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  • 1
    Electronic Resource
    Electronic Resource
    Cycloviolaxanthin (= (3S,5R,6R,3′S,5′R,6′R)-3,6:3′,6′-Diepoxy-5,6,5′,6′-tetrahydro-β,β-carotin-5,5′-diol), ein neues Carotinoid aus Paprika (Capsicum annuum) (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 819-824 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cycloviolaxanthin (= (3S,5R,6R,3′S,5′R,6′R)-3.6:3′,6′-Diepoxy-5,6,5′,6′-tetrahydro-β,β-carotene-5,5′-diol), a Novel Carotenoid from Red Paprika (Capsicum annuum)From red paprika (Capsicum annuum var. longum nigrum) cycloviolaxanthin was isolated as a minor carotenoid and, based on spectral data, assigned the symmetrical structure 8.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19910740416
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  • 2
    Electronic Resource
    Electronic Resource
    Synthese von (6R, all-E)-Neoxanthin und verwandten Allen-Carotinoiden (1992)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 75 (1992), S. 773-790 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of (6R, all-E)-Neoxanthin and Related Allenic CarotenoidsWe present the first synthesis of enantiomerically pure neoxanthin (1) by a Wittig-Horner condensation between the ylide from the novel diethyl 12′-apo-15, 15′-didehydroviolaxanthin-12′-phosphonate (35) and the allenic C15-aldehyde 31 (Scheme 4) via the crystalline 15, 15′-didehydroneoxanthin (36; 70% yield). After partial hydrogenation of the triple bond of 36 and isomerisation of the (15Z)-intermediate 37, neoxanthin (1) was obtained in good yield. Similar syntheses gave (15Z, 9′Z)-neoxanthin (45; Scheme 5) and (9Z)-15, 15′-didehydroneoxanthin (47; Scheme 6). Comparison of the physical data of synthetic 1 with those of a freshly isolated sample of neoxanthin from the flowers of Trollius europaeus confirmed their identity. The unusually low melting point of 1 is caused by a very easy thermal isomerisation into a mixture of the neochromes 4 and 5 (Scheme 1). Such a thermal rearrangement is not observed with 15, 15′-didehydroneoxanthin (36). To explain this, we assume a zwitterionic excited state of the allenic group that induces the rearrangement of the violaxanthin end group into the furanoid epoxide (Scheme 7).
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19920750314
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  • 3
    Electronic Resource
    Electronic Resource
    Optisch aktive 4,5-Epoxy-4,5-dihydro-α-ionone und Synthese der stereoisomeren 4,5:4′,5′-Diepoxy-4,5,4′,5′-tetrahydro-∊,∊-carotine und der sterische Verlauf ihrer Hydrolyse (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 816-834 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Optically Active 4,5-Epoxy-4,5-dihydro-α-ionones; Synthesis of the Stereoisomeric 4,5:4′,5′-Diepoxy-4,5,4′,5′-tetrahydro-∊,∊-carotenes and the Steric Course of their HydrolysisWe prove that epoxidation with peracid of α-ionone, contrary to a recently published statement, predominantly leads to the cis-epoxide. Acid hydrolysis affords a single 4,5-glycol whose structure, established by an X-ray analysis, shows that oxirane opening occurred with inversion at the least substituted position (C(4)). Stable cis-and trans-epoxides are prepared by epoxidation of the C15-phosphonates derived from α-ionone. Both the racemic and optically active form are used for the synthesis of the 4,5:4′,5′-diepoxy-4,5,4′,5′-tetrahydro-∊,∊-carotenes having the following configuration in the end groups: meso-cis/cis, meso-trans/trans, rac-cis/trans, rac- and (6R, 6′ R)-cis/cis, rac- and (6R, 6′R)-trans/trans, rac- and (6R, 6′R)-cis/trans, and (6R, 6′ R)-cis/∊. Acid hydrolysis of the cis/cis-epoxycarotenoids under relatively strong conditions occurs again with inversion at C(4)/C(4′) in case of the cis/cis-epoxycarotenoids, but at C(5)/C(5′) in case of the trans/trans-epoxycarotenoids. An independent synthesis of this 4,5,4′,5′-tetrahydro-∊,∊-carotene-4,5,4′,5′-tetrol is presented. The irregular results of the oxirane hydrolysis are explained by assumption of neighbouring effects of the lateral chain. 400-Mz-1H-NMR data are given for each of the stereoisomeric sets. In the visible range of the CD spectra, the (6R, 6R′)-epoxycarotenoids compared with (6R, 6R′)-∊,∊-carotene exhibit an inversion of the Cotton effects.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19860690409
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  • 4
    Electronic Resource
    Electronic Resource
    (6R,9′Z)-Neoxanthin: Synthese, Schmelzverhalten, Spektren und Konformationsberechnungen (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 909-930 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (6R,9′Z)-Neoxanthin: Synthesis, Physical Properties, Spectra, and Calculations of Its Conformation in SolutionThe synthesis of pure and crystalline (9′Z)-neoxanthin (6) is described. MnO2 Oxidation of (9Z)-C15-alcohol 7 at room temperature produces a mixture 8/9 of (9Z)- and (9E)-aldehydes. Predominant formation of the required (9Z)-aldehyde 8 is achieved by performing the oxidation at - 10°. Condensation of 8 with the mono-Li salt of the symmetrical C10-diphosphonate 10 gave the (9Z)-C25-monophosphonate 11. The Wittig-Horner condensation of 10 with the allenic C15-aldehyde 1b, under selected conditions allows the preparation of pure and crystalline (9′Z)-15,15′-didehydroneoxanthin (12) and, after subsequent semireduction, of crystalline (15Z,9′Z)-neoxanthin (13). Thermal isomerisation of a AcOEt solution of 13 at 95° yields preferentially (9′Z)-neoxanthin (6). Our crystalline sample shows the highest ∊-values in the UV/VIS spectra ever recorded. The CD spectra display a pronounced similarity with those of corresponding violaxanthin isomers. In contrast to the (all-E)-isomer 5, (9′Z)-neoxanthin undergoes very little isomerisation when heated to its melting point. For comparison purposes, a crystalline probe of 6 is also isolated from lawn mowings. Extensive 1H-and 13C-NMR investigations at 600 MHz of a (D6)benzene solution using 2D-experiments such as COSY, TOCSY, ROESY, HMBC, and HMQC techniques permit the unambiguous assignment of all signals. Force-field calculations of a model system of 6 indicate the presence of several interconverting conformers of the violaxanthin end group, 66% of which possess a pseudoequatorial and 34% a pseudoaxial OH—C(3′). The torsion angle (ω1) around the C(6′)—C(7′) bond, known to be of prime importance for the shape of the CD spectra, varies with values of 87° for 55% and 263° for 45% of the molecules. Therefore, the molecules clearly display a preference for the ‘syn’-position of the C(7′)=C(8′) bond and the epoxy group. Unexpectedly, the double bonds of C(7′)=C(8′) and C(9′)=C(10′) are not coplanar. The deviation amounts to ± 20°, both in the ‘syn’ - and the ‘anti’-conformation.
    Additional Material: 20 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19940770405
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  • 5
    Electronic Resource
    Electronic Resource
    Detection of Noncovalent Complexes of Hydroxamic-Acid Derivatives by means of electrospray mass spectrometry (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 1701-1709 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The complexes of isolated benzoxazinone derivatives with FeIII were investigated by means of electrospray ionization mass spectrometry. The hydroxamic-acid derivatives could be differentiated from the lactam or the methyl-hydroxamate derivatives by the formation of FeIII complexes with two or three ligands. These complexes or adducts of them have been identified in the mass spectra. Moreover, the mass-spectral behavior of these complexes was not markedly influenced by the presence of a β-D-glucopyranosyloxy substituent.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790620
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  • 6
    Electronic Resource
    Electronic Resource
    Synthese von enantiomerenreinen ‘Grasshopper’-Ketonen und verwandten Verbindungen (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 700-715 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of Optically Pure Grasshopper Ketone and of Its Diastereoisomers and Related CompoundsStarting from our previously described synthon 1, the synthesis of four enantiomerically pure grasshopper ketons (diastereoisomeric 4-(2′,4′-dihydroxy-2′,6′,6′-trimethylcyclohexylidene)but-3-en-2-ons) and of their oxo derivatives was performed. Spectral and chiroptical data are presented.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730319
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  • 7
    Electronic Resource
    Electronic Resource
    Synthese von enantiomerenreinem Mimulaxanthin und seiner (9Z,9′Z)- und (15Z)-Isomeren (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 469-486 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of Enantiomerically Pure Mimulaxanthin and of Its (9Z,9′Z)- and (15Z)IsomersWe present the details of a synthesis of optically active, enantiomerically pure stereoisomers of mimulaxanthin (=(3s,5R,6R,3′S,5′R,6′R)-6,7,6′,7′-tetradehydro-5,6,5′,6′-tetrahydro-β,β-carotin-3,5,3′,5′-tetrol) either as free alcohols 1a and 24a or as their crystalline (t-Bu)Me2Si ethers 1b and 24b. Grasshopper ketone 2a, a presumed synthon, unexpectedly showed a very sluggish reaction with Wittig-Horner reagents. Upon heating with the ylide of ester phosphonates, an addition across the allenic bond occurred. On the contrary, a slow but normal 1,2-addition took place with the ylide from (cyanomethyl)phosphonate but, unexpectedly, with concomitant inversion at the chiral axis. So a mixture of(6R,6S,9E,9Z)-isomers 6-9 was produced {(Scheme 1). However, a fast and very clean 1,2-addition occurred with the ethynyl ketone 12 to yield the esters 13 and 14 (Scheme 2). DIBAH reduction of the separated stereoisomers gave the allenic alcohols 15 and 16 in high yield. Mild oxidation to the aldehydes 17 and 18 followed by their condensation with the acetylenic C10-bis-ylide 19 led to the stereoisomeric 15,15′-didehydromimulaxanthins 20 and 22, respectively (Schemes 3 and 4). Mimulaxanthins 1 and 24 were prepared by partial hydrogenation of 20 and 22 followed by a thermal (Z/E)-isomerization. As expected, the mimulaxanthins exhibit very weak CD curves, obviously caused by the allenic bond that insulates the chiral centers in the end group from the chromophor. On the contrary, some of the C15-allenic synthons showed not only fairly strong CD effects but also a split CD curve which, in our interpretation, results from an exciton coupling between the allene and the C(9)=C(10) bond. We postulate a rotation around the C(8)—C(9) bond, presumably caused by an intramolecular H-bond in 16 or by a dipol interaction between the polarized double bonds in 6, 7, 8, and 17.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19910740303
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