Synthesis and Structure Determination of Substituted Thiazole Derivatives as EGFR/BRAFV600E Dual Inhibitors Endowed with Antiproliferative Activity.

2,3,4-trisubstituted thiazoles 3a-i, having a methyl group in position four, were synthesized by the reaction of 1,4-disubstituted thiosemicarbazides with chloroacetone in ethyl acetate/Et3N at room temperature or in ethanol under reflux. The structures of new compounds were determined using NMR spectroscopy, mass spectrometry, and elemental analyses. Moreover, the structure of compound 3a was unambiguously confirmed with X-ray analysis. The cell viability assay of 3a-i at 50 µM was greater than 87%, and none of the tested substances were cytotoxic. Compounds 3a-i demonstrated good antiproliferative activity, with GI50 values ranging from 37 to 86 nM against the four tested human cancer cell lines, compared to the reference erlotinib, which had a GI50 value of 33 nM. The most potent derivatives were found to be compounds 3a, 3c, 3d, and 3f, with GI50 values ranging from 37 nM to 54 nM. The EGFR-TK and BRAFV600E inhibitory assays' results matched the antiproliferative assay's results, with the most potent derivatives, as antiproliferative agents, also being the most potent EGFR and BRAFV600E inhibitors. The docking computations were employed to investigate the docking modes and scores of compounds 3a, 3c, 3d, and 3f toward BRAFV600E and EGFR. Docking computations demonstrated the good affinity of compound 3f against BRAFV600E and EGFR, with values of -8.7 and -8.5 kcal/mol, respectively.

Fluorescent annulated imidazo[4,5-c]isoquinolines via a GBB-3CR/imidoylation sequence - DNA-interactions in pUC-19 gel electrophoresis mobility shift assay.

Herein we report the development of a sequential synthesis route towards annulated imidazo[4,5-c]isoquinolines comprising a GBB-3CR, followed by an intramolecular imidoylative cyclisation. X-Ray crystallography revealed a flat 3D structure of the obtained polyheterocycles. Thus, we evaluated their interactions with double-stranded DNA by establishing a pUC-19 plasmid-based gel electrophoresis mobility shift assay, revealing a stabilising effect on ds-DNA against strand-break inducing conditions.

Isolable N-heterocyclic carbene adducts of the elusive diiodophosphine.

Reactions of PH-substituted phosphinidene-imidazolylidenes with I2 afford isolable NHC-adducts of the transient diiodophosphine PHI2. The products, which show a surprising structural diversity, are according to DFT studies best formulated as charge-transfer complexes of onio-substituted cationic phosphines with I- and are capable of reaction under formal transfer of an NHC-P+ unit.

Synthesis, spectroscopic characterisation and transmetalation of lithium and potassium diaminophosphanide-boranes.

A secondary diaminophosphane-borane (Et2N)2PH(BH3) was prepared from a chlorophosphane precursor and LiBH4 and metalated by reaction with anion bases (n-BuLi, KN(SiMe3)2) to yield the corresponding metal diaminophosphanide-boranes [(Et2N)2P(BH3)]M (M = Li, K). Multinuclear NMR studies permitted the first spectroscopic characterisation of the metalation products and revealed the presence of monomeric (for M = Li) contact ion pairs in solution. NMR spectroscopic evidence that the ions in each pair interact via LiP- rather than LiH3B-interactions as had been inferred for a Ph-substituted analogue was confirmed by DFT studies, which revealed also that the borane coordination plays a decisive role in boosting the PH-acidity of the original secondary diaminophosphane precursor. Transmetalation of the potassium and lithium diaminophosphanide-boranes with Cu(i) and Zn(ii) chlorides afforded the first functional transition metal complexes of a P-heteroatom-functionalised phosphanide-borane ligand. Both products were fully characterised. Thermolysis of the Cu-complex induced a reaction which involved transfer of an NHC ligand from the metal to the phosphorus atom and yielded a phosphaalkene NHC[double bond, length as m-dash]PH (NHC = N-heterocyclic carbene) as the major phosphorus-containing product.

Replacing C6F5 groups with Cl and H atoms in frustrated Lewis pairs: H2 additions and catalytic hydrogenations.

2-(Dialkylamino)phenylboranes containing the BXZ group, where X, Z = C6F5, Cl, and H, were prepared in a few synthetic steps and demonstrated the cleavage of H2 under mild conditions. Depending on the nature of the dialkylamino group, X, and Z, the stability of the produced zwitterionic H2 adducts varies from isolated solids indefinitely stable in an inert atmosphere to those quickly equilibrating with the initial aminoborane and H2. Using a combined experimental/computational approach on a series of isostructural aminoboranes (dialkylamino = 2,2,6,6-tetramethylpiperid-1-yl), it was demonstrated that the electronegativity and the steric effect of the substituents generally follow the trend C6F5 ∼ Cl ≫ H. This observation is useful for designing new FLPs for practical applications. As an example, we demonstrated the hydrogenation of alkynes to cis-alkenes under mild conditions that was catalyzed by a chloro-analogue of the C6F5-substituted aminoborane developed previously. The presence of a BHCl group in the aminochloroboranes or in their H2 adducts features facile redistribution of the H and Cl atoms and the formation of polychloro and polyhydrido species.

Synthesis of aminopyrazoles from sydnones and ynamides.

Aminopyrazoles are prepared from readily accessible sydnones and sulfonyl ynamides using either a copper-mediated sydnone alkyne cycloaddition (CuSAC) or in situ generated strained cyclic ynamides.

On the energetics of P-P bond dissociation of sterically strained tetraamino-diphosphanes.

The homolytic P-P bond fission in a series of sterically congested tetraaminodiphosphanes (R2N)2P-P(NR2)2 ({4}2-{9}2, two of which were newly synthesized and fully characterized) into diaminophosphanyl radicals (R2N)2P˙ (4-9) was monitored by VT EPR spectroscopy. Determination of the radical concentration from the EPR spectra permitted to calculate free dissociation energies ΔGDiss(295) as well as dissociation enthalpies ΔHDiss and entropies ΔSDiss, respectively. Large positive values of ΔGDiss(295) indicate that the degree of dissociation is in most cases low, and the concentration of persistent radicals--even if they are spectroscopically observable at ambient temperature--remains small. Appreciable dissociation was established only for the sterically highly congested acyclic derivative {9}2. Analysis of the trends in experimental data in connection with DFT studies indicate that radical formation is favoured by large entropy contributions and the energetic effect of structural relaxation (geometrical distortions and conformational changes in acyclic derivatives) in the radicals, and disfavoured by attractive dispersion forces. Comparison of the energetics of formation for CC-saturated N-heterocyclic diphosphanes and the 7π-radical 3c indicates that the effect of energetic stabilization by π-electron delocalization in the latter is visible, but stands back behind those of steric and entropic contributions. Evaluation of spectroscopic and computational data indicates that diaminophosphanyl radicals exhibit, in contrast to aminophosphenium cations, no strong energetic preference for a planar arrangement of the (R2N)2P unit.

An anionic phosphenium complex as an ambident nucleophile.

A unique anionic phosphenium complex was prepared from reaction of an N-heterocyclic chlorophosphine with Collman's reagent or K[HFe(CO)4]/NaH and characterized by spectral and XRD data. The complex behaves as an ambident nucleophile. Reactions with acetic acid, ClSnPh3, and a further equivalent of an N-heterocyclic chlorophosphine proceed via electrophilic functionalization at the metal site to yield appropriate mono- or bis-phosphenium complexes. Reaction with MeI at -70 °C produces a P-alkylation product as the first spectroscopically detectable intermediate, which decays at a higher temperature to give a mixture of free P-methylated N-heterocyclic phosphine and its Fe(CO)4 complex. The different reaction products were characterized by spectral and XRD data. Computational studies indicate that the NHP units in all complexes display π-acceptor behaviour but show no disposition to adopt phosphide-like character or formally oxidize the metal centre.

Heterobimetallic catechol-phosphine complexes with palladium and a group-13 element: structural flexibility and dynamics.

Group-13 metal acetylacetonates [M(acac)3] (M = Al, Ga, In) or Al(OiPr)3 react with a complex [Pd(catphosH)2] that may act as chelating ligand towards a second metal, or with a mixture of catechol phosphine (catphosH2) and [PdCl2(cod)], to give heterometallic complexes featuring either dinuclear M(catphos)2Pd or trinuclear M{(catphos)2Pd}2 motifs. Characterisation of the products by crystallographic and solution NMR studies gives insight into the structural diversity and flexibility of the coordination environments of the group-13 elements and their impact on the stability of the multinuclear complexes. The results indicate that gallium and indium are the most suitable elements for the stabilisation of di- and trinuclear assemblies, respectively. Dynamic NMR spectroscopy allowed to follow the dynamic averaging of the coordination environments of the four distinguishable catechol phosphines in the indium complex [M{(catphos)2Pd}2]H. The results revealed that the isomerisation follows a complicated pathway involving several distinguishable proton transfer steps, and allowed to propose a mechanistic explanation for the observed isomerisation.

Phosphines with N-heterocyclic boranyl substituents.

A lithio-diazaborole reacted with diamino-chlorophosphines via metathesis to yield previously unavailable phosphinoboranes bearing amino substituents at both the phosphorus and boron atoms, and with Ph2PCl and Mes*PCl2via chloride transfer and reductive PP coupling to give a chloro-diazaborole and the corresponding diphosphine or diphosphene, respectively. Diazaboroles with phenylphosphino- and PH2-substituents were nonetheless accessible via inverse metathesis upon treatment of a bromoborane precursor with phosphides PhnPH2-nM (n = 0-2, M = Li, K). The products were characterised by spectroscopic data and in most cases by single-crystal X-ray diffraction studies which show the molecules to exhibit strongly pyramidal coordination at the phosphorus atom and long BP bonds of 1.93-1.95 Å. The insensitivity of the BP distance towards substituent effects and the tolerance of large sterically induced torsional twists along the BP bond axis suggest the presence of pure single bonds without any contribution from P→B dative π-interactions. This view was confirmed by DFT studies which indicate further that the molecules lack a significant electrophilic character at boron but may act as potential σ-donor/π-acceptor ligands through the phosphorus atom.

Cleavable surfactants to tune the stability of W/O miniemulsions.

Recently, there has been growing interest towards the formation and use of miniemulsions as nanoreactors for polymerization and precipitation reactions. Regarding precipitation reactions in miniemulsions, emulsifiers are required that on the one hand stabilize droplets in a size range <1 µm and on the other hand allow break-up of the miniemulsion into its two initial phases after particle synthesis for purification reasons. In this work we report the synthesis and emulsifying abilities of low-mass cleavable emulsifiers based on monoesters of oxalic and malonic acids for the stabilization of water-in-oil miniemulsions. A systematic screening of compounds with respect to different polar groups as well as length, molecular branching and type of alkyl chains and their suitability as emulsifiers was performed. Our results show that the size of droplets stabilized by these emulsifiers strongly depends on the nature of the polar group and the length of the lipophilic chain. The targeted phase separation of the emulsions was triggered by the addition of a base cleaving the emulsifiers.

Structural revision and synthesis of altechromone A.

The chromone "altechromone A" was synthesized as a substructure in the course of natural product synthesis. Its architecture was verified by X-ray analysis, but spectroscopic data showed a strong deviation from the reported data. By comparison with the synthesized isomers the structure of altechromone A was revised.

NMR-spectroscopic and solid-state investigations of cometal-free asymmetric conjugate addition: a dinuclear paracyclophaneimine zinc methyl complex.

We present herein the first indications for dimeric structures in cometal-free asymmetric conjugate addition reactions of dialkylzinc reagents with aldehydes. These are revealed by nonlinear effect (NLE) studies. A monomer-dimer equilibrium can be assumed which explains the increase of the ee value in the product over time. Also, DOSY NMR spectroscopic measurements indicate the existence of the catalyst as [LZnEt](n) complexes in solution. Additionally, the first X-ray structure of a zinc complex with a [2.2]paracyclophane ligand was determined. The structures of the zinc complexes are supported by DFT calculations of monomeric and dimeric species.

tBuP(NH2)2--a reactive synthon for the synthesis of molecular imidophosphinates of group 13 metals.

Reactions of tBuP(NH(2))(2) with Group 13 trialkyls MR(3) (M=Al, Ga, In; R=Me, tBu) were investigated in detail. According to variable-temperature (VT) NMR investigations, the reaction proceeds stepwise with the initial formation of aminophosphane adducts, which subsequently react to give iminophosphorane adducts and finally the heterocyclic metallonitridophosphinates. BP86/TZVPP (DFT) calculations were performed to verify this reaction pathway, to elucidate the influence of the central Group 13 element on the stability of the reaction intermediates and the heterocycles, as well as to assess the thermodynamics of their formation. The relative stability of free and complexed aminophosphane RP(NH(2))(2) and iminophosphorane R(H(2)N)(H)P=NH (adducts) with P(III) and P(V) centers was studied in more detail with DFT and MP2 methods. In addition, the influence of the substituent R was investigated by variation of R from H to Me, tBu, F, and NH(2). In general, the aminophosphane form was found to be favored for the free ligand, however, upon complexation with MR(3) (M=Al, Ga; R=alkyl) both forms are almost equal in energy.

Reversible Tautomeric Transformation between a Bis(amino)cyclodiphosph(V)azene and a Bis(imino)cyclodiphosph(V)azane.

The tautomeric four-membered-ring P-N heterocycles 1, 2, and 3 can be interconverted; the formation of the cyclodiphosph(V)azene 1 is enthalpically and entropically favored. The crystal structures of the tautomers 1 and 3 have been determined and indications are given regarding the mechanism of the interconversion.

Stability and electrophilicity of phosphorus analogues of arduengo carbenes--an experimental and computational study

A variety of differently substituted 1,3,2-diazaphospholenium salts and P-halogeno-1,3,2-diazaphospholenes (X = F, Cl, Br) were synthesized, and their molecular structures, bonding situation, and Lewis acid properties were characterized by experimental (single-crystal X-ray diffraction, NMR and IR/Raman spectroscopy, MS, conductometry, titrations with Lewis bases) and computational methods. Both experimental and computational investigations confirmed that the structure and bonding in the diazaphospholenium cations of OTf and BF4 salts resembles that of neutral Arduengo carbenes and that the cations should not be described as genuinely aromatic. P-Halogenodiazaphospholenes are, in contrast to earlier assumptions, molecular species with covalent P-X bonds whose bonding situation can be expressed in terms of hyperconjugation between the six pi electrons in the C2N2 unit and the sigma*(P-X) orbital. This interaction induces a weakening of the P-X bonds, whose extent depends subtly on substituent influences and contributes fundamentally to the amazing structural similarity of ionic and covalent diazaphospholene compounds. A further consequence of this effect is the unique polarizability of the P-Cl bonds in P-chlorodiazaphospholenes, which is documented in a considerable spread of P-X distances and bond orders. Measurement of the stability constants for complexes of diazaphospholene compounds with Lewis bases confirmed the lower Lewis acidities and higher stabilities of diazaphospholenium ions as compared with nonconjugated phosphenium ions; this had been inferred from computed energies of isodesmotic halide-transfer reactions, and permitted also to determine equilibrium constants for P-Cl bond dissociation reactions. The results suggest, in accord with conductance measurements, that P-chlorodiazaphospholenes dissociate in solution only to a small extent. On the basis of these findings, the unique solvatochromatic behavior of NMR chemical shifts of these compounds was attributed to solvent-dependent P-Cl bond polarization rather than to shifts in dissociation equilibria.

Incorporation of chromium carbenes in a silica matrix by sol-gel processing: application to aminolysis of alkoxycarbene complexes

Chromium carbene complexes have been immobilized in a silica matrix by sol-gel processing based on the polycondensation of (trialkoxy)silylethylphosphane ligands and tetraalkoxysilanes. The microstructure of the material obtained depends on the gelation conditions. In situ gelation of alkoxy- or aminocarbene complexes with tetramethoxysilane (TMOS) affords mesoporous materials with a homogeneous distribution of the metal complex. The metal carbene moiety is accessible for small substrates as demonstrated for the aminolysis of the incorporated methoxy(phenyl)carbene complex which slows down with increasing bulk of the amine.