The optimized microwave-assisted decomposition of formamides and its synthetic utility in the amination reactions of purines

Synthesis of indole-linked β-cyano-enones: a pathway to indolyl-2-pyrrolones

Herein, we report for the first time an additive- and catalyst-free dehydrogenative multicomponent reaction of arylglyoxal, malononitrile, and indoles for the one-pot synthesis of indole-linked β-cyano-enones in DMF medium. The reaction was performed at 100 °C in DMF, forming one C-C single bond and one CC double bond in a single-flask. Furthermore, we developed an efficient method for the synthesis of indolyl-2-pyrrolones having a hydroxyl group-containing chiral carbon center from the β-cyano-enones using trifluoroacetic acid and water as reaction medium. The β-cyano-enones were also further transformed into indolyl-1,2-diketones via a base-mediated reaction, which yielded indolyl quinoxalines upon reaction with o-phenylenediamine (OPD).

Building Co16-N3-Based UiO-MOF to Expand Design Parameters for MOF Photosensitization

The construction of secondary building units (SBUs) in versatile metal-organic frameworks (MOFs) represents a promising method for developing multi-functional materials, especially for improving their sensitizing ability. Herein, we developed a dual small molecules auxiliary strategy to construct a high-nuclear transition-metal-based UiO-architecture Co16-MOF-BDC with visible-light-absorbing capacity. Remarkably, the N3 - molecule in hexadecameric cobalt azide SBU offers novel modification sites to precise bonding of strong visible-light-absorbing chromophores via click reaction. The resulting Bodipy@Co16-MOF-BDC exhibits extremely high performance for oxidative coupling benzylamine (~100 % yield) via both energy and electron transfer processes, which is much superior to that of Co16-MOF-BDC (31.5 %) and Carboxyl @Co16-MOF-BDC (37.5 %). Systematic investigations reveal that the advantages of Bodipy@Co16-MOF-BDC in dual light-absorbing channels, robust bonding between Bodipy/Co16 clusters and efficient electron-hole separation can greatly boost photosynthesis. This work provides an ideal molecular platform for synergy between photosensitizing MOFs and chromophores by constructing high-nuclear transition-metal-based SBUs with surface-modifiable small molecules.

Room-Temperature Dialkylamination of Chloroheteroarenes Using a Cu(II)/PTABS Catalytic System

The dimethylamino functionality has significant importance in industrially relevant molecules and methodologies to install these efficiently are highly desirable. We report herein a highly efficient, room-temperature dimethylamination of chloroheteroarenes performed via the in-situ generation of dimethylamine using N,N-dimethylformamide (DMF) as precursor wiith a large substrate scope that includes various heteroarenes, purines as well as commercially relevant drugs such as altretamine, ampyzine and puromycin precursor.

Room-Temperature Amination of Chloroheteroarenes in Water by a Recyclable Copper(II)-Phosphaadamantanium Sulfonate System

Buchwald-Hartwig amination of chloroheteroarenes has been a challenging synthetic process, with very few protocols promoting this important transformation at ambient temperature. The current report discusses about an efficient copper-based catalytic system (Cu/PTABS) for the amination of chloroheteroarenes at ambient temperature in water as the sole reaction solvent, a combination that is first to be reported. A wide variety of chloroheteroarenes could be coupled efficiently with primary and secondary amines as well as selected amino acid esters under mild reaction conditions. Catalytic efficiency of the developed protocol also promotes late-stage functionalization of active pharmaceutical ingredients (APIs) such as antibiotics (floxacins) and anticancer drugs. The catalytic system also performs efficiently at a very low concentration of 0.0001 mol % (TON = 980,000) and can be recycled 12 times without any appreciable loss in activity. Theoretical calculations reveal that the π-acceptor ability of the ligand PTABS is the main reason for the appreciably high reactivity of the catalytic system. Preliminary characterization of the catalytic species in the reaction was carried out using UV-VIS and ESR spectroscopy, providing evidence for the Cu(II) oxidation state.

Nucleotide Analog ARL67156 as a Lead Structure for the Development of CD39 and Dual CD39/CD73 Ectonucleotidase Inhibitors

Nucleoside triphosphate diphosphohydrolase1 (NTPDase1, CD39) inhibitors have potential as novel drugs for the (immuno)therapy of cancer. They increase the extracellular concentration of immunostimulatory ATP and reduce the formation of AMP, which can be further hydrolyzed by ecto-5'-nucleotidase (CD73) to immunosuppressive, cancer-promoting adenosine. In the present study, we synthesized analogs and derivatives of the standard CD39 inhibitor ARL67156, a nucleotide analog which displays a competitive mechanism of inhibition. Structure-activity relationships were analyzed at the human enzyme with respect to substituents in the N ⁶- and C8-position of the adenine core, and modifications of the triphosph(on)ate chain. Capillary electrophoresis coupled to laser-induced fluorescence detection employing a fluorescent-labeled ATP derivative was employed to determine the compounds' potency. Selected inhibitors were additionally evaluated in an orthogonal, malachite green assay versus the natural substrate ATP. The most potent CD39 inhibitors of the present series were ARL67156 and its derivatives 31 and 33 with K_i values of around 1 µM. Selectivity studies showed that all three nucleotide analogs additionally blocked CD73 acting as dual-target inhibitors. Docking studies provided plausible binding modes to both targets. The present study provides a full characterization of the frequently applied CD39 inhibitor ARL67156, presents structure-activity relationships, and provides a basis for future optimization towards selective CD39 and dual CD39/CD73 inhibitors.

Chemical evolution: from formamide to nucleobases and amino acids without the presence of catalyst

Abiotic synthesis of nucleobases and amino acids is of critical importance as it sheds light on potential prebiotic chemical reactions. During thermal decomposition of formamide in vacuum conditions, purine, cytosine, adenine, hypoxanthine, uracil, pterin, urea, urocanic acid, glycine, alanine and norvaline were detected. The compounds were obtained without catalyst by heating at 100-180 °C or microwave heating of formamide. Reaction network of self-catalyzed chemical reactions is suggested, showing how from only one parent molecule, nucleobases, urea and the amino acid glycine can be produced. The reaction pathways are theoretically determined using SCS-MP2 calculations.Communicated by Ramaswamy H. Sarma.

A Green Approach for Organic Transformations Using Microwave Reactor

Microwave-assisted organic transformation (MAOR) is presently gaining wide popularity in the field of organic synthesis. The conventional heating technique is gradually being removed from the laboratory and a novel microwave heating technique established to be used in both academia and industry. As compared to the classical organic methodology, the green technology tools have several advantages like dramatically reduced reaction times, improved yields, site selectivity, and the increased product purities with simplification of work-up procedures. In the current study, we have briefly described the overview of recent developments and applications of microwave irradiation in organic transformation with schematic compiling of the organic reactions, bioactive heterocyclic compounds, and so on. This review also presents a critical analysis of the various advantages of microwave irradiation in organic synthesis/transformation compared to the classical or conventional heating. So, we believe that our current study of the green microwave heating technique will be highly beneficial for the researchers from both academia and industry in their near future.

A One-Pot Synthesis of Highly Functionalized Purines

Highly substituted purines were synthesized in good to high yields through a one-pot straightforward metal-free scalable method, using the Traube synthesis adapted to Vilsmeier-type reagents. From 5-amino-4-chloropyrimidines, new 9-aryl-substituted chloropurines and intermediates for peptide nucleic acid synthesis were prepared. Variant procedures allowing a rapid synthesis of ribonucleosides and 7-benzylpurine from 5-amidino-6-aminopyrimidines are also reported to illustrate the high potential of this versatile toolbox. This route appears to be particularly interesting in the field of nucleic acids for a direct and rapid access to various new 8-alkylpurine nucleosides.

A General Method for Nucleophilic Aromatic Substitution of Aryl Fluorides and Chlorides with Dimethylamine using Hydroxide-Assisted Decomposition of N,N-Dimethylforamide

A practical and convenient procedure for the nucleophilic aromatic substitution of aryl fluorides and chlorides with dimethylamine was developed using a hydroxide assisted, thermal decomposition of N,N-dimethylforamide. These conditions are tolerant of nitro, nitrile, aldehyde, ketone, and amide groups but will undergo acyl substitution to form amides for methyl esters and acyl chlorides. Isolated yields of the products range from 44 - 98%, with the majority being greater than 70% for seventeen examples.

Dimethylamine as the key intermediate generated in situ from dimethylformamide (DMF) for the synthesis of thioamides

An improved and efficient method for the synthesis of thioamides is presented. For this transformation, dimethylamine as the key intermediate is generated in situ from dimethylformamide (DMF). All the tested substrates produced the desired products with excellent isolated yields.

Purine and Guanine Thioglycoside Analogs: Novel Synthesis of a New Class of Pyrazolo[1,5-a][1,3,5]Triazine-4-Thioglycoside Derivatives under Microwave Activation

A first microwave-assisted synthesis of a new class of novel purine thioglycoside analogues from readily available starting materials has been described. The key step of this protocol is the formation of sodium pyrazolo[1,5-a][1,3,5]triazine-4-thiolates via condensation of 5-amino-1H-pyrazoles with sodium cyanocarbonimidodithioate salt under microwave irradiation, followed by coupling with halo sugars to give the corresponding purine thioglycoside analogues. Further studies on the application of this method for the synthesis of other highly functionalized biologically active glycosides are underway.

8-Triazolylpurines: Towards Fluorescent Inhibitors of the MDM2/p53 Interaction

Small molecule nonpeptidic mimics of α-helices are widely recognised as protein-protein interaction (PPIs) inhibitors. Protein-protein interactions mediate virtually all important regulatory pathways in a cell, and the ability to control and modulate PPIs is therefore of great significance to basic biology, where controlled disruption of protein networks is key to understanding network connectivity and function. We have designed and synthesised two series of 2,6,9-substituted 8-triazolylpurines as α-helix mimetics. The first series was designed based on low energy conformations but did not display any biological activity in a biochemical fluorescence polarisation assay targeting MDM2/p53. Although solution NMR conformation studies demonstrated that such molecules could mimic the topography of an α-helix, docking studies indicated that the same compounds were not optimal as inhibitors for the MDM2/p53 interaction. A new series of 8-triazolylpurines was designed based on a combination of docking studies and analysis of recently published inhibitors. The best compound displayed low micromolar inhibitory activity towards MDM2/p53 in a biochemical fluorescence polarisation assay. In order to evaluate the applicability of these compounds as biologically active and intrinsically fluorescent probes, their absorption/emission properties were measured. The compounds display fluorescent properties with quantum yields up to 50%.

From norbornane-based nucleotide analogs locked in South conformation to novel inhibitors of feline herpes virus

A synthetic route toward a series of unique cyclic nucleoside phosphonates locked in South conformation is described. The desired conformation is stabilized by a substitution of the sugar moiety by bicyclo[2.2.1]heptane (norbornane) bearing a purine or pyrimidine nucleobase in the bridgehead position. Although the final phosphonate derivatives are devoid of any significant antiviral activity probably due to the unfavorable conformational properties, several intermediates and their analogs exhibit surprising activity against feline herpes virus. Since these compounds do not possess an appropriate hydroxymethyl function allowing phosphorylation and subsequent incorporation into the polynucleotide chain, it seems to be likely that these compounds act by a novel unknown mechanism of action and may represent a new possible alternative for nucleoside and nucleotide therapeutics of this widely spread feline infection. A number of derivatives exerted also a significant antiviral activity against Coxsackievirus B3 and B4.

Direct N9-arylation of purines with aryl halides

The reported protocol is the first to be demonstrated to efficiently couple aryl halides to purines with predictable selectivity.

Continuous flow nucleophilic aromatic substitution with dimethylamine generated in situ by decomposition of DMF

A safe, practical, and scalable continuous flow protocol for the in situ generation of dimethylamine from DMF followed by nucleophilic aromatic substitution of a broad range of aromatic and heteroaromatic halides is reported.

Long-range heteronuclear coupling constants in 2,6-disubstituted purine derivatives

Four- and five-bond heteronuclear J-couplings between the hydrogen H-8 and carbons C-6 and C-2 in a series of 7- and 9-benzyl substituted purine derivaties with variuous substituents in positions 2 and 6 were studied by coupled (13)  C NMR and H,C-HMBC experiments and by DFT calculations. We have found that for some of the derivatives, the five-bond coupling H8-C2 is higher than the four-bond H8-C6 coupling, which is also evidenced by a stronger crosspeak in the HMBC. This finding contradicts the generally accepted opinion that only strong three-bond crosspeaks and one weak four-bond H8-C6 crosspeak can be observed in the HMBC spectra of purine derivatives. The misinterpretation of HMBC spectra may lead to an incorrect determination of the purine derivatives' structure.

An efficient microwave-assisted synthesis and biological properties of polysubstituted pyrimidinyl- and 1,3,5-triazinylphosphonic acids

Polysubstituted pyrimidinylphosphonic and 1,3,5-triazinylphosphonic acids with potential biological properties were prepared in high yields by the microwave-assisted Michaelis-Arbuzov reaction of trialkyl phosphite with the corresponding halopyrimidines and halo-1,3,5-triazines, respectively, followed by the standard deprotection of the phosphonate group using TMSBr in acetonitrile. 4,6-Diamino-5-chloropyrimidin-2-ylphosphonic acid (7a) was found to exhibit a weak to moderate anti-influenza activity (28-50 μM) and may represent a novel hit for further SAR studies and antiviral improvement.

Efficient one-pot synthesis of polysubstituted 6-[(1H-1,2,3-triazol-1-yl)methyl]uracils through the “click” protocol

The preparation of several triazolo acyclic nucleosides and triazolo acyclic nucleoside phosphonates is described. The synthetic methodology has been developed as an efficient one-pot Cu(I)-catalyzed azide alkyne Huisgen “click” cycloaddition. A novel Cu(I)-catalyzed decarboxylation reaction of 1-substituted 1H-1,2,3-triazole-4-carboxylic acids at room temperature was observed and used for the preparation of 1-substituted 1H-1,2,3-triazoles. As congeners of TPI (Taiho pharmaceutical inhibitor), the prepared compounds were screened as potential inhibitors of human thymidine phosphorylase, but no inhibitory activity was observed.