Synthesis of new 2,4-Diaminopyrido[2,3-d]pyrimidine and 2,4-Diaminopyrrolo[2,3-d]pyrimidine inhibitors of Pneumocystis carinii, Toxoplasma gondii, and Mycobacterium avium dihydrofolate reductase

TaqMan-quantitative PCR assays applied in Neospora caninum knock-outs generated through CRISPR-Cas9 allow to determine the copy numbers of integrated dihydrofolate reductase-thymidylate synthase drug selectable markers

As for many other organisms, CRISPR-Cas9 mediated genetic modification has gained increasing importance for the identification of vaccine candidates and drug targets in Neospora caninum, an apicomplexan parasite causing abortion in cattle and neuromuscular disease in dogs. A widely used approach for generating knock-out (KO) strains devoid of virulence factors is the integration of a drug selectable marker such as mutated dihydrofolate reductase-thymidylate synthase (mdhfr-ts) into the target gene, thus preventing the synthesis of respective protein and mediating resistance to pyrimethamine. However, CRISPR-Cas9 mutagenesis is not free of off-target effects, which can lead to integration of multiple mdhfr-ts copies into other sites of the genome. To determine the number of integrated mdhfr-ts in N. caninum, a duplex quantitative TaqMan PCR was developed. For this purpose, primers were designed that amplifies a 106 bp fragment from wild-type (WT) parasites corresponding to the single copy wtdhfrs-ts gene, as well as the mutated mdhfrs-ts present in KO parasites that confers resistance and were used simultaneously with primers amplifying the diagnostic NC5 gene. Thus, the dhfr-ts to NC5 ratio should be approximately 1 in WT parasites, while in KO parasites with a single integrated mdhrf-ts gene this ratio is doubled, and in case of multiple integration events even higher. This approach was applied to the Neospora KO strains NcΔGRA7 and NcΔROP40. For NcΔGRA7, the number of tachyzoites determined by dhfr-ts quantification was twice the number of tachyzoites determined by NC5 quantification, thus indicating that only one mdhfr-ts copy was integrated. The results obtained with the NcΔROP40 strain, however, showed that the number of dhfr-ts copies per genome was substantially higher, indicating that at least three copies of the selectable mdhfr-ts marker were integrated into the genomic DNA during gene editing by CRISPR-Cas9. This duplex TaqMan-qPCR provides a reliable and easy-to-use tool for assessing CRISPR-Cas9 mediated mutagenesis in WT N. caninum strains.

DMSO-DCE Triggered Chemodivergent C-Methylenation of Electron-Rich Arenes: An Easy Access to Diarylmethanes

The chemodivergent property of dimethyl sulfoxide (DMSO) along with 1,2-dichloroethane (DCE) was exploited for the incorporation of a methylene group to form diarylmethanes through a dearomatization/rearomatization process. Methyl(methylene)sulfonium ions (CH2=S+-Me) were generated by simple heating of commonly used solvents such as DMSO and DCE. These ions were subsequently trapped by electron-rich arenes and heteroarenes, resulting in the synthesis of both symmetrical and unsymmetrical diarylmethanes. This protocol was further extended to access N-methylenamides by reacting 2-naphthol with amides or nitriles in the presence of DMSO and DCE.

Supramolecular interactions in some organic hydrated 2,4,6-triaminopyrimidinium carboxylate and sulfate salts

Four salts, namely, 2,4,6-triaminopyrimidinium 6-chloronicotinate dihydrate, C4H8N5+·C6H3ClNO2-·2H2O, (I), 2,4,6-triaminopyrimidinediium pyridine-2,6-dicarboxylate dihydrate, C4H9N52+·C7H3NO42-·2H2O, (II), 2,4,6-triaminopyrimidinediium sulfate monohydrate, C4H9N52+·SO42-·H2O, (III), and 2,4,6-triaminopyrimidinium 3,5-dinitrobenzoate dihydrate, C4H8N5+·C7H3N2O6-·2H2O, (IV), were synthesized and characterized by X-ray diffraction techniques. Proton transfer from the corresponding acid to the pyrimidine base has occurred in all four crystal structures. Of the four salts, two [(I) and (IV)] exist as monoprotonated bases and two [(II) and (III)] exist as diprotonated bases. In all four crystal structures, the acid interacts with the pyrimidine base through N-H...O hydrogen bonds, generating an R22(8) ring motif. The sulfate group mimics the role of the carboxylate anions. The water molecules present in compounds (I)-(IV) form water-mediated large ring motifs. The formation of water-mediated interactions in these crystal structures can be used as a model in the study of the hydration of nucleobases. Water molecules play an important role in building supramolecular structures. In addition to these strong hydrogen-bonding interactions, some of the crystal structures are further enriched by aromatic π-π stacking interactions [(I) and (II)].

Supramolecular interactions in salts/cocrystals involving pyrimidine derivatives of sulfonate/carboxylic acid

The crystal structures of three compounds involving aminopyrimidine derivatives are reported, namely, 5-fluorocytosinium sulfanilate-5-fluorocytosine-4-azaniumylbenzene-1-sulfonate (1/1/1), C₄H₅FN₃O⁺·C₆H₆NO₃S^-·C₄H₄FN₃O·C₆H₇NO₃S, I, 5-fluorocytosine-indole-3-propionic acid (1/1), C₄H₄FN₃O·C₁₁H₁₁NO₂, II, and 2,4,6-triaminopyrimidinium 3-nitrobenzoate, C₄H₈N₅⁺·C₇H₄NO₄^-, III, which have been synthesized and characterized by single-crystal X-ray diffraction. In I, there are two 5-fluorocytosine (5FC) molecules (5FC-A and 5FC-B) in the asymmetric unit, with one of the protons disordered between them. 5FC-A and 5FC-B are linked by triple hydrogen bonds, generating two fused rings [two R₂²(8) ring motifs]. The 5FC-A molecules form a self-complementary base pair [R₂²(8) ring motif] via a pair of N-H...O hydrogen bonds and the 5FC-B molecules form a similar complementary base pair [R₂²(8) ring motif]. The combination of these two types of pairing generates a supramolecular ribbon. The 5FC molecules are further hydrogen bonded to the sulfanilate anions and sulfanilic acid molecules via N-H...O hydrogen bonds, generating R₄⁴(22) and R⁶₆(36) ring motifs. In cocrystal II, two types of base pairs (homosynthons) are observed via a pair of N-H...O/N-H...N hydrogen bonds, generating R₂²(8) ring motifs. The first type of base pair is formed by the interaction of an N-H group and the carbonyl O atom of 5FC molecules through a couple of N-H...O hydrogen bonds. Another type of base pair is formed via the amino group and a pyrimidine ring N atom of the 5FC molecules through a pair of N-H...N hydrogen bonds. The base pairs (via N-H...N hydrogen bonds) are further bridged by the carboxyl OH group of indole-3-propionic acid and the O atom of 5FC through O-H...O hydrogen bonds on either side of the R₂²(8) motif. This leads to a DDAA array. In salt III, one of the N atoms of the pyrimidine ring is protonated and interacts with the carboxylate group of the anion through N-H...O hydrogen bonds, leading to the primary ring motif R₂²(8). Furthermore, the 2,4,6-triaminopyrimidinium (TAP) cations form base pairs [R₂²(8) homosynthon] via N-H...N hydrogen bonds. A carboxylate O atom of the 3-nitrobenzoate anion bridges two of the amino groups on either side of the paired TAP cations to form another ring [R₃²(8)]. This leads to the generation of a quadruple DADA array. The crystal structures are further stabilized by π-π stacking (I and III), C-H...π (I and II), C-F...π (I) and C-O...π (II) interactions.

Synthesis and anti-Toxoplasma activity of indole-triazole compounds on tachyzoites of RH strain

Background

Conventional treatment for toxoplasmosis have severe side effects and the inability to completely eradicate the disease. Therefore, the acquisition of new anti-Toxoplasma drugs has always been of interest among researchers. In the present study, we prepare a new indole-triazole derivatives and evaluated their potential anti-parasitic activity against tachyzoites of Toxoplasma RH strain.

Materials and methods

In this study, after synthesis of the two new compounds of indole-triazole, the effect of their different concentrations (2–1024 μg/ml) were determined on Toxoplasma tachyzoites using flow cytometry. Furthermore, tachyzoites were exposed to different concentrations of compounds (4, 16, 64, 265, 1024 μg/ml) for 1.5 h and their infectivity were evaluated in BALB/c mice.

Results

The flow cytometry results indicated the benzyl derivative of indole-triazole in various concentrations had a lethal effect on tachyzoites between 11.93% and 89.66%, while the naphthalene derivative had a lethality of 26.63%–66.82%. The infectivity analysis showed that the survival time of mice at concentrations of 1024 μg/ml and 512 μg/ml of benzyl derivatives was significantly increased (P = 0.008 and P = 0.016, respectively), compared to that in the negative control group. Furthermore, survival time of mice was statistically significant at the concentration of 1024 μg/ml for naphthyl derivative (P = 0.012).

Conclusion

Findings of the current study suggested indole triazole compounds, based on their structure and enzymes targeting, have a considerable effect on tachyzoites of T. gondii RH strain and can be considered as a new anti-Toxoplasma agent.

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The Benzyl and Naphtyl derivatives of Indol-triazol have dose dependently effect on tachyzoites of T.gondii RH strain.

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The placement of naphthyl next to indole-triazole have dose dependently effects on Toxoplasma tachyzoites.

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The benzyl derivative of Indole triazole showed an ability of over 80% in eliminating Toxoplasma tachyzoites.

Selectfluor facilitated bridging of indoles to bis(indolyl)methanes using methyl tert-butyl ether as a new methylene precursor

A novel, green and efficient method is developed for the synthesis of methylene bridged bis(indolyl)methanes in good to excellent yields. The reaction employs methyl tert-butyl ether (MTBE) as the methylene source and selectfluor as an oxidizing agent. The scope and versatility of the methods have been successfully demonstrated with 48 examples. The metal-free transformation process is suitable for scale-up production. A selectfluor-promoted oxidative reaction mechanism is proposed based on the results of the experimental studies.

Recent Design and Structure-Activity Relationship Studies on the Modifications of DHFR Inhibitors as Anticancer Agents

BACKGROUND

Dihydrofolate reductase (DHFR) has been known for decades as a molecular target for antibacterial, antifungal and anti-malarial treatments. This enzyme is becoming increasingly important in the design of new anticancer drugs, which is confirmed by numerous studies including modelling, synthesis and in vitro biological research. This review aims to present and discuss some remarkable recent advances in the research of new DHFR inhibitors with potential anticancer activity.

METHODS

The scientific literature of the last decade on the different types of DHFR inhibitors has been searched. The studies on design, synthesis and investigation structure-activity relationships were summarized and divided into several subsections depending on the leading molecule and its structural modification. Various methods of synthesis, potential anticancer activity and possible practical applications as DHFR inhibitors of new chemical compounds were described and discussed.

RESULTS

This review presents the current state of knowledge on the modification of known DHFR inhibitors and the structures and searches for about eighty new molecules, designed as potential anticancer drugs. In addition, DHFR inhibitors acting on thymidylate synthase (TS), carbon anhydrase (CA) and even DNA-binding are presented in this paper.

CONCLUSION

Thorough physicochemical characterization and biological investigations highlight the structure-activity relationship of DHFR inhibitors. This will enable even better design and synthesis of active compounds, which would have the expected mechanism of action and the desired activity.

Trimethoprim and other nonclassical antifolates an excellent template for searching modifications of dihydrofolate reductase enzyme inhibitors

The development of new mechanisms of resistance among pathogens, the occurrence and transmission of genes responsible for antibiotic insensitivity, as well as cancer diseases have been a serious clinical problem around the world for over 50 years. Therefore, intense searching of new leading structures and active substances, which may be used as new drugs, especially against strain resistant to all available therapeutics, is very important. Dihydrofolate reductase (DHFR) has attracted a lot of attention as a molecular target for bacterial resistance over several decades, resulting in a number of useful agents. Trimethoprim (TMP), (2,4-diamino-5-(3′,4′,5′-trimethoxybenzyl)pyrimidine) is the well-known dihydrofolate reductase inhibitor and one of the standard antibiotics used in urinary tract infections (UTIs). This review highlights advances in design, synthesis, and biological evaluations in structural modifications of TMP as DHFR inhibitors. In addition, this report presents the differences in the active site of human and pathogen DHFR. Moreover, an excellent review of DHFR inhibition and their relevance to antimicrobial and parasitic chemotherapy was presented.

Synthesis of 1,1'-Diarylethanes and Related Systems by Displacement of Trichloroacetimidates with Trimethylaluminum

Benzylic trichloroacetimidates are readily displaced by trimethylaluminum under Lewis acid promoted conditions to provide the corresponding methyl substitution product. This method is a convenient way to access 1,1'-diarylethanes and related systems, which play a significant role in medicinal chemistry, with a number of systems owing their biological activity to this functionality. Most benzylic substrates undergo ready displacement, with electron deficient systems being the exception. The use of an enantiopure imidate showed significant racemization, implicating the formation of a cationic intermediate.

Host and Toxoplasma gondii genetic and non-genetic factors influencing the development of ocular toxoplasmosis: A systematic review

Toxoplasmosis is a cosmopolitan infection caused by the apicomplexan parasite Toxoplasma gondii. This infectious disease is widely distributed across the world where cats play an important role in its spread. The symptomatology caused by this parasite is diverse but the ocular affectation emerges as the most important clinical phenotype. Therefore, we conducted a systematic review of the current knowledge of ocular toxoplasmosis from the genetic diversity of the pathogen towards the treatment available for this infection. This review represents an update to the scientific community regarding the genetic diversity of the parasite, the genetic factors of the host, the molecular pathogenesis and its association with disease, the available diagnostic tools and the available treatment of patients undergoing ocular toxoplamosis. This review will be an update for the scientific community in order to encourage researchers to deploy cutting-edge investigation across this field.

Organocatalytic domino Knöevenagel–Michael reaction in water for the regioselective synthesis of benzo[4,5]imidazo[1,2-a]pyrimidines and pyrido[2,3-d]pyrimidin-2-amines

An organocatalyzed aqueous media domino reaction is developed for the regioselective synthesis of benzo[4,5]imidazo[1,2-a]pyrimidines and pyrido[2,3-d]pyrimidin-2-amines.

Palladium NPs supported on novel imino-pyridine-functionalized MWCNTs: efficient and highly reusable catalysts for the Suzuki–Miyaura and Sonogashira coupling reactions

In this article a new heterogeneous nanocatalyst based on palladium supported on functionalized multi-walled carbon nanotubes (MWCNTs) has been introduced.

Triazole-based compound as a candidate to develop novel medicines to treat toxoplasmosis

This article reports anti-Toxoplasma gondii activity of 3-(thiophen-2-yl)-1,2,4-triazole-5-thione. The compound displayed significant and reproducible antiparasitic effects at nontoxic concentrations for the host cells, with an experimentally determined 50% inhibitory concentration (IC50) at least 30 times better than that of the known chemotherapeutic agent sulfadiazine. Purine nucleoside phosphorylase was defined as the probable target for anti-Toxoplasma activity of the tested compound. These results provide the foundation for future work to develop a new class of medicines to better treat toxoplasmosis.

1,4-Disubstituted thiosemicarbazide derivatives are potent inhibitors of Toxoplasma gondii proliferation

A series of 4-arylthiosemicarbazides substituted at the N1 position with a 5-membered heteroaryl ring was synthesized and evaluated in vitro for T. gondii inhibition proliferation and host cell cytotoxicity. At non-toxic concentrations for the host cells all studied compounds displayed excellent anti-parasitic effects when compared to sulfadiazine, indicating a high selectivity of their anti-T. gondii activity. The differences in bioactivity investigated by DFT calculations suggest that the inhibitory activity of 4-aryl-thiosemicarbazides towards T. gondii proliferation is connected with the electronic structure of the molecule. Further, these compounds were tested as potential antibacterial agents. No growth-inhibiting effect on any of the test microorganisms was observed for all the compounds, even at high concentrations.

Cu-Catalyzed Suzuki–Miyaura reactions of primary and secondary benzyl halides with arylboronates

A copper-catalyzed coupling of arylboronates with primary and secondary benzyl halides with β hydrogens or steric hindrance is described.

Antimicrobial Dihydrofolate Reductase Inhibitors - Achievements and Future Options: Review

Despite all progress made in the fight against infections caused by bacteria, fungi, protozoa or viruses, there is a need for more and new active agents. Intensive efforts are currently directed against many new and attractive targets, and are hoped to result in new useful agents. The opportunities offered by some known and validated targets are, however, by far not exhausted. Dihydrofolate reductase (DHFR, EC 1.5.1.3) attracted much attention over several decades, which yielded several useful agents. There are excellent chances for new drugs in this field, and they are thought to increase by limiting the spectrum of activity. Whereas trimethoprim seems to present the optimum which can be achieved for a broad spectrum antibacterial agent, specific agents could probably be designed for well defined groups or specific organisms, such as staphylococci among the bacteria, or for a number of parasites, such as Plasmodium falciparum, the fungus Pneumocystis carinii, and several protozoa, such as Trypanosoma, Toxoplasma, and others. This would even extend to herbicides or specific plant pathogens. Achievements and current efforts directed against new DHFR-inhibitors are reviewed, considering only the most recent literature.

Design, synthesis, and molecular modeling of novel pyrido[2,3-d]pyrimidine analogues as antifolates; application of Buchwald-Hartwig aminations of heterocycles

Opportunistic infections caused by Pneumocystis jirovecii (P. jirovecii, pj), Toxoplasma gondii (T. gondii, tg), and Mycobacterium avium (M. avium, ma) are the principal causes of morbidity and mortality in patients with acquired immunodeficiency syndrome (AIDS). The absence of any animal models for human Pneumocystis jirovecii pneumonia and the lack of crystal structures of pjDHFR and tgDHFR make the design of inhibitors challenging. A novel series of pyrido[2,3-d]pyrimidines as selective and potent DHFR inhibitors against these opportunistic infections are presented. Buchwald-Hartwig coupling reaction of substituted anilines with pivaloyl protected 2,4-diamino-6-bromo-pyrido[2,3-d]pyrimidine was successfully explored to synthesize these analogues. Compound 26 was the most selective inhibitor with excellent potency against pjDHFR. Molecular modeling studies with a pjDHFR homology model explained the potency and selectivity of 26. Structural data are also reported for 26 with pcDHFR and 16 and 22 with variants of pcDHFR.

Dihydrofolate reductase inhibitors: developments in antiparasitic chemotherapy

BACKGROUND

Infections caused by parasitic protozoa present a growing health concern, particularly in developing parts of the world. Although malaria is clearly the most well-known and deadly of these diseases, infections caused by other parasites, such as Toxoplasma, Cryptosporidia and Trypanosoma are emerging infectious threats. The success of inhibitors of the enzyme dihydrofolate reductase (DHFR) against malaria has encouraged further exploration of this strategy against other parasites.

OBJECTIVE

This review presents antifolate inhibitors that have appeared in the patent literature and elaborates on their potency and selectivity against the DHFR enzyme from parasitic protozoa.

METHODS

The patent literature since 1994 was surveyed for antiparasitic DHFR inhibitors.

RESULTS/CONCLUSIONS

Over the past several years, there have been a variety of novel, potent and selective inhibitors disclosed in patents, primarily from academic researchers. This review summarizes the recent development of antifolates as specific agents against parasitic protozoa.

Synthesis, Characterisation and Bioactivity of Polysubstituted 1-(4-(1H-Pyrrol-1-yl)Phenyl)-1H-Pyrrole Derivatives

1,4-Phenylenediamine reacted readily with chloroacetone to give 1,4-bis[(2-oxopropyl)amino]benzene which was used to prepare 1-(4-(1H-pyrrol-1-yl)phenyl)-1H-pyrrole derivatives in a one pot reaction with dimethylformamide dimethylacetal or triethyl orthoformate and an active methylene nitrile, an active methylene ketone or an ylidene-malononitrile. Reaction of 1,4-bis[(2-oxopropyl)amino]benzene with arene diazonium salts afforded the hydrazone derivatives which readily cyclised when reacted with malononitrile to give bispyrrole derivatives. The antibacterial activity of some of the products was determined.

Electrochemical behavior and voltammetric determination of 2,4,6-triaminopyrimidine at glassy carbon electrode modified with multi-walled carbon nanotubes/nafion

A multi-wall carbon nanotubes (MWCNTs) composite with Nafion was modified on a glass carbon electrode. The modified electrode was then used as a voltammetric sensor in detecting 2,4,6-triaminopyrimidine (TAP). The surface morphology of the Nafion/MWCNTs composite film was characterized by atomic force microscopy (AFM), and the electrochemical behavior of TAP at this sensor was investigated in detail. The results indicated that the Nafion/MWCNTs modified electrode exhibited efficient electrocatalytic oxidation for TAP with relatively high sensitivity, stability and lifetime. Under the optimized condition using linear sweep voltammetry (LSV), the Nafion/MWCNTs modified electrode exhibited a linear voltammetric response for TAP in the concentration range of 2.0 × 10(-7) to 3.6 × 10(-5) mol L(-1), with a detection limit of 5.0 × 10(-8) mol L(-1). The electrode was applied to detect TAP added to human blood serum, with an average recovery value of 101.3%.

Cross-couplings between benzylic and aryl halides "on water": synthesis of diarylmethanes

A remarkably simple entry to unsymmetrical diarylmethanes has been developed that relies on an in situ organozinc-mediated, palladium-catalyzed cross-coupling. Thus, by mixing a benzyl and aryl halide together in the presence of Zn metal and a Pd catalyst, diarylmethanes are formed at room temperature without assistance by a surfactant; hence, "on water".