Synthesis of Fluorinated Purine and 1-Deazapurine Glycosides as Potential Inhibitors of Adenosine Deaminase

Trifluoromethyl-β-dicarbonyls as Versatile Synthons in Synthesis of Heterocycles

Trifluoromethyl group relishes a privileged position in the realm of medicinal chemistry because its incorporation into organic molecules often enhances the bioactivity by altering pharmacological profile of molecule. Trifluoromethyl-β-dicarbonyls have emerged as pivotal building blocks in synthetic organic chemistry due to their facile accessibility, stability and remarkable versatility. Owing to presence of nucleophilic and electrophilic sites, they offer multifunctional sites for the reaction. This review covers a meticulous exploration of their multifaceted role, encompassing an in-depth analysis of mechanism, extensive scope, limitations and wide-ranging applications in diverse organic synthesis, covering the literature from the 21st century. This comprehensive review encapsulates the applications of trifluoromethyl-β-dicarbonyls and their synthetic equivalents as precursors of complex and diverse heterocyclic scaffolds, fused heterocycles and spirocyclic compounds having medicinal and material importance. Their potent synthetic utility in cyclocondensation reactions with binucleophiles, cycloaddition reactions, C-C bond formations, asymmetric multicomponent reactions using classical/solvent-free/catalytic synthesis have been presented. Influence of unsymmetrical trifluoromethyl-β-diketones on regioselectivity of transformation is also reviewed. This review will benefit the synthetic and pharmaceutical communities to explore trifluoromethyl-β-dicarbonyls as trifluoromethyl building blocks for fabrication of heterocyclic scaffolds having implementation into drug discovery programs in the imminent future.

A new route for the synthesis of 1-deazaguanine and 1-deazahypoxanthine

Imidazopyridines and pyrrolopyrimidines are an important class of compounds in medicinal chemistry. They can also be considered as deaza-modified purine nucleobases, and as such have attracted a lot of interest recently in the context of RNA atomic mutagenesis. In particular, for 1-deazaguanine (c1G base), a significant increase in demand is apparent. Synthetic access is challenging and the few reports found in the literature suffer from the requirement of hazardous intermediates and harsh reaction conditions. Here, we report a new six-step synthesis for c1G base, starting from 6-iodo-1-deazapurine. The key transformations are copper catalyzed C–O-bond formation followed by site-specific nitration. A further strength of our route is divergency, additionally enabling the synthesis of 1-deazahypoxanthine (c1I base).

Zinc enzymes in medicinal chemistry

In humans, more than three hundred diverse enzymes that require zinc as an essential cofactor have been identified. These zinc enzymes have demonstrated different and important physiological functions and some of them have been considered as valuable therapeutic targets for drug discovery. Indeed, many drugs targeting a few zinc enzymes have been marketed to treat a variety of diseases. This review discusses drug discovery and drug development based on a dozen of zinc enzymes, including their biological functions and pathogenic roles, their best in class inhibitors (and clinical trial data when available), coordination and binding modes of representative inhibitors, and their implications for further drug design. The opportunities and challenges in developing zinc enzyme inhibitors for the treatment of human disorders are highlighted, too.

Synthesis of Purines and Related Molecules by Cyclization ­Reactions of Heterocyclic Enamines

A great variety of pharmacologically relevant fluorinated purine analogues are available by cyclization reactions of heterocyclic enamines with 1,3-dielectrophiles. The reactions usually proceed with excellent regioselectivities. As electrophiles, 1,3-diketones, enaminones or 3-chloro-2-en-1-ones were used. Other synthetic strategies are based on inverse-electron-demand Diels–Alder reactions of heterocyclic enamines with triazines. Purine analogues were further functionalized by transition-metal-catalyzed CH-coupling reactions or oxidative cyclizations, giving rise to more complex polycyclic products. Amidino-C-glycosides in their reactions with 1,3-dielectrophiles afforded pyrimidine-C-glycosides. Multicomponent reactions of heterocyclic enamines afforded complex products, including spirocyclic derivatives.

1 Introduction

2 1,3-Diketones

3 Enaminones

4 3-Chloro-2-en-1-ones

5 Triazines

6 Transition-Metal-Catalyzed Functionalizations

7 Pyrimidine-C-Nucleosides

8 Multicomponent Reactions

9 Conclusions

Efficient Synthesis of Trifluoromethylated Purine Ribonucleosides and Ribonucleotides

The protocols presented in this article describe highly detailed synthesis of trifluoromethylated purine nucleotides and nucleosides (G and A). The procedure involves trifluoromethylation of properly protected (acetylated) nucleosides, followed by deprotection leading to key CF₃ -containing nucleosides. This gives synthetic access to 8-CF₃ -substituted guanosine derivatives and three adenosine derivatives (8-CF₃ , 2-CF₃ , and 2,8-diCF₃ ). In further steps, phosphorylation and phosphate elongation (for selected examples) result in respective trifluoromethylated nucleoside mono-, di-, and triphosphates. Support protocols are included for compound handling, purification procedures, analytical sample preparation, and analytical techniques used throughout the performance of the basic protocols. © 2020 Wiley Periodicals LLC. Basic Protocol 1: Synthesis of trifluoromethylated guanosine and adenosine derivatives Basic Protocol 2: Synthesis of trifluoromethylated guanosine and adenosine monophosphates Basic Protocol 3: Synthesis of phosphorimidazolides of ^8-CF3 GMP and ^8-CF3 AMP Basic Protocol 4: Synthesis of trifluoromethylated guanosine and adenosine oligophosphates Support Protocol 1: TLC sample preparation and analysis Support Protocol 2: Purification protocol for Basic Protocol 1 Support Protocol 3: HPLC analysis and preparative HPLC Support Protocol 4: Ion-exchange chromatography.

Floro-pyrazolo[3,4-d]pyrimidine derivative as a novel plant activator induces two-pathway immune system

Plants are known to develop a multi-faceted innate immune system for pathogenic defense. Systemic acquired resistance (SAR) and induced systemic resistance (ISR) are the two main pathways. Many chemical inducers known as plant activators that activate innate immunity to defend against pathogens have been discovered. Currently, the exploitation of new plant activators is mainly done to develop analogs of salicylic acid as SAR-signaling molecules; however, the ISR pathway is hardly investigated for new plant activators. Based on recent studies on 1-methyl pyrazolo [3,4-d]pyrimidine bioactivity and ATP-induced resistance to biotrophic and necrotrophic pathogens, a new lead compound, 1-methyl-4-amino-pyrazolo [3,4-d]pyrimidine, was obtained as a new scaffold of plant activators for possible inducing ISR immunity system. Additionally, fluorine atom plays an important role in the design and development of new pesticides due to the unique physical chemistry effect, a series of pyrazolo [3,4-d]pyrimidine derivatives were designed and synthesized. Several compounds showed good broad-spectrum induced resistance in vivo, but there was no direct antibacterial activity in vitro. Notably, the introduction of fluorine atom at the para-position of the benzene ring greatly enhanced the induction activity of P1d both involved in SAR and ISR pathways, which implied the inducing resistance both in defending pathogens and insects.

Reynoutria Japonica from Traditional Chinese Medicine: A Source of Competitive Adenosine Deaminase Inhibitors for Anticancer

BACKGROUND

Adenosine deaminase (ADA) is an important enzyme in purine metabolism and is known as a potential therapeutic target for the treatment of lymphoproliferative disorders and cancer. Traditional Chinese Herbal Medicine (TCHM) is widely used alone or in combination with chemotherapy to treat cancer, due to its ability to deliver a broad variety of bioactive secondary metabolites as promising sources of novel organic natural agents.

OBJECTIVE

In the present study, 29 varieties of medicinal plants were screened for the presence of ADA inhibitors.

RESULTS

Extracts from Reynoutria japonica, Glycyrrhiza uralensis, Lithospermum erythrorhizon, Magnolia officinalis, Gardenia jasminoides, Stephania tetrandra, Commiphora myrrha, Raphanus sativus and Corydalis yanhusuo demonstrated strong ADA inhibition with rates greater than 50%. However, Reynoutria japonica possessed the highest ADA inhibitory activity at 95.26% and so was used in our study for isolating the ADA inhibitor to be further studied. Eight compounds were obtained and their structures were identified. The compound H1 had strong ADA inhibitory activity and was deduced to be emodin by 1H and 13C-NMR spectroscopic analysis with an IC50 of 0.629 mM. The molecular docking data showed that emodin could bind tightly to the active site of ADA. Our results demonstrated that emodin displayed a new biological activity which is ADA inhibitory activity with high cytotoxic activity against K562 leukemia cells. The bioactivity of cordycepin was significantly increased when used in combination with emodin.

CONCLUSION

Emodin may represent a good candidate anti-cancer therapy and adenosine protective agent.

Synthesis of Trifluoromethylated Purine Ribonucleotides and Their Evaluation as 19F NMR Probes

Protected guanosine and adenosine ribonucleosides and guanine nucleotides are readily functionalized with CF₃ substituents within the nucleobase. Protected guanosine is trifluoromethylated at the C8 position under radical-generating conditions in up to 95% yield and guanosine 5'-oligophosphates in up to 35% yield. In the case of adenosine, the selectivity of trifluoromethylation depends heavily on the functional group protection strategy and leads to a set of CF₃-modified nucleosides with different substitution patterns (C8, C2, or both) in up to 37% yield. Further transformations based on phosphorimidazolide chemistry afford various CF₃-substituted mono- and dinucleoside oligophosphates in good yields. The utility of the trifluoromethylated nucleotides as probes for ¹⁹F NMR-based real-time enzymatic reaction monitoring is demonstrated with three different human nucleotide hydrolases (Fhit, DcpS, and cNIIIB). Substrate and product(s) resonances were sufficiently separated to enable effective tracking of each enzymatic activity of interest.

Adenosine deaminase inhibition

Adenosine deaminase is a critical enzyme in purine metabolism that regulates intra and extracellular adenosine concentrations by converting it to inosine. Adenosine is an important purine that regulates numerous physiological functions by interacting with its receptors. Adenosine and consequently adenosine deaminase can have pro or anti-inflammatory effects on tissues depending on how much time has passed from the start of the injury. In addition, an increase in adenosine deaminase activity has been reported for various diseases and the significant effect of deaminase inhibition on the clinical course of different diseases has been reported. However, the use of inhibitors is limited to only a few medical indications. Data on the increase of adenosine deaminase activity in different diseases and the impact of its inhibition in various cases have been collected and are discussed in this review. Overall, the evidence shows that many studies have been done to introduce inhibitors, however, in vivo studies have been much less than in vitro, and often have not been expanded for clinical use.

A new mixed inhibitor of adenosine deaminase produced by endophytic Cochliobolus sp. from medicinal plant seeds

Medicinal plants have been studied for potential endophytic interactions and numerous studies have provided evidence that seeds harbor diverse microbial communities, not only on their surfaces but also within the embryo. Adenosine deaminase (ADA) is known as a potential therapeutic target for the treatment of lymphoproliferative disorders and cancer. Therefore, in this study, 20 types of medicinal plant seeds were used to screen endophytic fungi with tissue homogenate and streak. In addition, 128 morphologically distinct endophyte strains were isolated and their ADA inhibitory activity determined by a spectrophotometric assay. The strain with the highest inhibitory activity was identified as Cochliobolus sp. Seven compounds were isolated from the strain using a chromatography method. Compound 3 showed the highest ADA inhibitory activity and was identified as 5-hydroxy-2-hydroxymethyl-4H-pyran-4-one, based on the results of 1H and 13C NMR spectroscopy. The results of molecular docking suggested that compound 3 binds to the active site and the nonspecific binding site of the ADA. Furthermore, we found that compound 3 is a mixed ADA inhibitor. These results indicate that endophytic strains are a promising source of ADA inhibitors and that compound 3 may be a superior source for use in the preparation of biologically active ADA inhibitor compounds used to treat cancer.

Identification of a New Uncompetitive Inhibitor of Adenosine Deaminase from Endophyte Aspergillus niger sp

Adenosine deaminase (ADA) is an enzyme widely distributed from bacteria to humans. ADA is known as a potential therapeutic target for the treatment of lymphoproliferative disorders and cancer. Endophytes are endosymbionts, often bacteria or fungi, which live within plant tissues and internal organs or intercellular space. Endophytes have a broad variety of bioactive metabolites that are used for the identification of novel natural compounds. Here, 54 morphologically distinct endophyte strains were isolated from six plants such as Peganum harmala Linn., Rheum officinale Baill., Gentiana macrophylla Pall., Radix stephaniae tetrandrae, Myrrha, and Equisetum hyemale Linn. The isolated strains were used for the search of ADA inhibitors that resulted in the identification of the strain with the highest inhibition activity, Aspergillus niger sp. Four compounds were isolated from this strain using three-step chromatography procedure, and compound 2 was determined as the compound with the highest inhibition activity of ADA. Based on the results of ¹H and ¹³C NMR spectroscopies, compound 2 was identified as 3-(4-nitrophenyl)-5-phenyl isoxazole. We showed that compound 2 was a new uncompetitive inhibitor of ADA with high cytotoxic effect on HepG2 and SMCC-7721 cells (the IC₅₀ values were 0.347 and 0.380 mM, respectively). These results suggest that endophyte strains serve as promising sources for the identification of ADA inhibitors, and compound 2 could be an effective drug in the cancer treatment.

Effect of Bronsted Acids and Bases, and Lewis Acid (Sn(2+)) on the Regiochemistry of the Reaction of Amines with Trifluoromethyl-β-diketones: Reaction of 3-Aminopyrrole to Selectively Produce Regioisomeric 1H-Pyrrolo[3,2-b]pyridines

Reaction of 3-aminopyrrole (as its salt) with trifluoromethyl-β-diketones gave γ-1H-pyrrolo[3,2-b]pyridines via reaction at the less reactive carbonyl group. The trifluoromethyl group increased the electrophilicity of the adjacent carbonyl group and decreased the basicity of the hydroxyl group of the CF3 amino alcohol formed. This amino alcohol was formed faster, but its subsequent dehydration to the β-enaminone was slow resulting in the preferential formation of the γ-regioisomer. Reaction of 4,4,4-trifluoro-1-phenyl-1,3-butadione with 3-aminopyrrole was carried out using a series of 6 amine buffers. Yields of the α-1H-pyrrolo[3,2-b]pyridine increased as the pKa of the amine buffer decreased. Surprisingly the yield went down at higher pKas. There was a change in mechanism as the reaction mixture became more basic. With strong amines trifluoromethyl-β-diketones were present mainly or completely as the enolate. Under reductive conditions (3-nitropyrrole/Sn/AcOH/trifluoromethyl-β-diketone) the α-1H-pyrrolo[3,2-b]pyridine was the major product as a result of Lewis acid catalysis by Sn(2+). Similar α-regiochemistry was observed when the reaction of the 3-aminopyrrole salt with trifluoromethyl-β-diketones was carried out in the presence of base and tin(II) acetate.

Polyfluorinated groups in medicinal chemistry

Introduction of novel and diverse functional groups in drug discovery is always seen with hesitancy until good activity and low toxicity characteristics are proven. The introduction of fluorine in drug-like compounds is now a well-accepted strategy in medicinal chemistry. However, polyfluoroalkyl groups, with the exception of trifluoromethyl substituents, are not well explored yet. Our aim is to show to the readers how polyfluorinated groups can be beneficial to the properties of pharmaceutically active compounds by highlighting the structure–activity relationship (SAR) studies that led to the selection of polyfluorinated moieties as key structural features. Despite the fact that the use of higher polyfluoroalkyl/aryl moieties is still in its infancy, we believe that they will soon acquire the same importance of their lower parents.