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1.
Maslinic acid, a naturally occurring compound isolated from the solid wastes of olive‐oil pressing, was fragmented through the C‐ring via oxidative procedures to obtain two structural fragments. The chemical behaviors of cis‐decalin, from the D and E rings, and of trans‐decalin fragments, from the A and B rings, were investigated in depth using several chemical and enzymatic reactions. These decalin chiral synthons are interesting intermediates to semisynthesize phenanthrene‐ and drimane‐type compounds and natural tricyclic triterpenes. 相似文献
2.
Control of the Stereochemical Course of [4+2] Cycloaddition during trans‐Decalin Formation by Fsa2‐Family Enzymes 下载免费PDF全文
Dr. Naoki Kato Dr. Toshihiko Nogawa Dr. Ryo Takita Kiyomi Kinugasa Dr. Misae Kanai Dr. Masanobu Uchiyama Dr. Hiroyuki Osada Dr. Shunji Takahashi 《Angewandte Chemie (International ed. in English)》2018,57(31):9754-9758
Enzyme‐catalyzed [4+2] cycloaddition has been proposed to be a key transformation process in various natural product biosynthetic pathways. Recently Fsa2 was found to be involved in stereospecific trans‐decalin formation during the biosynthesis of equisetin, a potent HIV‐1 integrase inhibitor. To understand the mechanisms by which fsa2 determines the stereochemistry of reaction products, we sought an fsa2 homologue that is involved in trans‐decalin formation in the biosynthetic pathway of an enantiomerically opposite analogue, and we found phm7, which is involved in the biosynthesis of phomasetin. A decalin skeleton with an unnatural configuration was successfully constructed by gene replacement of phm7 with fsa2, thus demonstrating enzymatic control of all stereochemistry in the [4+2] cycloaddition. Our findings highlight enzyme‐catalyzed [4+2] cycloaddition as a stereochemically divergent step in natural product biosynthetic pathways and open new avenues for generating derivatives with different stereochemistry. 相似文献
3.
Roland Frhlich Guido F. Pauli 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(12):1476-1477
The triterpenoid natural product α‐onocerin [8,14‐secogammacera‐8(26),14(27)‐diene‐3,21‐diol], determined here as the chloroform hemisolvate, C30H50O2·0.5CHCl3, consists of two independent symmetric trans‐decalin C15 building blocks. Hydrogen bonds between the hydroxyl groups form an infinite two‐dimensional network perpendicular to the c axis. 相似文献
4.
Masood Parvez Veejendra K. Yadav Rengarajan Balamurugan 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(9):1084-1088
The crystal structures of the p‐bromobenzoates of cis‐4‐oxa‐1‐decalinyl (C16H19BrO3), trans‐4‐oxa‐1‐decalinyl (C16H19BrO3), N‐benzyl‐cis‐4‐aza‐1‐decalinyl (C23H26BrNO2), N‐benzyl‐trans‐4‐aza‐1‐decalinyl (C23H26BrNO2) and trans‐4‐thia‐1‐decalinyl (C16H19BrO2S) (decalin is perhydronaphthalene) have been determined as part of a study directed at predicting and interpreting the π‐facial selectivities of diastereotopic ketones in reactions with nucleophiles. All five structures are composed of molecules that are separated by normal van der Waals distances. In all five structures, the heterocyclic and cyclohexyl rings adopt chair conformations, and the p‐bromobenzoate groups are planar. 相似文献
5.
Jun Wang Jian‐Qing Tao Xiao‐Juan Xu 《Acta Crystallographica. Section C, Structural Chemistry》2011,67(6):m173-m175
The title compound, [Cd(C10H8O4)(C8H12N6)]n, crystallizes with an asymmetric unit comprising a divalent CdII atom, a benzene‐1,4‐diacetate (PBEA2−) ligand and a complete 1,4‐bis(1,2,4‐triazol‐1‐yl)butane (BTB) ligand. [Cd(PBEA)]n double chains, arranged parallel to the c axis, are formed through an exo‐tridentate binding mode of the PBEA2− ligands. These [Cd(PBEA)]n double chains are pillared by tethering BTB ligands, in which the BTB shows a trans–trans–trans conformation, to establish [Cd(PBEA)(BTB)]n two‐dimensional coordination polymer (4,4)‐layer slab patterns. The three‐dimensional supramolecular architecture is formed by C—H...O hydrogen bonds and C—H...π interactions. 相似文献
6.
Fascione MA Kilner CA Leach AG Turnbull WB 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(1):321-333
Neighbouring‐group participation has long been used to control the synthesis of 1,2‐trans‐glycosides. More recently there has been a growing interest in the development of similar strategies for the synthesis of 1,2‐cis‐glycosides, in particular the use of auxiliary groups that generate sulfonium ion intermediates. However, there has been some debate over the role of sulfonium ion intermediates in these reactions: do sulfonium ions actually engage in neighbouring‐group participation, or are they a resting state of the system prior to reaction through an oxacarbenium ion intermediate? Herein, we describe the reactivities and stereoselectivities of a family of bicyclic thioglycosides in which an oxathiane ring is fused to the sugar to form a trans‐decalin‐like structure. A methyl sulfonium ion derived from one such glycosyl donor is so stable that it can be crystallised from ethanol, yet it reacts with complete stereoselectivity at high temperature. The importance of a ketal group in the oxathiane ring for maintaining this high stereoselectivity is investigated using a combination of experiment and ab initio calculations. The data are discussed in terms of SN1 and SN2 type mechanisms. Trends in stereoselectivity across a series of compounds are more consistent with selective addition to oxacarbenium ions rather than a shift between SN1 and SN2 mechanisms. 相似文献
7.
《无机化学与普通化学杂志》2018,644(1):19-22
Novel poly[Mn(H2O)(dmb)(muco)] ( 1 ) (H2muco = trans,trans‐muconic acid; dmb = 5,5′‐dimethyl‐2,2′‐bipyridine) was obtained by self‐assembly, one‐pot, solution reaction. 1 crystallizes in a monoclinic system with P21 space group and forms an infinite one‐dimensional (1D) polymer. Remarkably, the six‐coordinate MnII display a rare distorted trigonal prismatic configuration. This unusual coordination arrangement appears to be acquired due to the supramolecular interactions of the polymeric structure of 1 , mainly throughout hydrogen bonding, giving rise to a 2D framework. Magnetic properties measurements reveal that 1 possesses weak antiferromagnetic interactions with θ(C–W) = –1.0 K and J = 458 cm–1. 相似文献
8.
A cheap synthesis of the so‐called ‘decalin‐1,8‐diones’ started with the conjugate (1,4‐) addition of cyclohex‐2‐en‐1‐one derivatives to the γ‐position of the dilithium derivative (buta‐1,3‐diene‐1,1‐bis(olate)) of crotonic acid. Hydrogenation of these ‘1,4‐γ’ adducts and final cyclization afforded the enol tautomers of decalin‐1,8‐diones. Nucleophilic substitutions at these 3‐oxoenols by NH3 or primary amines created only monoamino products (namely, 3‐oxoenamines) whose reactions with OPCl3 yielded dihydro(1,3,2)oxazaphosphinin‐2‐one derivatives. The two regioisomers of a trimethyl‐3‐oxoenamine served as models for the constitutional assignments of the two rapidly interconverting (hence, individually NMR‐invisible), tautomeric trimethyl‐3‐oxoenols. Such methyl substitutions served to break the ‘pretended’ symmetry of ‘decalin‐1,8‐dione’. Hydrazine and 3‐oxoenols furnished oxygen‐free indazole derivatives whose N?H bonds exchanged with t1/2=ca. 0.00035 s at ca. ?58(9) °C. 相似文献
9.
Richard Goddard Stephan Hütte Manfred T. Reetz 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(7):878-880
The title compound, C16H36N+·C6H7O3?, crystallizes with two independent anions and two independent cations in the asymmetric unit. Each anion adopts an s‐trans conformation and forms O?H—C hydrogen bonds to the α‐methylene groups of four neighbouring tetrabutylammonium cations, to create a three‐dimensional hydrogen‐bonded network. 相似文献
10.
Bernard Omondi Manuel A. Fernandes Marcus Layh Demetrius C. Levendis 《Acta Crystallographica. Section C, Structural Chemistry》2008,64(3):o137-o138
N‐Phenylformamide, C7H7NO, crystallizes with two molecules in the asymmetric unit which have different conformations of the formylamino group, one being cis and the other trans. This is the first example of an arylformamide crystal containing both conformational isomers and it may thus be considered a cocrystal of the two conformers. The two molecules in the unit cell are linked through N—H...O hydrogen bonding to two other molecules, thereby forming hydrogen‐bonded tetramers within the crystal structure. 相似文献
11.
Shi‐Dong Qin Miao‐Li Zhu Li‐Ping Lu Si‐Si Feng Hong‐Mei Zhang Pin Yang 《无机化学与普通化学杂志》2005,631(10):1761-1762
The novel dinuclear Ni2+ complex [Ni2(μ‐Cl)(μ‐OAc) (EGTB)]·Cl·ClO4·2CH3OH, where EGTB is N, N, N′, N′‐tetrakis (2‐benzimidazolyl methyl‐1, 4‐di‐ethylene amino)glycol ether, crystallizes in the orthorhombic space group Pnma with a = 15.272(2), b = 14.768(2), c = 22.486(3) Å, V = 5071.4(12) Å3, Z = 4, Dcalc = 1.414 g cm?3, and is bridged by triply bridging agents of a chloride ion, an acetate and an intra‐ligand (‐OCH2CH2O‐) group. The nickel coordination geometry is that of a slightly distorted octahedron with a NiN3O2Cl arrangement of the ligand donor atoms. The Ni–Cl distance is 2.361(2) Å, and two Ni–O distances are 1.996(5) and 2.279(6) Å. The three Ni–N distances are 2.033(7), 2.060(6), and 2.166(6) Å with the Ni–N bond trans to an ether oxygen the shortest, the Ni–N bond trans to an acetate oxygen the middle and the Ni–N bond trans to Cl the longest. 相似文献
12.
Daniela Giardina‐Papa Francesco Paolo Intini Giovanni Natile Concetta Pacifico 《Acta Crystallographica. Section C, Structural Chemistry》2012,68(11):m300-m302
The title compound, [PtCl(C3H7NO)2(C18H15P)]Cl·H2O or trans‐[PtCl{Z‐HN=C(Me)OMe}2(PPh3)]Cl·H2O, crystallizes from an acetone solution of isomeric trans‐[PtCl{E‐HN=C(Me)OMe}2(PPh3)]Cl. The two HN=C(Me)OMe ligands show typical π‐bond delocalization over the N—C—O group [Cini, Caputo, Intini & Natile (1995). Inorg. Chem. 34 , 1130–1137] and have the unprecedented Z–anti configuration. The relative orientation of the imino ether ligands is head‐to‐tail. 相似文献
13.
Jiwen Cai Xiaopeng Hu Cai‐Hong Chen Liang‐Nian Ji 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(4):394-396
The racemic title compound, trans‐[N,N‐bis(2‐aminoethyl)‐1,2‐ethanediamine‐κ4N](dl ‐isoleucinato‐N,O)cobalt(III) diperchlorate, [Co(C6H18N4)(C6H12NO2)](ClO4)2, crystallizes in the enantiomorphous space group P212121 with Z = 12 (Z′ = 3). Each of the three cations in the asymmetric unit represents a different chirality of the isoleucine ligand; two of them are R (or d ) and the third is the S (or l ) enantiomer. The mixture crystallizes in a so‐called unbalanced crystallization, in which the cations adopt a chiral array of composition RRS or SSR, depending on the crystal selected for data collection. 相似文献
14.
Alan Hazell Christine J. McKenzie Jimmi Nielsen 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(7):859-860
The title compound, C9H9NS3, crystallizes with two molecules in the asymmetric unit. In both molecules, the dithiane‐2‐thione rings adopt a symmetric half‐boat conformation with the C atom opposite the C—Sthione bond out of the plane. The pyridine ring is in an equatorial position and is twisted out of the plane of the half‐boat by 82.7 (2) and 84.5 (2)° in the two molecules, so that the N atom is trans to the axial C—H bond in both cases. 相似文献
15.
Stefanus Otto Andreas Roodt 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(5):540-541
The crystal structure of the title compound, trans‐[PtI2(C6H12N3P)2], describes one of the few platinum(II) complexes containing two of the water‐soluble 1,3,5‐triaza‐7‐phosphaadamantane ligands reported to date. The complex crystallizes on an inversion centre with the most important bond lengths and angles being Pt—P 2.3128 (12) Å, Pt—I 2.6022 (6) Å, P—Pt—I 90.94 (3)° and P′—Pt—I 89.06 (3)°. 相似文献
16.
Georgia M. Arvanitis Michael E. Berardini Douglas M. Ho 《Acta Crystallographica. Section C, Structural Chemistry》2004,60(3):m126-m128
The title complex [systematic name: trans‐bis(3‐isopropyl‐7‐oxocyclohepta‐1,3,5‐trienolato)copper(II)], [Cu(C10H11O2)2],is a substance possessing antimicrobial activity. The compound crystallizes in a number of polymorphic forms, the structures for two of which are reported here. Stacks of square‐planar molecules exhibiting weak intermolecular copper–olefin π interactions (not observed in earlier reports on this substance) are described. The molecules have crystallographically imposed inversion symmetry, with stacking and copper–olefin π distances ranging from 3.226 (2) to 3.336 (1) Å. 相似文献
17.
Peter N. Bungu Leo Kirsten Stefanus Otto 《Acta Crystallographica. Section C, Structural Chemistry》2011,67(5):m154-m156
The crystal structure of the title compound, trans‐[PtCl2(C16H23P)2], has been determined at 100 K. The Pt atom is located on a twofold axis and adopts a distorted square‐planar coordination geometry. The structure is only the second example of a coordination complex containing a derivative of the 4,8‐dimethyl‐2‐phosphabicyclo[3.3.1]nonane (Lim) phosphine ligand family. The ligand contains four chiral C atoms, with the stereochemistry at three of these fixed during synthesis, therefore resulting in two possible ligand stereoisomers. The compound crystallizes in the chiral space group P43212 but is racemic, comprising an equimolar mixture of both stereoisomers disordered on a single ligand site. The effective cone angles for both isomers are the same at 146°. 相似文献
18.
The decomposition mechanism of 2‐ethyl‐hexylnitrate (2‐EHN), an important additive to diesel fuel to improve the cetane number, was investigated in solution and in the gas phase. In trans‐decalin as solvent, an activation barrier for the thermal decomposition of 39 kcal/mol was determined, and thus the decomposition is slow at temperatures below 100°C. Under high pressure conditions (2.4 kbar) the decomposition rates decrease, in accordance with a radical mechanism. Flash vacuum pyrolysis with subsequent detection of the products via mass spectroscopy or matrix IR spectroscopy allows to identify NO2, formaldehyde, and several olefins as the major decomposition products. These data allow proposing a consistent mechanistic scheme for the 2‐EHN decay. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 34: 34–38, 2002 相似文献
19.
The reaction of Te(OH)6 with Ph3SnOH in ethanol leads to the formation of trans‐[(Ph3SnO)4Te(OH)2] ( 1 ). Compound 1 crystallizes triclinic in the space group P\bar{1} with a = 996.6(2) pm, b = 1365.4(3) pm, c = 1368.2(3) pm and α = 71.15(2)°, β = 71.48(2)°, γ = 74.81(3)° (at 220 K). The molecular structure of 1 consists of a tellurium atom, which is coordinated nearly octahedrally by four Ph3SnO units and two hydroxyl groups that are trans to each other. The Te–O bond lengths are in the range of 190.5(2) and 193.7(2) pm. Treatment of 1 with methanol under reflux yields trans‐[(Ph3SnO)2Te(OMe)4] ( 2 ). Compound 2 crystallizes triclinic in the space group P\bar{1} with a = 1012.8(1) pm, b = 1422.4(2) pm, c = 1618.1(2) pm, and α = 100.44(1)°, β = 107.92(1)°, γ = 110.66(1)° (at 220 K). 2 forms centrosymmetric molecules in which the tellurium atom is surrounded nearly octahedrally by four methoxy groups and two trans arranged Ph3SnO units. The Te–O bond lengths of 187.9(3)–194.5(3) pm are similar to those observed in 1 . 相似文献
20.
Jo C. Davison Mark R. St J. Foreman R. Alan Howie M. John Plater Janet M. S. Skakle 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(6):690-693
The title compound, [NiCl2(C26H24P2)], has arisen as a result of the unexpected reduction (hydrogenation) of the trans‐1,2‐bis(diphenylphosphino)ethene ligand. The hydrothermal reaction conditions have produced a third polymorphic form of the compound which has twofold symmetry, crystallizes in an enantiomer‐selective manner and contains an unexpectedly short C—C (ethane) bond. Contacts of the form C—H?Cl are present, one involving alkyl and the other aryl hydrogen, with C?Cl distances of 3.556 (4) and 3.664 (6) Å, respectively. 相似文献