[3+2] Cycloaddition of Alkynyl Boronates and in†situ Generated Azomethine Ylide.

Scalable [3+2] cycloaddition of alkynyl boronates and in situ generated unstabilized azomethine ylide is reported for the first time. The selective formation of either 1 : 1 or 1 : 2 cycloaddition products was achieved by carefully optimizing the reaction conditions, mainly by controlling the reactant stoichiometry, catalyst loading, and internal temperature. The developed protocol tolerated many valuable functional groups, including TMS, protected alcohol (as ether or THP derivatives), or aldehyde (as acetal). Further common C-C and C-heteroatom bond-forming reactions, as well as scaled-up procedures demonstrate the utility of the prepared compounds as building blocks for organic synthesis and drug discovery.

Cyclic Sulfinamides.

The literature on cyclic sulfinamides (put simply, sultims) published from 1989 to 2022 has been summarized and reviewed. The information is divided into two sections: the analysis of synthetic methods on the preparation of cyclic sulfinamides and the discussion of the chemical properties of cyclic sulfinamides focusing on their reactions and applications. The survey of the reaction conditions, provided in the most detailed way, and a critical view of the reaction mechanisms add an extra dimension to the text. The data presented will be useful to specialists in different areas, especially those who work in the field of synthetic organic and pharmaceutical chemistry.

Photochemical [2+2] Cycloaddition of Alkynyl Boronates.

A photochemical [2+2] cycloaddition of alkynyl boronates and maleimides is reported. The developed protocol provided 35-70 % yield of maleimide-derived cyclobutenyl boronates and demonstrated wide compatibility with various functional groups. The synthetic utility of the prepared building blocks was demonstrated for a range of transformations, including Suzuki cross-coupling, catalytic or metal-hydride reduction, oxidation, and cycloaddition reactions. With aryl-substituted alkynyl boronates, the products of double [2+2] cycloaddition were obtained predominantly. Using the developed protocol, a cyclobutene-derived analogue of Thalidomide was prepared in one step. Mechanistic studies supported the participation of the triplet-excited state maleimides and ground state alkynyl boronates in the key step of the process.

2-Azahetaryl-2-(oxoindolin-2-ylidene)acetonitriles as Colorimetric Probes for Zn: Synthesis and Optical Properties.

A new one-pot approach for the synthesis of the Zn2+-sensitive probes 2-azahetaryl-2-(oxoindolin-2-ylidene)acetonitriles 3a-c and 4 is described. The method includes the in situ formation of imidoylchloride and its further condensation with azahetarylacetonitrile 1. The structure of the obtained compounds is studied using 1H nuclear magnetic resonance (NMR), 13C NMR, infrared (IR), high-resolution mass spectrometry (HRMS), and UV-Vis spectroscopy techniques. Two model ligands both exhibiting the highest extinction coefficient and the best solubility in a Tris buffer pH 7.2/dimethyl sulfoxide (DMSO) solution, namely 5-methyl-benzothiazole derivative 3b and benzoxazole derivative 4, are thoroughly studied as colorimetric probes for Zn2+. The probe 3b has the highest sensitivity to Zn2+, showing a limit of ion detection (LOD) calculated by the 3S criterion of 0.43 µM and selectivity upon masking Cu2+ ions with Na2S2O3. The composition of the complexes in the solution was determined by the limited logarithm method. The stability constant (lg K) values of 3b-Zn of 10.27 ± 0.02 and 4-Zn of 12.5 ± 0.2 indicate the formation of complexes of average stability.

Synthesis of 3-Borylated Pyrrolidines by 1,3-Dipolar Cycloaddition of Alkenyl Boronates and Azomethine Ylide.

A scalable and efficient process for the preparation of 3-borylated pyrrolidines by 1,3-dipolar cycloaddition of N-benzyl azomethine ylide generated in situ has been developed. The optimized method included the use of LiF in DMSO at 110 °C and was suitable for α-mono-, α,ß-di-, and α,ß,ß-trialkyl-, ß,ß-(hetera)cycloalkylidene-, CO2 Et-, as well as most ß-(het)aryl-substituted alkenyl boropinacolates. The 1,3-dipolar reaction proceeded on a multigram scale providing 3-borylated pyrrolidines with diverse substitution patterns (including fused and spirocyclic ones) in a diastereoselective manner. The Pd(OH)2 -mediated N-debenzylation of pyrrolidine hydrochlorides was successfully performed to give the corresponding bifunctional building blocks on an up to 130 g scale, thus providing a substantial expansion of the synthetic and medicinal chemist's toolbox. Other reactions included the preparation of trifluoroborates, Zweifel-Aggarwal sp3 -sp2 coupling, and oxidative deborylation as an example of C-heteroatom bond formation.

Synthesis of spirocyclic ß- and γ-sultams by one-pot reductive cyclization of cyanoalkylsulfonyl fluorides.

One-pot intramolecular cyclization of novel sp3-enriched cyanoalkylsulfonyl fluorides into spirocyclic ß- or γ-sultams is disclosed. The method relies on nitrile group reduction followed by sulfonylation of amino group thus formed upon mild conditions (NaBH4, NiCl2·6H2O in MeOH). Cyclization proceeds smoothly with considerable efficiency (48-84%, 10 examples) on up to 30 g scale. The cyanoalkylsulfonyl fluoride intermediates can be obtained via S-nucleophilic substitution in ß-functionalized alkanenitriles or double alkylation of α-alkylthioacetonitrile, followed by oxidative chlorination with Cl2 and further reaction with KHF2. The title mono- and bifunctional sultams are advanced sp3-enriched building blocks for drug discovery and organic synthesis providing novel substitution patterns and frameworks mimicking saturated nitrogen heterocycles such as pyrrolidine/pyrrolidone.

1,1,6-Trimethyl-1,2-dihydronaphthalene (TDN) Sensory Thresholds in Riesling Wine.

1,1,6-Trimethyl-1,2-dihydronaphthalene (TDN) is an aroma compound responsible for the kerosene/petrol notes in Riesling wines. In the current article, three sensory thresholds for TDN were determined in young Riesling wine: detection threshold (about 4 µg/L), recognition threshold (10-12 µg/L), and rejection threshold (71-82 µg/L). It was demonstrated that an elevated content of free SO2 in wine may have a certain masking effect on the TDN aroma perception. In addition, the influence of wine serving temperature on the recognition of kerosene/petrol notes was studied. It was found, that a lower wine serving temperature (about 11 °C) facilitated identification of the TDN aroma compared to the same wine samples at room temperature.

An optimized method for synthesis and purification of 1,1,6-trimethyl-1,2-dihydronaphthalene (TDN).

1,1,6-Trimethyl-1,2-dihydronaphthalene (TDN), an aroma compound present in wine, is used for sensory and physicochemical analyses. Therefore, synthesis of TDN of high purity is required for these purposes. Optimization of TDN synthesis in order to facilitate its subsequent purification was described. As a result, ≥99.5 % of TDN purity was reached. •The possibility of using both α-ionone and ß-ionone as starting substances was demonstrated•Modifications of the use of reagents in the second and third steps of TDN synthesis were proposed.

Synthesis and biological activity of 4-amino-3-chloro-1H-pyrrole-2,5-diones.

4-Amino-3-chloro-1H-pyrrole-2,5-dione derivatives were designed and synthesized as potential tyrosine kinase inhibitors. One of them has been shown to inhibit growth of cancer cell lines and in vivo tumors. To determine the impact of side groups on biological activity the ability of different 4-amino-3-chloro-1H-pyrrole-2,5-diones to interact with ATP-binding domains of growth factor receptors and with model cell membranes were aimed to be discovered. The methods of molecular docking, short-molecular dynamics (in silico) and non-steady cyclic current-voltage characteristics (in vitro) were used. Five 4-amino-3-chloro-1H-pyrrole-2,5-diones were synthesized from 3,4-dichloro-1H-pyrrole-2,5-diones. All of them demonstrated the potential ability to form complexes with ATP-binding domains of EGFR and VEGFR2. These complexes were more stable compared to those with ANP. 4-Amino-3-chloro-1H-pyrrole-2,5-diones while interact with different bilayer lipid membranes caused an increase of their specific conductance and electric capacity, demonstrating the certain disturbance in lipid packing. Obtained data allowed us to suggest that proposed chemicals can interact with the surface of lipid bilayer, do likely intercalate into the membrane and form stable complexes with EGFR and VEGFR2. So, the prospect of developed chemicals to be effective EGFR and VEGFR2 inhibitors and therefore realize antitumor activity was concluded.

4-Amino-2,3-dihydro-1λ6-isothiazole-1,1-dioxides and their chemical properties evaluation.

The reactivity of the 4-amino-2,3-dihydro-1H-1λ6-isothiazole-1,1-dioxide (ß-amino-γ-sultam) framework has not been studied sufficiently. Here we describe the chemical properties of this heterocyclic system toward electrophiles on spiranic and non-spiranic substrates. A variety of C-electrophiles (acetic anhydride, benzoyl chloride, DMFDMA, 4,4-dimethoxybutan-2-one) and heteroatom electrophiles (bromine, nitrosyl acetate) have been explored. Both the C-5 and 4-amino positions of the ß-amino-γ-sultam system are able to undergo electrophilic reactions. Heteroatom electrophiles attack the C-5 position, whereas carbo-electrophiles affect the amino group. ß-Amino-γ-sultams also were used as starting compounds for the synthesis of 6- or 7-substituted 1λ6-isothiazolo[4,5-b]pyridine-1,1-dioxides through condensation reaction and palladium-catalyzed oxidative coupling.

Expedited Route to Fully Substituted Amino-Pyrazole Building Blocks and Their Further Transformations.

We report here an efficient and easily reproducible two-step approach to heterocycle-substituted amino-pyrazoles from heterocyclic acetonitriles and their unprecedented subsequent transformations to fully substituted pyrazoles. Such transformations include regioselective derivatization from polyamino derivatives, formation of tetracyclic compounds in up to 45% overall yield, and deaminative transformations through diazotization, followed by arylation through Suzuki-Miyaura cross-coupling and C-H activation, providing arylated pyrazoles in up to 71% yield over four steps. This strategy allows the swift introduction of significant molecular complexity to a range of scaffolds.

Fluorophore-tagged pharmacophores for antitumor cytotoxicity: Modified chiral lipidic dialkynylcarbinols for cell imaging.

Chiral lipidic dialkynylcarbinols (DACs), recently highlighted as antitumoral pharmacophores, have been conjugated to difluoroboron-dipyrromethene (bodipy), 7-hydroxy-coumarine, and 7-nitro-benzoxadiazole (NBD) fluorophore motifs through triazole clips. The labeled lipids preserve cytotoxic activity against HCT116 cells, and fluorescence microscopy of the stained cells showed clear signals in the intra-cellular membrane system. While the bodipy conjugate also labels lipid droplets very brightly, as expected, the coumarine and NBD probes appear as promising specific tools for the identification of the intra-cellular targets of DACs' cytotoxicity.

Asymmetric synthesis and biological evaluation of natural or bioinspired cytotoxic C2-symmetrical lipids with two terminal chiral alkynylcarbinol pharmacophores.

Bidirectional syntheses of C2-symmetrical lipids embedding two terminal alkynylcarbinol pharmacophores are reported. Naturally occurring chiral alkenylalkynylcarbinol units were generated using Pu's procedure for enantioselective addition of terminal alkynes to aldehydes, allowing the first asymmetric synthesis of (3R,4E,16E,18R)-icosa-4,16-diene-1,19-diyne-3,18-diol, isolated from Callyspongia pseudoreticulata. Two synthetic analogues embedding the recently uncovered (S)-dialkynylcarbinol pharmacophore were secured using Carreira's procedure adapted to ynal substrates. The dramatic effect of the carbinol configuration on cytotoxicity was confirmed with submicromolar IC50 values against HCT116 cells.

Carbo-cyclohexadienes vs. carbo-benzenes: structure and conjugative properties.

Ideally Cs-/C2v-symmetric chromophores, constituted by two electro-active groups conjugated through the carbo-mer of the cyclohexa-1,3-diene core, are selectively prepared by the SnCl2-mediated reduction of tailored hexaoxy-[6]pericyclynes: in the latter substrates, one of the 1,4-dioxybut-2-yne edges is "chemically locked" by two CF3 substituents preventing complete reduction to the corresponding aromatic carbo-benzenic core, which is expected to be more "π-insulating" between the electro-active ends. The bis-trifluoromethylated carbo-cyclohexadiene products are also shown to be significantly stabilized with respect to their bis-phenylated analogues. Their structural (crystal X-ray diffraction analyses), spectroscopical (NMR and UV-vis spectra), physio-optical (dichromism in solution) and electrochemical (cyclic voltammograms) properties are compared on the basis of the electron-donating/electron-withdrawing nature of the substituents. These properties are also compared with those of their aromatic carbo-benzene and flexible carbo-n-butadiene counterparts.

Enhanced π-frustration in carbo-benzenic chromophores.

The synthesis, structure, and absorption spectra of highly π-frustrated carbo-benzenes with indolic enamine substituents more or less directly conjugated to the C18 macro-aromatic core are described, and their peculiar reactivity is analyzed.

High throughput synthesis of extended pyrazolo[3,4-d]dihydropyrimidines.

Thirteen 5-hetarylaminopyrazoles were synthesized in 62-93% yield through the arylation of 1-isopropyl- and 1-phenyl-5-aminopyrazoles with electrophilic hetarylhalides under optimized conditions. Condensation of 5-hetarylaminopyrazoles with carbonyl compounds facilitated by AcOH or Me(3)SiCl furnished 23 pyrazolo[3,4-d]dihydropyrimidines in 69-86% yield. The target compounds were isolated through simple crystallization. The scope and limitation of the method are discussed.

10-Methoxy-benzo[g]imidazo[1,2-a][1,8]naphthyridine-4-carbonitrile.

In the title compound, C(16)H(10)N(4)O, both the meth-oxy and nitrile substituents lie in the plane defined by the benzo[g]imidazo[1,2-a]-1,8-naphthyridine ring system, resulting in a nearly planar geometry for the entire mol-ecule (r.m.s. deviation of the non-H atoms from the mean plane is 0.044 Å). In the solid-state, the mol-ecules form a three-dimensional polymer through inter-molecular C-H⋯N and C-H⋯O hydrogen bonds. In addition, the packing mode results in stabilizing π-π stacking inter-actions between the asymmetric units.

14-(2,3-Dichloro-phen-yl)-9,10-dimethyl-benzimidazo[1,2-a]benzo[f][1,8]naphthyridine-6-carbonitrile.

In the title compound, C(27)H(16)Cl(2)N(4), the benzimidazo[1,2-a]benzo[f][1,8]naphthyridine system is nearly planar (r.m.s. deviation for all non-H atoms = 0.033 Å). The dichloro-phenyl substituent is rotated by -67.5 (2)° from this plane. In the crystal structure, mol-ecules form stacks along the crystallographic (100) direction due to π-π stacking inter-actions with a centroid-centroid distance of 3.4283 (9) Å.

Aromaticity-controlled tautomerism and resonance-assisted hydrogen bonding in heterocyclic enaminone-iminoenol systems.

The contribution of aromaticity and intramolecular hydrogen bonding to relative stability, for a set of (1H-azahetero-2-ylidene)-acetaldehyde and 2-azahetero-2-yl-ethanol tautomeric pairs, has been investigated by means of quantum chemical DFT and ab initio methods up to the MP4(SDTQ)/AUG-cc-pVDZ and MP2/AUG-cc-pVTZ levels of theory. It is found that the relative energy of the tautomers is governed by the change in the degree of heterocycle aromaticity upon intramolecular hydrogen transfer. An analysis of geometrical parameters of a hydrogen-bonded system reveals a clear relationship between the aromaticity of the heterocycle, the conjugation in a resonant spacer, and the strengths of the intramolecular hydrogen bonds. This allows the conclusion to be drawn that intramolecular N-H...O and O-H...N hydrogen bonds formed are found to be resonance-assisted and their strength is dependent on the pi-donating/accepting properties of the heterocycle. On the basis of the results of the calculations, a simple model describing the mechanism of resonance assistance of hydrogen bonding has been suggested.