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1.
Rashmi Pathak Déborah Perez‐Fernandez Rahul Nandurdikar Sarath K. Kalapala Erik C. Böttger Andrea Vasella 《Helvetica chimica acta》2008,91(8):1533-1552
The 2‐amino‐2‐deoxy‐α‐D ‐glucopyranosyl moiety (ring I) of paromomycin was replaced by a 2,4‐diamino‐2,4‐dideoxy‐α‐D ‐glucopyranosyl, 2,4‐diamino‐2,4‐dideoxy‐α‐D ‐galactopyranosyl, 2‐amino‐2‐deoxy‐α‐D ‐galactopyranosyl, or 3,4,5‐trideoxy‐4‐aza‐α‐D ‐erythro‐heptoseptanosyl moiety to investigate the effect of the substituent at C(4′) on the interaction with ribosomal RNA. The triflate 6 was prepared from the key intermediate pentaazido 3′,6′‐dibenzyl ether 5 , and the hexosulose 10 was obtained by oxidation of 5 with Dess–Martin's periodinane. Stereoselective reduction of 10 with NaBH4 gave the alcohol 11 that was transformed into the triflate 12 . The epimeric hexaazides 7 and 13 were obtained by treating the triflates 6 and 12 , respectively, with tetrabutylammonium azide. Periodate cleavage of glycol 2 yielded the dialdehyde 24 that was reductively aminated with aniline and benzylamine to give the 3,4,5‐trideoxy‐4‐aza‐α‐D ‐erythro‐heptoseptanosides 25 and 26 , respectively. Standard azide reduction and debenzylation yielded 9 (2,4‐diamino‐2,4‐dideoxy‐α‐D ‐galactopyranosyl ring I), 13 (2‐amino‐2‐deoxy‐α‐D ‐galactopyranosyl ring I), 17 (2,4‐diamino‐2,4‐dideoxy‐α‐D ‐glucopyranosyl ring I), and 27 and 28 (3,4,5‐trideoxy‐4‐aza‐α‐D ‐erythro‐heptoseptanosyl ring I). The derivatives 9 and 13 possessing a D ‐galacto‐configured ring I were less active than the corresponding D ‐gluco‐analogues 17 and paromomycin ( 1 ), respectively. The C(4′)‐aminodeoxy derivative 17 (D ‐gluco ring I) and the known 4′‐deoxyparomomycin ( 23 ), prepared by a new route, displayed slightly lower antibacterial activities than paromomycin ( 1 ). Cell‐wall permeability is not responsible for the unexpectedly low activity for 17 , as shown by cell‐free translation assays. The results evidence that the orientation of the substituent at C(4′) is more important than its nature for drug binding and activity. 相似文献
2.
Ying Fu Yin‐Xia He Hong‐Xia Hou Wen‐Bo Zhu Hu‐Lin Li Chao Wu Fang‐Yan Xian 《Acta Crystallographica. Section C, Structural Chemistry》2013,69(3):282-284
2,2′‐Anhydro‐1‐(3′,5′‐di‐O‐acetyl‐β‐D‐arabinofuranosyl)uracil, C13H14N2O7, was obtained by refluxing 2′,3′‐O‐(methoxymethylene)uridine in acetic anhydride. The structure exhibits a nearly perfect C4′‐endo (4E) conformation. The best four‐atom plane of the five‐membered furanose ring is O—C—C—C, involving the C atoms of the fused five‐membered oxazolidine ring, and the torsion angle is only −0.4 (2)°. The oxazolidine ring is essentially coplanar with the six‐membered uracil ring [r.m.s. deviation = 0.012 (5) Å and dihedral angle = −3.2 (3)°]. The conformation at the exocyclic C—C bond is gauche–trans which is stabilized by various C—H...π and C—O...π interactions. 相似文献
3.
Riccardo Destro Emanuele Ortoleva Giorgio Modena Lucia Pasquato Vittorio Lucchini 《Helvetica chimica acta》2001,84(4):860-866
Four‐membered ring thiosulfonium ions may be obtained quantitatively and under mild conditions by anionotropic rearrangement of C‐(tert‐butyl)‐substituted thiiranium ion precursors. Thus, t‐4‐(tert‐butyl)‐r‐1,2,2,c‐3‐tetramethylthietanium tetrafluoroborate or hexachloroantimonate ( 2a or 2b , resp.) were formed from thiiranium ion 1 . The thietanium salts 2a and 2b were characterized by X‐ray crystal‐structure analysis. Their cation geometry was also optimized by ab initio calculations at the RHF/6‐31G*//RHF/6‐31G* level, as were those of its stereoisomer 3 and of the unsubstituted S‐methylthietanium ion 5 . Comparison of 2 , 3 , and 5 with 4 – the only other thietanium ion studied by XRD, where the C‐atoms of the thioniacyclobutane ring are part of a trinorbornane skeleton – indicates that, in these systems, relief from substituent overcrowding is easily achieved by a folding of the four‐membered ring along the line connecting the two opposite C‐atoms. The corresponding ring‐deformation normal mode has a calculated frequency as low as 109 cm−1 in ion 5 , to be compared with a frequency of 138 cm−1 in methylcyclobutane. For thietanium ion 2 , the frequencies of the two normal modes involving such ring deformation have calculated values of 61 and 85 cm−1. 相似文献
4.
Yi‐Ping Ye Hong‐Xiang Sun Yuan‐Jiang Pan 《Acta Crystallographica. Section C, Structural Chemistry》2004,60(6):o397-o398
The title compound, 4‐methoxy‐2‐[(1S,2R,3S,4S,5R)‐3,4,5,6‐tetrahydro‐3,4,5‐trihydroxy‐6‐(hydroxymethyl)‐2H‐pyran‐2‐yl]‐α‐resorcylic acid δ‐lactone monohydrate, C14H16O9·H2O, is a C‐glucoside of 4‐O‐methylgallic acid which has antiasthmatic, antitussive, anti‐inflammatory, antifungal, anti‐HIV and antihepatotoxic activity. The molecule is composed of three six‐membered rings: an aromatic ring, a glucopyranose ring and an annellated δ‐lactone ring. The glucopyranose ring exhibits only small deviations from an ideal chair conformation. The annellated δ‐lactone ring possesses the expected half‐chair conformation. There is one intra‐ and six intermolecular hydrogen bonds which form an extensive hydrogen‐bonding network within the crystal. 相似文献
5.
Mikhail A. Tlenkopatchev Adriana Barcenas Serguei Fomine 《Macromolecular theory and simulations》2001,10(5):441-446
The results of molecular modeling of the ring distributions for the intramolecular metathesis degradation of natural rubber (NR) at HF/6–31G(d) level of theory showed that in the ring‐ring equilibrium participate cyclic oligomers containing from two to four isoprene units with all‐trans cyclic isoprene trimer being the main product. The formation of trans,trans,trans‐1,5,9‐trimethyl‐1,5,9‐cyclododecatriene from larger rings is thermodynamically favored. According to the calculations, the ring‐ring equilibrium for the intramolecular metathesis degradation of cis‐polybutadiene (cis‐PB) is completely shifted towards the all‐trans cyclic butadiene trimer. These results are in reasonable agreement with recent experimental data. 相似文献
6.
Global Aromaticity in Macrocyclic Cyclopenta‐Fused Tetraphenanthrenylene Tetraradicaloid and Its Charged Species 下载免费PDF全文
Dr. Xuefeng Lu Dr. Tullimilli Y. Gopalakrishna Dr. Hoa Phan Dr. Tun Seng Herng Dr. Qing Jiang Chunchen Liu Dr. Guangwu Li Prof. Jun Ding Prof. Jishan Wu 《Angewandte Chemie (International ed. in English)》2018,57(40):13052-13056
A stable cyclopenta‐fused tetraphenanthrenylene macrocycle, CPTP‐M , was synthesized, and the structure was confirmed by X‐ray crystallographic analysis. It exhibits a large radical character (number of unpaired electron, NU=3.52) and a small singlet–triplet energy gap (ΔES‐T=?2.8 kcal mol?1 by SQUID). Its backbone contains 60 ([4n]) conjugated π electrons and is globally antiaromatic. NMR measurements and theoretical calculations revealed that its dication/dianion is globally aromatic owing to the existence of [4n?2]/[4n+2] π‐conjugated electrons. Remarkably, the ring‐current map of the tetraanion shows a unique ring‐in‐ring structure, with a diamagnetic outer ring and a paramagnetic inner ring. Accordingly, both the inner‐rim and outer‐rim protons are deshielded in its 1H NMR spectrum. The tetraanion can be regarded as an isoelectronic structure of the known octulene, which shows similar electronic properties. 相似文献
7.
Atsushi Takano Atsushi Nonaka Osamu Kadoi Kazuhiro Hirahara Seiichi Kawahara Yoshinobu Isono Naoya Torikai Yushu Matsushita 《Journal of Polymer Science.Polymer Physics》2002,40(15):1582-1589
A polystyrene‐block‐oligo(2‐tert‐butylbutadiene)‐block‐polystyrene triblock copolymer was prepared and cyclized by end‐to‐end ring closure. Ring‐shaped polystyrene‐block‐oligo(2‐tert‐butylbutadiene) was isolated from the coupling product via gel permeation chromatography (GPC) fractionation. The ring polymer was ozonized for decomposition of the oligo(2‐tert‐butylbutadiene) sequences selectively referring to the linear molecule. From GPC analysis of the decomposed products by ozonolysis, it was quantitatively confirmed that the fractionated product was 86% ring molecules. Single chain dimensions of the ring and linear molecules in a good solvent, benzene, and in a θ solvent, cyclohexane, were measured with small‐angle neutron scattering. The ratios of the radii of gyration, Rg(ring)/Rg(linear), were 0.780 in benzene and 0.789 in cyclohexane. These were compared with theoretically predicted values. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1582–1589, 2002 相似文献
8.
K. Ravikumar B. Sridhar M. Mahesh V. V. Narayana Reddy 《Acta Crystallographica. Section C, Structural Chemistry》2005,61(5):o267-o269
8‐Chloro‐9‐fluoro‐5‐phenyl‐3,4,4a,5,6,10b‐hexahydro‐2H‐pyrano[3,2‐c]quinoline and 10‐chloro‐9‐fluoro‐5‐phenyl‐3,4,4a,5,6,10b‐hexahydro‐2H‐pyrano[3,2‐c]quinoline, both C18H17ClFNO, are diastereoisomers, formed as the result of the imino Diels–Alder reactions of N‐benzylideneanilines with 3,4‐dihydro‐2H‐pyran. The crystal structures reveal the stereochemistry of the pyran ring, which is endo/exo to the quinoline ring system formed in the cycloaddition step. In both structures, the pyran ring adopts a chair conformation, while the nitrogen‐containing heterocyclic ring prefers a half‐chair conformation. The structures differ essentially in the relative orientation of the ring junction H atoms. 相似文献
9.
Dr. Chenbo Wang Miao Yu Andrew F. Kyle Dr. Pavol Jakubec Prof. Darren J. Dixon Prof. Richard R. Schrock Prof. Amir H. Hoveyda 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(8):2726-2740
The first broadly applicable set of protocols for efficient Z‐selective formation of macrocyclic disubstituted alkenes through catalytic ring‐closing metathesis (RCM) is described. Cyclizations are performed with 1.2–7.5 mol % of a Mo‐ or W‐based monoaryloxide pyrrolide (MAP) complex at 22 °C and proceed to complete conversion typically within two hours. Utility is demonstrated by synthesis of representative macrocyclic alkenes, such as natural products yuzu lactone (13‐membered ring: 73 % Z) epilachnene (15‐membered ring: 91 % Z), ambrettolide (17‐membered ring: 91 % Z), an advanced precursor to epothilones C and A (16‐membered ring: up to 97 % Z), and nakadomarin A (15‐membered ring: up to 97 % Z). We show that catalytic Z‐selective cyclizations can be performed efficiently on gram‐scale with complex molecule starting materials and catalysts that can be handled in air. We elucidate several critical principles of the catalytic protocol: 1) The complementary nature of the Mo catalysts, which deliver high activity but can be more prone towards engendering post‐RCM stereoisomerization, versus W variants, which furnish lower activity but are less inclined to cause loss of kinetic Z selectivity. 2) Reaction time is critical to retaining kinetic Z selectivity not only with MAP species but with the widely used Mo bis(hexafluoro‐tert‐butoxide) complex as well. 3) Polycyclic structures can be accessed without significant isomerization at the existing Z alkenes within the molecule. 相似文献
10.
A set of structurally varied indano[1,2‐d][1,3]oxazines and thiazines, which are new ring systems, were prepared by ring‐closure reactions of amino alcohols 4–6. The reactions of cis‐ and trans‐1‐amino‐ and cis‐ 1‐benzylamino‐2‐hydroxymethylindane (4–6) with 1 equivalent of an aromatic aldehyde in methanol at room temperature resulted in three‐component equilibria (15a‐g), or a Schiff base (16), or a ring‐closure product alone (17a‐c), respectively, depending on the substitution or configuration of the starting amino alcohol. The ring‐chain tautomeric equilibria can be described by an equation of Hammett type. 相似文献
11.
Anthony J. Burke Helmut W. Schmalle Bernard A. Brady W. Ivo O'Sullivan 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(4):484-486
The title compound, C17H14O4, is an unprecedented new synthetic isoaurone‐type enol ether that has the E configuration. The planar furanone ring is fused to a methoxybenzene ring system, with an interplanar angle of 175.7 (1)°. Due to this ring fusion, the six‐membered ring has a significant amount of ring strain, as shown by the internal ring angle range of 115.8 (1)–124.7 (1)°, whereas the vinylic phenyl ring has internal angles between 119.7 (1) and 120.2 (1)°. The molecules form infinite hydrogen‐bonding layers along the b direction of the form C—H?O, where the keto O atom acts as a bifurcated acceptor. These layers are connected along the c direction by another hydrogen bond with a methoxy H atom as donor. In addition to this connection, the layers are stacked via centres of symmetry by a pair of symmetry‐related benzofuranone ring systems. 相似文献
12.
Gopeswar Chaudhuri Madeleine Helliwell Nitya G. Kundu 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(6):740-741
In the title compound, C22H17Cl2NO3S, the molecule is a substituted 3,4‐dihydro‐2H‐1,4‐benzoxazine compound which has three phenyl rings which are essentially planar. The 3,4‐dihydro‐2H‐oxazine part of the molecule is fused to the benzo ring and has a half‐boat conformation; the dihedral angle between the planar part of the oxazine ring and the benzo ring is 10.2 (2)°. The (3‐chlorophenyl)methylidene substituent has a Z configuration in relation to the ring N atom of the oxazine moiety. Interestingly, the p‐toluenesulfonyl (p‐tosyl) substituent on the ring N atom protrudes away from the 3‐chlorophenyl substituent thus avoiding any steric interaction. 相似文献
13.
Dr. Shinichiro Fuse Ayako Ikebe Kazuya Oosumi Tomoya Karasawa Keisuke Matsumura Dr. Miho Izumikawa Dr. Kohei Johmoto Dr. Hidehiro Uekusa Dr. Kazuo Shin‐ya Prof. Takayuki Doi Prof. Takashi Takahashi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(26):9454-9460
An asymmetric total synthesis of ent‐pyripyropene A was achieved by a convergent synthetic route. We used our originally developed TiIII‐catalyzed radical cyclization to construct an AB‐ring portion that consisted of a trans‐decalin skeleton with five contiguous stereogenic centers. The coupling between the AB‐ring and the DE‐ring portions, and a subsequent C‐ring cyclization, led to the total synthesis of ent‐pyripyropene A. An evaluation of the insecticidal activity of ent‐pyripyropene A against two aphid species revealed that ent‐pyripyropene A was 35–175 times less active than naturally occurring pyripyropene A. This result indicated that the biological target of pyripyropene A recognizes the absolute configuration of pyripyropene A. 相似文献
14.
Daniel Vega Daniel Fernndez Gustavo Echeverría 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(7):848-850
The title compound, 11‐chloro‐8,12b‐dihydro‐2,8‐dimethyl‐12b‐phenyl‐4H‐[1,3]oxazino[3,2‐d][1,4]benzodiazepine‐4,7(6H)‐dione, C20H17ClN2O3, is a benzodiazepine with an additional d‐face‐fused heterocyclic ring. In the molecule, a dihedral angle of 86.2 (1)° is formed by the planes of the phenyl and benzo rings and the former is axially oriented from the core, i.e. the fused 6,7,6‐tricyclic system. Both heterocycles in the core suffer significant deviations from planarity. The central diazepine ring is a twist–boat and the oxazine ring exhibits a conformation intermediate between half‐chair and sofa. 相似文献
15.
A variety of single component rare earth aryloxides substituted by various alkyl groups [Ln(OAr)3] such as methyl, isopropyl, tert‐butyl have been surveyed in the ring‐opening copolymerization of 2,2‐dimethyltrimethylene carbonate (DTC) and ε‐caprolactone (ε‐CL). It was worthwhile to note that activity of the catalyst varied with both the ligands' structure and the number of alkyl groups on phenyl ring. The stronger ability of electron‐donation of alkyl groups on phenyl ring, and the more numbers of alkyl groups on phenyl ring, the higher catalytic activity. The experimental results show that lanthanum tris(2,4,6‐tri‐tert‐butylphenolate) [La(OTTBP)3] exhibits highest activity in all lanthanum aryloxides. 1H NMR spectral data of copolymer obtained showed that the polymerization mechanism is in agreement with the coordination insertion mechanism. 相似文献
16.
Theoretical Study on the Relationship between Diradical Character and Second Hyperpolarizabilities of Four‐Membered‐Ring Diradicals Involving Heavy Main‐Group Elements 下载免费PDF全文
Hiroshi Matsui Kotaro Fukuda Shota Takamuku Prof. Dr. Akira Sekiguchi Prof. Dr. Masayoshi Nakano 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(5):2157-2164
By using spin‐unrestricted density functional theory methods, the relationship between the diradical character y and the second hyperpolarizability γ (the third‐order nonlinear optical (NLO) properties at the molecular scale) for four‐membered‐ring diradical compounds, that is, cyclobutane‐1,3‐diyl, Niecke‐type diradicals, and Bertrand‐type diradicals, were investigated by focusing on the substitution effects of heavy main‐group elements as well as of donor/acceptor groups on the y and γ values. It has been found that i) γ is enhanced in the intermediate y region for these four‐membered‐ring diradicals, ii) Niecke‐type diradicals with intermediate y values, which are realized by tuning the combination of the main‐group elements involved, exhibit larger γ values than Bertrand‐type diradicals, and iii) the y value and thus γ value can be controlled by modifying the both‐end donor/acceptor substituents attached to carbon atoms in Nicke‐type C2P2 diradicals. These results demonstrate that four‐membered‐ring diradicals involving heavy main‐group elements exhibit high controllability of the y and γ, which indicates the potential applications of four‐membered‐ring diradicals as a building block of highly efficient open‐shell NLO materials. 相似文献
17.
In the course of the last two decades, the use of transition metals as templates for constructing catenanes has almost exclusively been restricted to tetrahedral copper(I). The present work is dealing with an octahedral metal, ruthenium(II), coordinated to three bidentate chelates. Incorporation of two chelates (1,10‐phenanthroline) in a ring allows to prepare a C2‐symmetric ruthenium complex, the two chelates being disposed cis to one another (see 14 2+ and 16 2+ in Scheme 5 and 6, resp.). The ring is large enough to accomodate a third chelate, thus allowing the metal‐directed threading of a long fragment containing the third chelate (2,2′‐bipyridine derivative; see 23 2+ and 24 2+ in Scheme 8). The last step consists of a ring‐closing metathesis reaction with two terminal olefins. The two ruthenium(II)‐complexed catenanes 25 2+ and 26 2+ were prepared by using this strategy, each containing a 42‐membered ring interlocked to a larger macrocycle (50‐ or 63‐membered ring) incorporating the two 1,10‐phenanthroline chelates. It is expected that these catenanes can be set in motion under light‐irradiation, thus behaving as photochemically driven molecular machines. 相似文献
18.
Enantioselective Synthesis of Macrocyclic Heterobiaryl Derivatives of Molecular Asymmetry by Molybdenum‐Catalyzed Asymmetric Ring‐Closing Metathesis 下载免费PDF全文
Yoichi Okayama Satoru Tsuji Yuka Toyomori Prof. Dr. Atsunori Mori Dr. Sachie Arae Dr. Wei‐Yi Wu Prof. Dr. Tamotsu Takahashi Prof. Dr. Masamichi Ogasawara 《Angewandte Chemie (International ed. in English)》2015,54(16):4927-4931
Winding vine‐shaped molecular asymmetry is induced by enantioselective ring‐closing metathesis with a chiral molybdenum catalyst. The reaction proceeds under mild conditions through an E‐selective ring‐closing metathesis leading to macrocyclic bisazoles with enantioselectivities of up to 96 % ee. 相似文献
19.
Diversity Oriented Synthesis of Indoloazepinobenzimidazole and Benzimidazotriazolobenzodiazepine from N1‐Alkyne‐1,2‐diamines 下载免费PDF全文
Ravi Kumar Rajesh K. Arigela Srinivas Samala Dr. Bijoy Kundu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(51):18828-18833
A one‐pot protocol for the diversity oriented synthesis of two N‐polyheterocycles indoloazepinobenzimidazole and benzimidazotriazolobenzodiazepine from a common N1‐alkyne‐1,2‐diamine building block is described. The approach involves sequential formation of benzimidazole through cyclocondensation and oxidation, which is followed by the formation of either an azepine ring (through alkyne activation and 6‐endo‐dig cyclization, 1,2‐migration with ring expansion, and re‐aromatization), or diazepine and triazole rings through 1,3‐dipolar cycloaddition. 相似文献
20.
The retention behavior of five disubstituted benzene derivatives and two naphthalene derivatives is examined by using a chemically bonded β‐cyclodextrin silica stationary phase with the moiety containing the s‐triazine. The chromatographic results of five disubstituted benzene derivatives and two naphthalene derivatives show that effective separation is achieved on this stationary phase by high‐performance liquid chromatography. The results of the present investigation indicate that the formation of inclusion complexes plays a dominant role in the separation mechanism. However, the selectivity can be significantly enhanced by the n‐n interactions between the s‐triazine ring of the chemically bonded β‐cyclodextrin silica stationary phase and the aromatic ring of solutes. For example, the effective separation of the o‐, m‐, and p‐toluidine isomers on this stationary phase with the moiety containing the s‐triazine ring was better than on that of some β‐cyclodextrin bonded stationary phases without the moiety containing s‐triazine ring. 相似文献