X-Ray Structure Analysis of 15-Apoviolaxanth-15-al

The X-ray structure of 15-apoviolaxanth-15-al ( = (1′S,2′R,4′S,2E,4E,6E,8E)-9-(1′,2′-epoxy-4′-hydroxy-2′,6′,6′-trimethylcyclohexyl)-3,7-dimethylnona-2,4,6,8-tetraenal) is reported. The four symmetry-independent molecules in the asymmetric unit are linked into X-shaped spirals by intermolecular H-bonds. Additional H-bonds interconnect the spirals, forming wave-like chains. The geometry of the polyene side chain possesses the same in-plane bending observed for related retinal and carotenoid compounds. The polyene side chain deviates from planarity by twists of up to 10° about each bond; some of the largest twists are about C?C bonds. The epoxycyclohexane ring possesses a distorted ‘C(3)-sofa’ conformation. The torsion angles about the bond connecting the polyene chain to the cyclohexane ring are compared with equivalent torsion angles in molecules containing epoxide rings substituted with a π-system in order to examine possible interactions between the epoxide group and the π-system, either through pseudoconjugation, or through an interaction of the nonbonding orbitals of the epoxy O-atom with the π-orbitals of the polyene chain. The latter is considered to be more likely.     

Identification of subsurface oxygen species created during oxidation of Ru(0001)

The oxidation states formed during low-temperature oxidation (T < 500 K) of a Ru(0001) surface are identified with photoelectron spectromicroscopy and thermal desorption (TD) spectroscopy. Adsorption and consecutive incorporation of oxygen are studied following the distinct chemical shifts of the Ru 3d(5/2) core levels of the two topmost Ru layers. The evolution of the Ru 3d(5/2) spectra with oxygen exposure at 475 K and the corresponding O2 desorption spectra reveal that about 2 ML of oxygen incorporate into the subsurface region, residing between the first and second Ru layer. Our results suggest that the subsurface oxygen binds to the first and second layer Ru atoms, yielding a metastable surface "oxide", which represents the oxidation state of an atomically well ordered Ru(0001) surface under low-temperature oxidation conditions. Accumulation of more than 3 ML of oxygen is possible via defect-promoted penetration below the second layer when the initial Ru(0001) surface is disordered. Despite its higher capacity for oxygen accumulation, also the disordered Ru surface does not show features characteristic for the crystalline RuO2 islands. Development of lateral heterogeneity in the oxygen concentration is evidenced by the Ru 3d(5/2) images and microspot spectra after the onset of oxygen incorporation, which becomes very pronounced when the oxidation is carried out at T > 550 K. This is attributed to facilitated O incorporation and oxide nucleation in microregions with a high density of defects.     

Diterpenoide Drüsenfarbstoffe: Coleon L,ein neues Diosphenol aus Coleus somaliensis S. MOORE; Revision der Strukturen von Coleon H,I, I′ und K

Leaf-gland Pigments: Coleon L, a New Diosphenolic Compound from Coleus somaliensis, S. MOORE ; Revision of the Structures of Coleon H, I, I′ and K From leaf-glands of C. somaliensis a new, highly oxidized diosphenolic hydroquinone belonging to the abietane series was isolated in minute quantities. The new compound, coleon L ( 4c ; C₂₄H₃₀O₁₀), is very labile and transformed into its tautomer coleon K (5d) on standing in solution. ¹H-NMR. spectra of coleon L showed clearly that the points of attachment of the two acetoxy groups are at C(3) and C(16) contrary to the positions expected from our previously published structure 3 for coleon K. Application of a recently elaborated conversion of trans-A/B-6,7-diketones of type 5 into the cis-isomers 6 allowed to assign unambiguously the β-configuration to the hydroxyl group at C(3) using pyridin induced solvent shifts. This confirmed structure 4c and 5d for coleon L and K, respectively. Based on similar reasons, the configuration at C(3) of coleon H, I and I′ had to be revised, the structures of these coleons being 4b , 5b and 5c , respectively.     

Synthese von (6R,all-E)-Neoxanthin und verwandten Allen-Carotinoiden

Synthesis of (6R, all-E)-Neoxanthin and Related Allenic Carotenoids We 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).     

Isozeaxanthine: Chiralität und enantioselektive Synthese von (4R,4′R)-Isozeaxanthin ((−)-(4R, 4′R)-β, β-Carotin-4,4′-diol)

Isozeaxanthin: Chirality and Enantioselective Synthesis of (4R,4′R)-Isozeaxanthin ((?)-(4R,4′R)-β, β-Carotin-4,4′-diol) The absolute configuration of optically active isozeaxanthin was established by synthesis using (?)-(R)-4-hydroxy-β-ionon ( 2 ) [18] as starting material.     

Notiz über Ellagitannine und Flavonol-glycoside aus Rosenblüten

Note on Ellagitannins and Flavonol Glycosides from Rose Petals Petals from two garden roses proved to be very rich in ellagitannins and flavonol glycosides. Rutin ( 1 ), spiraeoside ( 2 ), quercitrin ( 3 ), isoquercitrin ( 4 ), nicotiflorin ( 5 ), eugeniin ( 6 ), rugosin A (7), rugosin D ( 10 ), casuarictin ( 8 ), and tellimagrandin I (9) were isolated. Spiraeoside, at physiological pH, exerts a pronounced stabilisation of the anthocyanin colour with enhancement of extinction and bathochromic shift of the absorption maximum in the visible range. The abundance of gallic-acid derivatives 6–10 is in contrast to the apparent inability of rose flowers to produce anthocyanins with a trihydroxylated ring B , a prerequisite in breeding true blue-coloured roses.     

Synthese der vier stereoisomeren Dihydropalustraminsäuren. 13. Mitteilung über Schachtelhalmalkaloide

Syntheses of the four stereoisomeric dihydropalustramic acids ([6-(1-hydroxypropyl)-2-piperidyl]acetic acids) (?)-Dihydropalustramic acid, a key product in the structure elucidation of the alkaloid palustrin, has been assigned the threo-cis structure 20 by comparison with the four stereoisomeric (±)-dihydropalustramic acids (threo-cis, threo-trans, erythro-cis, erythro-trans). The latter were synthesized by a new route to α, α′-di-substituted piperidines of this type. Ring closure to the piperidine ring with simultaneous stereospecific formation of the hydroxylated side chain has been achieved by reaction of the stereoisomeric methylesters of 7,8-epoxy-2-decenoic acids with benzylamine. Assignment of the configuration at the piperidine ring is based on careful comparison of the H-NMR. spectra of the N-benzylpiperidines and with the help of lanthanide shift reagents.     

High-pressure [2 + 4]-cycloaddition of dimethylmaleic anhydride to 3,4-dimethoxyfuran; synthesis of dimethoxycantharidin preliminary communication

As an active diene (more active than furan itself), 3,4-dimethoxyfuran ( 1 ) affords with many dienophiles the respective cycloadducts in a high yield [2]. It has recently been found that under thermal conditions 1 easily reacts with maleic anhydride and its monomethyl derivative, but not with dimethylmaleic anhydride ( 2 ) [3]. This is probably due to steric hindrance resulting from the location of two methyl groups on the double bond of the dienophile. Since all Diels-Alder reactions in particular those with steric hindrance are pressure-sensitive [4]. we resolved to perform the title reaction under conditions of static high pressure.     

Absolute Konfiguration von Antheraxanthin, «cis-Antheraxantliirt» und der diastereomeren Mutatoxanthine

Absolute Configuration of Antheraxanthin, ‘cis-Aritheraxanthin’ and of the Stereoisomeric Mutatdxanthins The assignement of structure 2 to antheraxanthin (all-E)-(3 S, 5 R, 6 S, 3′ R)-5,6-epoxy-5,6-dihydro-β,β-carotene-3,3′-diol and of 1 to ‘cis-antheraxanthin’ (9Z)-(3 S, 5 R, 6 S, 3′ R)-5,6-epoxy-5,6-dihydro-β,β-carotene-3,3′-diol is based on chemical correlation with (3 R, 3′ R)-zeaxanthin and extensive ¹H-NMR. measurements at 400 MHz. ‘Semisynthetic antheraxanthin’ ( = ‘antheraxanthin B’) has structure 6 . For the first time the so-called ‘mutatoxanthin’, a known rearrangement product of either 1 or 2 , has been separated into pure and crystalline C(8)-epimers (epimer A of m.p. 213° and epimer B of m.p. 159°). Their structures were assigned by spectroscopical and chiroptical correlations with flavoxanthin and chrysanthemaxanthin. Epimer A is (3 S, 5 R, 8 S, 3′ R)-5,8-epoxy-5,8-dihydro-β,β-carotene-3,3′-diol ( 4 ; = (8 S)mutatoxanthin) and epimer B is (3 S, 5 R, 8 R, 3′ R)-5,8-epoxy-5,8-dihydro-β,β-carotene-3,3′-diol ( 3 ; = (8 R)-mutatoxanthin). The carotenoids 1 – 4 have a widespread occurrence in plants. We also describe their separation by HPLC. techniques. CD. spectra measured at room temperature and at ? 180° are presented for 1 – 4 and 6 . Antheraxanthin ( 2 ) and (9Z)-antheraxanthin ( 1 ) exhibit a typical conservative CD. The CD. Spectra also allow an easy differentiation of 6 from its epimer 2 . The isomeric (9Z)-antheraxanthin ( 1 ) shows the expected inversion of the CD. curve in the UV. range. The CD. spectra of the epimeric mutatoxanthins 3 and 4 (β end group) are dissimilar to those of flavoxanthin/chrysanthemaxanthin (ε end group). They allow an easy differentiation of the C (8)-epimers.     

Trennung und absolute Konfiguration der C(8)-epimeren (all-E)-Neochrome (Trollichrome) und -Dinochrome

Separation and Absolute Configuration of the C(8)-Epimeric (app-E)-Neochromes (Trollichromes) and -Dinochromes The C(8′)-epimers of (all-E)-neochrome were separated by HPLC and carefully characterized. The faster eluted isomer, m.p. 197.8–198.3°, is shown to have structure 3 ((3S,5R,6R,3′S,5′R,8′R)-5′,8′-epoxy-6,7-dodehydro-5,6,5′,8′-tetrahydro-β,β-carotene-3,5,3′-triol). To the other isomer, m.p. 195-195.5°, we assign structure 6 , ((3S,5R,6R,3′S,5′R,8′R)-5′,8′-epoxy-6,7-didehydro-5,6,5′,8′-tetrahydro-β,β-carotene-3,5,3′-triol). The already known epimeric dinochromes (= 3-O-acetylneochromes) can now be formulated as 4 and 5 , (‘epimer 1’ and its trimethylsilyl ether) and 7 and 8 , (‘epimer 2’ and its trimethylsilyl ether), respectively.