Crystal structure and Hirshfeld surface analysis of dimethyl 2-oxo-4-(pyridin-2-yl)-6-(thio-phen-2-yl)cyclo-hex-3-ene-1,3-di-carboxyl-ate.

In the title compound, C19H17NO5S, the cyclo-hexene ring adopts nearly an envelope conformation. In the crystal, mol-ecules are linked by C-H⋯O hydrogen bonds, forming a three-dimensional network. In addition, C-H⋯π inter-actions connect the mol-ecules by forming layers parallel to the (010) plane. According to the Hirshfeld surface analysis, H⋯H (36.9%), O⋯H/H⋯O (31.0%), C⋯H/H⋯C (18.9%) and S⋯H/H⋯S (7.9%) inter-actions are the most significant contributors to the crystal packing.

Crystal structure and Hirshfeld surface analysis of 2,4-di-amino-6-[(1Z,3E)-1-cyano-2,4-di-phenyl-penta-1,3-dien-1-yl]pyridine-3,5-dicarbo-nitrile monohydrate.

The asymmetric unit of the title compound, C25H18N6·H2O, comproses two mol-ecules (I and II), together with a water mol-ecule. The terminal phenyl groups attached to the methyl groups of the mol-ecules I and II do not overlap completely, but are approximately perpendicular. In the crystal, the mol-ecules are connected by N-H⋯N, C-H⋯N, O-H⋯N and N-H⋯O hydrogen bonds with each other directly and through water mol-ecules, forming layers parallel to the (001) plane. C-H⋯π inter-actions between these layers ensure the cohesion of the crystal structure. A Hirshfeld surface analysis indicates that H⋯H (39.1% for mol-ecule I; 40.0% for mol-ecule II), C⋯H/H⋯C (26.6% for mol-ecule I and 25.8% for mol-ecule II) and N⋯H/H⋯N (24.3% for mol-ecules I and II) inter-actions are the most important contributors to the crystal packing.

Crystal structure and Hirshfeld surface analysis of 6-imino-8-(4-methyl-phen-yl)-1,3,4,6-tetra-hydro-2H-pyrido[1,2-a]pyrimidine-7,9-dicarbo-nitrile.

In the ten-membered 1,3,4,6-tetra-hydro-2H-pyrido[1,2-a]pyrimidine ring system of the title compound, C17H15N5, the 1,2-di-hydro-pyridine ring is essentially planar (r.m.s. deviation = 0.001 Å), while the 1,3-diazinane ring has a distorted twist-boat conformation. In the crystal, mol-ecules are linked by N-H⋯N and C-H⋯N hydrogen bonds, forming a three-dimensional network. In addition, C-H⋯π inter-actions form layers parallel to the (100) plane. Thus, crystal-structure cohesion is ensured. According to a Hirshfeld surface study, H⋯H (40.4%), N⋯H/H⋯N (28.6%) and C⋯H/H⋯C (24.1%) inter-actions are the most important contributors to the crystal packing.

Syntheses, characterizations, crystal structures and Hirshfeld surface analyses of methyl 4-[4-(di-fluorometh-oxy)phen-yl]-2,7,7-trimethyl-5-oxo-1,4,5,6,7,8-hexa-hydro-quinoline-3-carboxyl-ate, isopropyl 4-[4-(di-fluoro-meth-oxy)phen-yl]-2,6,6-trimethyl-5-oxo-1,4,5,6,7,8-hexa-hydro-quinoline-3-carboxyl-ate and tert-butyl 4-[4-(di-fluoro-meth-oxy)phen-yl]-2,6,6-trimethyl-5-oxo-1,4,5,6,7,8-hexa-hydro-quinoline-3-carboxyl-ate.

The crystal structures and Hirshfeld surface analyses of three similar compounds are reported. Methyl 4-[4-(di-fluoro-meth-oxy)phen-yl]-2,7,7-trimethyl-5-oxo-1,4,5,6,7,8-hexa-hydro-quinoline-3-carboxyl-ate, (C21H23F2NO4), (I), crystallizes in the monoclinic space group C2/c with Z = 8, while isopropyl 4-[4-(di-fluoro-meth-oxy)phen-yl]-2,6,6-trimethyl-5-oxo-1,4,5,6,7,8-hexa-hydro-quinoline-3-carb-oxyl-ate, (C23H27F2NO4), (II) and tert-butyl 4-[4-(di-fluoro-meth-oxy)phen-yl]-2,6,6-trimethyl-5-oxo-1,4,5,6,7,8-hexa-hydro-quinoline-3-carboxyl-ate, (C24H29F2NO4), (III) crystallize in the ortho-rhom-bic space group Pbca with Z = 8. In the crystal structure of (I), mol-ecules are linked by N-H⋯O and C-H⋯O inter-actions, forming a tri-periodic network, while mol-ecules of (II) and (III) are linked by N-H⋯O, C-H⋯F and C-H⋯π inter-actions, forming layers parallel to (002). The cohesion of the mol-ecular packing is ensured by van der Waals forces between these layers. In (I), the atoms of the 4-di-fluoro-meth-oxy-phenyl group are disordered over two sets of sites in a 0.647 (3): 0.353 (3) ratio. In (III), the atoms of the dimethyl group attached to the cyclo-hexane ring, and the two carbon atoms of the cyclo-hexane ring are disordered over two sets of sites in a 0.646 (3):0.354 (3) ratio.

Crystal structure and Hirshfeld surface analysis of 2-amino-6-[(1-phenyl-eth-yl)amino]-4-(thio-phen-2-yl)pyridine-3,5-dicarbo-nitrile.

In the title compound, C19H15N5S, the thio-phene ring is disordered in a 0.6:0.4 ratio by an approximate 180° rotation of the ring around the C-C bond linking it to the pyridine ring. In the crystal, the mol-ecules are linked by N-H⋯N hydrogen bonds into dimers with an R 2 2(12) motif, forming chains along the b-axis direction. These chains are connected to each other by further N-H⋯N hydrogen bonds, forming a three-dimensional network. Furthermore, N-H⋯π and π-π [centroid-centroid separations = 3.899 (8) and 3.7938 (12) Å] inter-actions also contribute to the crystal cohesion. A Hirshfeld surface analysis indicated that the most important contributions to the surface contacts are from H⋯H (46.1%), N⋯H/H⋯N (20.4%) and C⋯H/H⋯C (17.4%) inter-actions.

Crystal structure and Hirshfeld surface analysis of isopropyl 4-[2-fluoro-5-(tri-fluoro-meth-yl)phen-yl]-2,6,6-trimethyl-5-oxo-1,4,5,6,7,8-hexa-hydro-quinoline-3-carboxyl-ate.

In the title compound, C23H25F4NO3, the 1,4-di-hydro-pyridine ring adopts a distorted boat conformation, while the cyclo-hexene ring is almost showing a half-chair conformation. In the crystal, inter-molecular N-H⋯O hydrogen bonds connect the mol-ecules into chains with graph-set motif C(6) parallel to the a-axis. These chains are linked together by C-H⋯O and C-H⋯F inter-actions, forming a three-dimensional network. In addition, C-H⋯π inter-actions link the mol-ecules into layers parallel to the (100) plane. A Hirshfeld surface analysis was performed to further investigate the inter-molecular inter-actions.

Synthesis, characterization, crystal structure and Hirshfeld surface analysis of isobutyl 4-[4-(di-fluoro-meth-oxy)phen-yl]-2,6,6-trimethyl-5-oxo-1,4,5,6,7,8-hexa-hydro-quinoline-3-carboxyl-ate.

In the title compound, C24H29F2NO4, which crystallizes in the ortho-rhom-bic Pca21 space group with Z = 4, the 1,4-di-hydro-pyridine ring adopts a distorted boat conformation, while the cyclo-hexene ring is in a distorted half-chair conformation. In the crystal, the mol-ecules are linked by N-H⋯O and C-H⋯O inter-actions, forming supra-molecular chains parallel to the a axis. These chains pack with C-H⋯π inter-actions between them, forming layers parallel to the (010) plane. The cohesion of the crystal structure is ensured by van der Waals inter-actions between these layers. Hirshfeld surface analysis shows the major contributions to the crystal packing are from H⋯H (56.9%), F⋯H/H⋯F (15.7%), O⋯H/H⋯O (13.7%) and C⋯H/H⋯C (9.5%) contacts.

Synthesis, characterization, crystal structure and Hirshfeld surface analysis of a hexa-hydro-quinoline derivative: tert-butyl 4-([1,1'-biphen-yl]-4-yl)-2,6,6-trimethyl-5-oxo-1,4,5,6,7,8-hexa-hydro-quinoline-3-carboxyl-ate.

The title compound, C29H33NO3, crystallizes with three mol-ecules (A, B and C) in the asymmetric unit. They differ in the twist of the phenyl and benzene rings of the 1,1'-biphenyl ring with respect to the plane of the 1,4-di-hydro-pyridine ring. In all three mol-ecules, the 1,4-di-hydro-pyridine ring adopts a distorted boat conformation. The cyclo-hexene ring has an envelope conformation in mol-ecules A and B, while it exhibits a distorted half-chair conformation for both the major and minor components in the disordered mol-ecule C. In the crystal, mol-ecules are linked by C-H⋯O and N-H⋯O hydrogen bonds, forming layers parallel to (100) defining R 1 4(6) and C(7) graph-set motifs. Additional C-H⋯π inter-actions consolidate the layered structure. Between the layers, van der Waals inter-actions stabilize the packing, as revealed by Hirshfeld surface analysis. The greatest contributions to the crystal packing are from H⋯H (69.6% in A, 69.9% in B, 70.1% in C), C⋯H/H⋯C (20.3% in A, 20.6% in B, 20.3% in C) and O⋯H/H⋯O (8.6% in A, 8.6% in B, 8.4% in C) inter-actions.

Crystal structure and Hirshfeld surface analysis of (Z)-2-amino-4-(2,6-di-chloro-phen-yl)-5-(1-hy-droxy-ethyl-idene)-6-oxo-1-phenyl-1,4,5,6-tetra-hydro-pyridine-3-carbo-nitrile.

The mol-ecular conformation of the title compound, C20H15Cl2N3O2, is stabilized by an intra-molecular O-H⋯O hydrogen bond, forming an S(6) ring motif. The central pyridine ring is almost planar [maximum deviation = 0.074 (3) Å]. It subtends dihedral angles of 86.10 (15) and 87.17 (14)°, respectively, with the phenyl and di-chloro-phenyl rings, which are at an angle of 21.28 (15)° to each other. The =C(-OH)CH3 group is coplanar. In the crystal, mol-ecules are linked by inter-molecular N-H⋯N and C-H⋯N hydrogen bonds, and N-H⋯π and C-H⋯π inter-actions, forming a three-dimensional network. The most important contributions to the crystal packing are from H⋯H (33.1%), C⋯H/H⋯C (22.5%), Cl⋯H/H⋯Cl (14.1%), O⋯H/H⋯O (11.9%) and N⋯H/H⋯N (9.7%) inter-actions.

Crystal structure and Hirshfeld surface analysis of 5,7-diphenyl-1,2,3,5,6,7-hexa-hydro-imidazo[1,2-a]pyridine-6,6,8-tricarbo-nitrile methanol mono-solvate.

In the title compound, C22H17N5·CH4O, the imidazolidine ring of the 1,2,3,5,6,7-hexa-hydro-imidazo[1,2-a]pyridine ring system is a twisted envelope, while the 1,2,3,4-tetra-hydro-pyridine ring adopts a twisted boat conformation. In the crystal, pairs of mol-ecules are linked by O-H⋯N and N-H⋯O hydrogen bonds via two methanol mol-ecules, forming a centrosymmetric R 4 4(16) ring motif. These motifs are connected to each other by C-H⋯N hydrogen bonds and form columns along the a axis. The columns form a stable mol-ecular packing, being connected to each other by van der Waals inter-actions. A Hirshfeld surface analysis indicates that the most significant contributions to the crystal packing are from H⋯H (43.8%), N⋯H/H⋯N (31.7%) and C⋯H/H⋯C (18.4%) contacts.

Crystal structures of 1-(4-chloro-phen-yl)-4-(4-methyl-phen-yl)-2,5-dioxo-1,2,5,6,7,8-hexa-hydro-quinoline-3-carb-oxy-lic acid and 4-(4-meth-oxy-phen-yl)-1-(4-methyl-phen-yl)-2,5-dioxo-1,2,5,6,7,8-hexa-hydro-quinoline-3-carbo-nitrile.

In the title compounds C23H21ClN2O3 [I, namely 1-(4-chloro-phen-yl)-4-(4-methyl-phen-yl)-3,8-dioxo-1,2,5,6,7,8-hexa-hydro-quine-3-carb-oxy-lic acid] and C24H22N2O3 [II, namely 4-(4-meth-oxy-phen-yl)-1-(4-methyl-phen-yl)-2,5-dioxo-1,2,5,6,7,8-hexa-hydro-quinoline-3-carbo-nitrile], each of the cyclo-hexene and di-hydro-pyridine rings of the 1,2,5,6,7,8-hexa-hydro-quinoline moieties adopts a twisted-boat conformation. The asymmetric units of both compounds I and II consist of two independent mol-ecules (A and B). In II A, three carbon atoms of the cyclo-hexene ring are disordered over two sets of sites in a 0.670 (11):0.330 (11) occupancy ratio. In the crystal of I, mol-ecules are linked through classical N-H⋯O hydrogen bonds, forming inversion dimers with an R 2 2(8) ring motif and with their mol-ecular planes parallel to the crystallographic (020) plane. Non-classical C-H⋯O hydrogen-bonding inter-actions connect the dimers, resulting in a three-dimensional network. In the crystal of II, mol-ecules are linked by C-H⋯N, C-H⋯O and C-H⋯π inter-actions, forming a three-dimensional network.

Crystal structure and Hirshfeld surface analysis of phen-yl(5,7,8a-triphenyl-1,2,3,7,8,8a-hexa-hydro-imidazo[1,2-a]pyridin-6-yl)methanone with an unknown solvent.

In the title compound, C32H28N2O, the imidazolidine and pyridine rings of the central hexa-hydro-imidazo[1,2-a]pyridine ring system adopt envelope and screw-boat conformations, respectively. The mol-ecule exhibits two weak intra-molecular π-π inter-actions between phenyl rings. In the crystal, mol-ecules are linked via pairs of C-H⋯ O hydrogen bonds, forming inversion dimers. The dimers are further linked by pairs of C-H⋯π inter-actions, forming infinite chains along the c-axis direction. A Hirshfeld surface analysis indicates that the most important contributions to the crystal packing are from H⋯H (73.4%), C⋯H/H⋯C (18.8%) and O⋯H/H⋯O (5.7%) contacts. The contribution of some disordered solvent to the scattering was removed using the SQUEEZE routine [Spek (2015 ▸). Acta Cryst. C71, 9-18] in PLATON. The solvent contribution was not included in the reported mol-ecular weight and density.

A state-of-the-art review of quinoline degradation and technical bottlenecks.

Quinoline is a critical raw material for the dye, metallurgy, pharmaceutical, rubber, and agrochemical industries, and its use poses a serious threat to human health and the ecological environment. Quinoline has carcinogenic, teratogenic and mutagenic effects on the human body through food accumulation. However, due to the steric hindrance of its bicyclic fused structure and its long photooxidation half-life, quinoline is too difficult to decompose naturally. To date, numerous technologies have been used to degrade quinoline, whereas only a few have been reviewed. Therefore, this paper is focused on offering a comprehensive overview of the state of quinoline degradation in an effort to improve its degradation efficiency and fully utilize the carbon and nitrogen within quinoline without causing any damage to the environment. Accordingly, the strains, research progress and mechanisms of various methods for degrading quinoline are explored and elucidated in detail, especially quinoline biodegradation and the combination of these technologies for efficient removal. The state-of-the-art processes and new findings of our team on the biofortification of quinoline degradation are also presented. Finally, research bottlenecks and gaps for future research were identified along with the prospects and resource utilization of quinoline. These discussions facilitate the realization of the zero discharge of quinoline.

(3Z,5E)-2-Amino-4,6-bis(pyridin-3-yl)hepta-1,3,5-triene-1,1,3-tricarbo-nitrile.

In the title compound, C20H14N6, the dihedral angle between the pyridine rings is 37.98 (7)°. In the crystal, N-H⋯N hydrogen bonds link the mol-ecules into (10) sheets.

6-(3,4-Di-fluoro-phen-yl)-7,8,13,14-tetra-hydro-dibenzo[c,k]phenanthridine.

In the title compound, C27H19F2N, the five-fused-ring system is highly puckered and the dihedral angle between the central pyridine ring and pendant di-fluoro-benzene ring is 45.12 (12)°. In the crystal, inversion dimers linked by pairwise weak C-H⋯N hydrogen bonds generate R 2 2(12) loops and the dimers are further linked by weak C-H⋯F inter-actions to form [01] chains.

New insights into clopyralid degradation by sulfate radical: Pyridine ring cleavage pathways.

Contamination by herbicides such as clopyralid (CLP) poses a significant threat to human health and ecological systems. In the present study, efficient removal of CLP was achieved by thermo activated persulfate, among which sulfate radical was identified as the predominant oxidizing species responsible for the decontamination. Based on high resolution LC-MS, derivatization method and density functional theory (DFT) computation, the detailed oxidation pathways and mechanisms were proposed. The primary oxidation pathways included dechlorination-hydroxylation, decarboxylation and the formation of quinone-like moieties. Afterwards, numerous intermediate byproducts ranging from high molecular to very small ones were identified, suggesting the pyridine ring was damaged during the thermo activated persulfate process. The detected products containing six and five carbons indicated the pyridine ring cleavage would take place on the quinone-structure intermediate. Further oxidation could continue by breaking each bond on the ring-cleavage product, yielding a series of short-chain carbonyl chemicals, carboxylic acids and inorganic ions. In addition, the presence of dissolved oxygen (DO) was favorable to CLP degradation, indicating DO played an important role in applying such technology. The degradation rate constants of CLP increased appreciably with increasing temperature, and acidic pH facilitated the CLP degradation. The results obtained in this work would increase our understanding on the environmental fates of nitrogen heterocyclic compounds during sulfate radical (SO4•-)-based advanced oxidation processes (SR-AOPs).

Facile Synthesis of Polysubstituted Indolizines via One-Pot Reaction of 1-Acetylaryl 2-Formylpyrroles and Enals.

An efficient method for the synthesis of polysubstituted indolizines has been developed based on formal [4+2] annulation of 1-acetylaryl 2-formylpyrroles with enals, followed by oxidative aromatization. Pyridine-type six-membered rings were constructed in this transformation. This transition metal-free reaction features mild reaction conditions, a broad substrate scope, and excellent functional group tolerance. Notably, the formyl group is well tolerated under reaction conditions.

Crystal structure and Hirshfeld surface analysis of (E)-5-phenyl-3-[(pyridin-4-yl-methyl-idene)amino]-thia-zolidin-2-iminium bromide monohydrate.

In the cation of the title salt, C15H15N4S+·Br-·H2O, the central thia-zolidine ring adopts an envelope conformation with puckering parameters Q(2) = 0.279 (4) Šand φ(2) = 222.5 (9)°. The mean plane of the thia-zolidine ring makes dihedral angles of 12.4 (2) and 66.8 (3)° with the pyridine and phenyl rings, respectively. The pyridine ring in the title mol-ecule is essentially planar (r.m.s deviation = 0.005 Å). In the crystal, the cations, anions and water mol-ecules are linked into a three-dimensional network, which forms cross layers parallel to the (120) and (20) planes via O-H⋯Br, N-H⋯Br and N-H⋯N hydrogen bonds. C-H⋯π inter-actions also help in the stabilization of the mol-ecular packing. Hirshfeld surface analysis and 2D (two-dimensional) fingerprint plots indicate that the most important contributions to the crystal packing are from H⋯H (35.5%), C⋯H/H⋯C (23.9%), Br⋯H/H⋯Br (16.4%), N⋯H/H⋯N (10.6%) and S⋯H/H⋯S (7.9%) inter-actions.

Role of the Tyr270 residue in 2-methyl-3-hydroxypyridine-5-carboxylic acid oxygenase from Mesorhizobium loti.

The flavoenzyme 2-Methyl-3-hydroxypyridine-5-carboxylic acid oxygenase (MHPCO) catalyzes the cleavage of the pyridine ring of 2-methyl-3-hydroxypyridine-5-carboxylic acid (MHPC) in the presence of NADH, molecular oxygen, and water. MHPCO also catalyzes the NADH oxidation reaction uncoupled with ring opening in the absence of MHPC (the basal activity). The enzyme shows activity toward not only MHPC but also 5-hydroxynicotinic acid (5HN) and 5-pyridoxic acid (5PA). The reaction rate toward 5PA is extremely low (5% of the activity toward MHPC or 5HN). We determined the crystal structures of MHPCO without substrate and the MHPCO/5HN and MHPCO/5PA complexes, together with a Y270F mutant without substrate and its 5HN complex. The Tyr270 residue was located in the active site and formed hydrogen bonds between the Oη and water molecules to make the active site hydrophilic. Although Tyr270 took a fixed conformation in the structures of the MHPCO and MHPCO/5HN complex, it took two conformations in its 5PA complex, accompanied by two conformations of the bound 5PA. In the wild-type (WT) enzyme, the turnover number of the ring-opening activity was 6800 times that of the basal activity (1300 and 0.19 s-1, respectively), whereas no such difference was observed in the Y270F (19 and 7.4 s-1) or Y270A (0.05 and 0.84 s-1) mutants. In the Y270F/5HN complex, the substrate bound ∼1 Å farther away than in the WT enzyme. These results revealed that Tyr270 is essential to maintain the WT conformation, which in turn enhances the coupling of the NADH oxidation with the ring-opening reaction.

Inhibition of chikungunya virus by picolinate that targets viral capsid protein.

The protein-protein interactions (PPIs) of the transmembrane glycoprotein E2 with the hydrophobic pocket on the surface of capsid protein (CP) plays a critical role in alphavirus life cycle. Dioxane based derivatives targeting PPIs have been reported to possess antiviral activity against Sindbis Virus (SINV), the prototype alphavirus. In this study, the binding of picolinic acid (PCA) to the conserved hydrophobic pocket of capsid protein was analyzed by molecular docking, isothermal titration calorimetry (ITC), surface plasmon resonance (SPR) and fluorescence spectroscopy. The binding constant KD obtained for PCA was 2.1×10(-7)M. Additionally, PCA significantly inhibited CHIKV replication in infected Vero cells, decreasing viral mRNA and viral load as assessed by qRT-PCR and plaque reduction assay, respectively. This study is suggestive of the potential of pyridine ring compounds as antivirals against alphaviruses and may serve as the basis for the development of PCA based drugs against alphaviral diseases.