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  • 1
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1992 (1992), S. 1213-1216 
    ISSN: 0170-2041
    Keywords: (+)-Cyclosarkomycin ; Catalpol ; Iridoids ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chemistry and Stereochemistry of Iridoids, XVIII.  -  Enantiomerically Pure (+)-Cyclosarkomycin from CatalpolThe reaction of hexaacetylcatalpol (2) with peroxyformic acid results in hexaacetyl-3-formyloxy-4-hydroxycatalpol (3), which is cleaved to 4 and sorbit (4a) by reduction with LiAlH4. The mixture of 4/4a was acetylated and the resulting acetates 5/5a separated by column chromatography. The following reactions from 5 to 9 (reactions e - i of Scheme 1) are each nearly quantitative. Therefore, the isolation of the intermediates 6-8 was not necessary. The constitutions of 6-8 were proven by 13C-NMR spectroscopy. The (1S,2RS,5R)-2-hydroxy-3-oxabicyclo[3.3.0]octan-6-one (9) was purified by column chromatography and its oxidation by pyridinium chlorochromate (PCC) in dichloromethane leads to crystalline (+)-cyclosarkomycin (10) [yield 85%, based on 5].
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1993 (1993), S. 287-291 
    ISSN: 0170-2041
    Keywords: Ginkgolide derivatives ; 14-Epiginkgolide derivatives ; Ginkgo biloba L. ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 3,14-Didehydro-10-hydroxyginkgolideOn the nomenclature: The skeleton of the ginkgolides A, B, C, M and J with the natural configuration is called “ginkgolide” since the systematic IUPAC nomenclature is too complicated. According to our nomenclature ginkgolide “A” is 3,10-dihydroxyginkgolide, ginkgolide “B” is 1,3,10-trihydroxyginkgolide etc. The numbering of the C atoms (formula 1) and the indexing of the H atoms (formula 2) are those proposed by Nakanishi[2]. (1) was prepared by reaction of 3,10-dihydroxyginkgolide (3) (ginkgolide “A”) by reaction with phosphoryl chloride in pyridine. Catalytic hydrogenation of 1 leads to 10-hydroxy-14-epiginkgolide (2a), which was epimerized with 4-(dimethylamino)pyridine (DMAP) in acetonitrile to give 10-hydroxyginkgolide (3a). 14-Epiginkgolide (2d) and ginkgolide (3d) were obtained from 2a and 3a via the 10-O-phenylthiocarbonyl derivatives 2c and 3c by means of a free-radical reduction with tri-n-butyltin hydride/α,α′-azobis(isobutyronitrile) (AIBN). By heating the 14-epiginkgolides 2a and 2b and the ginkgolides 3a and 3b in acetonitrile with DMAP an equilibrium on the side of the ginkgolides was established. The constitution and configuration of the compounds were proven by their 1H- and 13C-NMR spectra.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1991 (1991), S. 893-902 
    ISSN: 0170-2041
    Keywords: (-)-Hypnophilin, enantiomerically pure ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chemistry and Stereochemistry of Iridoids, XVI. - EPC-Synthesis of (-)-HypnophilinThe synthesis of enantiomerically pure (-)-hypnophilin (27) from (6R,7R)-(-)-7-hydroxy-3-oxabicyclo[4.3.0]non-1-en-9-one (1) is described. 1 was obtained in 93% yield from catalpol, which is readily available from the aqueous sodium carbonate extract of Picrorhiza kurrooa (Scrophulariaceae). The specific rotation, MS, 1H- and 13C-NMR data of synthetic (-)-hypnophilin were identical with those of the natural product.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1991 (1991), S. 1109-1111 
    ISSN: 0170-2041
    Keywords: Hexaacetylaucubin ; Palladium-catalysed substitution ; Iridoidglucosides, N-containing ; Carbohydrates ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chemistry and Stereochemistry of Iridoids, XVII. - Palladium-Catalysed Substitution of HexaacetylacubinAcetoxy groups, in allylic position, can be replaced by nucleophiles in a palladium-catalysed reaction. The reaction of hexaacetylaucubin (2) with piperidine or benzylamine regioselectively gives the crystalline, N-containing iridoidglucosides 3 and 4. With the anion of diemethyl malonate, 5 was obtained along with the byproduct 7. Adding triethylammonium formate as a hydride donor, then the reaction gives 6; a reaction mechanism is discussed.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 0170-2041
    Keywords: Cyclopenta[b]furan-2-one, (3aS,6aR)-(+)-3,3a,6,6a-tetrahydro-2H- ; Radicals ; Cyclization ; Carvone ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Radical-Type Cyclization of Dienes, VI. - Substrate-Controlled Asymmetric Synthesis of (3aS,6aR)-(+)-3,3a,6,6a-Tetrahydro-2H-cyclopenta[b]furan-2-one(R)-(-)-Carvone (1) was converted via straightforward reactions into 10-hydroxycarvone (4) which was cyclized to 5 via the mercury-mediated free-radical method. Periodate cleavage of 5 yields the bicyclic dione 6. Regio- and stereoselective reduction of 6 with lithium tri(tert-butyloxy)hydridoaluminate results in 7 (80% yield). 7 was directly converted into γ-lactone 8 via Baeyer-Villiger oxidation. Saponification of 8 to 9, mesylation of 9 to 10 followed by elimination of methanesulfonic acid yield enantiomerically pure (3aS,6aR)-(+)-3,3a,6,6a-Tetrahydro-2H-cyclopenta[b]furan-2-one (11). The synthesis can be carried out with readily available, and economical, (S)-(+)-carvone to yield ent-11.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1993 (1993), S. 1023-1027 
    ISSN: 0170-2041
    Keywords: 1,10-Dihydroxyginkgolide ; 7-Deoxyginkgolide M ; 3-Deoxyginkgolide B ; 1,7,10-Trihydroxyginkgolide ; Ginkgolide M ; 14-Epiginkgolide ; Ginkgo biloba L. ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chemistry of the Ginkgolides, VI. - Preparation of 1,10-Dihydroxy- and 1,7,10-Trihydroxyginkgolide from 1,3,7,10-Tetrahydroxyginkgolide1,3,7,10-Tetrahydroxyginkgolide (“ginkgolide C”, 1) which can be isolated in large quantities from the terpene fraction of Ginkgo leaves, can be converted into 1-(tert-butyldiphenylsilyloxy)-3,7,10-trihydroxyginkgolide (2) in 95% yield. 2 was converted via straightforward reactions into 1,7,10-trihydroxyginkgolide (“ginkgolide M”, 9) and into the until now unknown 1,10-dihydroxyginkgolide (15). 15 can also be obtained from 1,3,10-trihydroxyginkgolide (“ginkgolide B”, 10). The intermediate products 14-epiginkgolides 8 and 14 were epimerized to the ginkgolides with natural configuration at C-14 by reaction with 4-(dimethylamino)pyridine in acetonitrile. The title compounds are of interest for their possible activity as antagonists of the platelet activating factor (PAF).
    Additional Material: 6 Tab.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 0170-2041
    Keywords: (+)-Mitsugashiwa-lactone ; (4aR,7aR,7S)-(+)-7-Methylhexahydrocyclopenta[c]pyran-1-one ; Iridoids ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chemistry and Stereochemistry of Iridoids, XIX. - Two Straightforward EPC Syntheses with Chemical Evidence of Absolute Configuration of (+)-Mitsugashiwa Lactone from (S)-(-)-Citronellol and AucubinEnantiomerically pure (+)-Mitsugashiwa lactone (9) was prepared in eight steps from (S)-(-)-citronellol (1), whereas only four steps were required for the conversion of hexaacetylaucubin (10) into 9. Both starting materials are readily available in large quantities. The synthesis of 9 from 1 establishes the absolute configuration at C-7 in 9. Conversely, the synthesis of 9 from 10 confirms the absolute configuration at C-4a and C-7a in 9.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1992 (1992), S. 293-295 
    ISSN: 0170-2041
    Keywords: Radical deoxygenation ; (+)-Catechin epimerization ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: On the Radical Deoxygenation of Secondary AlcoholsThe derivatives 1c-1f were prepared from tetramethyl-(+)-catechin (1b). Their radical reduction with tri-n-butyltin hydride or tris(trimethylsilyl)silane in the presence of azobis-(isobutyronitrile) as initiator led to (2R)-( - )-3′,4′,5,7-tetramethoxyflavan (1g). The best yield of 1g (about 75% from 1b) was achieved via the N-(imidazolyl)thiocarbonyl derivative 1c. Analogously the enantiomeric (2S)-(+)-3′,4′,5,7-tetramethoxyflavan (2g) was obtained from tetramethyl-(+)-epicatechin (2b) via 2c. Experimental evidence is given which shows that in aqueous solution, with a catalytic amount of potassium hydrogen carbonate, (+)-catechin (1a) epimerises at the C-2 position of the flavan skeleton to give (+)-epicatechin (2a).
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 0170-2041
    Keywords: (-)-Coriolin ; (-)-Epicoriolin ; Radicals ; Cyclization ; Triquinans ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Radical-Type Cyclization of Dines, VI. - Total Synthesis of (-)-Coriolin and (-)-Epicoriolin from (S)-(+)-Carvone(3aR,4S,6aS)-(+)-4-(4-Methoxybenzyloxy)-6a-methyl-3,3a,4,6a-tetrahydro-2H-cyclopenta[b]furan-2-one (10) and (3aR,3bR,4R,6aS,7S,7aS)-(-)-decahydro-4,7-dihydroxy-3a,5,5-trimethyl-3-methylene-2H-cyclopenta[a]pentalen-2-one (21) are the key intermediates in the synthesis of the title compounds 1 and 1a. Enantiomerically pure 10 is produced from (S)-(+)-carvone (4) in seven straightforward reactions. Compound 21 is produced from 10 by analogy with the method developed for the synthesis of (-)-hirsutene. Through the introduction of the double bond into 21 via the silylenolether 23 one arrives at precoriolin 25, which is converted into (-)-coriolin (1) and the C-3 epimer (-)-epicoriolin (1a) (63:37) with hydrogen peroxide. The structures of 1 and 1a were confirmed via X-ray crystallography.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1990 (1990), S. 751-754 
    ISSN: 0170-2041
    Keywords: Jasmine oil, fragrance of ; (+)-epi-Jasmonate, methyl, enantiomerically pure ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chemistry and Stereochemistry of Iridoids, XIII.  -  Synthesis of Enantiomerically Pure Methyl (1R,2S,2″Z)-(+)-Jasmonate Starting from CatalpolEnantiomerically pure methyl (1R,2S,2″Z)-(+)-jasmonate (2), which was recognized as a component of the fragrance of the jasmine flower oil, was synthesized starting from catalpol (3). 2 is easily epimerized to 1. Thus, it is necessary to use very mild conditions in the course of the synthesis and purification. These results raise the question whether 2 exists as a natural product in the flower of jasmine and 1 arises during the isolation.
    Type of Medium: Electronic Resource
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