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991.
An electrochemical synthesis of oxazol‐2‐ones and imidazol‐2‐ones has been developed via 5‐exo‐dig cyclization of propargylic carbamates‐ and ureas‐derived amidyl radicals. The electrosynthesis relies on the dual function of 2,2,6,6‐tetramethylpiperidin‐ 1‐yl)oxyl (TEMPO) as a redox mediator for amidyl radical formation and an oxygen atom donor. The reactions are conducted under mild conditions using a simple setup and provide convenient access to functionalized oxazol‐2‐ones and imidazol‐2‐ones from readily available materials. 相似文献
992.
Stefan Sahli Brian Frank W.Bernd Schweizer Franois Diederich Denise Blum‐Kaelin JohannesD. Aebi Hans‐Joachim Bhm Christian Oefner GlennE. Dale 《Helvetica chimica acta》2005,88(4):731-750
A new class of nonpeptidic inhibitors of the ZnII‐dependent metalloprotease neprilysin with IC50 values in the nanomolar activity range (0.034–0.30 μM ) were developed based on structure‐based de novo design (Figs. 1 and 2). The inhibitors feature benzimidazole and imidazo[4,5‐c]pyridine moieties as central scaffolds to undergo H‐bonding to Asn542 and Arg717 and to engage in favorable π‐π stacking interactions with the imidazole ring of His711. The platform is decorated with a thiol vector to coordinate to the ZnII ion and an aryl residue to occupy the hydrophobic S1′ pocket, but lack a substituent for binding in the S2′ pocket, which remains closed by the side chains of Phe106 and Arg110 when not occupied. The enantioselective syntheses of the active compounds (+)‐ 1 , (+)‐ 2 , (+)‐ 25 , and (+)‐ 26 were accomplished using Evans auxiliaries (Schemes 2, 4, and 5). The inhibitors (+)‐ 2 and (+)‐ 26 with an imidazo[4,5‐c]pyridine core are ca. 8 times more active than those with a benzimidazole core ((+)‐ 1 and (+)‐ 25 ) (Table 1). The predicted binding mode was established by X‐ray analysis of the complex of neprilysin with (+)‐ 2 at 2.25‐Å resolution (Fig. 4 and Table 2). The ligand coordinates with its sulfanyl residue to the ZnII ion, and the benzyl residue occupies the S1′ pocket. The 1H‐imidazole moiety of the central scaffold forms the required H‐bonds to the side chains of Asn542 and Arg717. The heterobicyclic platform additionally undergoes π‐π stacking with the side chain of His711 as well as edge‐to‐face‐type interactions with the side chain of Trp693. According to the X‐ray analysis, the substantial advantage in biological activity of the imidazo‐pyridine inhibitors over the benzimidazole ligands arises from favorable interactions of the pyridine N‐atom in the former with the side chain of Arg102. Unexpectedly, replacement of the phenyl group pointing into the deep S1′ pocket by a biphenyl group does not enhance the binding affinity for this class of inhibitors. 相似文献
993.
For an abstract single-strand RNA, a combinatorial analysis is given for two important structures, hairpins and cloverleaves. The total number of hairpins and cloverleaves of a given length with minimal hairpin loop length m(m > 0) and with minimal stack length l(l > 0) is computed, under the assumption that all base pairs can occur. 相似文献
994.
The 1,3,4,6‐tetra‐O‐acetyl‐2‐azido‐2‐deoxy‐β‐D ‐mannopyranose ( 4 ) or the mixture of 1,3,6‐tri‐O‐acetyl‐2‐azido‐2‐deoxy‐4‐O‐(2,3,4,6‐tetra‐O‐acetyl‐β‐D ‐galactopyranosyl)‐β‐D ‐mannopyranose ( 10 ) and the corresponding α‐D ‐glucopyranose‐type glycosyl donor 9 / 10 reacted at room temperature with protected nucleosides 12 – 15 in CH2Cl2 solution in the presence of BF3?OEt2 as promoter to give 5′‐O‐(2‐azido‐2‐deoxy‐α‐D ‐glycosyl)nucleosides in reasonable yields (Schemes 2 and 3). Only the 5′‐O‐(α‐D ‐mannopyranosyl)nucleosides were obtained. Compounds 21, 28, 30 , and 31 showed growth inhibition of HeLa cells and hepatoma Bel‐7402 cells at a concentration of 10 μM in vitro. 相似文献
995.
A new dihydrobenzodioxane derivative, origalignanol ( 10 ), together with nine polyphenolic compounds, salvianolic acid A ( 1 ), salvianolic acid C ( 2 ), lithospermic acid ( 3 ), apigenin 7‐O‐β‐D‐glucuronide ( 4 ), apigenin 7‐O‐β‐D‐(6″‐methyl)glucuronide ( 5 ), luteolin, ( 6 ), luteolin 7‐O‐β‐D‐glucopyranoside ( 7 ), luteolin 7‐O‐β‐D‐glucuronide ( 8 ), and luteolin 7‐O‐β‐D‐xylopyranoside ( 9 ), were isolated from the aqueous ethanolic extract of the aerial parts of Origanum vulgare for the first time. The structure of new compound 10 was determined on the basis of spectroscopic methods. Compound 5 is probably an artifact formed during the isolation. Compounds 1, 2 and 3 showed strong DPPH radical scavenging activity with an EC50 of 7.2 ± 0.4, 9.6 ± 0.9, and 9.5 ± 0.7 μM, respectively, and protected rat hepatocytes from CCl4‐damage at 100 μM. 相似文献
996.
A method for direct de termination of total in organic arsenic (III+V), arsenic (III) and dimethylarsinate (DMA) in sea water was developed by combining continuous‐flow selective hydride generation and inductively coupled plasma mass spectrometry (ICP‐MS) is presented. The principle underlying selective hydride generation is based on proper control of the reaction conditions for achieving separation of the respective arsenic species. The effects of pH and composition of reaction media on mutual interference between the arsenic species were investigated in detail. The results indicate that the appropriate media for the selective determination of total in organic arsenic, DMA and As(III) are 6 M HNO3, acetate buffer at pH = 4.63 and citrate buffer at pH = 6.54, respectively. The concentrations of total inorganic arsenic species, As(III+V), and As(III) were respectively deter mined and that of As(V) was obtained by the difference between them. As to the concentration of DMA, it was obtained after correction from the interference caused by As(III) and As(V). By following the established procedure, the detection lim its (as based on 3‐sigma criterion) for As(III+V), As(III) and DMA were 0.050, 0.009, and 0.002 ng/mL, respectively. There liability of the pro posed method was evaluated in terms of precision and spike addition. The results indicated that the precision of better than 3% and spike recovery of 95 to 105% for all the arsenic species tested in the natural sea water samples can be obtained. 相似文献
997.
Nikolaos C. Papandreou Stella Makedonopoulou Ekaterini A. Antoniadou‐Vyza Irene M. Mavridis Stavros J. Hamodrakas 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(12):o730-o732
The title salt, C18H22N5+·Cl?, is a member of a new series of lipophilic 4,6‐diamino spiro‐s‐triazines which are potent inhibitors of dihydrofolate reductase. The protonated triazine ring deviates from planarity, whereas the cyclohexane ring adopts a chair conformation. A rather unusual hydrogen‐bonding scheme exists in the crystal. There is a centrosymmetric arrangement involving two amino groups and two triazine ring N atoms, with graph‐set R(8) and an N?N distance of 3.098 (3) Å, flanked by two additional R(8) systems, involving two amino groups, a triazine ring N atom and a Cl? anion, with N?Cl distances in the range 3.179 (2)–3.278 (2) Å. Furthermore, the Cl? anion, the protonated triazine ring N atom and an amino group form a hydrogen‐bonding system with graph‐set R(6). 相似文献
998.
Zhen‐Feng Zhang Dong‐Chao Wang Jian‐Ge Wang Gui‐Rong Qu 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(9):o524-o527
The molecules of 2,2,2‐trichloro‐N,N′‐diphenylethane‐1,1‐diamine, C14H13Cl3N2, are linked into (040) sheets by a combination of C—H...Cl and C—H...π(arene) hydrogen bonds. In 2,2,2‐trichloro‐N,N′‐bis(4‐methylphenyl)ethane‐1,1‐diamine, C16H17Cl3N2, the molecules are linked into C(7) chains by two independent C—H...Cl hydrogen bonds and one Cl...Cl contact. 相似文献
999.
Hai‐Yang Liu Hong‐Ping He Suo Gao Chang‐Xiang Chen Yue‐Mao Shen Xiao‐Jiang Hao 《Helvetica chimica acta》2006,89(5):1017-1022
Two new diterpenoids, pedunculatic acid A (= (4R,5α,7α)‐7‐ethoxy‐9β,13β‐dioxyabiet‐8(14)‐en‐18‐oic acid; 1 ) and pedunculatic acid B (= (4S,5α,12β)‐8β,14β‐epoxy‐12‐hydroxy‐11‐oxototaran‐19‐oic acid; 2 ), together with three known sesquiterpenoids, were isolated from the Chinese medicinal herb Callicarpa pedunculata R. Brown . Their structures were elucidated by spectroscopic analyses, including 1D‐ and 2D‐NMR, and by high‐resolution mass spectrometry. 相似文献
1000.
State Miao Ming-Ming Liao Dai-Zheng Jiang Zong-Hui Cheng Peng Wang Geng-Lin 《中国化学》1996,14(4):326-330
Four new heterotrinuclear complexes have been synthesized and characterized, namely {[Ni(L)2]2[Cu(opba)]}(ClO4)2, where opba denotes o-phenylenebis(oxamato) and L stands for 1,10-phenanthroline(phen) (1), 5-nitro-l,10-phenanthroline(NO2-phen) (2), 2,2′-bipyridyl(bpy) (S) and 4,4′-dimethyl-2,2′-bipyridyl(Me2bpy) (4). The temperature dependence of the magnetic susceptibility of {[Ni(phen)2]2[Cu(opba)]}(ClO4)23H2O has been studied in the 4–300 K range, giving the exchange integral J—109 cm?1. The HMT vs. T plot exhibits a minimum at about 100 K, characteristic of this kind of coupled polymetallic complex with an irregular spin-state structure. 相似文献