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  • 1
    Electronic Resource
    Electronic Resource
    Synthesis of (4E,7S)-(-)-7-Methoxy-4-tetradecenoic Acid, a Major Constituent of the Marine Cyanophyte Lyngbya Majuscula (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 673-676 
    Details
    ISSN: 0947-3440
    Keywords: 4-Tetradecenoic acid, (E,S)-(-)-7-methoxy- ; Oxiranes, optically active ; Orthoesters as carboxyl protecting groups ; Lyngbya majuscula ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The metabolite of the marine cyanophyte Lyngbya majuscula (4E,7S)-(-)-7-methoxy-4-tetradecenoic acid (1) has been synthesized for the first time in optically active form in eight steps in 20% overall yield, Heptyloxirane (3) and the alkyne 4 containing the carboxyl group masked as a tricyclic orthoester were prepared by known methods from 5 and 6 as starting materials. Reaction of lithiated 4 with 3 afforded in 74% yield the alkyne 2 which could easily be transformed into the target molecule. Hydrogenation with Lindlar catalyst produced 7 which could be isomerized to 8 with (E) configuration. Methylation of the 7-hydroxy group in 8 gave 9 which could be transformed into the methyl ester 10 and the (4E,7S)-acid 1 in high yield.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199519950495
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  • 2
    Electronic Resource
    Electronic Resource
    Synthesis of anacardic acids (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 2209-2220 
    Details
    ISSN: 0947-3440
    Keywords: Anacardic acids ; Benzoates, methyl 6-alkyl-2-methoxy- ; 2-Alkynoates, methyl ; Aluminium triiodide, demethylation by treatment with ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The anacardic acids 1-11, isolated from various plants, were synthesized by a new general method. Reaction of the methyl alkynoates 12-18 with 1-methoxy-1,4-cyclohexadiene at 200°C afforded directly the methyl 2-methoxybenzoates 19-25 with long chain substituents in 6-position in 74-85% yield. The dienophiles 12-16 were prepared by pyrolysis of the corresponding acylphosphoranes 26-30, the dienophiles 17 and 18 by methoxycarbonylation of the corresponding alkynes 31 and 32 via the hydroxy esters 33 and 34. Demethylation of 19-23 with All3 gave the methyl salicylates 35-39 which could be hydrolized to the anacardic acids 1-4 and 7. Hydrolysis of 24 and 25 provided the hydroxy acids 40 and 41, which were converted by treatment with CBr4/PPh3 into the acids 42 and 43 bearing bromoalkyl side chains. These were transformed into 44-47 by reaction with 1-hexynyllithium and 1-octynyllithium. Stereoselective hydrogenation of 44-47 gave 48-51 with (Z)-alkene side chains. In a similar approach 42 was converted into 52 and then into 53, which gave upon treatment with 1-pentynylmagnesium bromide or 1-heptynylmagnesium bromide the acids 54 and 55 with alkadiyne side chains. Stereoselective hydrogenation provided 56 and 57 with (Z,Z)-alkadiene side chains. The 2-methoxy group in 48-51, 56, 57 was demethylated by treatment with All3 to give the anacardic acids 5, 6, 8-11.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1995199512307
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  • 3
    Electronic Resource
    Electronic Resource
    Relative and Absolute Configuration of the 3,12-Dihydroxypalmitic AcidsDedicated to Prof. Dr. Vladimir Prelog on the occasion of his 90th birthday. (1996)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1996 (1996), S. 2123-2129 
    Details
    ISSN: 0947-3440
    Keywords: Ipomea operculata M ; Operculinic acid ; Absolute configurations ; 3,12-Dihydroxyhexadecanoic acids ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The relative and absolute configuration of (+)-3,12-dihydroxypalmitic acid, a constituent of the Ipomea operculata M. resin, has been determined by synthesis. Dimethyl L-malate was converted via (S)-(+)-1 into the oxirane (S)-(-)-2. Reaction of (-)-2 with the Grignard reagent of 8-benzyloxybromooctane provided (S)-(+)-3 in 84% yield, and this was converted into the aldehyde (S)-(-)-6 via (S)-(-)-4 and (S)-(-)-5. Reaction with the lithium enolate of methyl acetate gave 7 and 8, which could be converted via 9 and 10, 11 and 12, 13 and 14 into the lactones (4S,13S)-(+)-15 and (4R,13S)-(+)-16 and finally into the methyl esters (3S,12S)-(+)-17 and (3R,12S)-(+)-18 and acids (-)-19 and (+)-20. The erythro configuration of (+)-17 was established by a stereoselective synthesis starting from (S)-(-)-2 via (S)-(+)-21, (+)-22, (+)-23, the Grignard reagent of (+)-24 and (R)-(+)-2-(2-benzyloxyethyl)oxirane to give (3S,12S)-(-)-25, (-)-26, (+)-27 and (+)-28, which could be oxidized to the diacetoxy acid (3S,12S)-(+)-29. Saponification and esterification gave (3S,12S)-(-)-19 and (3S,12S)-(+)-17, with properties identical to those of (+)-17 obtained from the resin glycoside.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199619961226
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  • 4
    Electronic Resource
    Electronic Resource
    Synthese von Naturstoffen mit Alkyl-methoxy-1,4-benzochinon-Struktur (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 131-137 
    Details
    ISSN: 0947-3440
    Keywords: Tetrahydropyranyl-ethers ; ortho-Lithiation ; ortho-Alkylation ; 1,4-Benzoquinones, alkyl-methoxy ; 1,4-Benzoquinones, alkyl-hydroxy-methoxy- ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of Natural Compounds with Alkyl-methoxy-1,4-benzoquinone StructureThe 1,4-benzoquinones 1-7 occurring in various plants and having interesting biological properties have been synthesized from the tetrahydropyranyl ethers 17 and 21. Reaction with n-butyllithium gave selectively the ortho-lithiated compounds. These could be alkylated with the haloalkenes 13-16 and haloalkanes to give the substituted phenols 18-20 and 22-25 in high yield after methanolysis. Alkylations of the methoxyisopropylether 8 of 10-undecyn-1-ol with bromobutane and bromohexane gave 9 and 10. These alkynols could be selectively hydrogenated with Lindlar-Palladium catalyst to give the (Z)-alkenols 11 and 12 which could be converted into the bromoalkenes 13, 14 and the iodoalkenes 15, 16. Oxidation of the phenols 18-20 and 22-25 with molecular oxygen in the presence of salcomine as catalyst produced the substituted 1,4-benzoquinones 1-3 and 26-29 in high yield. Selective hydrolysis with perchloric acid converted 26-29 into the natural products 4-7.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199519950118
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  • 5
    Electronic Resource
    Electronic Resource
    Enantioselective synthesis of the polyketide antibiotic (3R,4S)-(-)-citrinin (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 885-888 
    Details
    ISSN: 0947-3440
    Keywords: Citrinin, (3R,4S)-(-)- ; 2,3-Dimethyloxirane, trans-(-)- and cis- ; Synthesis of erythro- and threo-3-arylbutan-2-ols ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The fungal metabolite (-)-citrinin (1) was synthesized for the first time. Reaction of the Grignard reagent of 2,4-bis(benzyloxy)-6-bromotoluene (3) with (2S)-trans-(-)-2,3-dimethyloxirane (6) in the presence of 1,5-cyclooctadienecopper(I) chloride as catalyst leads to the formation of (2S,3S)-(-)-7 with erythro configuration. Compound (-)-7 could be transformed into (2R,3S)-(-)-9 with threo configuration via the formate (1R,2S)-(+)-8 by a Mitsunobu reaction. Reaction of the Grignard reagent of 3 with the achiral cis-2,3-dimethyl-oxirane yielded directly (±)-9. The starting material 3 was readily available from 1,3-bis(benzyloxy)-5-bromobenzene (4). Formylation of 4 furnished the aldehyde 5 which could be reduced to 3 with borane. Hydrogenolysis of the benzyl ether groups in (-)-9 gave (-)-2 with threo configuration. The remaining steps to produce citrinin [(-)-1] from (-)-2 required carboxylation to 11, formylation and in situ ring closure with ethyl orthoformate to produce the required quinomethide structure. Application of the same reactions to (±)-9 and (±)-2 afforded (±)-citrinin in 40% overall yield.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1995199505129
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  • 6
    Electronic Resource
    Electronic Resource
    Enantioselective Synthesis of (R)-(+)-Pulvilloric Acid (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 213-216 
    Details
    ISSN: 0947-3440
    Keywords: Pulvilloric acid ; 2-Heptyloxirane ; Synthesis of 1-(3,5-dihydroxyphenyl)heptan-2-ols ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The fungal metabolite (R)-(+)-pulvilloric acid [(+)-1] was synthesized for the first time. Reaction of the Grignard reagent of 5 with 2-pentyloxirane (S)-(-)-4 in the presence of 1,5-cyclooctadienecopper(I) chloride as the catalyst led to (S)-(+)-6. The enantiomer (S)-(-)-4 was prepared from dimethyl L-malate via the dioxolane (S)-(+)-3. The alcohol (S)-(+)-6 was transformed into (R)-(-)-6 via the benzoate (R)-(-)-7 by a Mitsunobu reaction. Hydrogenolysis of (-)-6 gave the resorcyl alcohol (R)-(+)-2. The remaining steps to produce (R)-(+)-1 from (+)-2 required carboxylation to (R)-(-)-8, formylation and in situ ring closure with triethyl orthoformate to furnish the required quinomethide structure. Application of the same reactions to (S)-(+)-6 afforded (S)-(-)-1 via the intermediates (S)-(-)-2 and (S)-(+)-8. With (±)-6 as starting material (±)-2, (±)-8 and (±)-1 were prepared.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970131
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