bluuebunny/crossref_metadata_2025_split huggingface dataset:
Panicutin, ein neues Alkaloid aus Aconitum paniculatum LAM. 4. Mitteilung über Aconitum
Authors: Katz Alfred , Staehelin Esther 
Published: December 2004

Panicutin, a New Alkaloid from Aconitum paniculatum LAM.A new diterpene alkaloid, which we named panicutine (2), was isolated from the paniculatine‐containing chemovariety of Aconitum paniculatum LAM. Investigation by spectral methods showed that 2 has the formula C23H29N44 and belongs to the hetidine (1)‐type alkaloids. It has one acetoxy group at C(2) and one carbonyl group each at C (6) and C (11).
C45‐ and C50‐Carotinoide. 1. Mitteilung. Synthese von (R)‐ and (S)‐Lavandulol
Authors: Kramer Andreas , Pfander Hanspeter 
Published: December 2004

C45‐ and C50‐Carotenoids, 1st Communication. Synthesis of (R)‐ and (S)‐LavandulolStarting with methyl (3 R)‐3‐hydroxybutanoate ((R)‐7) and ethyl (3 S)‐3‐ hydroxybutanoate ((S)‐11), respectively, (R)‐ and (S)‐lavandulol ((R)‐1 and (S)‐1) were synthesized with high optical purity. The synthesized key intermediates (R)‐6 and (S)‐6 are suitable compounds for the synthesis of optically active acyclic C45‐ and C50‐carotenoids.
Determination of the Relative Configurations in the Side Chains of the Antibiotics Hedamycin and Pluramycin A; Synthesis and NMR. Data of Suitable Model Compounds
Authors: Ceroni Mario , Séquin Urs 
Published: December 2004

AbstractSeveral diepoxyhexanoates and epoxyhexenoates were prepared by epoxidation of methyl 2‐methyl‐2,4‐hexadienoate or by Darzens condensation. Their 1 H‐ and 13C‐NMR. spectra were measured and assigned. Comparison of these data with the spectra of the antibiotics hedamycin (1) and pluramycin A (2) allowed the determi‐nation of the relative configurations in the side chains of these antibiotics. They were found to be (14R*,16S*,17R*,18S*) for hedamycin (1) and (14R*,16S*,17Z) for pluramycin A (2).
On the Construction of the C/D‐Ring Systems of Aphidicolin and Stemodin: a Regio‐ and Stereospecific Synthesis of 17‐Noraphidicolaii‐16 one and 17‐Norstemodan‐16‐one Preliminary Communication
Authors: Bravetti Doriano , Bettolot Rinaldo Marini , Lupi Alessandro 
Published: December 2004

AbstractA very simple regio‐ and stereospecific synthesis of 17‐noraphidicolan‐16‐one and 17‐norstemodan‐16‐one by solvolytic rearrangement of suitable bicyclo[2.2.2]‐‐octenyl methanesulfonate is described.
Eine einfache Synthese für 2‐Aminomethyl‐indene. 11. Mitteilung über metallorganische Reaktionen and Folgeprodukte
Authors: Marxer Adrian 
Published: December 2004

AbstractTo obtain the title compounds 1‐aminomethyl‐substituted α‐vinyl‐benzyl alcohols of type 13 are treated with concentrated sulfuric acid in acetic or propionic acid containing small amounts of their anhydrides to give aminomethyl ‐ indenes in excellent yield. Depending on the benzyl alcohols used, the new indenes are substituted at C(2) by an aminomethyl group, and at C(3) by various substituents, examples of which are given in Table 3, according to R in the benzyl alcohols of Table 1. To obtain a ring closure, the benzyl alcohol 13 must at least contain one free ortho position.The starting benzyl alcohols are easily obtainable by Grignard reaction, e.g. from 2‐bromo‐3‐(dimethylamino)‐l‐propen, originally detected by Normant et al. [7], and various ketones.If a tricyclic ketone is used, benzyl alcohols of types 19, 20 and 21 (Table 2) are obtained in excellent yields. From these, ring closures lead to tetracyclic compounds of types 22, 23 and 24 (Table 4) but in lower yields (13‐42%).
Identification and Synthesis of New γ‐Lactones from Tuberose Absolute (Polianthes tuberosa)
Authors: Maurer Bruno , Hauser Arnold 
Published: December 2004

AbstractSix unsaturated γ‐lactones, (Z)‐5‐octen‐4‐olide (1), (Z)‐5‐decen‐4‐olide (2).(Z)‐6‐nonen‐4‐olide (3), (Z)‐6‐dodecen‐4‐olide (4), (Z, Z)‐6,9‐dodecadien‐4‐olide (5), and tuberolide (6) have been identified for the first time in tuberose absolute (from Polianthes tuberosa L.). All structures were corroborated by synthesis and all, except 3 and 4, are new.The name ‘tuberolactone’ has been suggested for (Z, Z)‐2,7‐decadien‐5‐olide [1]. We propose the name ‘tuberolide’ for the bicyclic lactone 6. (IUPAC name (1R*,5S*,Z)‐6‐(2′‐pentenyl)‐2‐oxabicyclo[3.3.0]octan‐3‐one).
An improved method for the stereoselective synthesis of (±)‐cis‐bicyclo [4.3.0]‐non‐3‐en‐7‐one (23) by an AlCl3‐catalyzed Diels‐Alder reaction is reported.
Structures cristallines et moléculaires des muscs macrocycliques. I. La cis‐civettone et les variétés polymorphes α et β de sa 2,4‐dinitrophénylhydrazone
Authors: Bernardinelli Gérald , Gerdil Raymond 
Published: December 2004

Crystal and Molecular Structure of Macrocyclic Musks. I. cis‐Civetone and polymorphous α‐ and β‐forms of his 2,4‐dinitrophenylhydrazonecis‐Civetone (C17H30O) forms tetragonal plastic crystals, space groupe 141; a = 9.95(4), c = 32.79(1) Å; Z = 8. The plastic phase exists in a wide temperature range and 731 reflexions could be collected at 153 K. The highly disordered structure model was obtained by the use of direct methods. The molecules appear as ring‐shaped diffuse electron‐density distributions located in special position.Two polymorphous crystalline forms were isolated for the 2,4‐dinitrophenyl‐hydrazone of cis‐civetone (DNPHCC). Both forms are triclinic, space group P1. Z = 2 (α‐Form: a = 6.279(5), b = 12.605(8), c = 15.253(10) Å, α = 105.49(7). β = 100.31 (6), γ = 91.23(7)°; β‐Form: a = 7.950(2). b = 8.405 (2). c = 18.233(4) Å, α = 100.28(2), β = 92.29(3), γ = 94.18(2)°). The structures were solved by direct methods and refined to R = 0.11. Each polymorph is associated with a different quinquangular conformation of the macrocycle. In the crystals the intermolecular interactions between macrocycles and aromatic substituents are minimized, the DNPH group being oriented in a face‐to‐face arrangement across a centre of symmetry.Empirical force field calculations show that the overall intluence of the DNPH moiety on the attached cycle does not significantly modify its conformation with regard to that of the ketone itself.
Synthesis and Photo‐oxygenation of Some Substituted 1‐Benzyl‐3,4‐dihydroisoquinolines. Mechanism of Enamine Photo‐oxygenation
Authors: Martin Ned H. , Jefford Charles W. 
Published: December 2004

AbstractThe synthesis of a series of substituted 1‐benzyl‐3,4‐dihydroisoquinolines by Bischler‐Napieralski cyclization is described. Competitive methylene blue sensitized photo‐oxygenation experiments allowed the determination of relative rates of photo‐oxygenation of 1‐benzyl‐3,4‐dihydroisoquinolines, Substituents were shown to affect both the equilibrium concentration of the tautomeric enamine and the overall photo‐oxygenation rate. After correcting for differences in enamine concentration, the relative rate data provided a diagnostic probe of the reaction mechanism, which involves transfer of charge in the rate‐limiting step.
Technische Verfahren zur Synthese von Carotinoiden und verwandten Verbindungen aus 6‐Oxo‐isophoron. VI. Synthese Von Rhodoxanthin und (3‐RS, 3′RS)‐Zeaxanthin; Zugänge zur C15‐Ringkomponente über 3‐Oxo‐jonon‐Derivate
Authors: Widmer Erich , Soukup Milan , Zell Reinhard , Broger Emil , Lohri Bruno , Marbet Roman , Lukáč Teodor 
Published: December 2004

Technical Procedures for the Synthesis of Carotenoids and Related Compounds from 6‐Oxo‐isophorone, VI. Synthesis of Rhodoxanthin and (3RS, 3′RS)‐Zeaxanthin; Routes to the C15‐Ring Component via 3‐Oxo‐ionone DerivativesThe C15‐ring component 4, key intermediate of a new scheme for the synthesis of rhodoxanthin (1) and (3RS, 3RS)‐zeaxanthin (3), has been synthesized starting from 6‐oxo‐isophorone (7) via 3‐oxo‐cyclocitral and 3‐oxo‐ionone derivatives.
High‐pressure [2 + 4]‐cycloaddition of dimethylmaleic anhydride to 3,4‐dimethoxyfuran; synthesis of dimethoxycantharidin preliminary communication
Authors: Jurczak Jamisz , Koz̀luk Tomasz , Filipek Stanislaw , Eugster Conrad Hans 
Published: December 2004

AbstractAs 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.
Spectrophotometric and Nuclear Magnetic Resonance Study of Temperature‐ and Pressure‐induced Changes in the Intimate Solvation of Neodymium (III) in N, N‐Dimethylformamide and Trimethylphosphate
Authors: Pisaniello Dino L. , Nichols Peter J. , Ducommun Yves , Merhach André E. 
Published: December 2004

AbstractThe temperature‐ and pressure‐dependent equilibria for the addition of an extra N, N‐dimethylforrnamide (DMF) or trimethylphosphate (TMP) ligand onto [Nd (DMF)8]3+‐ and [Nd(TMP)6]3+‐species respectively have been measured by visible spectrophotometry. Complementary NMR. studies on other lanthanide ions show a gradual shift in preference for the lower coordination number across the lanthanide series.
Photochemical Synthesis of 2‐Alkylidene‐4‐pyrrolin‐3‐ones
Authors: Ghaffari‐Tabrizi Ramin , Margaretha Paul 
Published: December 2004

AbstractIrradiation (λ =313 nm) of the 4‐pyrrolin‐3‐ones 1a–1c in acetone‐, 3‐pentanone‐and cyclopentanone solution affords the title compounds 2, formally via H‐abstrac‐tion by the excited ketone and recombination of the radical pair formed.
Diastereoselective Synthesis of Nitroaldol Derivatives
Authors: Seebach Dieter , Beck Albert K. , Mukhopadhyay Triptikumar , Thomas Elizabeth 
Published: December 2004

AbstractThree methods are described by which diastereomerically enriched nitroaldols and their O‐silylated derivatives can be prepared. threo‐Nitroaldols prevail up to 10:1 over the erythro‐isomers if doubly deprotonated nitroaldols 28 are quenched with acetic acid (THF/HMPT or DMPU, − 100°) (see Scheme 5 and Table 2). O‐Trimethyl‐ or O‐(t‐butyl)dimethylsilylated (TBDMSi) erythro‐nitroaldols can be obtained by protonation of the corresponding lithium nitronates (35, 39) in THF at low temperature (see Schemes 6 and 7). The erythro‐O‐TBDMSi‐nitroaldol derivatives are also formed in the fluoride catalyzed addition of TBDMSi‐nitronates (40–45) to aldehydes (see Schemes 8 and 9), In the latter reaction no 1,2‐asymmetric induction is observed if a‐branched silylnitronates or aldehydes are employed (see 48/49 and 50/51) – The stereochemical course of the reactions leading to erythro‐O‐TBDMSi‐nitroaldols follows topological rules of broad applicability (see Scheme 10); possible mechnisms are discussed. ‐ The configuration of diasteromerically 13C‐NMR. Spectroscopy. – Some examples of the preparation of diastereimerically enriched 1,2‐aminolcohols by reduction of the correspondence nitro compounds without loss of configurational purity are described (see Schemes 11 and 12).
The Synthesis of 4,11,18,25‐Tetrachloro [14]metacyclophane‐7,14,21,28‐tetroi, Structural Analogues of Phloroglucides
Authors: Moshfegh Ali A. , Badri Rashid , Hojjatie Massoud , Kaviani Mehrangiz , Naderi Basirat , Nazmi Aboul H. , Ramezanian Merrikh , Roozpeikar Bizhan , Haakimelahi Gholam H. 
Published: December 2004

AbstractThe synthesis of the title compounds is described. Some of the compounds prepared exhibited antimicrobial activity in vitro. Structure‐activity relationship is briefly discussed.
Synthesen von tetrathiafulvalen‐homologen Molekülsystemen mit zentraler Bicyclo [4.4.1]undeca‐1(10),3,5,8‐tetraen‐2,7‐diyliden‐ und Bicyclo [4.4.1]undeca‐1(10), 3,6,8‐tetraen‐2,5‐diyliden‐Gruppe
Authors: Neidlein Richard , Zeiner Hartmut 
Published: December 2004

Synthesen of Tetrathiafulvalene‐homologous Systems with Central Bucyclo[4.4.1]undeca‐1 (10), 3,5,8‐tetraen‐2, 7‐diyliden‐ und Bicyclo[4.4.1]undeca‐1 (10), 3,6,8‐tetraen‐2,5‐diyliden‐GruppeThe syntheses, the spectroscopic and electrochemical properties of the heterocyclic‐substituted l,6‐Methano[10]annulene (= 1,6‐methanobicydo[4.4.1]deca‐1,3,5,7,9‐pentaene)‐derivatives 2 and 7 (derivatives of tetrathiafulvalene‐homologous systems) are described.
Polarographic Properties and Electrochemical Reduction of 1,2‐Dimethyl‐3‐indolyl Heteroaryl Ketones
Authors: Naef Rudolf 
Published: December 2004

AbstractThe reduction of a series of 1,2‐dimethyl‐3‐indolyl heteroaryl ketones, where the heteroaryl components are 2‐benzoxazolyl, 2‐behzpthiuzolyl. 1‐methyl‐2‐benz‐imidazolyl, 4‐ and 2‐pyridyl, in aprotic and prone solution are described by means of DC. and AC. polarography, cyclic voltammetry and coulometry.In acetonitrile a two‐step reduction mechanism with a reversible first and an irreversible second one‐electron transfer has been observed, confirmed by AC.‐polarographic and cyclovoltammetric measurements. The reduction potentials, between −1.377 and −1.787 V for the first step, and between −1.937 and −2.250 V (vs. Ag/AgCl) for the second, could not be correlated with the LUMO energies from HMO calculations which was explained as being due to a distorted configuration of the π systems.In protic media (ethanol/water) reduction occurs in an irreversible one‐step mechanism. Measurements of the pH dependence of the half‐wave potential in the pH* range 0–12 and the evaluated transfer coefficients show that the reduction step represents the transfer of two electrons and two protons yielding secondary alcohols and no dimerization products under any condition. These findings are supported by coulometric and macroscale electrolysis of the ketones; the products isolated were characterized by IR. and 1H‐NMR. data.
π‐Orbital Interactions in Möbius‐Type Molecules as Studied by Photoelectron Spectroscopy
Authors: Haselbach Edwin , Neuhaus Louis , Johnson Richard P. , Houk Kendall N. , Paddon‐Row Michael N. 
Published: December 2004

AbstractSome benzobarrelenes were studied by photoelectron (PE.) spectroscopy. The results can be interpreted by considering dominant through‐space interaction of the π‐molecular fragments in a Möbius‐fashion, Some chemical features of the substrates are rationalized on the basis of these findings.
1,3‐Dipolare Cycloadditionen von 2‐(Benzonitrilio)‐2‐propanid mit 4,4‐Dimethyl‐2‐phenyl‐2‐thiazolin‐5‐thion und Schwefelkohlenstoff
Authors: Obrecht Daniel , Prewo Roland , Bieri Jost H. , Heimgartner Heinz 
Published: December 2004

1,3‐Dipolar Cycloadditions of 2‐(Benzonitrilio)‐2‐propanide with 4,4‐Dimethyl‐2‐phenyl‐2‐thiazolin‐5‐thione and Carbon DisulfideIrradiation of 2,2‐dimethyl‐3‐phenyl‐2H‐azirine (11) in the presence of 4,4‐dimethyl‐2‐phenyl‐2‐thiazolin‐5‐thione (7) yields a mixture of the three (1:1)‐ad‐ducts 8, 12 and 13 (Schemes 3 and 6). The formation of 8 and 12 can be explained by 1,3‐dipolar cycloaddition of 2‐(benzonitrilio)‐2‐propanide (1b) to the C, S‐double bond of 7. Photochemical isomerization of 12 leads to the third isomer 13 (Schemes 3 and 7). Photolysis of the azirine 11 in the presence of carbon disulfide gives a mixture of two (2:l)‐adducts, namely 12 and 13(Scheme 4). A reaction mechanism via the intermediate formation of the 3‐thiazolin‐5‐thione b is postulated. The structure of the heterocyclic spiro compound 13 has been established by single‐crystal X‐ray structure determination (cf. Fig. 1 and 2).
Speleands. Macropolycyclic receptor cages based on binding and shaping sub‐units. Synthesis and properties of macrocycle cyclotriveratrylene combinations. Preliminary communication
Authors: Canceill Josette , Collet André , Gabard Jacqueline , Kotzyba‐Hibert Florence , Lehn Jean‐Marie 
Published: December 2004

AbstractCombination of a receptor unit with a rigid shaping unit produces a new type of receptor molecules of the cryptand class, hollow macropolycyclic molecules termed speleands, capable of substrate inclusion. Two members of this category of compounds 1 and 2, have been synthesized by connecting in a single step, a macro‐cyclic [18]‐N3O3 binding unit with a rigid cyclotriveratrylene unit via three bridges. Compound 1 binds the rnethylammonium cation forming both external and internal complexes; for the latter a ‘speleme’ structure, schematically represented by 15, may be proposed.
Synthesis of a Tetracyclo [4.4.0.02,4.03,8]decanone via Intramolecular Reductive Coupling
Authors: Margaretha Paul , Tissot Paul 
Published: December 2004

AbstractThe reduction of cis‐4 a‐methyl‐1,2,4a,7,8,8 a‐hexahydronaphthalene‐2,7‐dione (1) was studied by cyclic voltammetry and product analysis. On a preparative scale, 6‐hydroxy‐3‐methyltetracyclo[4.4.0.02,4.03,8]decan‐10‐one (2) was obtained in 22% yield via an intramolecular hydrodimerization/aldol reaction sequence. The CV. results (Hg, DMF) suggest that the cyclopropane ring is formed after the first electron transfer by coupling of the anion radical with the second C. C‐double bond.
Asymmetric Synthesis of α‐Aminophosphonic Acids by Cycloaddition of N‐Glycosyl‐C‐dialkoxyphosphonoylnitrones
Authors: Vaseila Andrea , Voeffray Robert 
Published: December 2004

AbstractAddition of dialkyl phosphites to the nitrone 6, formed in situ from the oxime 5 and formaldehyde gave the hydroxylamines 7 (86%) and 8 (88%), which reacted with p‐benzoquinone in the presence of ethylene via the C‐dialkoxyphosphonoylnitrones 9 and 10 to yield the cycloaddition products 11–14 (80–85%) with a diastereoselectivity of about 50%. The cycloaddition products were transformed into the monoisopropylidene derivatives 15–18 and the diacetates 19–22. Comparison of the NMR spectra and the specific rotations of the compounds 19–22 with those of the corresponding α‐ammo‐acid derivatives 23–26 of known configuration indicated preferential formation of the L‐isomers. The cycloaddition products were transformed in good yield into the L‐α‐aminophosphonic acids 29, 30, 36, and 39.
The Electronic Structure of Pentaprismane (C10H10), as Revealed by its Photoelectron Spectrum
Authors: Honegger Evi , Eaton Philip E. , Shankar B. K. Ravi , Heilbronner Edgar 
Published: December 2004

AbstractThe photoelectron (PE.) spectrum of the title compound has been assigned by comparison with the PE. spectrum of cubane (2), aided by ab initio STO‐3G calculations using localized molecular orbitals. On the basis of the information available to date, the most satisfactory orbital sequence, Koopmans theorem implied, is, in descending order of energy: band system : (2e″2, 3e′2 2e″1, 3e′1); band system : 3a′1 (2e′2, 2a″2); band : 2e′1.(Sequence of orbitals in parenthesis uncertain).
Circular Dichroism of Some Isomeric Alkyl Pyridines
Authors: Pino Piero , Piccolo Oreste , Straub Barbara , Consiglio Giambattista , Tran Dich Cong 
Published: December 2004

AbstractThe UV. and CD. spectra of the optically active 2‐, 3‐ and 4‐(l‐methylpropyl)‐pyridines (1a, b, c) and of the corresponding (2‐methylbutyl)pyridines (2a, b, c) have been investigated in hexane at RT. and at −85°, in hexane/TFA and in aqueous HCl‐solution. In 1c and 2c both the n → π* and the π → π* transitions are optically active, an n → π* transition being located above 265 nm. The position and the sign of the CD. bands are greatly influenced by the position and the nature of the alkyl substituent.
The electron affinities of (E)‐ and (Z)‐cyclooctene. Preliminary communication
Authors: Allan Michael , Haselbach Edwin , von Büren Martin , Hansen Hans‐Jürgen 
Published: December 2004

AbstractElectron transmission measurements yield vertical electron affinities of −1.93 eV for (Z)‐ and of −1.79 eV for (E)‐cyclooctene (Z and E, respectively). It is concluded that the ‘out of plane’ bending effect in torsioned E does not influence its LUMO‐energy to a larger degree than its HOMO‐energy (as determined by photoelectron (PE.) spectroscopy) with respect to non‐torsioned Z.
Diterpenoide Chinomethane, vinyloge Chinone und ein Phyllocladan‐Derivat aus Plectranthus purpuratus HARV. (Labiatae)
Authors: Katti Seturam Bandacharaya , Rüedi Peter , Eugster Conrad Hans 
Published: December 2004

Diterpenoids from Leaf Glands of Plectranthus purpuratus: p‐Quinomethanes, Extended Quinones, p‐Acylcatechols and a Novel Phyllocladanon DerivativeFrom the complex mixture of terpenoids from the title plant, the following novel diterpenoids have been isolated: 11‐hydroxy‐19‐(3‐methyl‐2‐butenoyloxy)‐ and 11‐hydroxy‐19‐(3‐methylbutanoyloxy)‐5,7,9 (11), 13‐abietatetraen‐12‐one (1a/1b), 11‐hydroxy‐19‐(3‐methyl‐2‐butenoyloxy)‐ and 11‐hydroxy‐19‐(3‐methylbutanoyl‐oxy)‐7,9(11), 13‐abietatrien‐6,12‐dione (2a/2b), 6α, 11‐dihydroxy‐19‐(3‐methyl‐2‐butenoyloxy)‐ and 6α, 11 ‐dihydroxy‐19‐(3‐methylbutanoyloxy)‐7,9 (11), 13‐abieta‐trien‐12‐one (3a/3b), 11,12‐dihydroxy‐19‐(3‐methyl‐2‐butenoyloxy)‐ and 11,12‐di‐hydroxy‐19‐(3‐methylbutanoyloxy)‐8,11,13‐abietatrien‐7‐one (4a/4b), and (16R)‐17,19‐diacetoxy‐16‐hydroxy‐13β‐kauran‐3‐one (=(16R)‐17,19‐diacetoxy‐16‐hydro‐xyphyllocladan‐3‐one; 10). Compounds 2 and 3 are derivates of taxodione and taxodone, respectively, 4 is a derivative of cryptojaponol. The structure of 10 is Wised on a single‐crystal‐X‐ray analysis and CD. data.
Absolute Konfiguration von Antheraxanthin, «cis‐Antheraxantliirt» und der diastereomeren Mutatoxanthine
Authors: Märki‐Fischer Edith , Buchecker Richard , Eugster Conrad Mans , Englert Gerhard , Noack Klaus , Vecchi Max 
Published: December 2004

Absolute Configuration of Antheraxanthin, ‘cis‐Aritheraxanthin’ and of the Stereoisomeric MutatdxanthinsThe 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.
Studies on Natural Products from Cuban Plants. Alkaloids from Tabernaemontana citrifolia
Authors: Kutney James P. , Perez Ileana 
Published: December 2004

AbstractA detailed study of the alkaloids from Tabernaemontana citrifolia, a species growing in Cuba is presented. Thirteen alkaloids were isolated and characterized. One of these, (−)‐19‐oxovoacristine (7), is a new compound isolated for the first lime from a natural source.
17O‐RMN. d'éthers, de cétones et d'esters cycliques. Détermination de constante de couplage quadrupolaire
Authors: Delseth Claude , Kintzingcr Jean‐Pierre 
Published: December 2004

Abstract13C‐ and 17O‐relaxation times measured in cyclic ethers, cyclic ketones, and lactones allowed the determination of the quadrupolar interaction at the O‐site. Values obtained for six‐membered rings can be used as standard values for ethers (χ = 13 MHz), ketones (χ = 10.5 MHz), and esters (χ = 11.5 MHz for dicoordinated and 9.5 MHz for monocoordinated O‐atom). Even within a series, no correlation is found between the 17O‐chemical shift and the value of quadrupolar interaction.