NVP-BHG712: Effects of Regioisomers on the Affinity and Selectivity toward the EPHrin Family

Erythropoietin-producing hepatocellular (EPH) receptors are transmembrane receptor tyrosine kinases. Their extracellular domains bind specifically to ephrin A/B ligands, and this binding modulates intracellular kinase activity. EPHs are key players in bidirectional intercellular signaling, controlling cell morphology, adhesion, and migration. They are increasingly recognized as cancer drug targets. We analyzed the binding of NVP-BHG712 (NVP) to EPHA2 and EPHB4. Unexpectedly, all tested commercially available NVP samples turned out to be a regioisomer (NVPiso) of the inhibitor, initially described in a Novartis patent application. They only differ by the localization of a single methyl group on either one of two adjacent nitrogen atoms. The two compounds of identical mass revealed different binding modes. Furthermore, both in vitro and in vivo experiments showed that the isomers differ in their kinase affinity and selectivity.

Aryl Insertion vs Aryl-Aryl Coupling in C,C-Chelated Organoborates: The "Missing Link" of Tetraarylborate Photochemistry

The photoreactivity of 9-borafluorene-based, C,C-chelated organoborates was investigated. Unlike the related tetraarylborates, the charge-transfer transitions imparted by the biphenyl chelate lead to selective insertion of one aryl substituent into the endocyclic B-C bond of the 9-borafluorene moiety, resulting in the formation of boratanorcaradienes. This photoreaction likely proceeds according to a Zimmerman rearrangement, which is analogous to one of the initially proposed mechanisms for tetraarylborates and provides additional insight into these long-debated photochemical reactions.

A redox-active diborane platform performs C(sp3)-H activation and nucleophilic substitution reactions

Targeted C(sp³)–H activation or nucleophilic substitution reactions have been achieved through the interaction of a diborane dianion with haloalkanes.

Organoboranes are among the most versatile and widely used reagents in synthetic chemistry. A significant further expansion of their application spectrum would be achievable if boron-containing reactive intermediates capable of inserting into C–H bonds or performing nucleophilic substitution reactions were readily available. However, current progress in the field is still hampered by a lack of universal design concepts and mechanistic understanding. Herein we report that the doubly arylene-bridged diborane(6) 1H₂ and its B Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> B-bonded formal deprotonation product Li₂[1] can activate the particularly inert C(sp³)–H bonds of added H₃CLi and H₃CCl, respectively. The first case involves the attack of [H₃C]^– on a Lewis-acidic boron center, whereas the second case follows a polarity-inverted pathway with nucleophilic attack of the B Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> B double bond on H₃CCl. Mechanistic details were elucidated by means of deuterium-labeled reagents, a radical clock, α,ω-dihaloalkane substrates, the experimental identification of key intermediates, and quantum-chemical calculations. It turned out that both systems, H₃CLi/1H₂ and H₃CCl/Li₂[1], ultimately funnel into the same reaction pathway, which likely proceeds past a borylene-type intermediate and requires the cooperative interaction of both boron atoms.

Stereoselective One-Pot Synthesis of Dihydropyrimido[2,1-a]isoindole-6(2H)-ones

A diastereoselective one-pot synthesis of highly substituted dihydropyrimido[2,1-a]isoindole-6(2H)-ones containing three continuous stereocenters is reported. The reaction sequence is based on a hetero-Diels-Alder reaction between an enimide and a N-acylimine followed by an unprecedented Brønsted acid mediated rearrangement of an intermediate 5,6-dihydro-4H-1,3-oxazine to a pyrimido[2,1-a]isoindole.

Sulfur as hydrogen-bond acceptor in cocrystals of 2-thio-modified thymine

Doubly and triply hydrogen-bonded supramolecular synthons are of particular interest for the rational design of crystal and cocrystal structures in crystal engineering since they show a high robustness due to their high stability and good reliability. The compound 5-methyl-2-thiouracil (2-thiothymine) contains an ADA hydrogen-bonding site (A = acceptor and D = donor) if the S atom is considered as an acceptor. We report herein the results of cocrystallization experiments with the coformers 2,4-diaminopyrimidine, 2,4-diamino-6-phenyl-1,3,5-triazine, 6-amino-3H-isocytosine and melamine, which contain complementary DAD hydrogen-bonding sites and, therefore, should be capable of forming a mixed ADA–DAD N—H...S/N—H...N/N—H...O synthon (denoted synthon 3s N·S;N·N;N·O), consisting of three different hydrogen bonds with 5-methyl-2-thiouracil. The experiments yielded one cocrystal and five solvated cocrystals, namely 5-methyl-2-thiouracil–2,4-diaminopyrimidine (1/2), C5H6N2OS·2C4H6N4, (I), 5-methyl-2-thiouracil–2,4-diaminopyrimidine–N,N-dimethylformamide (2/2/1), 2C5H6N2OS·2C4H6N4·C3H7NO, (II), 5-methyl-2-thiouracil–2,4-diamino-6-phenyl-1,3,5-triazine–N,N-dimethylformamide (2/2/1), 2C5H6N2OS·2C9H9N5·C3H7NO, (III), 5-methyl-2-thiouracil–6-amino-3H-isocytosine–N,N-dimethylformamide (2/2/1), (IV), 2C5H6N2OS·2C4H6N4O·C3H7NO, (IV), 5-methyl-2-thiouracil–6-amino-3H-isocytosine–N,N-dimethylacetamide (2/2/1), 2C5H6N2OS·2C4H6N4O·C4H9NO, (V), and 5-methyl-2-thiouracil–melamine (3/2), 3C5H6N2OS·2C3H6N6, (VI). Synthon 3s N·S;N·N;N·O was formed in three structures in which two-dimensional hydrogen-bonded networks are observed, while doubly hydrogen-bonded interactions were formed instead in the remaining three cocrystals whereby three-dimensional networks are preferred. As desired, the S atoms are involved in hydrogen-bonding interactions in all six structures, thus illustrating the ability of sulfur to act as a hydrogen-bond acceptor and, therefore, its value for application in crystal engineering.

Deca-chloro-cyclo-penta-silanes coordinated by pairs of chloride anions, with different cations, but the same solvent mol-ecules

We have determined the crystal structures of two deca-chloro-cyclo-penta-silanes, namely bis-(tetra-n-butyl-ammonium) dichloride deca-chloro-cyclo-penta-silane di-chloro-methane disolvate, 2C16H36N+·2Cl-·Si5Cl10·2CH2Cl2, (I), and bis-(tetra-ethyl-ammonium) dichloride deca-chloro-cyclo-penta-silane di-chloro-methane disolvate, 2C8H20N+·2Cl-·Si5Cl10·2CH2Cl2, (II), both of which crystallize with discrete cations, anions, and solvent mol-ecules. In (I), the complete deca-chloro-cyclo-penta-silane ring is generated by a crystallographic twofold rotation axis. In (II), one cation is located on a general position and the other two are disordered about centres of inversion. These are the first structures featuring the structural motif of a five-membered cyclo-penta-silane ring coordinated from both sides by a chloride ion. The extended structures of (I) and (II) feature numerous C-H⋯Cl inter-actions. In (II), the N atoms are located on centres of inversion and as a result, the ethyl-ene chains are disordered over equally occupied orientations.

On the stacking disorder of DL-norleucine

DL-Norleucine (2-aminohexanoic acid, C6H13NO2) forms a double-layer structure in all known phases (α, β, γ). The crystal structure of the β-phase was redetermined at 173 K. Diffraction patterns of the α- and β-phases frequently show diffuse streaks parallel to c*, which indicates a stacking disorder of the layers. A symmetry analysis was carried out to derive possible stacking sequences. Lattice-energy minimizations by force fields and by dispersion-corrected density functional theory (DFT-D) were performed on a set of ordered model structures with Z = 4, 8 and 16 with different stacking sequences. The calculated energies depend not only on the arrangement of neighbouring double layers, but also of next-neighbouring double layers. Stacking probabilities were calculated from the DFT-D energies. According to the calculated stacking probabilities large models containing 100 double layers were constructed. Their simulated diffraction patterns show sharp reflections for h + k = 2n and diffuse streaks parallel to c* through all reflections with h + k = 2n + 1. Experimental single-crystal X-ray diffraction revealed that at 173 K norleucine exists in the β-phase with stacking disorder. After reheating to room temperature, the investigated crystal showed a diffraction pattern with strong diffuse scattering parallel to c* through all reflections with h + k = 2n + 1, which is in good agreement with the simulated disordered structure.

Crystal structure of the co-crystalline adduct 1,3,6,8-tetra-aza-tri-cyclo-[4.4.1.13,8]dodecane (TATD)-4-iodo-phenol (1/2): supra-molecular assembly mediated by halogen and hydrogen bonding

The asymmetric unit of the title co-crystalline adduct, 1,3,6,8-tetra-aza-tri-cyclo[4.4.1.13,8]dodecane (TATD)-4-iodo-phenol (1/2), C8H16N4·2C6H5IO, comprises a half mol-ecule of the aminal cage polyamine plus a 4-iodo-phenol mol-ecule. A twofold rotation axis generates the other half of the adduct. The components are linked by two inter-molecular O-H⋯N hydrogen bonds. The adducts are further linked into a three-dimensional framework structure by a combination of N⋯I halogen bonds and weak non-conventional C-H⋯O and C-H⋯I hydrogen bonds.

Synthesis and bioelectrochemical behavior of aromatic amines

Four aromatic amines 1-amino-4-phenoxybenzene (A₁), 4-(4-aminophenyloxy) biphenyl (A₂), 1-(4-aminophenoxy) naphthalene (A₃) and 2-(4-aminophenoxy) naphthalene (A₄) were synthesized and characterized by elemental, spectroscopic (FTIR, NMR), mass spectrometric and single crystal X-ray diffraction methods. The compounds crystallized in monoclinic crystal system with space group P2₁. Intermolecular hydrogen bonds were observed between the amine group and amine/ether acceptors of neighboring molecules. Electrochemical investigations were done using cyclic voltammetry (CV), square wave voltammetry (SWV) and differential pulse voltammetry (DPV). CV studies showed that oxidation of aromatic amines takes place at about 0.9 V (vs. Ag/AgCl) and the electron transfer (ET) process has irreversible nature. After first scan reactive intermediate were generated electrochemically and some other cathodic and anodic peaks also appeared in the succeeding scans. DPV study revealed that ET process is accompanied by one electron. DNA binding study of aromatic amines was performed by CV and UV-visible spectroscopy. These investigations revealed groove binding mode of interaction of aromatic amines with DNA.

Synthesis and properties of 1,3-Bis(2,6-diisopropylphenyl)-2-(trimethylstannyl)- 2,3-dihydro-1H-1,3,2-diazaborole

The diazaborole Me3Sn–B{N(Dipp)CH}2 (1; B{N(Dipp)CH}2=N,N′-bis(2,6-diisopropylphenyl)-2,3-dihydro-1H-1,3,2-diazaborolyl) was prepared by the reaction of Me3SnCl with one equivalent of Li[B{N(Dipp)CH}2]. Single crystals of 1 were obtained from hexane (triclinic space group P1̅). The diazaborole 1 was mono-deprotonated at the heterocycle upon treatment with Li[Me] to give product 2. In contrast to Li[B{N(Dipp)CH}2] which reacted with P4 to give the tetraphosphenediide Li2[{HC(Dipp)N}2B–P(1)P(2)P(3)P(4)–B{N(Dipp)CH}2] (3; δ P=364.5, –29.4; 1 J P(2),P(3)=–509.8 Hz, 1 J P(1),P(2)=–434.3 Hz, 2 J P(1),P(3)=–3.7 Hz, 3 J P(1),P(4)=178.9 Hz) and the triphosphenide Li[{HC(Dipp)N}2B–PPP–B{N(Dipp)CH}2] (δ P=665.1, 175.4; 1 J P,P=500 Hz), the stannyl derivative 1 did not activate white phosphorus. The reaction of 1 with GaCl3 yielded either Me2ClSn–B{N(Dipp)CH}2 (4) or MeCl2Sn–B{N(Dipp)CH}2 (5) depending on the molar ratio of the reactants. The monochlorinated diazaborole Me2ClSn–B{N(Dipp)CH}2 was also obtained by the reaction of 1 with AsCl3.

Reaction of the thermo-labile triazenide Na[tBu3SiNNNSiMe3] with CO2: formation of the imido carbonate (tBu3SiO)(Me3SiO)C[double bond, length as m-dash]N-SitBu3 and carbamine acid (tBu3SiO)CONH2

The thermo-labile triazenide Na[tBu₃SiNNNSiMe₃] was prepared by the reaction of Me₃SiN₃ with Na(thf)₂[SitBu₃] in pentane at -78 °C. Treatment of Na[tBu₃SiNNNSiMe₃] with an excess of carbon dioxide in pentane at -78 °C yielded the imido carbonate (tBu₃SiO)(Me₃SiO)C[double bond, length as m-dash]N-SitBu₃ and the carbamine acid (tBu₃SiO)CONH₂ along with other products. From the reaction solution we could isolate the imido carbonate (tBu₃SiO)(Me₃SiO)C[double bond, length as m-dash]N-SitBu₃ and carbamine acid (tBu₃SiO)CONH₂. At first single crystals of the carbamine acid (tBu₃SiO)CONH₂ (triclinic, space group P1[combining macron]) were grown from this solution at room temperature. A second crop of crystals were obtained by concentrating the solution. The second charge consisted of the imido carbonate (tBu₃SiO)(Me₃SiO)C[double bond, length as m-dash]N-SitBu₃ (monoclinic, space group P2₁/n).

Synthesis and crystal structures of two structurally related kryptoracemates

Kryptoracemates are racemic compounds (pairs of enantiomers) that crystallize in Sohnke space groups (space groups that contain neither inversion centres nor mirror or glide planes nor rotoinversion axes). Thus, the two symmetry-independent molecules cannot be transformed into one another by any symmetry element present in the crystal structure. Usually, the conformation of the two enantiomers is rather similar if not identical. Sometimes, the two enantiomers are related by a pseudosymmetry element, which is often a pseudocentre of inversion, because inversion symmetry is thought to be favourable for crystal packing. We obtained crystals of two kryptoracemates of two very similar compounds differing in just one residue, namely rac-N-[(1S,2R,3S)-2-methyl-3-(5-methylfuran-2-yl)-1-phenyl-3-(pivalamido)propyl]benzamide, C₂₇H₃₂N₂O₃, (I), and rac-N-[(1S,2S,3R)-2-methyl-3-(5-methylfuran-2-yl)-1-phenyl-3-(propionamido)propyl]benzamide dichloromethane hemisolvate, C₂₅H₂₈N₂O₃·0.5CH₂Cl₂, (II). The crystals of both compounds contain both enantiomers of these chiral molecules. However, since the space groups [P2₁2₁2₁ for (I) and P1 for (II)] contain neither inversion centres nor mirror or glide planes nor rotoinversion axes, there are both enantiomers in the asymmetric unit, which is a rather uncommon phenomenon. In addition, it is remarkable that (II) contains two pairs of enantiomers in the asymmetric unit. In the crystal, molecules are connected by intermolecular N-H...O hydrogen bonds to form chains or layered structures.

Crystal structure of 2,2'-(ethane-1,2-di-yl)bis-(2,3-di-hydro-1H-naphtho-[1,2-e][1,3]oxazine): a prospective raw material for polybenzoxazines

In the title compound, C26H24N2O2, the oxazine moiety is fused to a naphthalene ring system. The asymmetric unit consists of one half of the mol-ecule, which lies about an inversion centre. The C atoms of the ethyl-ene spacer group adopt an anti-periplanar arrangement. The oxazine ring adopts a half-chair conformation. In the crystal, supra-molecular chains running along the b axis are formed via short C-H⋯π contacts. The crystal studied was a non-merohedral twin with a fractional contribution of 0.168 (2) of the minor twin component.

1,3-Bis{(E)-[4-(di-methyl-amino)-benzyl-idene]amino}-propan-2-ol: chain structure formation via an O-H⋯N hydrogen bond

The asymmetric unit of the title compound, C21H28N4O, consists of two unique mol-ecules linked by an O-H⋯N hydrogen bond. The conformation of both C=N bonds is E and the azomethine functional groups lie close to the plane of their associated benzene rings in each of the independent mol-ecules. The dihedral angles between the two benzene rings are 83.14 (4) and 75.45 (4)°. The plane of the one of the N(CH3)2 units is twisted away from the benzene ring by 18.8 (2)°, indicating loss of conjugation between the lone electron pair and the benzene ring. In the crystal structure, O-H⋯N hydrogen bonds together with C-H⋯O hydrogen bonds link neighbouring supra-molecular dimers into a three-dimensional network.