| 1. |
- Bergman, Jan, et al.
(författare)
-
Studies of the reactions between indole-2,3-diones (isatins) and 2-aminobenzylamine
- 2003
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Ingår i: Tetrahedron. - 0040-4020 .- 1464-5416. ; 59:7, s. 1033-1048
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Tidskriftsartikel (refereegranskat)abstract
- Reflux of equimolecular amounts 2-aminobenzylamine and isatins in acetic acid produced indolo[3,2-c]quinolin-6-ones in good yields. A proposed mechanism involving initial formation of a spiro compound is given. This isolable intermediate subsequently rearranges via a sequential isocyanate ring opening and a cyclisation process to a urea derivative which finally cyclized to the indolo[3,2-c]quinolin-6-ones. The urea derivative could be prepared separately and cyclized selectively to indolo[3,2-c]quinolin-6-one. Reaction of N-acetylisatin with 2-aminobenzylamine at room temperature yielded the 1,4-benzodiazepinone 3-(2-acetamidophenyl)-1,5-dihydro-1,4-benzodiazepin-2one whereas its isomer 2(2-acetamidophenyl)-4,5-dihydro-1,4-benzodiazepin-3-one was obtained from 2-(2-acetylaminophenyl)-N-(2-aminobenzyl)-2-oxoacetamide in acetic acid at room temperature. The previously unknown linear isomer of indolo[3,2-c]quinolin-6-one, i.e. indolo[2,3-blquinolin-11-one, has been prepared by thermal (260degreesC) cyclization of methyl 2-phenylamino indole-3-carboxylate, which in turn was prepared in two steps from methyl indole-3-carboxyl ate. (C) 2003 Elsevier Science Ltd. All rights reserved.
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| 2. |
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| 3. |
- Ek, Fredrik, et al.
(författare)
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Synthesis of Fused Tertazole- and Imidazole Derivatives via Iodocyclization.
- 2003
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Ingår i: Tetrahedron. - 0040-4020. ; 59:35, s. 6759-6769
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Tidskriftsartikel (refereegranskat)abstract
- The possibility to prepare fused tetrazole- and imidazole derivatives by iodocyclization in moderate to excellent yields is demonstrated. In some examples the cyclizations were not following Baldwin's rules entirely, i.e. exo-selectivity. Nucleophilic substitution of the formed iodides gave different results depending on the hardness of the nucleophile. Thus, elimination of the iodide could be a problem but a substitution reaction with ethyl potassium xanthate and a radical reaction using acrylonitrile were tolerated. In addition, we showed that it is possible to selectively use three iodo substituents individually in one of the fused imidazole derivatives.
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| 4. |
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| 5. |
- Kahnberg, Pia, et al.
(författare)
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Alternative routes to pterulone
- 2002
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Ingår i: Tetrahedron. - 0040-4020. ; 58:26, s. 5203-5208
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Tidskriftsartikel (refereegranskat)abstract
- Two new synthetic routes to pterulone, a fungal metabolite possessing potent antifungal activity as an inhibitor of NADH/ubiquinone oxidoreductase, are reported. (C) 2002 Elsevier Science Ltd. All rights reserved.
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| 6. |
- Leclercq, Sabine, et al.
(författare)
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Furanocembranoid Diterpenes as Defensive Compounds in the Dufour Gland of the Ant Crematogaster brevispinosa rochai
- 2000
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Ingår i: Tetrahedron. - 0040-4020. ; 56:14, s. 2037-2042
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Tidskriftsartikel (refereegranskat)abstract
- Two new furanocembranoid diterpenes, crematofuran [(1R∗,11R∗,12R∗)-6,19:11,12-bisepoxycembra-3,6,8(19),15-tetraene] (1) and isocrematofuran [(1R∗,3S∗,4S∗)-3,4:6,19-bisepoxycembra-6,8(19),11,15-tetraene] (2), have been isolated from the Dufour gland secretion of the Brazilian ant Crematogaster brevispinosa rochai. Their structures, including the relative configuration, have been determined by a combination of NMR and molecular mechanics methods. The toxicity of 1 towards other ants is on the same level as that of nicotine. This is the first report of cembranoid diterpenes as defensive compounds in an ant.
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| 7. |
- Maricic, Suzana, et al.
(författare)
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Synthesis and conformational studies of a Leu-enkephalin amide analogue containing a ferrocene substructure
- 2002
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Ingår i: Tetrahedron. - 0040-4020. ; 58:15, s. 3085-3093
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Tidskriftsartikel (refereegranskat)abstract
- Solution phase synthesis of a constrained Leu(5)-enkephalin amide analogue 10 is reported, in which the cyclic ferrocenyl containing subunit 7 was introduced as a mimetic of the tetrapeptide Tyr-Gly-Gly-Phe unit. Temperature dependence of the chemical shift of the amide protons of 10 indicated a hydrogen bond between the same amino acid residues as observed for the natural Leu-enkepalin in the single-bend conformation. The rotational barrier (DeltaG(c)(not equal)=16.8 kcal/mol) of the C-terminal amide group, which was determined by DNMR spectroscopy, and NOESY experiments indicated that the two termini were more distant as compared to the single-bend conformation of natural Leu-enkephalin amide. (C) 2002 Elsevier Science Ltd. All rights reserved.
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| 8. |
- Rasser, F, et al.
(författare)
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Terpenoids from Bovista sp 96042
- 2002
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Ingår i: Tetrahedron. - 0040-4020. ; 58:39, s. 7785-7789
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Tidskriftsartikel (refereegranskat)abstract
- The novel cytotoxic hexacyclic illudane-illudalane bis-sesquiterpene bovistol (la) was obtained from the basidiomycete Bovista sp. 96042, together with several new sesquiterpenes. la is formed in the fungus by a heteroatom Diels-Alder dimerisation of psathyrellon B (2). (C) 2002 Elsevier Science Ltd. All rights reserved.
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| 9. |
- Tsopmo, Apollinaire, et al.
(författare)
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A norbislabdane and other labdanes from Aframomum sulcatum
- 2002
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Ingår i: Tetrahedron. - 0040-4020. ; 58:14, s. 2725-2728
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Tidskriftsartikel (refereegranskat)abstract
- Extracts of the seeds of Aframomum sulcatum (Oliv. & Hanb) K. Schum (Zingiberaceae) yielded a novel norbislabdane derivative, sulcanal (1) and the new labdane (12E)-8beta,17-epoxy-11-hydroxy-12-labden-15.16-dial-11,15-hemiacetal (2) (as a 1:1 C-15 epimeric mixture), along with known labdane diterpenes.
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| 10. |
- Bergman, Jan, et al.
(författare)
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Reactions of 1,2-bis(1H-indol-2-yl)ethane : Formation of indolo[2,3-c]carbazole and cyclohept[1,2-b : 5,4-b ']bisindole derivatives
- 2000
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Ingår i: Tetrahedron. - 0040-4020 .- 1464-5416. ; 56:13, s. 1911-1916
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Tidskriftsartikel (refereegranskat)abstract
- 1,2-Bis(1H-indol-2-yl)ethane (9) has been prepared and converted into indolo[2,3-c]carbazole (8) using palladium acetate in refluxing acetic acid. Reaction of 9 with CoF3 in hot TFA led to isolation of cyclohept[1,2-b:5,4-b']bisindole derivatives 11 and 12, which could be elaborated into further derivatives. Treatment of 9 with orthoesters, aldehydes and ketones under acidic conditions afforded additional bisindoles containing a seven-membered ring.
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| 11. |
- Bergman, Jan, et al.
(författare)
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Synthesis of 4-oxo-4,5-dihydro-3H-pyrrolo[2,3-c]quinoline-1-carboxylic acid ethyl ester and its isomer 1-oxo-2,9-dihydro-1H-beta-carboline-4-carboxylic acid ethyl ester
- 2002
-
Ingår i: Tetrahedron. - 0040-4020 .- 1464-5416. ; 58:45, s. 9179-9185
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Tidskriftsartikel (refereegranskat)abstract
- 4-Oxo-4,5-dihydro-3H-pyrrolo[2,3-c]quinoline-1-carboxylic acid ethyl ester was obtained when TosMIC was reacted with 3-methylene-oxindole acetic acid ethyl ester. An alternative synthesis to this pyrroloquinolone was performed via a reduction of a 2,3,4-trisubstituted pyrrole obtained in turn by treatment of a vinyl sulfone with ethyl isocyanoacetate under basic conditions. A beta-carboline, isomeric with the pyrroloquinolone, was synthesised utilizing a tosylimine.
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| 12. |
- Bergman, Jan, et al.
(författare)
-
Synthesis of indolocarbazole quinones; potent aryl hydrocarbon receptor ligands
- 2002
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Ingår i: Tetrahedron. - 0040-4020 .- 1464-5416. ; 58:7, s. 1443-1452
-
Tidskriftsartikel (refereegranskat)abstract
- Syntheses of indolo[2,3-b]carbazole-6,12-dione and the isomeric indolo[3,2-b]carbazole-6,12-dione, an extremely efficient inducer of the aryl hydrocarbon (Ah) receptor are described. Initial oxidation of the parent indolo[3,2-b]carbazole followed by several different ring-closing strategies produced the latter compound. Entries into syntheses of unsymmetrical 6,12-disubstituted indolo[2,3-b]carbazoles are also described.
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| 13. |
- Janosik, Tomasz, et al.
(författare)
-
Synthesis of the marine alkaloids rhopaladins A, B, C and D
- 2002
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Ingår i: Tetrahedron. - 0040-4020 .- 1464-5416. ; 58:14, s. 2813-2819
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Tidskriftsartikel (refereegranskat)abstract
- The total synthesis of all four known rhopaladins, A-D, isolated from the Okinawan marine tunicate Rhopalaea sp., in two synthetic steps is described, involving an imidate based cyclization with tryptophan esters as the key step to afford the appropriately substituted imidazolinone unit. A short and efficient new synthesis of indol-3-yl-carbonyl nitriles from indol-3-yl-carboxaldehydes and trimethylsilyl cyanide, followed by oxidation with DDQ is also described.
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| 14. |
- Larsson, Michael, et al.
(författare)
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Diastereoselective addition of methylmetal reagents to 2-methylaldehydes.
- 2001
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Ingår i: Tetrahedron. - 0040-4020 .- 1464-5416. ; 57:35, s. 7541-7548
-
Tidskriftsartikel (refereegranskat)abstract
- The preparation of compounds incorporating the 3-hydroxy-2-methyl-1-butyl moiety of high diastereomeric purity is described. These compounds can serve as potential building blocks for the preparation of several kinds of natural products. The diastereoselective addition of a number of methylmetal derivatives to three 3-substituted 2-methylaldehydes in various solvents was studied. An excellent diastereomeric. ratio (95:5 anti-Cram/Crain) was obtained with 2-methyl-3-(phenylsulfanyl)propanal (5) and Me2Zn in the presence of TiCl4.
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| 15. |
- Lindberg, Jan, et al.
(författare)
-
Efficient routes to glucosamine-myo-inositol derivatives, key building blocks in the synthesis of glycosylphosphatidylinositol anchor substances
- 2002
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Ingår i: Tetrahedron. - 0040-4020 .- 1464-5416. ; 58:7, s. 1387-1398
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Tidskriftsartikel (refereegranskat)abstract
- Short synthetic routes to protected derivatives of 2-amino-2-deoxy-a-D-glucopyranosyl-(1?6)-D-myo-inositol are described. Various 2-azido-2-deoxy-glucosyl donors were synthesized, starting from D-glucal or glucosamine hydrochloride. Derivatives of 1,2- and 2,3- D-myo-inositol-camphanylidene acetals were prepared to function as glycosyl acceptors. The subsequent glycosylations produced useful building blocks for the synthesis of GPI-anchor substances. © 2002 Elsevier Science Ltd. All rights reserved.
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| 16. |
- Lindberg, Jan, et al.
(författare)
-
Synthesis of galactoglycerolipids found in the HT29 human colon carcinoma cell line
- 2002
-
Ingår i: Tetrahedron. - 0040-4020 .- 1464-5416. ; 58:25, s. 5109-5117
-
Tidskriftsartikel (refereegranskat)abstract
- Synthesis of three galactoglycerolipids (3-O-(ß-D-galactopyranosyl)-1-O-hexadecyl-2-O-palmitoyl-sn-glycerol, 3-O-(a-D-galactopyranosyl-(1?4)-ß-D-galactopyranosyl)-1-O- hexadecyl-2-O-palmitoyl-sn-glycerol, 3-O-(a-D-galactopyranosyl-(1?4)-ß-D-galactopyranosyl)-1-O- hexadecyl-sn-glycerol), and the corresponding glycerolipid (1-O-hexadecyl-2-O-palmitoyl-sn-glycerol) is described. The first two compounds were recently identified in the human colon carcinoma cell line HT29. The three-carbon synthon (S)-glycidol was used for construction of the glycerol moiety. Glycosylation of (S)-glycidol with protected galactosyl and digalactosyl donors produced galactosyl and digalactosyl glycidols. Lewis acid catalyzed opening of the epoxide produced protected galactosyl and digalactosyl glycerolipids. Deprotection, or palmitoylation followed by deprotection, yielded the target compounds. The corresponding glycerolipid was synthesized analogously and an oxidation-reduction procedure for tritiation was developed. The synthesized compounds will be used in studies of the role of galactosyl glycerolipids in differentiation and colon cancer development. © 2002 Elsevier Science Ltd. All rights reserved.
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| 17. |
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| 18. |
- Olofsson, Berit, et al.
(författare)
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Synthesis of N-H vinylaziridines : a comparative study
- 2002
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Ingår i: Tetrahedron. - 0040-4020 .- 1464-5416. ; 58:30, s. 5979-5982
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Tidskriftsartikel (refereegranskat)abstract
- Vinylaziridines are useful and versatile synthetic intermediates, as the relief of ring-strain provides a driving force for efficient ring-opening or ring-expansion reactions. Furthermore, the vinyl group can be derivatized into interesting functionalities. The ring-closure of vicinal amino alcohols constitutes a straightforward route to aziridines. Several methods exist for this transformation, although many cannot be applied to vinylaziridines due to their acid lability. This comparative study describes the most effective sequences for the formation of N-H vinylaziridines.
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| 19. |
- Ray, C. A., et al.
(författare)
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Diastereoselective Lewis acid-catalysed 4+2 cycloadditions of 3-alkyl-, 3-aryl- and 3-carboxyl-2H-azirines : a route to aziridine containing azabicyclo 4.1.0 heptanes and azatricyclo 2.2.1.0 nonanes
- 2002
-
Ingår i: Tetrahedron. - 0040-4020 .- 1464-5416. ; 58:30, s. 5983-5987
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Tidskriftsartikel (refereegranskat)abstract
- 3-Substituted-2H-azirines have been employed as 2pi components in Lewis acid-catalysed hetero Diels-Alder reactions with a variety of diene systems. A series of Lewis acids were screened for catalytic behaviour in the reaction between Danishefsky's diene and 3-phenyl-2H-azirine to give the cycloaddition adduct, and in most cases elevated temperature were required to effect cycloaddition. A noteworthy exception was a BF3.Et2O-catalysed cycloaddition which proceeded in less than I h between -70degreesC and -60degreesC. The cycloadditions were found to proceed with endo selectivity providing a single diastereoisomeric product. Benzyl 2H-azirine-3-carboxylates were found to be activated by Lewis acids and participate in endo selective cycloadditions at -20degreesC.
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| 20. |
- Rewcastle, G W, et al.
(författare)
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Reactions of 2-lithiated indoles with elemental sulfur. Formation of pentathiepino[6,7-b]indoles and indoline-2-thiones
- 2001
-
Ingår i: Tetrahedron. - 0040-4020 .- 1464-5416. ; 57:33, s. 7185-7189
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Tidskriftsartikel (refereegranskat)abstract
- The reactions of 2-lithiated indole and 1-methylindole with elemental sulfur have been studied, leading e.g. to a rational approach to pentathiepino[6,7-b]indoles 5 and 10. Notable amounts of the previously known tetrathiocino[5,6-b:8,7-b ' ]diindole 11 could be observed as a side reaction in the preparation of 10. Treatment of the anions of indoline-2-thiones 6 or 7 with sulfur also gave the pentathiepins 5 or 10, respectively. In addition, a convenient and clean lithiation route to indoline-2-thione (6) has been developed.
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| 21. |
- Ruda, K., et al.
(författare)
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Synthesis of an inositol phosphoglycan fragment found in Leishmania parasites
- 2000
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Ingår i: Tetrahedron. - 0040-4020 .- 1464-5416. ; 56:24, s. 3969-3975
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Tidskriftsartikel (refereegranskat)abstract
- Synthesis of 1 and 2a is described using a block synthetic strategy. Compound 4 was used as precursor for the two mannose derivatives which, coupled together, forms the dimannoside building block. Thioglycoside 7 was coupled to 8 yielding inositol phosphoglycan 9a, which was selectively deprotected and reacted with 2,3,4,6-tetra-O-benzyl-a-D-glucopyranos-1-yl H- phosphonate to form the protected target molecule 12. Deprotection of 12 by acidic deacetalisation/desilylation and subsequent catalytic hydrogenolysis resulted in cleavage of the anomeric phosphodiester to produce 1. Debenzylation with sodium in liquid ammonia followed by acidic deacetalisation/desilylation gave the target compound 2a. (C) 2000 Published by Elsevier Science Ltd.
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| 22. |
- Slätt, Johnny, 1976-, et al.
(författare)
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Oxygenation of 2,3-dihydroindoles.
- 2002
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Ingår i: Tetrahedron. - 0040-4020 .- 1464-5416. ; 58:45, s. 9187-9191
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Tidskriftsartikel (refereegranskat)abstract
- Indolines (2,3-dihydroindoles) and isatogens (3-oxo-3H-indole 1-oxides) have been prepd. in an efficient route starting from indoles substituted in position 2. Redn. of the 2-substituted indoles was performed with tin and hydrochloric acid to give racemic indolines, which were converted to isatogens by 3-chloroperoxybenzoic acid (m-CPBA). [on SciFinder(R)]
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| 23. |
- Smitt, Olof, et al.
(författare)
-
Syntheses of a prenylbisabolane diterpene, a natural insecticide from Croton linearis, and of the bisabolane sesquiterpenes (-)-delobanone and (-)-epi-delobanone
- 2002
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Ingår i: Tetrahedron. - 0040-4020. ; 58:38, s. 7691-7700
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Tidskriftsartikel (refereegranskat)abstract
- An enantioselective first total synthesis of a constituent of Croton linearis, the (-)-7-hydroxy-3,10-prenylbisaboladien-2-one 1, is described as well as the syntheses of the 7-hydroxy-3,10-bisaboladien-2-ones (-)-epi-delobanone (14a) and (-)-delobanone (14b). The model compounds, 7-hydroxy-11-nor-methyl-3-bisabolen-2-one (8a), and 11,15-nor-dimethyl-7-hydroxy-3-bisabolen-2-one (8b), were successfully prepared by opening of the protected carvone epoxide derivative 6 with the appropriate organocuprates. An alternative approach was used for compounds 1 and 14. Thus, these were obtained from homogeranyllithium or homoprenyl Grignard reagent, which reacted successfully with a masked nor-carvone, ketone 11, prepared in four steps from (R)-carvone.
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| 24. |
- Somfai, Peter, et al.
(författare)
-
Asymmetric synthesis of (+)-1-deoxynojirimycin and (+)-castanospermine
- 2003
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Ingår i: Tetrahedron. - 0040-4020 .- 1464-5416. ; 59:8, s. 1293-1299
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Tidskriftsartikel (refereegranskat)abstract
- Asymmetric total syntheses of (+)-1-deoxynojirimycin (1) and (+)-castanospermine (2) are described. Starting from diene 3, the required absolute stereochemistry is introduced by an asymmetric hydroxylation followed by epoxidation. An intramolecular cyclization of amine 17 gives access to the corresponding tetrasubstituted piperidine 18, which is a precursor to compounds 1 and 2. (+)-Deoxynojirimicyn (1) was obtained in 36% yield over 11 steps from diene 3, while (+)-castanospermine (2) was achieved in 13% after 19 steps from the same starting material.
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| 25. |
- Wachtmeister, J., et al.
(författare)
-
Impact of the central hydroxyl groups on the activity of symmetrical HIV-1 protease inhibitors derived from L-mannaric acid
- 2000
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Ingår i: Tetrahedron. - 0040-4020 .- 1464-5416. ; 56:20, s. 3219-3225
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Tidskriftsartikel (refereegranskat)abstract
- The influence of the central hydroxyl groups on the anti-viral activity of symmetrical HIV-1 protease inhibitors derived from L-mannaric acid has been examined. L-Iditol was synthesized and used as a chiral precursor for the synthesis of the corresponding inhibitor with inverted configuration at C-3 and C-4. Key intermediates were 3,4-O-isopropylidene-L-iditol and the activated L-idaric acid succinimidyI ester. The configurations of the central hydroxyl groups required for optimal inhibition of the HIV-1 protease were determined to be the C-3R and C-4R, i.e. the L-manno-configuration. Three C2-symmetric inhibitors were converted to their thiocarbonates and reduced to provide the corresponding hydroxyethyl transition-state mimics. Deletion of the C-4 hydroxyl group in these inhibitors gave no further improvement in the anti-viral activity. (C) 2000 Published by Elsevier Science Ltd.
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| 26. |
- Witt, A, et al.
(författare)
-
Synthesis and reactions of some 2-vinyl-3H-quinazolin-4-ones
- 2000
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Ingår i: Tetrahedron. - 0040-4020 .- 1464-5416. ; 56:37, s. 7245-7253
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Tidskriftsartikel (refereegranskat)abstract
- A simple, high-yielding synthesis of 2-vinyl-3H-quinazolin-4-one, 2-(1-chlorovinyl)-3H-quinazolin-4-one and 2-(1-bromovinyl)-3H-quinazolin-4-one. The 2-vinylquinazolinones 11a and 14 participate readily in nucleophilic addition reactions. Treatment with both carbon and nitrogen nucleophiles results in a clean conversion into a variety of 2-substituted 3H-quinazolin-4-one derivatives. The 2-(1-halovinyl)-3H-quinazolin-4-ones 11b and Ile reacted with carbon nucleophiles to give several derivatives of 2-substituted 3H-quinazolin-4-one, such as dihydrofurancarboxylic ethyl ester 23.
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| 27. |
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| 28. |
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| 29. |
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| 30. |
- Bhattacharyya, T, et al.
(författare)
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Synthesis of chiral, amphiphilic, and water-soluble chiral macrocycles via urea formation.
- 2003
-
Ingår i: Tetrahedron. - : Elsevier BV. - 0040-4020. ; 59:40, s. 7921-7928
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Tidskriftsartikel (refereegranskat)abstract
- A simple, efficient, and flexible procedure for the synthesis of chiral, amphiphilic, and water-soluble macrocycles is reported. Acylation of p-xylylenediamine with N-Fmoc-protected glycine, -aspartic acid, -glutamic acid, and -arginine, followed by removal of Fmoc-groups, gave amino acid:p-xylylene conjugate diamines, which were converted to ten macrocycles via stepwise urea formation using p-nitrophenyl chloroformate. -Aspartic acid-containing macrocyles proved to be soluble in aqueous buffers and a macrocycle containing four aspartate residues was found to recognize arginine and arginine esters with moderate affinity.
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| 31. |
- Bourguignon, J., et al.
(författare)
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Chiral ditopic receptors. Application to palladium-catalyzed allylic alkylation
- 2003
-
Ingår i: Tetrahedron. - : Elsevier BV. - 0040-4020 .- 1464-5416. ; 59:48, s. 9583-9589
-
Tidskriftsartikel (refereegranskat)abstract
- Chiral pyridinooxazoline, quinolinooxazoline, bis(oxazolino)pyridine (pybox), and bisoxazoline (box) derivatives containing crown ether residues were prepared. Some of the ligands were assessed in substrate binding studies and in palladium catalyzed allylic alkylations.
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| 32. |
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| 33. |
- Hellberg, Jonas, et al.
(författare)
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Synthesis of annulated dioxins as electron-rich donors for cation radical salts
- 2004
-
Ingår i: Tetrahedron. - : Elsevier BV. - 0040-4020 .- 1464-5416. ; 60:40, s. 8899-8912
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Tidskriftsartikel (refereegranskat)abstract
- The synthesis of a series of new alkoxylated linearly annulated dioxins is described together with their cyclic voltammetric behavior and some preliminary result on their ability to form cation radical salts. Of these dioxins, seven (8, 12, 19, 21, 27, 33, 34) are the first representatives of entirely new heterocyclic systems. Dioxins 8, 21, 22 and 27 gave good quality cation radical salts upon electrocrystallization.
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| 34. |
- Johansson, Tommy, et al.
(författare)
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Nucleoside H-phosphonates. : Part 19. Efficient entry to novel nucleotide analogues with 2-pyridyl and 4-pyridylphosphonothioate internucleotide linkages
- 2004
-
Ingår i: Tetrahedron. - : Elsevier. - 0040-4020. ; 60:2, s. 389-395
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Tidskriftsartikel (refereegranskat)abstract
- Synthetic and 31P NMR spectroscopy studies resulted in the development of efficient protocols for the stereospecific synthesis of a novel type of nucleotide analogues, 2-pyridyl- and 4-pyridylphosphonothioates. The underlying chemistry involves formation of the P–C bond via a base-promoted reaction of suitably protected dithymidine H-phosphonothioates with N-methoxypyridinium tosylate in acetonitrile, or with trityl chloride in pyridine, to produce high yields of nucleotide analogues with a 2-pyridyl- or 4-pyridyl moiety directly bound to the phosphorus centre.
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| 35. |
- Johnson, Ann-Louise, et al.
(författare)
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Synthesis of barettin
- 2004
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Ingår i: Tetrahedron. - : Elsevier BV. - 0040-4020 .- 1464-5416. ; 60:4, s. 961-965
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Tidskriftsartikel (refereegranskat)abstract
- The indole alkaloid barettin (with bromine in 6-position), isolated from the marine sponge Geodia Barretti, has been synthesised via a Horner-Wadsworth-Emmons type reaction from 6-bromoindole-3-carboxaldehyde to introduce the dehydro-functionality. Subsequent deprotection and cyclisation afforded the natural product in Z-conformation.
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| 36. |
- Jönsson, Christina, et al.
(författare)
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Asymmetric Catalysis in a Micro Reactor : Ce, Yb and Lu Catalysed Enantioselective Addition of Trimethylsilyl Cyanide to Benzaldehyde
- 2004
-
Ingår i: Tetrahedron. - : Elsevier BV. - 0040-4020 .- 1464-5416. ; 60:46, s. 10515-10520
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Tidskriftsartikel (refereegranskat)abstract
- A T-shaped micro reactor was used for the optimisation of reaction conditions for the enantioselective silyleyanation of benzaldehyde catalysed by lanthanide-pybox complexes. Compared to a conventional batch procedure, higher conversion was observed within shorter reaction time. The micro reactor process involving Lu(III) afforded essentially the same enantioselectivity as the batch process (73 vs 76% ee), whereas the enantioselectivity was lower in the micro reactor for catalysts containing Yb(III) (53 compared to 72%). Ce(III) provided very low selectivity in both types of processes (1 and 11 % ee, respectively). A study of the effect of additives showed that the enantioselectivity in the Yb catalysed reaction performed in the micro reactor could be increased to 66%, whereas only a minor improvement, to 78% ee, was observed in the reaction with Lu.
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| 37. |
- Larsson, Michael, et al.
(författare)
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Diastereoselective addition of organozinc reagents to 2-alkyl-3-(arylsulfanyl)propanals
- 2004
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Ingår i: Tetrahedron. - : Elsevier BV. - 0040-4020 .- 1464-5416. ; 60:47, s. 10659-10669
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Tidskriftsartikel (refereegranskat)abstract
- The preparation of compounds incorporating the 3-hydroxy-2-methyl-1-alkyl moiety of high diastereomeric purity is described. Such compounds can serve as potential building blocks for the preparation of several kinds of natural products. Diastereoselective synthesis of two potential pine sawfly pheromone components, one the pure racemic threo-isomer of 3-methylpentadecan-2-ol and the other the racemic erythro-isomer of 3-methyltridecan-2-ol are described. The diastereoselective addition of R2Zn (R = Me, Et and n-Bu) to several 2-alkyl-3-(arylsulfanyl)propanals in the presence of a Lewis acid and CH2Cl2 as solvent was studied. An excellent diastereomeric ratio (95/5 anti-Cram/Cram) was obtained with 2-[(phenylsulfanyl)methyl]pentanal, 2-[(phenylsulfanyl)methyl]decanal and 2-[(phenylsulfanyl)methyl]dodecanal and Me2Zn in the presence of TiCl4.
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| 38. |
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| 39. |
- Pinho, P, et al.
(författare)
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Asymmetric addition of diethylzinc to N-(diphenylphosphinoyl) imines
- 2001
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Ingår i: TETRAHEDRON. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0040-4020. ; 57:8, s. 1615-1618
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Tidskriftsartikel (refereegranskat)abstract
- The addition of dialkylzinc reagents to N-(diphenylphosphinoyl) imines is a convenient method for the preparation of optically enriched amines. Herein we present our most recent results on this reaction, including solvent effects on the enantioselectivity
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| 40. |
- Quiroz-García, Beatriz, et al.
(författare)
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Transformations of the natural dimeric phthalide diligustilide
- 2004
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Ingår i: Tetrahedron. - : Elsevier BV. - 0040-4020. ; 60:16, s. 3681-3688
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Tidskriftsartikel (refereegranskat)abstract
- A series of intramolecular condensation products were obtained by base-catalyzed treatment of the natural bioactive dimeric phthalide diligustilide (1) using different reaction conditions and the yields remarkably depend on these. The reaction conditions to obtain selectively the intramolecular condensation derivatives or the hydrolysis products of diligustilide (1) are described.
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| 41. |
- Saitton, Stina, 1972, et al.
(författare)
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A synthetic approach to 2,3,4-substituted pyridines useful as scaffolds for tripeptidomimetics
- 2004
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Ingår i: Tetrahedron. - : Elsevier BV. - 0040-4020. ; 60:29, s. 6113-6120
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Tidskriftsartikel (refereegranskat)abstract
- The synthesis of 2,3,4-substituted pyridine derivatives useful as scaffolds in the development of peptidomimetics is described. The use of a variety of electrophiles in a halogen-dance reaction to produce 3-alkyl-2-fluoro-4-iodo-pyridine derivatives as 'functionalized scaffolds' and the possibility to differentiate between the reactivities of the two halogen handles have been explored. Coupling of amino acid derivatives in the 4-position of the pyridine was found to proceed efficiently by conversion of iodo-pyridine to a Grignard derivative, which was allowed to react with a protected amino aldehyde. Substitution of fluorine in the 2-position of the pyridine was found to be facile with alkoxide nucleophiles, whereas amines were much less reactive. (C) 2004 Elsevier Ltd. All rights reserved.
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| 42. |
- Syeda, Baquer M., et al.
(författare)
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9-BBN as a convenient protecting group in functionalisation of hydroxylysine
- 2004
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Ingår i: Tetrahedron. - : Elsevier BV. - 0040-4020. ; 60:26, s. 5571-5
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Tidskriftsartikel (refereegranskat)abstract
- 9-BBN was used for regioselective protection of the α-amino and α-carboxyl groups of (5R)-5-hydroxy--lysine. The resulting 9-BBN complex was then employed in transformations such as N-Cbz protection, azido transfer, O-glycosylation, and O-silylation. Further manipulations led to improved methods for preparation of hydroxylysine and galactosylated hydroxylysine building blocks, suitable for direct use in peptide synthesis under standard Fmoc conditions.
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| 43. |
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| 44. |
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| 45. |
- Wahlström, Niklas, et al.
(författare)
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Synthesis of the marine alkaloid caulersin
- 2004
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Ingår i: Tetrahedron. - : Elsevier BV. - 0040-4020 .- 1464-5416. ; 60:9, s. 2147-2153
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Tidskriftsartikel (refereegranskat)abstract
- A three-step synthesis of caulersin (3) from indole-2-acetic acid methyl ester and indole-2-carbonyl chloride is described. As the spectral data of the synthetic sample differed from those reported for the natural product, the structure was determined by X-ray crystallography.
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| 46. |
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