Alkaloids of Arundo donax. XIV. Crystal and Molecular Structure of N-Methyl-tetrahydro- β-carboline

An indole alkaloid of the N-methyl-tetrahydro--carboline series was isolated for the first time from Arundo donax, Poaceae. Its structure was solved by X-ray structure analysis.     

Chemical Components of Helicai nilagirica Beed.I.Structure of Three New Flavonol Glycosides

Three new flavonol glycosides were isolated from the leaves of Helicia nilagirica Beed.The structures were elucidated as kaempferol-3-O-β-D-xylopyranosyl-(1→6)-β-D-glyco-pyranosyl-(1→2)-α-L－rhamnopyranoside,quercetin-3-O-β-D-xylopyranosyl-(1→6)-β-D-glycopy-ranosyl-(1→2)-[-β-D-xylopyranosyl-(1→4)]-α-L-rhamnopyranoside,and quercetin-3-O-β-D-xylopyranosyl-(1→6)-β-D-glycopyranosyl-(1→2)-α-L-rhamnopyranoside,nmaed as Hcilcianeoside A、B and C ,respectively.     

Chemical Components of Helicia nilagirica Beed.I.Structure of Three New Flavonol Glycosides

Helicia nilagirica Beed. belongs to the plant of Proteaceae family. The seeds of the plant is for treatment of insomnia and neurasthenia in Jingpo nationality in Yunnan Province1. Helicid and helicidol were isolated from the seeds of the plant2,3, and the helicid was recorded in the Yunnan Pharmacopoea at the 1987 edition. The chemical constituents of the leaves of this plant has not been reported yet in the literature. This paper is concerning the study of the chemical component of the…     

Electronic Structure of π Systems: XIX. Keto-Enol Tautomerism of Dihydrofurocoumarinones

Tautomeric transformations of 4-methyldihydrofuro[2,3-h]coumarin-9-one and its 8-substituted derivatives were studied by ¹H NMR, electronic absorption spectroscopy, and quantum chemistry. The ¹H NMR spectra of these compounds in CDCl₃ show that they exist in the ketone form, and in more polar sol- vents they can pass into the enol form. By electronic absorption spectroscopy it was established that the derivatives containing electron-acceptor substituents in the 8 position of the furanone ring undergo tautomeric transformations as the composition of the solvent is varied from 100% methanol to 100% CCl₄. At the same time, the derivatives with electron-donor substituents in the same position do not show any specific alterations in the absorption spectra with solvent. Analogous pattern was observed in the enolization of substituted di- hydrofurocoumarinones by acetylation: In presence of electron-donor substituents in the 8 position, no acetyla- tion occurred, while with the compounds containing electron-acceptor substituents, the corresponding 9-acet- oxy-4-methylangelicins were prepared in high yields. Calculations by the PPP/CI method of the electronic absorption spectra 4-methyldihydrofuro[2,3-h]coumarin-9-one showed that in polar solvents (methanol) it prefers the enol form. Data of spectral measurements were compared with results of semiempirical (MNDO, AM1, and PM3) and nonempirical quantum-chemical calculations (with 3-21G, 6-31G^*, and 31G^** basis sets).     

Halogenated pyridines 5. Structure of the products of cyclization of chlorine-containingδ-oxonitriles

Cyclization of the nitriles of polychlorinated-oxoacids — products the addition of chloral to acrylonitrile and methacrylonitrile — yielded chlorine-containing tetrahydropyridines. Their structure and some of their chemical properties have been studied.For communication 4, see [8].A. N. Kosygin Moscow State Textile Academy, Moscow 117918. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 365–370, March, 1995. Original article submitted December 26, 1994.     

Structure and Energetics of β-Diketonates. XII. Structure of Lanthanide tris-Dipivaloylmethanates for Er(thd)3 Used as an Example

A simultaneous electron diffraction and mass spectroscopic study of saturated vapors of erbium tris-dipivalylmethanate has revealed that at 136(5)°C, the vapor consists solely of Er(thd)₃ molecules. Electron diffraction data may be described by two alternative models (of C_3 and D_3 symmetry), for which r_a, r_g, and r structural parameters have been determined. D₃ symmetry is recognized to be preferable for free Er(thd)₃ molecules. The main structural parameters of the model are r (Er – O) 2.218(5), r (O – C) 1.279(5), r (C – C_r) 1.404(6), r (C – C_t) 1.512(3), r(C_t – C_m) 1.542(5), r (rm C_m– H) 1.804(4) , The ErO 75.0(0.4)°. The ErO₆ coordination polyhedron has a structure close to an antiprism. A rotational angle of the O–O–O trigonal face relative to the position in a regular prism is 20.7(0.8)°. Possible reasons for the differences in the structure of Er(thd)₃ molecules in the gas phase and crystal are discussed.     

Structure of Potassium of Undecatungstomononickelosilicate

ＳｔｒｕｃｔｕｒｅｏｆＰｏｔａｓｓｉｕｍｏｆＵｎｄｅｃａｔｕｎｇｓｔｏｍｏｎｏｎｉｃｋｅｌｏｓｉｌｉｃａｔｅＱｕＬｕｎ－Ｙｕ；ＭａＲｏｎｇ－Ｈｕａ；ＣｈｅｎＹａ－Ｇｕａｎｇ（ＤｅｐａｒｔｍｅｎｔｏｆＣｈｅｍｉｓｔｒｙ，ＮｏｒｔｈｅａｓｔＮｏｒｍａｌＵ...     

Structure and Energy Studies of β-Diketonates. X. Molecular Structure of Sc(aa)3 According to Gas-Phase Electron Diffraction Data

Synchronous electron diffraction and mass spectrometric investigation of the saturated vapor of scandium tris-acetylacetonate was carried out. It was stated that at 155(5)°C the vapor contains only monomeric Sc(aa)₃ molecules, whose structural parameters r _a , r _g , and r were determined. The internuclear distances in the chelate ring were found to be r (Sc–O) = 2.076(4) , r (O–C) = 1.271(3) , r (C–C_r) = 1.386(4) . The coordination polyhedron ScO₆ has a nearly antiprism structure of D ₃ symmetry. The angle of rotation of the O–O–O trigonal faces relative to their position in a regular prism is 26.8(1.1)°.     

Synthesis and Structure of Solvated Protons Incorporating Weakly Coordinating Anions. Precursors of Superacids

ＩｎｔｒｏｄｕｃｔｉｏｎＩｔｉｓｕｎｉｖｅｒｓａｌｌｙｕｎｄｅｒｓｔｏｏｄｔｈａｔｗｒｉｔｉｎｇＨ+ ｉｓｓｈｏｒｔ ｈａｎｄｆｏｒａｓｏｌｖａｔｅｄｐｒｏｔｏｎ ,[Ｈ(ｓｏｌｖｅｎｔ) ｎ]+ ,ｔｈｅｖａｌｕｅｏｆｎａｎｄｔｈｅｄｅｔａｉｌｓｏｆｔｈｅｃｏｏｒｄｉｎａｔｉｏｎｅｎｖｉｒｏｎｍｅｎｔａｒｅｏｆｔｅｎｕｎｓｐｅｃｉｆｉｅｄ .Ｉｓｏｌａｔｉｏｎａｎｄｓｔｒｕｃｔｕｒａｌｃｈａｒａｃｔｅｒｉｚａｔｉｏｎｏｆｖａｒｉｏｕｓｓａｌｔｓｃｏｎｔａｉｎｉｎｇｒｅｐｒｅｓｅｎｔａｔｉｖｅ [Ｈ(ｓｏｌｖｅｎ…     

Polymorphism of Inclusion Complexes and Unsolvated Hosts. I. Trimorphism of the Host-Guest Complex of Gossypol with Dichloromethane. The Structure of the β-Phase

The formation of host-guest complexes of gossypol at different temperatures has been investigated for the same pressure and concentration. Gossypol forms three different clathrates with dichloromethane within the temperature interval of 22-36 °C. Single crystals of these three modifications (phases) were obtained and their crystallographic parameters measured. The structure of the -phase has been determined previously and the -phase is isostructural to the inclusion complex of gossypol with benzene, while the structure of the -phase has been solved during the present research. Crystals of C30H30O8·CH2Cl2 are triclinic, space group P1, a = 8.604(1), b = 11.858(2), c = 14.405(2) (Å), = 84.60(1), = 89.14(1), = 89.73(1)°, V = 1463(1) Å3, Z = 2, R = 0.089 for 2419 observed reflections.Under ambient conditions gossypol forms unstable tubulates of the -phase; the -phase is a stable cage-type clathrate (cryptate) and the host-guest complex of the -phase is a clathrate of intermediate tubulato-cryptate type.     

Crystal Structure of N-Phenylisothiocyanatido-Phosphonamidothioate

1INTRODUCTIONLawess0n,Sreagent(LR),2,4-Bis(4-meth0xyphenyl)-1,3,2'4-dithiadiphosphetane-2,4-disulfide,notonlyisaselectivereagentf0rthi0natingcar-bonylcompounds,buta1soreactswithcertainsubstratestogivephosph0rushetero-cyclecompoundswhichcontainthe(4-methoxyphenyl)phosphinothi0ylidene"4-CH,OC,H'P(S)"m0iety.Theseheterocycliccompoundshavesomepotentialbiologi-calactivitiesasherbicides,fungicides,andinsecticides[l'2J.Wehavestudiedthecy-clizationofthebifunctionalsubstrateswithLRtogive5-and6…     

The Structure of Cellulose by Conformational Analysis. 1. Cellobiose and Methyl-β-cellobioside

Conformational analysis studies on the tertiary structure of cellobiose and methyl-β-cellobioside were carried out by using calculations of van der Waals, H-bond, electrostatic, and torsional energy interactions between the atoms and groups of the molecules. Energy maps as functions of the rotational anglesΨo and Φ° of the glucosidic bond were obtained in increments of 20° and refined in increments of 1°. Two “primary” and one “secondary” conformations of minimum energy were obtained for both cellobiose and methyl-β-cellobioside, some of which are equivalent to results obtained by x-ray diffraction. The H-bond forces are shown to be, together with the van der Waals forces, the predominant factors in the fixation of the conformations of minimum energy. The position and energy contributions of the H-bonds patterns for the favored conformations are identified.     

Polymorphism of Inclusion Complexes and Unsolvated Hosts. II. Structure of the β-Dimorph of the Host-Guest Complex of Dianilinegossypol with Ethylacetate

Depending on crystallization conditions, dianilinegossypol and ethylacetate form low (ambient temperature, -phase) and high temperature (t = 35°C, -phase) clathrate modifications. The structure of the -phase has been discussed earlier [1]. Crystals of the 1 : 1 -phase complex, C42H40O6N2·C4O2H8, are monoclinic, space group P21/c, a = 11.362(6), b = 19.479(9), c = 19.085(9) Å, = 103.21(4)°, V = 4112(3)Å3, Z = 4, R = 0.084 for 3210 observed reflections.In these complexes centrosymmetric dimers of dianilinegossypol molecules formed via O(5)—H···O(3) hydrogen bonds are associated into columns by a weak O(8)—H···O(7) H-bond. A difference in the structure of these two phases is in the packing mode of the columns. The angle formed by intersecting host columns is about 126° for the -phase and 104° for the -modification. Guest molecules are hydrogen bonded to the host molecules via an O(1)—H···O(10) bond and are accommodated in channels in -phase complex and in cavities in -phase complex.     

Isolation and Structure of 1-Deoxybaccatin VI from the Root of Taxus chinensis, Rehd. var. mairei

Deoxybaccatin Ⅵ (4α,7β,9α,10β,13α-penta-acetoxy-2α-benzoyloxy-5β,20-epoxytax-11-ene) was isolated from the roots of Taxus chinensis, Rehd. var. mairei. The structural assignments of the compound were based on their spectral data, including 2D NMR experiments and chemical correlation. The X-ray crystallographic analysis of 1-deoxybaccatin Ⅵ provided unambiguous characterization for the structures. In the structure, the six-membered A ring exhibits boat conformation, the eight-membered B ring adopts boat-chair conformation, and the six-membered C ring exhibits a sofa conformation.     

Supramolecular Ribbons. Crystal Structure and Spectroscopic Properties of 2,2′-Bipyrroyl

Summary.  A crystal structure determination of 2,2′-bipyrroyl (1; 2,2′-dipyrryl-diketone, bis (2-pyrrolyl)ethanedione) and its spectroscopic properties in solution are reported. In the crystal, 1 self-assembles via hydrogen bonding into supramolecular ribbons that extend indefinitely through the crystal lattice. The observed molecular conformation is one where each pyrrole ring and adjacent carbonyl group are co-planar (torsion angle ∼ 0.9°), with the N-H pointing in the same direction as the C=O. The two carbonyls have a transoid but not co-planar geometry with a torsion angle of ∼128°. Adjacent molecules in the crystal are linked by pairs of intermolecular hydrogen bonds, pyrrole NH to carbonyl oxygen, to form a matrix of polymeric chains that lie like neatly stacked, parallel streams of ribbons. Molecular mechanics calculations on the monomer indicate an intra-molecularly hydrogen bonded planar conformation (sp, ap, sp) at the global energy minimum. In CHCl₃, 1 is monomeric according to vapor pressure osmometry (MW _obs=179±10 vsċMW _calc=188). In THF, the measured molecular weight is 340±15, which corresponds best to one molecule of 1 solvated by two THF molecules (MW=322 for C₁₀H₈N₂O₄ċ2 C₄H₈O) rather than to a dimer. Received October 21, 1999. Accepted November 2, 1999     

Supramolecular Ribbons. Crystal Structure and Spectroscopic Properties of 2,2′-Bipyrroyl

 A crystal structure determination of 2,2′-bipyrroyl (1; 2,2′-dipyrryl-diketone, bis (2-pyrrolyl)ethanedione) and its spectroscopic properties in solution are reported. In the crystal, 1 self-assembles via hydrogen bonding into supramolecular ribbons that extend indefinitely through the crystal lattice. The observed molecular conformation is one where each pyrrole ring and adjacent carbonyl group are co-planar (torsion angle ∼ 0.9°), with the N-H pointing in the same direction as the C=O. The two carbonyls have a transoid but not co-planar geometry with a torsion angle of ∼128°. Adjacent molecules in the crystal are linked by pairs of intermolecular hydrogen bonds, pyrrole NH to carbonyl oxygen, to form a matrix of polymeric chains that lie like neatly stacked, parallel streams of ribbons. Molecular mechanics calculations on the monomer indicate an intra-molecularly hydrogen bonded planar conformation (sp, ap, sp) at the global energy minimum. In CHCl₃, 1 is monomeric according to vapor pressure osmometry (MW _obs=179±10 vsċMW _calc=188). In THF, the measured molecular weight is 340±15, which corresponds best to one molecule of 1 solvated by two THF molecules (MW=322 for C₁₀H₈N₂O₄ċ2 C₄H₈O) rather than to a dimer.     

Structure of the lowest triplet states of poly-α-methylstyryl sodium.Ab initio calculations

Ab initio optimization of a poly-α-methylstyryl sodium (PMSNa) fragment consisting of two eis units yields a triplet state energy which is close to the ground state energy. A new mechanism is proposed for depolymerization of “living” polymers, which implies that an elementary step involves excitation to the low-lying triplet state with a charge transfer and with further bond cleavage. In the reaction structure, electronic excitation occurs with a minor (≈0.5 Å) displacement of the Na⁺ cation between the last and the last but one monomer units. The reversible polymerization/depolymerization reaction of PMSNa in THF was studied experimentally. The experimental (5.6 kcal/mole) and calculated (7.3 kcal/mole) polymerization enthalpies are in reasonable agreement.     

Extraction and Structure Investigation of the Poly-saccharides from the Pollen of Typha Angustifolia L.

Three polysaccharides, TAA, TAB, TAC have been isolated from the pollen of Typha angustifolia L. , and purified by hot water extraction, alcohol precipitation, Sevage method, gel filtration (Sephadex G50) and ion-exchange chromatography on DEAE Sephadex A25 and DEAE-cellulose. Their purities were tested by gel filtration and electrophoresis. Their structures were characterized by paper chromatography of the hydrolysis products, GLC analysis of the alditol acetates, alkylation analysis, 1H NMR and 13C NMR spectra. TAA is mainly composed of a-L-arabinofuanose, β-D-galactose and α-D-galacturonic acid, while the backbones of TAB and TAC are composed of (1→5)-linked α- L-arabinofuranosyl residues.