent at inducing IFN-ß secretion from human THP1 monocytes. Studies in mouse Enpp1(-/-) lung fibroblasts indicate that resistance to hydrolysis contributes substantially to its higher potency. 2'3'-cG(s)A(s)MP is therefore improved over natural 2'3'-cGAMP as a model agonist and has potential as a vaccine adjuvant and cancer therapeutic.

Copper-catalyzed reductive coupling of aryl sulfonyl chlorides with H-phosphonates leading to S-aryl phosphorothioates.

An efficient protocol for copper-catalyzed reductive cross-coupling of aryl sulfonyl chlorides with H-phosphonates has been developed. The various S-aryl phosphorothioates were afforded in up to 86% yield for 20 examples. This protocol features high efficiency, wide functional group tolerance, commercially available aryl sulfonyl chlorides as starting materials and base-free conditions.

A novel synthesis of antiviral nucleoside phosphoramidate and thiophosphoramidate prodrugs via nucleoside H-phosphonamidates.

A novel and efficient method for the preparation of antiviral nucleoside 5'-H-phosphonamidates has been developed. The oxidization of the H-phosphonamidate intermediates with iodine and sulfur afforded nucleoside 5'-phosphoramidates and 5'-thiophosphoramidates in high yields.

Synthesis of novel nucleoside analogue phosphorothioamidate prodrugs and in vitro anticancer evaluation against RKO human colon carcinoma cells.

Novel phosphorothioamidates of pyrimidine nucleoside analogues have been prepared and evaluated in vitro against RKO human colon cancer cell by the MTT cytotoxicity assay. The parent nucleoside analogues were inactive in this assay, while the phosphorothioamidate prodrugs were active at low uM levels in some cases. The O-isopropyl phosphorothioamidate of 2 ',3 '-O-isopropylidene-uridine containing the L-phenylalanine ethyl ester 6f was the most active at 148 uM, a 10-fold enhancement in anticancer activity compared with the parent nucleoside 2 with no increase in cytotoxicity.

A new tridentate sulfur receptor as a highly sensitive and selective fluorescent sensor for Cu2+ ions.

The introduction of Lawesson's reagent into a bis-rhodamine spirolactam system afforded a new fluorescent sensor for Cu(2+) ions, SRR, which contained a new tridentate sulfur ligand. SRR showed excellent specificity for Cu(2+) ions over other cations (including Cu(+), Hg(2+), and Fe(3+)), very high sensitivity (10 nM), and a rapid response time (3 min). The detection mechanism was investigated by (1)H NMR, (13)C NMR, (31)P NMR, and ESR spectroscopy, MS, and Gaussian calculations. Coordination of a Cu(2+) ion to the tridentate sulfur ligand, which promotes ring-opening of the rhodamine groups, followed by a spontaneous reduction reaction (Cu(2+) into Cu(+)), has been proposed as the sensing mechanism.

Nucleoside-(5'→P) methylenebisphosphonodithioate analogues: synthesis and chemical properties.

Nucleoside-(5'→P) methylenebisphosphonodithioate analogues are bioisosteres of natural nucleotides. The potential therapeutic applications of these analogues are limited by their relative instability. With a view toward improving their chemical and metabolic stability as well as their affinity toward zinc ions, we developed a novel nucleotide scaffold, nucleoside-5'-tetrathiobisphosphonate. We synthesized P1-(uridine/adenosine-5')-methylenebisphosphonodithioate, 2 and 3, and P1,P2-di(uridine/adenosine-5')-methylenebisphosphonodithioate, 4 and 5. Using (1)H and (31)P NMR-monitored Zn(2+)/Mg(2+) titrations, we found that 5 coordinated Zn(2+) by both N7 nitrogen atoms and both dithiophosphonate moieties, whereas 3 coordinated Zn(2+) by an N7 nitrogen atom and Pß. Both 3 and 5 did not coordinate Mg(2+) ions. (31)P NMR-monitored kinetic studies showed that 3 was more stable at pD 1.5 than 5, with t(1/2) of 44 versus 9 h, respectively, and at pD 11 both showed no degradation for at least 2 weeks. However, 5 was more stable than 3 under an air-oxidizing atmosphere, with t1/2 of at least 3 days versus 14 h, respectively. Analogues 3 and 5 were highly stable to NPP1,3 and NTPDase1,2,3,8 hydrolysis (0-7%). However, they were found to be poor ectonucleotidase inhibitors. Although 3 and 5 did not prove to be effective inhibitors of zinc-containing NPP1/3, which is involved in the pathology of osteoarthritis and diabetes, they may be promising zinc chelators for the treatment of other health disorders involving an excess of zinc ions.

Methylenediphosphonotetrathioate: synthesis, characterization, and chemical properties.

Metal chelators are potential therapeutic agents for treating diseases such as Wilson's and Alzheimer's where the pathology involves an excess of metal-ions (Cu(II) and Zn(II)/Cu(II)/Fe(II/III), respectively). In addition to the high affinity of the metal-ion to the chelators, metal selectivity of the chelators is essential to achieve the therapeutic goal, that is, the successful removal of excess of harmful metal-ions in a physiological extracellular medium rich in alkali and alkali earth metal-ions. For this purpose, we synthesized a novel chelator, methylenediphosphonotetrathioate (MDPT) which is the tetrathio analogue of methylenediphosphonic acid (MDP). MDPT was synthesized from bis-methylene(phosphonicdichloride) in a 3-step synthesis and a 31% overall yield. MDPT formed a stable complex with Zn(II) (log K = 10.84), which is 10(7) times more stable than the corresponding Ca(II) complex. Moreover, the MDPT-Zn(II) complex was 50-fold more stable than the MDP-Zn(II) complex. In addition, MDPT was found to inhibit the Cu(I)-catalyzed Fenton reaction (IC50 26 µM) 2.5 times more potently than a Fe(II)-catalyzed Fenton reaction, and 2.5 times more potently than EDTA (IC50 64 µM) in the Cu(I)/H2O2 system, as monitored by electron spin resonance (ESR). Furthermore, MDPT was found to be relatively stable in both acidic (pD 1.9, t(½) = 71.5 h) and basic media (pD 12.4, t(½) = 81 h) as monitored by (31)P/(1)H NMR. However, MDPT was not stable in air because of intramolecular oxidation and disulfide formation (33% oxidation after 27 h). In conclusion, MDPT was found to be a water-soluble chelator showing a clear preference to soft/borderline metal-ions and a remarkable selectivity to those metal-ions vs Ca(II) ions. The relative sensitivity of MDPT to oxidation may limit its use; however, the application of MDPT in acidic or basic media will increase its lifetime.

Structure-activity relationship for the reactivators of acetylcholinesterase inhibited by nerve agent VX.

Nerve agents such as sarin, VX and tabun are organophosphorus compounds able to inhibit an enzyme acetylcholinesterase (AChE). AChE reactivators and anticholinergics are generally used as antidotes in the case of intoxication with these agents. None from the known AChE reactivators is able to reactivate AChE inhibited by all kinds of nerve agents. In this work, reactivation potency of seventeen structurally different AChE reactivators was tested in vitro and subsequently, relationship between their chemical structure and biological activity was outlined. VX was chosen as appropriate member of the nerve agent family.

Synthesis and evaluation of phosphoramidate and phosphorothioamidate analogues of amiprophos methyl as potential antimalarial agents.

A series of phosphoramidate and phosphorothioamidate compounds based on the lead antitubulin herbicidal agents amiprophos methyl (APM) and butamifos were synthesised and evaluated for antimalarial activity. Of these compounds, phosphorothioamidates were more active than their oxo congeners and the nature of both aryl and amido substituents influenced the desired activity. The most active compound was 46, O-ethyl-O-(2-methyl-4-nitrophenyl)-N-cyclopentyl phosphorothioamidate, which was more effective than the lead compound.

Efficient synthesis of 3-O-thia-cPA and preliminary analysis of its biological activity toward autotaxin.

The efficient synthesis of 3-O-thia-cPAs (4a-d), sulfur analogues of cyclic phosphatidic acid (cPA), has been achieved. The key step of the synthesis is an intramolecular Arbuzov reaction to construct the cyclic thiophosphate moiety. The present synthetic route enables the synthesis of 4a-d in only four steps from the commercially available glycidol. Preliminary biological experiments showed that 4a-d exhibited a similar inhibitory effect on autotaxin (ATX) as original cPA.

A study of the kinetics of La3+-promoted methanolysis of S-aryl methylphosphonothioates: possible methodology for decontamination of EA 2192, the toxic byproduct of VX hydrolysis.

The kinetics of the La3+-catalyzed methanolysis of a series of S-aryl methylphosphonothioates (4a-e, phenyl substituents = 3,5-dichloro, 4-chloro, 4-fluoro, 4-H, 4-methoxy) were studied at 25 °C with s(s)pH control. The reaction involves saturation binding of the anionic substrates to dimeric La3+/methoxide catalysts formulated as La2(3+)(-OCH3)x, where x = 2-5 depending on the solution s(s)pH. Cleavage of the La3+-bound methylphosphonothioates is fast, ranging from 5 × 10(-3) s(-1) to 5.5 × 10-(5) s(-1) for substrates 4a-e at a s(s)pH of 8.4 and 1.6 × 10(-1) s(-1) to 4 × 10(-3) s(-1) at a s(s)pH of 11.7. The rate accelerations for the methanolysis of substrates 4a-e, relative to their background methoxide-promoted reactions, average 7 × 10(10) and 1.5 × 10(9), respectively, at s(s)pH's of 8.4 and 11.7. The catalytic system is predicted to cleave EA 2192 (S-2(N,N-di-iso-propylaminoethyl)methylphosphonothioate), a toxic byproduct of the hydrolysis of VX, with a t1/2 between 4 and 8 min at a s(s)pH of 8.4, and 27 min at a s(s)pH of 11.7.

Preparation and identification of generic antigens and broad-spectrum monoclonal antibodies for detection of organophosphorus pesticides.

A simple, rapid, and high-sensitivity assay was developed to detect the multiresidue of organophosphorus pesticides (OPs) in the environment and food. Two separate generic haptens (Hapten A and B) with same O,O-dimethyl phosphorothioate group and aromatic ring and different spacer arms were synthesized and conjugated to bovine serum albumin (BSA) for immunogens and to ovalbumin (OVA) for coating antigens to study the effect of hapten and coating antigen heterology on immunoassay sensitivity. A broad-spectrum monoclonal antibody (MAb) was produced and a competitive ELISA developed using Hapten B-BSA as the immunogen and Hapten A-OVA as the coating antigen for the multiresidue determination of OPs, including parathionmethyl, fenitrothion, fenthion, chlorthion, and fenchlorphos. Several assay conditions, including organic solvent, pH, ionic strength, and incubation time, were studied sequentially to optimize the immunoassay. Using the optimal assay, 50% inhibition concentration values were estimated to be 34.5, 47.5, 79.8, 125.2, and 373.1 ng/mL for parathionmethyl, fenitrothion, fenthion, chlorthion, and fenchlorphos, respectively. The results indicated that the MAb showed specificity to all the above five OPs, and the assay could be developed for multiresidue determinations.

[Effect of synthesized GYY4137, a slowly releasing hydrogen sulfide donor, on cell viability and distribution of hydrogen sulfide in mice].

OBJECTIVE: To improve a method of a new hydrogen sulfide slow-releasing donor, to observe its cellular toxicity in HepG2 cells and tissue distribution and metabolic pathway after administration of the donor by intraperitoneal injection in ICR mice and to afford experimental evidences for rationally using this donor in hydrogen sulfide research. METHODS: We synthesized the new chemical compound which slowly released hydrogen sulfide. After administration of the donor, the cell toxicity was evaluated for cell viability using trypan blue staining in HepG2 cells and lactate dehydrogenase (LDH) activity in culture medium. After administration of this donor by intrasperitoneal injection, we measured the tissue hydrogen sulfide content in the liver, heart, kidney and brain using sensitive-sulfur electrode assay. RESULTS: We successfully prepared the donor which could release hydrogen sulfide. The releasing ability of the donor solution stored at 4 °C or 20 °C did not change as compared with the freshly-prepared one. Treated at various concentrations of the donor (0.062 5, 0.125, 0.25, 0.5, 1 and 2 mmol/L) for 24 hours in HepG2 cells, the cell viability and LDH leak from the cells were not different as compared with the controls. The donor (2 mmol/L) was administrated everyday and the culture medium was changed every 3 days. After 9 days, the cell viability and LDH leak did not change. Administration of the donor (200 µmol/kg) quickly increased the tissue hydrogen sulfide concentrations in the liver and heart and maintained about 20 min; the hydrogen sulfide level in the kidney elevated and maintained a longer time, then recovered after 2 hours, which implicated that the donor might exclude the kidney; the hydrogen sulfide concentration in the brain did not change in the present study, which suggested that the donor could not pass the blood-brain barrier. Long time (4 weeks) treatment with this compound might induce hepatic or cutaneous injury. CONCLUSION: The new chemical compound is a relative stable, slow-releasing donor of hydrogen sulfide with low cellular toxicity, which may be used to study the regulatory role of hydrogen sulfide in the cellular physiological and pathophysiological mechanism of the animal model with acute diseases.

Chemical synthesis of two series of nerve agent model compounds and their stereoselective interaction with human acetylcholinesterase and human butyrylcholinesterase.

Both G and V type nerve agents possess a center of chirality about phosphorus. The S(p) enantiomers are generally more potent inhibitors than their R(p) counterparts toward acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). To develop model compounds with defined centers of chirality that mimic the target nerve agent structures, we synthesized both the S(p) and the R(p) stereoisomers of two series of G type nerve agent model compounds in enantiomerically enriched form. The two series of model compounds contained identical substituents on the phosphorus as the G type agents, except that thiomethyl (CH(3)-S-) and thiocholine [(CH(3))(3)NCH(2)CH(2)-S-] groups were used to replace the traditional nerve agent leaving groups (i.e., fluoro for GB, GF, and GD and cyano for GA). Inhibition kinetic studies of the thiomethyl- and thiocholine-substituted series of nerve agent model compounds revealed that the S(p) enantiomers of both series of compounds showed greater inhibition potency toward AChE and BChE. The level of stereoselectivity, as indicated by the ratio of the bimolecular inhibition rate constants between S(p) and R(p) enantiomers, was greatest for the GF model compounds in both series. The thiocholine analogues were much more potent than the corresponding thiomethyl analogues. With the exception of the GA model compounds, both series showed greater potency against AChE than BChE. The stereoselectivity (i.e., S(p) > R(p)), enzyme selectivity, and dynamic range of inhibition potency contributed from these two series of compounds suggest that the combined application of these model compounds will provide useful research tools for understanding interactions of nerve agents with cholinesterase and other enzymes involved in nerve agent and organophosphate pharmacology. The potential of and limitations for using these model compounds in the development of biological therapeutics against nerve agent toxicity are also discussed.

Synthesis of novel phosphorothioates and phosphorodithioates and their differential inhibition of cholinesterases.

The anticholinesterase activities of newly synthesized phosphorothioates and phosphorodithioates were investigated. The compounds were evaluated for their acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibition potency through IC(50) determination. The selectivities of the synthesized compounds toward both enzymes were determined and compared in terms of their molecular structures.

The synthesis of di- and oligo-nucleotides containing a phosphorodithioate internucleotide linkage with one of the sulfur atoms in a 5'-bridging position.

A new type of internucleotide phosphorodithioate linkage is described, wherein one of the sulfur atoms occupies a 5'-bridging position. Representative dinucleotides possessing such a bond were synthesized by S-alkylation of nucleoside-3'-O-phosphorodithioates with 5'-halogeno-5'-deoxy-nucleosides. A fully protected dithymidylate containing internucleotide 5'-S-phosphorodithioate linkage was converted into a 3'-O-phosphoramidite derivative and employed for introduction of a modified dinucleotide into a predetermined position of the oligonucleotide sequence. The 5'-S-phosphorodithioate linkage in dinucleotide analogues was found to be resistant toward nucleolytic degradation with snake venom PDE and nuclease P1. However, P-stereoselective degradation was observed for diastereomers of 5'-S-phosphorodithioate dithymidine analogs under treatment with calf spleen PDE. The new 5'-S-phosphorodithioate linkage was readily degraded by iodine solutions in the presence of water. It was also found that oligothymidylates containing a single 5'-S-phosphorodithioate linkage form much weaker duplexes with their complementary sequences.