Twist-boat Conformation Research Articles

IMDAV reaction between phenyl-maleic anhydride and thien-yl(fur-yl)allyl-amines: synthesis and mol-ecular structure of (3aSR,4RS,4aRS,7aSR)-5-oxothieno- and (3aSR,4SR,4aRS,7aSR)-5-oxofuro[2,3-f]iso-indole-4-carb-oxy-lic acids.

The title compounds C24H21NO3S, I, and C24H21NO4, II, are the products of the IMDAV reaction between phenyl-maleic anhydride and thien-yl(fur-yl)allyl-amines. Their mol-ecular structures comprise fused tricyclic systems containing thio-phene, cyclo-hexene and pyrrolidine rings (I) or furan, cyclo-hexene and pyrrolidine rings (II). The central cyclo-hexene and pyrrolidine rings in both compounds adopt slightly twisted boat and envelope conformations, respectively. The dihedral angles between the basal plane of the pyrrolidine ring and the thio-phene (in I) or furan (in II) ring plane are 22.74 (16) and 26.29 (5)°, respectively. The nitro-gen atom both in I and II has practically planar environment [the sums of the bond angles are 359.8 and 358.9°, respectively]. In the crystal of I, the mol-ecules form hydrogen-bonded zigzag chains along [010] through strong inter-molecular O-H⋯O hydrogen bonds involving carb-oxy-lic and keto groups, whereas in the crystal of II, the mol-ecules are joined into centrosymmetric dimers by strong O-H⋯O hydrogen bonds between the carb-oxy-lic groups. In II, the atoms involved into these hydrogen bonds (and hence the whole carb-oxy-lic group) are disordered over two sets of sites with an occupancy ratio of 0.6:0.4. Compounds I and II crystallize as racemates consisting of enanti-omeric pairs of the 3aSR,4RS,4aRS,7aSR and 3aSR,4SR,4aRS,7aSR diastereomers, respectively.

Structural Characterization of 11-Ethyl-6,11-Dihydro-5H-Dibenzo[b,e]Azepine

The title compound C16H17N, a potential pharmaceutical agent, crystallizes in the monoclinic P21/n space group with unit cell parameters a = 9.911(7) A, b = 5.542(3) A, c = 23.245(16) A, β = 96.25(2)°. The dibenzazepine ring adopts a twist-boat conformation. The crystal packing is entirely dominated by cohesive weak N–H⋯Cg(π) and Cg(π)⋯Cg(π) interactions among the neighboring molecules producing an efficient packing with 66.4% of the occupied space.

Fragilides K and L, New Briaranes from the Gorgonian Coral Junceella fragilis.

Two new briarane metabolites—fragilides K (1) and L (2)—along with five known analogues—gemmacolide X, praelolide, juncins P and ZI, and gemmacolide V (3–7)—were extracted and purified from Junceella fragilis, a gorgonian coral. Based on data obtained via spectroscopic techniques, the structures of new briaranes 1 and 2 were determined and the cyclohexane rings in 1 and 2 were found to exist in chair and twist boat conformation, respectively. Additionally, anti-inflammatory analysis showed that briaranes 2, 3, and 6 inhibited pro-inflammatory inducible nitric oxide synthase protein expression and briaranes 3 and 7 suppressed the cyclooxygenase-2 level, in LPS-stimulated murine macrophage-like RAW264.7 cells.

Qualitative and quantitative analysis of intermolecular interactions in xanthenedione derivatives.

The existence of intermolecular interactions and the conformational geometry adopted by molecules are related to biological activity. Xanthenedione molecules are promising and emerging antioxidants and acetylcholinesterase inhibitors. To examine the role of different functional groups involved in the intermolecular interactions and conformational geometries adopted in xanthenediones, a series of three substituted xanthenediones have been crystallized [9-(3-hydroxyphenyl)-3,3,6,6-tetramethyl-3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H)-dione, C23H26O4, 9-(5-bromo-2-methoxyphenyl)-3,3,6,6-tetramethyl-3,4,6,7-tetrahydro-2H-xanthene-1,8(5H,9H)-dione, C24H27BrO4, and 3,3,6,6-tetramethyl-9-(pyridin-2-yl)-3,4,6,7-tetrahydro-2H-xanthene-1,8(5H,9H)-dione, C22H25NO3] and their intermolecular interactions analyzed via Hirshfeld analysis. The results show that all the derivatives adopt the same structural conformation, where the central ring has a shallow boat conformation and the outer rings have a twisted boat conformation. The intermolecular interactions in the molecules are predominantly O-H...O, C-H...O and π-π interactions. The optimized structures of the derivatives from theoretical B3LYP/6-311G** calculations show a good correlation with the experimental structures. The lattice energy involved in the intermolecular interactions has been explored using PIXELC.

Hexakis(3,6-di-tert-butyl-4-oxo-2,5-cyclohexadien-1-ylidene)cyclohexane: Closed-Shell [6]Radialene or Open-Shell Hexa-Radicaloid?

A star-shaped hexaquinocyclohexane molecule 4 c is reported, which turns out to be a closed-shell extended [6]radialene with a twisted-boat conformation according to X-ray crystallographic analysis. It was formed by an unusually slow decay of its in situ generated open-shell valence isomer, the hexa-radicaloid 4 o, with a half-life time of about 156 min at room temperature. Reaction progress kinetic analysis revealed a large energy barrier of about 95.5±4.3 kJ mol-1 at room temperature from the hexa-radical form 4 o to the contorted [6]radialene form 4 c, because the transformation needs to overcome large steric repulsion between the neighboring phenoxyl units. Compound 4 c can be chemically reduced to radical anion and dianion, and the dianion is actually a diradical dianion, with a calculated diradical character of 71.9 %. This study demonstrates the unique chemical bonding nature of contorted quinoidal π-conjugated molecules and a very unusual valence isomerization process.

2-Amino-4-(4-methoxyphenyl)-1-(4-methylphenyl)-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carbonitrile

In the title compound, C24H23N3O2, the cyclohexene and 1,4-dihydropyridine rings of the 1,4,5,6,7,8-hexahydroquinoline ring system each adopt a twisted-boat conformation. The dihedral angle between the benzene rings is 13.89 (10)°. In the crystal, molecules are linked through pairs of amino–nitrile N—H...N hydrogen bonds, forming inversion dimers. Weak C—H...O and C—H...π interactions connect the dimers, forming a three-dimensional network.

Crystal structure of ethyl 2-methyl-5,10-dioxo-4-phenyl-5,10-di-hydro-4H-11-thia-1,4a-di-aza-benzo[b]fluorene-3-carb-oxy-late.

The title compound, C24H18N2O4S, crystallizes in the ortho-rhom-bic P212121 space group, indicating the existence of only one enanti-omer with an S configuration of the chiral center in the crystal phase. The di-hydro-pyrimidine ring adopts a twist-boat conformation while the quinone ring is slightly non-planar. In the crystal, mol-ecules are linked by weak C-H⋯O and C-H⋯S hydrogen bonds and C-H⋯π inter-actions. In addition, a short inter-molecular S⋯N contact of 3.250 (3) Å indicates an inter-action between the S atom and the π-system of the thia-zole ring.

Crystal structure of ethyl 2-cyano-2-(1,3-di-thian-2-yl-idene)acetate.

The title compound, C9H11NO2S2, contains a 1,3-di-thiane ring which has a twist-boat conformation. The dihedral angle between the mean planes of the ethyl acetate group and the di-thiane ring is 17.56 (13)°. In the crystal, mol-ecules stack in layers up the a-axis direction, however, there are no significant inter-molecular inter-actions present.

Zinc Tin Chalcogenide Complexes and Their Evaluation as Molecular Precursors for Cu2ZnSnS4 (CZTS) and Cu2ZnSnSe4 (CZTSe).

A series of five heteronuclear zinc tin chalcogenide complexes with the general formula [(tmeda)Zn(SnR2)2E3] (1-R, E = S; R = Me, Ph, tBu; 2-R, E = Se; R = Ph, tBu) have been synthesized and characterized by X-ray crystal structure analysis. In all cases, the six-membered ZnSn2E3 rings exhibit twist boat conformation. The presence of the molecular structures in solution is confirmed by 119Sn and 77Se NMR spectroscopy. Cothermolysis experiments using a mixture of complexes 1-R or 2-R and [(iPr3PCu)2(EC2H4E)]2 as a copper source were monitored by thermogravimetry and temperature dependent X-ray powder diffraction to examine the thermolysis reaction. According to Rietveld refinement, the solid residue consists of Cu2ZnSnS4 (up to 78 wt %) or Cu2ZnSnSe4 (up to 43 wt %) as the main product, respectively.

A new approach to alkaloid-like systems: synthesis and crystal structure of 1-(2-acetyl-11-meth-oxy-5,6-di-hydro-[1,3]dioxolo[4,5-g]pyrrolo-[2,1-a]isoquinolin-1-yl)propan-2-one.

The title compound, C19H19NO5, (I), is the product of a domino reaction between cotarnine chloride and acetyl-acetylene catalysed by copper(I) iodide. The mol-ecule of (I) comprises a fused tetra-cyclic system containing two terminal five-membered rings (pyrrole and 1,3-dioxole) and two central six-membered rings (di-hydro-pyridine and benzene). The five-membered 1,3-dioxole ring has an envelope conformation and the central six-membered di-hydro-pyridine ring adopts a twist-boat conformation. The acyl substituent is almost coplanar with the pyrrole ring, whereas the meth-oxy substituent is twisted by 27.93 (16)° relative to the benzene ring. The 2-oxopropan-1-yl substituent is roughly perpendicular to the pyrrole ring. In the crystal, mol-ecules are stacked along the a-axis direction; the stacks are linked by weak C-H⋯O hydrogen bonds into puckered layers lying parallel to (001).

Spectral analysis and quantum chemical studies of chair and twist-boat conformers of cycloheximide in gas and solution phases

In this study the conformational behavior of cycloheximide in the gas and solution (CHCl3) phases has theoretically been investigated by spectroscopic and quantum chemical properties using density functional theory (wB97X-D) method with 6–31++G(d,p) basis set, for the first time. The calculated IR results reveal that in the ground state the molecule exits as a mixture of the chair and twist-boat conformers in the gas phase, while the calculated NMR results reveal that it only exits as the chair conformer in the solution phase. In order to obtain the contributions coming from intramolecular interactions to the stability of the conformers in the gas and solution phases, the quantum theory of atoms in molecules (QTAIM), noncovalent interactions (NCI) method, and natural bond orbital analysis (NBO) have been employed. The QTAIM and NCI methods indicated that by intramolecular interactions with bond critical point (BCP) the twist-boat conformer is more stabilized than the chair conformer, while by steric interactions it is more destabilized. Considering that these interactions balance each other, the stabilities of the conformers are understood to be dictated by the van der Waals interactions. The NBO analyses show that the hyperconjugative and steric effects play an important role in the stabilization in the gas and solution phases. Furthermore, to get a better understanding of the chemical behavior of this important antibiotic drug we have evaluated and, commented the global and local reactivity descriptors of the both conformers. Finally, the EPR analysis of γ-irradiated cycloheximide has been done. The comparison of the experimental and calculated data have showed the inducement of a radical structure of (CH2)2ĊCH2 in the molecule. The experimental EPR spectrum has also confirmed that the molecule simultaneously exists in the chair and twist-boat conformers in the solid phase.

Coordination mode of the N-[bis(diethylamino)phosphoryl]benzenesulfonamide ligand in Lu(III) and Ag(I) complexes. Mass spectra, thermal properties and DFT calculations

The sulfonylamidophosphate ligand C6H5SO2NHPO(N(C2H5)2)2 (HL) has been used for the synthesis of two novel complexes: LuL3 (1) and (AgL)n (2). According to an X-ray diffraction study, in the structure of HL, the molecules are linked into polymeric chains by strong N–H⋯O = P hydrogen bonds. The three acido-ligands (L−) in the structure of 1 are coordinated to the lutetium ion in a bidentate-chelate manner via two oxygen atoms of the phosphoryl and sulfonyl groups, forming six-membered metallocycles, which adopt a boat conformation. In the structure of 2, the ligand is coordinated in the bidentate-bridging mode via the oxygen atom of the phosphoryl group and the nitrogen atom of the imide group; the chelate adopts a twist-boat conformation. The thermal behavior of the complexes 1 and 2 was studied by means of TG analysis. Results of IR-spectroscopy and LDI, ESI MS are discussed and compared with those obtained from DFT calculations.

Synthesis, characterization, stereochemistry and biological investigation of certain N-dichloroacetyl-bis(2-chlorophenyl)piperidin-4-ones

A new series of N-dichloroacetyl-bis(2-chlorophenyl)piperidin-4-ones 4-6 has been synthesized and characterized using IR, 1H, 13C, DEPT and 2D (COSY and HSQC) NMR spectral techniques. The NMR spectral data indicate that the N-acylpiperidin-4-ones 4-6 prefer to exist in an equilibrium between the twist boat conformations with coplanar orientation of NCO moiety. Furthermore, the antibacterial and antifungal studies have been carried out for compounds 1-6 and the results show that they possess significant activity towards the bacterial organisms Staphylococcus aureus and Salmoneela paratyphi and better activity against the remaining bacterial organisms. All the compounds 1-6 possess moderate antifungal activity. The compounds 4-6 have been docked with the structure of MRSA and the results demonstrate that the compounds 4-6 have similar docking score and glide energy when compared to each other and thus having equal binding affinity. The antioxidant studies show greater activity for compound 4 and poor activity for compounds 5 &6 when compared to the standard drug.

Unusual formation of (E)-11-(amino-methyl-ene)-8,9,10,11-tetra-hydro-pyrido[2',3':4,5]pyrimido[1,2-a]azepin-5(7H)-one and its crystal structure.

Selective C-formyl-ation of 8,9,10,11-tetra-hydro-pyrido[2',3':4,5]pyrimido[1,2-a]-azepin-5(7H)-one has been studied for the first time. It was revealed that formyl-ation proceeds by the formation of an inter-mediate salt, which due to the re-amination process on treatment with aqueous ammonia transformed into the corresponding (E)-11-(amino-methyl-ene)-8,9,10,11-tetra-hydro-pyrido[2',3':4,5]-pyrimido[1,2-a]azepin-5(7H)-one, C13H14N4O, as an E-isomer. Formyl-ation was carried out by Vilsmeier-Haack reagent and the structure of the synthesized compound was confirmed by X-ray structural analysis, spectroscopic and LC-MS methods. In the mol-ecule, the seven-membered penta-methyl-ene ring adopts a twist-boat conformation.

Crystal structure of hexa-methyl 4,4',4'',4''',4'''',4'''''-[(1,3,5,2λ5,4λ5,6λ5-tri-aza-triphosphinine-2,2,4,4,6,6-hexa-yl)hexa-kis-(-oxy)]hexa-benzoate.

The title compound, C48H42N3O18P3, achieved in a two-step synthesis, comprises a cyclo-triphosphazene core and six 4-meth-oxy-carbonyl-phen-oxy groups. Each P atom is attached to two substituents located up and down with respect to the plane of the phosphazene ring, the central P3N3 ring having a twist-boat conformation. The three O/P/O planes and five of the six benzene rings are nearly perpendicular to the mean plane through the phosphazene ring [dihedral angles = 82.98 (8)-88.92 (8)°], while the remaining benzene ring forms a dihedral angle of 25.72 (7)°. The crystal packing is stabilized by van der Waals inter-actions only.

(E)-2-Phenyl-4-styryl-2,3-dihydro-1H-1,5-benzodiazepine hemihydrate

The unit cell contains eight molecules of the title compound, with half a water molecule per main molecule, C23H20N2·0.5H2O. The seven-membered diazepine ring adopts a twist-boat conformation and makes dihedral angles of 85.08 (7) and 32.79 (7)° with the phenyl and styryl substituents, respectively. In the crystal, the organic molecules are linked by C—H...N hydrogen bonds into chains running along the b-axis direction. The water molecule, located on a twofold rotation axis, forms hydrogen bridges, connecting two adjacent chains.

Methyl 2-cyano-2-(1,3-dithian-2-ylidene)acetate

The title compound, C8H9NO2S2, contains a 1,3-dithiane ring which has a twist-boat conformation. In the crystal, there are no significant intermolecuar interactions present. The dihedral angle between the planes of the acetate group and the dithiane ring is 177.1 (2)°

Asymmetric Synthesis of the Antiviral Diterpene Wickerol A

Wickerol A (1) is an unusual diterpene with remarkable activity against the H1N1 influenza virus. Its tetracyclic skeleton contains three quaternary carbons and is marked by several syn-pentane interactions which force a six-membered ring into a twist-boat conformation. We present an asymmetric synthesis of wickerol A (1) that is based on a Jung Diels-Alder reaction, an intramolecular alkylation to complete the 6-5-6-6 ring system, and a conjugate addition, all of which overcome considerable steric strain. During the synthesis, we isolated an unexpected cyclopropane that presumably stems from a carbonium ion intermediate.

(Z)-2-(2-Chlorobenzylidene)-4-(prop-2-ynyl)-2H-1,4-benzothiazin-3(4H)-one

In the title compound, C18H12ClNOS, the thiazine-3-one ring of the 1,4-thiazin-3-one moiety adopts a slightly distorted twist-boat conformation. The dihedral angle between the benzene rings is 86.2 (1)°. In the crystal, the crystal packing features a single weak C—H...O interaction and weak π–π stacking interactions.

Synthesis and characterization of 3-methyl-6-[(propyn-yloxy)meth-yl]-1,4-dioxane-2,5-dione.

The number of known asymmetrically substituted hemilactides, important precursors for obtaining regular derivatives of polylactide polymers, is still limited and structural characterization of most of them is incomplete. In the title racemic 1,4-dioxane-2,5-dione derivative, C9H10O5, the hemilactide heterocycle exhibits a twist-boat conformation. The bulkier propynyloxymethyl group is in an axial position with a gauche conformation for the CH2-O-CH2-C segment. In the crystal, mol-ecules are linked by pairs of C-H⋯O hydrogen bonds, forming inversion dimers. The dimers are linked by further C-H⋯O contacts, forming a three-dimensional structure.