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1.
Philippe Meresse 《Tetrahedron》2004,60(11):2657-2671
Non-epimerizable cis and trans δ-lactone analogues of podophyllotoxin have been prepared. Thus the synthesis of the cis isomer 4 has been achieved in 8 steps and 4% overall yield from podophyllotoxin 1 via the reduction of the γ lactone ring into the trans diol, selective protection of the 4-OH and 11-OH as a benzylidene acetal, and Wittig elongation at C-13 with inversion of configuration at C-2. Same elongation at C-13 but via the formation of a mesylate and introduction of a cyano group, led to the trans δ-lactone 5 (7 steps from 1 and 6% overall yied) with a small amount of its C-4 epimer 6. The synthesis of non-epimerizable δ-lactone analogues of 4′-demethyl-epipodophyllotoxin 7 and of 4-demethyl podophyllotoxin 8 are also reported. The synthesis of 7 and 8 was based upon the reduction of the γ-lactone ring of 4′-demethyl-4-epipodophyllotoxin followed by selective protection at C-11 and elongation at C-13. (8-15% and 4% overall yields). Compounds 4, 5 and 7 did not display relevant cytotoxicity in vitro against L1210 murine leukemia. 相似文献
2.
Isoxazolines 2 from the cycloaddition of imidazoline 3-oxides 1 with DMAD undergo rearrangement to 3,4-dihydro-2H-imidazol-1-ium-1-(1,2-bis-methoxycarbonyl-2-oxo-ethanides) 3, which spontaneously undergo elimination to give 3H-imidazol-1-ium-1-(1,2-bis-methoxycarbonyl-2-oxo-ethanides) 5 or 1H-imidazoles 6 when heated in toluene at reflux. The presence of the aromatic ring at C-6 decelerated the conversion and enhanced the yield of 5. Solvents more polar than toluene (e.g., DMSO) provided quantitative conversion of 2 into 6 in mild conditions, while in less polar solvents such as CCl4, the reaction rate was lowered and the yield of 5 enhanced. C-2 unsubstituted ylides 5 were treated with Ag2O or AgNO3 in the presence of Et3N at room temperature to give C-2 metallated derivatives 9 in excellent yields. 相似文献
3.
The diterpenoid acylglycerol fraction from an extract of the mantle of a new collection of the Antarctic dorid gastropod mollusc Austrodoris kerguelenensis has been chemically analysed. Two novel 2-monoacylglycerols 9 and 12, along with known 1,2-diacyl glyceryl esters 5 and 6, now reassigned as 7 and 8, have been isolated. The linkage of a diterpenoid moiety at C-2 of glycerol characterizes all the compounds. Because the R absolute stereochemistry at C-2 of glycerol has been established for the corresponding 1,3-glyceryl esters 1 and 2, derived from 7 and 8 by acyl-migration of the terpenoid moiety from C-2 to C-3, our finding implies that 1,2-derivatives from Antarctic nudibranchs have the same S stereochemistry as all 1,2-sn-diacylglycerols from the other dorids. 相似文献
4.
Margaret A Brimble Caryn Burgess Rosliana Halim Maria Petersson Jayanta Ray 《Tetrahedron》2004,60(27):5751-5758
The uncatalyzed reaction of N-(tert-butoxycarbonyl)-2-tert-butyldimethylsilyloxypyrrole 3 with 1,4-quinones bearing an electron withdrawing group at C-2 has been studied. Use of 1,4-quinones 4, 5 bearing an ester group at C-2 provided an efficient synthesis of the respective pyrrolidinobenzofuran adduct 9 or pyrrolidinonaphthofuran adduct 10 whereas use of 1,4-quinones 6, 7 and 8 bearing an acetyl group at C-2 afforded silyloxypyrroles 11, 12 and 13 resulting from direct electrophilic substitution of the silyloxypyrrole by the electrophilic quinone. Addition of Eu(fod)3 to the reaction of 2-acetyl-1,4-naphthoquinone 7 and 3-acetyl-5-methoxy-1,4-naphthoquinone 8 with N-(tert-butoxycarbonyl)-2-tert-butyldimethylsilyloxypyrrole 3 provided a method for obtaining the pyrrolidinonaphthofuran adducts 14 and 15 together with silyloxypyrroles 12 and 13. Oxidative rearrangement of pyrrolidinonaphthofuran adduct 15 to pyrrolidino pyranonaphthoquinone 16 using ceric ammonium nitrate in acetonitrile provided a novel approach for the synthesis of an aza-analogue of the pyranonaphthoquinone antibiotic kalafungin. 相似文献
5.
Sébastien Debarge Marie-Paule Jouannetaud Jean-Claude Jacquesy Alain Cousson 《Tetrahedron》2006,62(4):662-671
In HF-SbF5, quinidine 1a or its dihydrochloride cyclises previously obtained with usual acids. A similar reaction is observed in the presence of CCl4. Under similar conditions quinidine acetate 1b and epiquinidine acetate 2b dihydrochlorides both yield 10,10-difluoro derivatives epimeric at C-3, 6 and 7, and 9c and 10b, and a rearranged difluoro derivative 8b and 11b, respectively. Epiquinidine 2a leads to the expected analogues 10a and 11a and to a ketone 9a. Formation of gem-difluoro compounds implies chloro intermediates at C-10, precursors of α-chlorocarbenium ions, which are trapped by a fluoride ion and which lead by halogen exchange to the products. 相似文献
6.
The key intermediate 1,2:5,6-di-O-isopropylidene-3-deoxy-3β-allyl-α-d-glucofuranose (8) could be conveniently prepared through radical induced allyl substitution at C-3 of appropriate 1,2:5,6-di-O-isopropylidene-α-d-glucofuranose derivatives (7a,b) and used to synthesize enantiomeric bishydroxymethyl aminocyclopentanols 13 and 19 by the application of a 1,3-dipolar nitrone cycloaddition reaction involving the C-5 or C-1 aldehyde functionality. The products were subsequently transformed into carbanucleoside enantiomers 15 and 21. The diastereomeric isoxazolidinocyclopentane derivative 20 was similarly converted to carbanucleoside 22. 相似文献
7.
Dya Fita Dibwe Suresh Awale Shigetoshi Kadota Hiroyuki Morita Yasuhiro Tezuka 《Tetrahedron letters》2014
Two new highly oxygenated xanthones, named muchimangins E (1) and F (2), have been isolated from the root of Securidaca longepedunculata (Polygalaceae). Their structures were elucidated by the analyses of spectral data to be a novel xanthone with a diphenylmethyl substituent at C-2. Moreover, the structures of muchimangins B (4) and C (5) were revised by careful analysis of the spectral data and by comparing their NMR data with those of 1 and 2, to be xanthones with the diphenylmethyl substituent at C-2, not at C-4 reported previously. 相似文献
8.
Fabio Bellina 《Tetrahedron》2008,64(26):6060-6072
Highly selective, practical, and efficient protocols for the preparation of 4(5)-aryl-1H-imidazoles 2, 2,4(5)-diaryl-1H-imidazoles 3, and 4,5-diaryl-1H-imidazoles 1 are described. A key step of these protocols is the regioselective synthesis of 5-aryl-1-benzyl-1H-imidazoles 9 by Pd-catalyzed direct C-5 arylation of commercially available 1-benzyl-1H-imidazole (8) with aryl halides. The three-step synthesis of compounds 3 from 8 also involves the Pd-catalyzed and Cu-mediated direct C-2 arylation of imidazoles 9 with aryl halides under base-free and ligandless conditions. On the other hand, the four-step synthesis of imidazoles 1 from 8 also involves the regioselective bromination of compounds 9 and a Suzuki reaction of the resulting 5-aryl-1-benzyl-4-bromo-1H-imidazoles 11 with arylboronic acids 5 under phase-transfer conditions, followed by N-debenzylation. 相似文献
9.
Attempts to synthesise iso-cladospolide-B, cladospolide-B and cladospolide-C resulted in macrolides 1, 2 and 4 along with butenolide 3. Of the three stereogenic centres, the C-4/C-5 vic-diol was obtained from tartaric acid and d-glucose, while the C-11 stereocentre was created by Jacobsen’s method. 相似文献
10.
Mariko Kitajima Satoko Ohara Noriyuki Kogure Dammrong Santiarworn Hiromitsu Takayama 《Tetrahedron》2013
Six new β-carboline-type indole alkaloid glycosides, ophiorrhisides A–F (1–6), were isolated from Ophiorrhiza trichocarpon (Rubiaceae) collected in Thailand. Ophiorrhisides A (1) and B (2) possess a lactam function in the C ring and a unique biose residue in the molecule. Ophiorrhiside F (6) has a highly oxidized C ring with a 1,2-dicarbonyl function at C-5 and C-6 positions as well as a double bond between C-3 and C-14. 相似文献
11.
The uncatalyzed reaction of 2-tert-butyldimethylsilyloxythiophene 2 with 1,4-quinones bearing either an electron withdrawing acetyl or a carbomethoxy group at C-2, was investigated. No reaction was observed using 1,4-quinones 8 and 9 bearing an ester group at C-2 whereas use of 1,4-quinones 10 and 11 bearing an acetyl group at C-2 only provided low yields of the silyloxythiophenes 15 and 16 resulting from electrophilic substitution of the silyloxythiophene by the 1,4-quinone. Use of the Lewis acids InCl3, Cu(OTf)2 and BF3·Et2O were investigated in an effort to improve the yield of the desired annulation reaction. BF3·Et2O proved to be the optimum catalyst for the synthesis of thiolactone naphthofuran adducts 14 and 18 from 1,4-naphthoquinones 9 and 11, respectively. Reaction of 2-tert-butyldimethylsilyloxythiophene 2 with 1,4-benzoquinones 8 and 10 bearing a carbomethoxy or an acetyl group at C-2, respectively, afforded thiolactone benzofuran adducts 13 and 17, respectively, catalyzed by either InCl3 or Cu(OTf)2. Addition of 2-tert-butyldimethylsilyloxythiophene 2 to 3-acetyl-5-methoxy-1,4-naphthoquinone 12 afforded adduct 19 that underwent oxidative rearrangement to thiolactone pyranonaphthoquinone 20 using ceric ammonium nitrate in acetonitrile, thus providing a novel approach for the synthesis of a thia analogue of the pyranonaphthoquinone antibiotic kalafungin. 相似文献
12.
Ashim Roy 《Tetrahedron letters》2004,45(30):5811-5814
The [3+2] intramolecular nitrone cycloaddition (INC) reaction on appropriately designed olefinic nitrones derived from d-glucose, having the nitrone at C-1 and α,β-unsaturated ester functionalities at C-5 of the sugar backbone, afforded the isoxazolidine fused carbocycles 11-13, which were subsequently transformed into the chiral, tetrahydroxylated cis-azabicyclo[3.3.0]octanones 14-18 in good yields. 相似文献
13.
Chithaluri SudhakarParigi Raghavendar Reddy Tuniki Venugopal RajuBiswanath Das 《Tetrahedron letters》2012,53(30):3850-3852
Two cassane diterpenoids, pulcharrin G (1) and 6β-cinnamoyl-7β-hydroxy-voucapen-5-α-ol (2), the constituents of Caesalpinia pulcherrima, were treated with BF3·OEt2 to furnish two olefinic products 3 and 4, respectively. The products were formed by elimination of water and migration of a methyl group from C-4 to C-5. The cytotoxic and antimicrobial activities of 3 and 4 were examined. 相似文献
14.
Elena B. Erkhitueva Albina V. DogadinaAndrey V. Khramchikhin Boris I. Ionin 《Tetrahedron letters》2012,53(33):4304-4308
1-Chloroacetylene-2-phosphonates react with 1H-1,2,4-triazole-3-thiols in anhydrous acetonitrile with high regioselectivity to form the fused heterocycles, 6-(dialkoxyphosphoryl)-3H-thiazolo[3,2-b][1,2,4]triazol-7-ylium chlorides 1-5. A significant difference from the previously known reactions of binucleophiles with haloacetylenes is the involvement of both acetylenic carbon atoms in the heterocycle formation. A reaction mechanism is hypothesized that assumes the formation of a sulfenium cation at the acetylene C-1 atom followed by attack of the C-2 atom by the ring N-2 atom. Compounds 1-5 easily lose one alkyl group from the dialkoxyphosphoryl fragment to form zwitterions (e.g., 6-8) which further can be transformed into inner salts 9 and 10 when heated with concentrated hydrochloric acid. 相似文献
15.
New N-sulfonylpyrimidine derivatives 1-(p-toluenesulfonyl)uracil (1), 1-(p-toluenesulfonyl)thymine (2), 5-bromo-1-(p-toluenesulfonyl)uracil (3), 1-(methanesulfonyl)uracil (4), 1-(1-naphthylsulfonyl)uracil (5), and 1-(1-naphthylsulfonyl)thymine (6) were prepared by the condensation reaction of silylated pyrimidine derivatives with selected sulfonyl chlorides in acetonitrile. Some members of the series showed unexpected crystal properties as a consequence of their conformational chirality in the solid state. Compounds 1 and 5 exhibited chiral crystallization, which was, in the case of 1, accompanied by the formation of racemically twinned crystals regardless of the solvent used, while 5 gave a conglomerate of enantiomorphous crystals. For 2, 3, and 6, substituents at the C-5 position of the pyrimidine ring prevented chiral crystallization by influencing the crystal packing. Analysis of the crystal structures of 1, 4, and 5, reveals the influence of the arylsulfonyl group on the occurrence or absence of chiral crystallization. 相似文献
16.
Photochemistry of the title compounds in various solvents was studied using a broad band of light centered at 350 nm. C-4 spiroketal cyclohexenone 4 (1.0 M) afforded dimers and 12b with the predominance of the former in polar solvent and the latter in nonpolar solvent. When the concentration was reduced to, 4 underwent solvent addition in nonpolar solvent and ring-contraction in polar solvents. 4,4-Dimethoxycyclohexenones 5a–d in TFE exhibited a different photochemical behavior. The 5-vinyl-substituted enone afforded the bridged-bicyclic ketone 16. Cyclohexenone 5b with methyl moieties at C-2 and C-3 underwent aromatization whereas cyclohexenones with butyl substituent at C-5 and 5d with silylated alcohol at C-2 underwent solvent exchange. In γ-hydroxylated cyclohexenones 6a–c ring-contraction and solvent exchange were observed. Photochemistry of the title compounds from the mechanistic viewpoint is also described. 相似文献
17.
Two new spiroketals, didemnaketals D (1) and E (2) were isolated from a marine ascidian species belonging to the genus Didemnum. The structures of the compounds were elucidated by extensive 1D (1H, 13C, and DEPT) and 2D (COSY, TOCSY, HSQC, HMBC, NOESY, and ROESY) NMR studies and high-resolution mass spectroscopic data. The new didemnaketals differ from the reported ones in which that they lack the methyl functionality at C-6 and the hydroxy moiety at C-21. Instead, they possess an ester moiety at C-6 in addition to new oxygen functionality at C-20 of the didemnaketals. Compounds 1 and 2 were evaluated for their protein kinase inhibitory activity against different kinases (CDK5, CK1, DyrK1A, and GSK3) at 10 μg/mL. Compounds 1 and 2 showed moderate activity against these kinases. In addition, the compounds displayed moderate antimicrobial activity against Staphylococcus aureus and Bacillus subtilis, respectively. 相似文献
18.
Svjetlana Krištafor Andrijana Meš?i? Mario Cetina Silvija Korunda Damjan Makuc Janez Plavec Silvana Rai?-Mali? 《Journal of fluorine chemistry》2011,132(9):573-578
A new series of conformationally restricted pyrimidine derivatives bearing C-6 isobutenyl side-chain (2-9) has been prepared. The novel fluoroalkenyl pyrimidine nucleoside mimetic 3 as model compound for development of tracer molecule in positron emission tomography (PET) was synthesized by fluorination reaction of methoxytritylated pyrimidine derivative using diethylaminosulfur trifluoride (DAST). Conversion of one hydroxyl group to methoxytritylated, fluorinated, mesylated and acetylated pyrimidine derivatives (2, 3, 5-7 and 9) afforded a mixture of Z- and E-isomers in which Z-isomers were predominant. Conformational study of 1, and its fluorinated structural congeners 3 and 4 by the use of NOE experiments revealed predominant conformation of compounds where vinyl H-1′ proton is spatially close to N-1 methyl and H-3′b methylene protons and on the other hand H-3′a methylene protons are close to C-5 methyl protons. The stereostructure of 1,3-dihydroxyisobutenyl N-methyl thymine 1 was unambiguously confirmed by X-ray crystal structure analysis. 相似文献
19.
Magie M. Kapojos Taiko Oda Ohgi Takahashi Remy E.P. Mangindaan Defny S. Wewengkang Sachiko Tsukamoto Michio Namikoshi 《Tetrahedron》2010,66(3):641-3319
Two unusual cembranoids, sarcofuranocembrenolides A (1) and B (2), were isolated from a soft coral Sarcophyton sp. together with five known cembranoids (3-7). Compound 1 had a unique carbon skeleton of 8,19-bisnorfuranocembrenolide. Compound 2 was a furanocembrenolide, but a C1 unit (C-20) was attached to C-10 instead of C-12 of the ordinary cembrenolides. These rearrangements are unique in the biosynthesis of cembranoid diterpenes. Lobohedleolide (5), (7Z)-lobohedleolide (6), and denticulatolide (7) inhibited the colony formation of V79 cells at ED50 values of 4.6 (abt. 1.52), 3.7 (1.22), and 3.6 (1.40) μM (μg/mL), respectively, and reduced TNF-α production from LPS-stimulated RAW264.7 cells at 3.0-10.0 μM. 相似文献
20.
Hai-Bo Zhang Jian-Xin Pu Yong ZhaoFei He Xiao-Nian LiXiao Luo Li-Guang LouHan-Dong Sun 《Tetrahedron letters》2011,52(46):6061-6066
A phytochemical investigation of Isodon leucophyllus led to the isolation of four novel ent-kauranoid dimers: bisleuconins A-D (1-4), and one known compound, rabdoloxin A (5). It was interesting that the structures of bisleuconins A (1) and B (2) were elucidated as a pair of epimeric ent-kauranoid dimers with unique linkage pattern C-16→C-17′ to connect two monomers. Bisleuconins C (3) and D (4) were two new asymmetric ent-kauranoid dimers. A possible biogenetic pathway of 1 and 2 was also proposed. 相似文献