Synthesis of classical, four-carbon bridged 5-substituted furo[2,3-d]pyrimidine and 6-substituted pyrrolo[2,3-d]pyrimidine analogues as antifolates

Green and efficient one-pot three-component synthesis of novel drug-like furo[2,3–d]pyrimidines as potential active site inhibitors and putative allosteric hotspots modulators of both SARS-CoV-2 MPro and PLPro

In this paper, an environmentally benign, convenient, and efficient one-pot three-component reaction has been developed for the regioselective synthesis of novel 5-aroyl(or heteroaroyl)-6-(alkylamino)-1,3-dimethylfuro[2,3-d]pyrimidine-2,4(1H,3H)-diones (4a‒n) through the sequential condensation of aryl(or heteroaryl)glyoxal monohydrates (1a‒g), 1,3-dimethylbarbituric acid (2), and alkyl(viz. cyclohexyl or tert-butyl)isocyanides (3a or 3b) catalyzed by ultra-low loading ZrOCl₂•8H₂O (just 2 mol%) in water at 50 ˚C. After synthesis and characterization of the mentioned furo[2,3-d]pyrimidines (4a‒n), their multi-targeting inhibitory properties were investigated against the active site and putative allosteric hotspots of both SARS-CoV-2 main protease (M^Pro) and papain-like protease (PL^Pro) based on molecular docking studies and compare the attained results with various medicinal compounds which approximately in three past years were used, introduced, and or repurposed to fight against COVID-19. Furthermore, drug-likeness properties of the mentioned small heterocyclic frameworks (4a‒n) have been explored using in silico ADMET analyses. Interestingly, the molecular docking studies and ADMET-related data revealed that the novel series of furo[2,3-d]pyrimidines (4a‒n), especially 5-(3,4-methylendioxybenzoyl)-6-(cyclohexylamino)-1,3-dimethylfuro[2,3-d]pyrimidine-2,4(1H,3H)-dione (4g) as hit one is potential COVID-19 drug candidate, can subject to further in vitro and in vivo studies. It is worthwhile to note that the protein-ligand-type molecular docking studies on the human body temperature-dependent M^Pro protein that surprisingly contains zinc^II (Zn^II) ion between His41/Cys145 catalytic dyad in the active site, which undoubtedly can make new plans for designing novel SARS-CoV-2 M^Pro inhibitors, is performed for the first time in this paper, to the best of our knowledge.

Biology and therapeutic applications of the proton-coupled folate transporter

INTRODUCTION

The proton-coupled folate transporter (PCFT; SLC46A1) was discovered in 2006 as the principal mechanism by which folates are absorbed in the intestine and the causal basis for hereditary folate malabsorption (HFM). In 2011, it was found that PCFT is highly expressed in many tumors. This stimulated interest in using PCFT for cytotoxic drug targeting, taking advantage of the substantial levels of PCFT transport and acidic pH conditions commonly associated with tumors.

AREAS COVERED

We summarize the literature from 2006 to 2022 that explores the role of PCFT in the intestinal absorption of dietary folates and its role in HFM and as a transporter of folates and antifolates such as pemetrexed (Alimta) in relation to cancer. We provide the rationale for the discovery of a new generation of targeted pyrrolo[2,3-d]pyrimidine antifolates with selective PCFT transport and inhibitory activity toward de novo purine biosynthesis in solid tumors. We summarize the benefits of this approach to cancer therapy and exciting new developments in the structural biology of PCFT and its potential to foster refinement of active structures of PCFT-targeted anti-cancer drugs.

EXPERT OPINION

We summarize the promising future and potential challenges of implementing PCFT-targeted therapeutics for HFM and a variety of cancers.

One-pot synthesis of highly substituted poly(furopyrimidine)s via catalyst-free multicomponent polymerizations of diisocyanides, N,N′-dimethylbarbituric acid, and dialdehyde

In this work, the catalyst-free multicomponent polymerizations of diisocyanides, N,N′-dimethylbarbituric acid, and dialdehyde for highly substituted poly(furopyrimidine)s has been achieved. All the experimental conditions such as polymerization solvents, temperature and time were investigated in detail. Through the systematic optimization of the polymerization conditions, the obtained polymers could have molecular weights of up to 16 400 g mol⁻¹, and excellent yields (up to 84%) can be achieved. All the polymers were well characterized by gel permeation chromatography (GPC), nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy. The thermal properties of the polymers were investigated and the decomposition temperature (T_d, 5%) was 277 °C.

In this work, the catalyst-free multicomponent polymerizations of diisocyanides, N,N′-dimethylbarbituric acid, and dialdehyde for highly substituted poly(furopyrimidine)s has been achieved.

An efficient diastereoselective synthesis of novel fused 5H-furo[2,3-d]thiazolo[3,2-a]pyrimidin-5-ones via one-pot three-component reaction

Herein, a convenient and efficient synthesis of 7-benzoyl-6-(aryl)-6,7-dihydro-5H-furo[2,3-d]thiazolo[3,2-a]pyrimidin-5-one derivatives was achieved from the reaction of isoquinolinium N-ylides, aromatic aldehydes, and heterocyclic 1,3-dicarbonyl compounds via one-pot three-component diastereoselective domino reaction in good-to-excellent yields. The advantages of this protocol are easily available starting materials, operational simplicity, and avoidance of hazardous organic solvents and catalyst. The synthesized products were characterized by IR, ¹H NMR, ¹³C NMR and mass spectra. Additionally, the conclusive structure of target compounds was confirmed by X-Ray diffraction analysis.

Crystal structure of 2-(2-(6-methylpyridin-2-yl)naphthalen-1-yl)pyrimidine, C20H15N3

C20H15N3, orthorhombic, Pbca (no. 61), a = 11.0487(4) Å, b = 13.5000(6) Å, c = 21.1032(10) Å, V = 3147.7(2) Å3, Z = 8, R gt(F) = 0.0448, wR ref(F 2) = 0.1136, T = 293(2) K.

The promise and challenges of exploiting the proton-coupled folate transporter for selective therapeutic targeting of cancer

This review considers the "promise" of exploiting the proton-coupled folate transporter (PCFT) for selective therapeutic targeting of cancer. PCFT was discovered in 2006 and was identified as the principal folate transporter involved in the intestinal absorption of dietary folates. The recognition that PCFT was highly expressed in many tumors stimulated substantial interest in using PCFT for cytotoxic drug targeting, taking advantage of its high level transport activity under the acidic pH conditions that characterize many tumors. For pemetrexed, among the best PCFT substrates, transport by PCFT establishes its importance as a clinically important transporter in malignant pleural mesothelioma and non-small cell lung cancer. In recent years, the notion of PCFT-targeting has been extended to a new generation of tumor-targeted 6-substituted pyrrolo[2,3-d]pyrimidine compounds that are structurally and functionally distinct from pemetrexed, and that exhibit near exclusive transport by PCFT and potent inhibition of de novo purine nucleotide biosynthesis. Based on compelling preclinical evidence in a wide range of human tumor models, it is now time to advance the most optimized PCFT-targeted agents with the best balance of PCFT transport specificity and potent antitumor efficacy to the clinic to validate this novel paradigm of highly selective tumor targeting.

Synthesis of Trans-6-(4-Chlorobenzoyl)-7-(Aryl)-1,3-Dimethyl-6,7-Dihydrofuro[3,2-d]Pyrimidine-2,4-Diones Using Choline Hydroxide as an Efficient Catalyst in an Aqueous Medium

A green and efficient synthesis of the trans-6-(4-chlorobenzoyl)-7-(aryl)-1,3-dimethyl-6,7-dihydrofuro[3,2-d]pyrimidine-2,4-diones has been achieved via a three-component, one-pot condensation of 2-[2-(4-chlorophenyl)-2-oxoethyl)]isoquinolinium bromide with 1,3-dimethylbarbituric acid and an aromatic aldehyde in the presence of catalytic amounts of choline hydroxide in water under reflux conditions. This gives trans-6-(4-chlorobenzoyl)-7-(aryl)-1,3-dimethyl-6,7-dihydrofuro[3,2-d]pyrimidine-2,4-diones in excellent yield and in short reaction times.

Synthesis and Antioxidant Properties of Novel Pyrimidine-Containing Heterocycles

4-(Benzo[ d][1,3]dioxol-5-yl)-2-hydrazinyl-6-oxo-1,6-dihydropyrimidine-5-carbonitrile was utilised to construct fused heterocyclic systems, namely triazolopyrimidines, as well as non-fused heterocyclic systems such as pyrazole and dioxopyrazolidine derivatives. The antioxidant activity of the new compounds was evaluated. Most of the synthesised compounds have potent antioxidant activity.

Stereoselective synthesis of medicinally relevant furo[2,3-d]pyrimidine framework by thermal rearrangement of spirocyclic barbiturates

The thermally initiated transformation of substituted spirocyclic barbiturates in DMSO at 100 °C results in the stereoselective formation of medicinally relevant furo[2,3-d]pyrimidines in 50–75% yields.

First synthesis of unexpected functionalized trifluoromethylated 8-oxa-2,4-diazaspiro[5.5]undecanes via one-pot MCRs

The present study describes the first example of the synthesis of functionalized trifluoromethylated 8-oxa-2,4-diazaspiro[5.5]undecanes via one-pot MCRs.

The human proton-coupled folate transporter: Biology and therapeutic applications to cancer

This review summarizes the biology of the proton-coupled folate transporter (PCFT). PCFT was identified in 2006 as the primary transporter for intestinal absorption of dietary folates, as mutations in PCFT are causal in hereditary folate malabsorption (HFM) syndrome. Since 2006, there have been major advances in understanding the mechanistic roles of critical amino acids and/or domains in the PCFT protein, many of which were identified as mutated in HFM patients, and in characterizing transcriptional control of the human PCFT gene. With the recognition that PCFT is abundantly expressed in human tumors and is active at pHs characterizing the tumor microenvironment, attention turned to exploiting PCFT for delivering novel cytotoxic antifolates for solid tumors. The finding that pemetrexed is an excellent PCFT substrate explains its demonstrated clinical efficacy for mesothelioma and non-small cell lung cancer, and prompted development of more PCFT-selective tumor-targeted 6-substituted pyrrolo[2,3-d]pyrimidine antifolates that derive their cytotoxic effects by targeting de novo purine nucleotide biosynthesis.

Dihydrofolate reductase as a therapeutic target for infectious diseases: opportunities and challenges

Infectious diseases caused by parasites continue to take a massive toll on human health in the poor regions of the world. Filling the anti-infective drug-discovery pipeline has never been as challenging as it is now. The organisms responsible for these diseases have interesting biology with many potential biochemical targets. Inhibition of metabolic enzymes has been established as an attractive strategy for anti-infectious drug development. In this field, dihydrofolate reductase (DHFR) is an important enzyme in nucleic and amino acid synthesis and an extensively studied drug target over the past 50 years. The challenges for novel DHFR inhibition-based chemotherapeutics for the treatment of infectious diseases are now focused on overcoming the resistance problem as well as cost–effectiveness. Each year, the large number of literature citations attest the continued popularity of DHFR. It becomes truly the ‘enzyme of choice for all seasons and almost all reasons’. Herein, we summarize the opportunities and challenges in developing novel lead based on this target.

4,5,8a-Triphenyl-perhydro-pyrimido[4,5-d]pyrimidine-2,7-dione monohydrate

The title compound, C₂₄H₂₂N₄O₂·H₂O, was synthesized by the trimethyl­chloro­silane-catalysed reaction between urea, benzaldehyde and acetophenone. The organic mol­ecule comprises two fused tetra­hydro­pyrimidinone rings with phenyl substituents at the 4- and 5-positions on the tetra­hydro­pyrimidinone rings and a third phenyl substituent at the ring junction 8-position. The 4- and 5-substituted phenyl rings are inclined at a dihedral angle of 22.72 (11)° to one another and make angles of 47.95 (7) and 65.76 (7)° with the third phenyl substituent. In the crystal structure, inter­molecular N—H⋯O contacts link pyrimido[4,5-d]pyrimidine mol­ecules into centrosymmetric dimers. Additional N—H⋯O and O—H⋯O hydrogen bonds involving the water mol­ecule generate a three-dimensional network.

Diversity oriented syntheses of fused pyrimidines designed as potential antifolates

Diversity oriented syntheses of some furo[2,3-d]pyrimidines and pyrrolo[2,3-d]pyrimidines related to folate, guanine, and diaminopyrimidine-containing drugs have been developed for the preparation of potential anti-infective and anticancer compounds. Amide couplings and Suzuki couplings on the basic heterocyclic templates were used, in the latter case yields being especially high using aromatic trifluoroborates as the coupling partner. A new ring synthesis of 6-aryl-substituted deazaguanines bearing 2-alkylthio groups has been developed using Michael addition of substituted nitrostyrenes. Diversity at C-2 has been introduced by oxidation and substitution with a range of amino nucleophiles. The chemical reactivity of these pyrrolopyrimidines with respect to both electrophilic substitution in ring synthesis and nucleophilic substitution for diversity is discussed. Several compounds were found to inhibit pteridine reductases from the protozoan parasites Trypanosoma brucei and Leishmania major at the micromolar level and to inhibit the growth of Trypanosma brucei brucei in cell culture at higher concentrations. From these results, significant structural features required for inhibition of this important drug target enzyme have been identified.

Synthesis and discovery of high affinity folate receptor-specific glycinamide ribonucleotide formyltransferase inhibitors with antitumor activity

6-Substituted classical pyrrolo[2,3-d]pyrimidine antifolates with a three- to six-carbon bridge between the heterocycle and the benzoyl-L-glutamate (compounds 2-5, respectively) were synthesized starting from methyl 4-formylbenzoate and a Wittig reaction with the appropriate triphenylphosphonium bromide, followed by reduction and conversion to the alpha-bromomethylketones. Cyclocondensation of 2,4-diamino-4-oxopyrimidine with the alpha-bromoketones, coupling with diethyl-L-glutamate, and saponification afforded 2-5. Compounds 2-5 had negligible substrate activity for RFC but showed variably potent (nanomolar) and selective inhibitory activities toward Chinese hamster ovary cells that expressed FRalpha or FRbeta and toward FRalpha-expressing KB and IGROV1 human tumor cells. Inhibition of KB cell colony formation was also observed. Glycinamide ribonucleotide formyl transferase (GARFTase) was identified as the primary intracellular target of the pyrrolo[2,3-d]pyrimidines. The combined properties of selective FR targeting, lack of RFC transport, and GARFTase inhibition resulting in potent antitumor activity are unprecedented and warrant development of these analogues as antitumor agents.

Synthesis and activity of novel 5-substituted pyrrolo[2,3-d]pyrimidine analogues as pp60(c-Src) tyrosine kinase inhibitors

Therapy with receptor tyrosine kinase inhibitors provides an improved treatment option in a number of diseases such as cancer, myocardial infection, osteoporosis, stroke, and neurodegeneration. We have designed, synthesized, and evaluated a series of novel 2-amino-5-[(benzyl)imino]methyl-3,7-dihydro-4H-pyrrolo[2,3-d]pyrimidine-4-one 7a and 2-amino-5-[(substituted-benzyl)imino]methyl-3,7-dihydro-4H-pyrrolo[2,3-d]pyrimidine-4-one 7b-e derivatives as potential tyrosine kinase inhibitors. These compounds were synthesized by condensation reaction using 2-tritylamino-4-oxo-4,7-dihydro-3H-pyrrolo[2,3-d]pyrimidine-5-carbaldehyde 5 and appropriate benzylamines followed by detritylation. Compounds were evaluated for their inhibitory activity toward tyrosine phosphorylation for the pp60c-Src tyrosine kinase. Compounds 7a, 7d, and 7e demonstrated potent inhibitory activities against pp60c-Src tyrosine kinase with IC50 values of 13.9, 34.5, and 78.4 microM, respectively. Dihalogenated compounds 7d and 7e have 3 to 7-times lower IC50 values than that of the parent compound 7a.

Discovery of novel antitumor antimitotic agents that also reverse tumor resistance

We have discovered a novel series of 7-benzyl-4-methyl-5-[(2-substituted phenyl)ethyl]-7H-pyrrolo[2,3-d]pyrimidin-2-amines, which possess antimitotic and antitumor activities against antimitotic-sensitive as well as resistant tumor cells. These agents bind to a site on tubulin that is distinct from the colchicine, vinca alkaloid, and paclitaxel binding sites and some, in addition to their antitumor activity, remarkably also reverse tumor resistance to antimitotic agents mediated via the P-glycoprotein efflux pump. The compounds were synthesized from N-(7-benzyl-5-ethynyl-4-methyl-7H-pyrrolo[2,3-d]pyrimidin-2-yl)-2,2-dimethylpropanamide 11 or the corresponding 5-iodo analog 14 via Sonogashira couplings with appropriate iodobenzenes or phenylacetylene followed by reduction and deprotection to afford the target analogs. Sodium and liquid NH3 afforded the debenzylated analogs. The most potent analog 1 was one to three digit nanomolar against the growth of both sensitive and resistant tumor cells in culture. Compounds of this series are promising novel antimitotic agents that have the potential for treating both sensitive and resistant tumors.

Shaken not stirred: A facile synthesis of 1,4-bis(furo[2,3-d]-pyrimidine-2,4(1H,3H)-dione-5-yl)benzenes by one-pot reaction of isocyanides, N,N′-dimethylbarbituric acid, and terephthaldialdehyde

A simple and efficient synthesis of 1,4-bis(furo[2,3-d]pyrimidine-2,4(1H,3H)-dione-5-yl)benzene derivatives was achieved via a one-pot three-component reaction of isocyanides, N,N'-dimethylbarbituric acid, and terephthaldialdehyde in DMF at room temperature for 30 min. These improved reaction conditions allow the preparation of highly substituted furopyrimidinones in high yields and purity under mild reaction conditions.