bluuebunny/crossref_metadata_2025_split huggingface dataset:
14‐Hydroxytaxodion als Hauptditerpen in Plectranthus grandidentatus GÜRKE; Isolierung von sieben neuen dimeren Diterpenen aus P. grandidentatus, P. myrianthus BRIQ. und Coleus carnosus HASSK.: Strukturen der Grandidone A, 7‐Epi‐A, B, 7‐Epi‐B, C, D und 7‐Epi‐D
Authors: Uchida Masaaki , Miyase Toshio , Yoshizaki Fumihiko , Bieri Jost H. , Rüedi Peter , Eugster Conrad Hans 
Published: December 2004

Isolation of 14‐Hydroxytaxodione from Plectranthus grandidentatus GÜRKE and of Seven New Dimeric Diterpenoids from P. grandidentatus, P. myrianthus and Coleus carnosus Structures of Grandidone A, 7‐Epi‐A, B, C, D and 7‐Epi‐DFrom the leaf‐glands of the title plant the following abietane diterpenes have been isolated and their structures established by chemical, spectroscopical and X‐ray methods: 14‐hydroxytaxodione (5, 0,57%), new as a natural product, the already known coleons U (6, 0,17%) and V (7, 0,024%), and furthermore 7 novel dimeric compounds named grandidones (ca. 0,09%), Both grandidone A (1a) and 7‐epigrandidone A (1b) as well as grandidone B (2a) and 7‐epigrandidone B (2b) are C(7) acetals of 6, 7‐Dioxoroyleanone with catecholes such as coleon U (→ 1a, 1b) or coleon V (→ 2a, 2b). Based on the relative configuration at C(7) of 1a which was established by X‐ray analysis, the constitutions of 1b, 2a and 2b were assigned by HPLC. ‐ controlled interconversions. The unstable grandidone C (3) is a C(7)‐C(7′) linked bis‐6‐oxoroyleanone with C2‐symmetry. Grandidone D (4a) and 7‐epigrandidone D (4b) are spiro‐dihydrofurans formed from 3 via a hypothetical bis (14‐hydroxytaxodione) by intramolecular addition of HO‐C(14) or HO‐C(14′) to C(7′) to C(7′) or C(7). The relative configuration of 4a was established by X‐ray analysis of its diacetate 4c. The absolute configuration of all dimers was established by the partial syntheses from 14‐hydroxytaxodion (5) (entirely described in the following communication).
Reactions of 2‐Diisopropylamino‐3, 7‐dehydrotropone: Conversion to the thione and dimerization
Authors: Gray Robert W. , Dreiding André S. 
Published: December 2004

Reaktionen von 2‐Diisopropylamino‐3, 7‐dehydrotropon: Umwandlung in das Thion und DimerisierungBehandlung von 2‐Diisopropylamino‐3, 7‐dehydrotropon (1) mit Phosphorpentasulfid ergab 2‐Diisopropylamino‐3, 7‐dehydrotropothion (2). Mit Trifluoressigsäure entstand aus 1 ein stabiles Dimeres (5), das ein Dehydrotropon‐ sowie ein Tropon‐Ringsystem enthält. Die Strukturen von 2 und 5 ergeben sich aus ihren Spektraleigenschaften.
Iridoid and Aryl Glucosides from Globularia nudicaulis and Globularia nana
Authors: Chaudhuri Ratan K. , Salama Osama , Sticher Otto 
Published: December 2004

AbstractThe iridoid and aryl glycosidic constituents of Globularia nudicaulis L. and G. nana LAM. are reported. The structure determination of lytanthosalin (10‐O‐(E)‐cinnamoylaucubin), a new acylated iridoid glucoside, isolated from the latter species, is described.
Photoisomerization of Phenylazoalkenes
Authors: Schantl Joachim G. , Margaretha Paul 
Published: December 2004

Abstract(E)‐Phenylazocyclohexene (1) undergoes photoisomerization to s‐cis‐(Z)‐phenylazocyclohexene (2). Compound 2 reisomerizes to 1 at room temperature.
Nucleosides and Nucleotides. Part 18. p‐nitrobenzenesulfonyl nitroimidazole as a new condensing agent in the triester synthesis of oligonucleotides
Authors: Leach Colin A. , Waldmeier Felix , Tamm Christoph 
Published: December 2004

Abstractp‐Nitrobenzenesulfonyl nitroimidazole (p‐NBSNI) (5) has been shown to be an efficient and convenient condensing agent in the coupling of protected nucleotide fragments. Its utility has been demonstrated by a direct comparison with previously‐described condensing agents in the synthesis of various di‐ and tetradeoxy‐nucleotides.
Ru‐Catalyzed Oxidation of Acetylenes to α‐Diketones with Iodosylbenzene
Authors: Müller Paul , Godoy José 
Published: December 2004

AbstractDisubstituted acetylenes are oxidized with PhIO in presence of Ru‐catalysts to afford α‐diketones in 65–85% yield. Under the same conditions terminal acetylenes are cleaved to carboxylic acids.
Structure‐Activity Relationship of Oxygenated Morphinans. V. Narcotic agonist and antagonist activity in the 14‐hydroxymorphinan series. Preliminary communication
Authors: Schmidhammer Helmut , Jacobson Arthur E. , Atwell Louise , Brossi Arnold 
Published: December 2004

AbstractThe synthesis of several 14‐hydroxymorphinans, using oxymorphone (= 3, 14‐dihydroxy‐4,5‐epoxy‐N‐methylmorphinan‐6‐one, 1) as starting material, is described. The antinociceptive potency of the N‐methyl substituted 14‐hydroxy‐morphinans was determined. Thus, in order of antinociceptive potency, 14‐hydroxy‐4‐methoxy‐N‐methylmorphinan‐6‐one (5) >4,5‐epoxy‐14‐hydroxy‐N‐methyl‐morphinan‐6‐one (3)>4, 14‐dihydroxy‐N‐methylmorphinan‐6‐one (4)>14‐hydroxy‐4‐methoxy‐N‐methylmorphinan (11) ≈4, 14‐dihydroxy‐N‐methylmorphinan (12). The most potent compound in this series, 14‐hydroxy‐4‐methoxy‐N‐methyl‐morphinan‐6‐one (5), was found to have about six times the potency of morphine; it was equipotent with levorphanol.
Correct Structure of a Condensation Product C6H12N4O4 from Hydrazine, Formaldehyde and Hydrogen Peroxide
Authors: Whittleton Stephen N. , Seiler Paul , Dunitz Jack D. 
Published: December 2004

AbstractThe compound mentioned in the title is shown by X‐ray analysis to be 1, 2, 7, 8‐tetraaza‐4, 5, 10, 11‐tetraoxatricyclo [6.4.1.12, 7] tetradecane, contrary to previous suggestions. The torsion angle about the peroxo bonds in the seven‐membered rings in 100°, close to the value in hydrogen peroxide, which would not be possible in a six‐membered ring.
Synthesis and biological properties of p‐azidophenylalanine13‐β‐melanotropin, a potent photoaffinity label for MSH receptors
Authors: Eberle Alex N. , De Graan Pierre N. E. , Hübscher Willy 
Published: December 2004

Abstractp‐Azidophenylalanine13‐α‐melantropin ([Pap13]‐α‐MSH) was synthesized in homogeneous solution by the fragment condensation method, and its biological activity was determined in three different assay systems. The pigment‐dispersing activity relative to α‐MSH was 65%, measured with melanophores of Rana pipiens or of Xenopus laevis tadpoles. The tyrosinase‐stimulating activity was 50%, determined with cultured mouse melanoma cells. UV. irradiation of solutions containing ≤10−4M[Pap13]‐α‐MSH at 338 nm (intensity: 10−3 W · cm−2) led to complete photolysis of the photolabel within <20 min. Under these conditions [Pap13]‐α‐MSH was covalently inserted into MSH‐receptors which produced a longlasting pigment dispersion in Xenopus melanphores (see [3]). The extent of this prolonged stimulation depended on the hormone concentration used during photolysis. 1.8·10−9M [Pap13]‐α‐MSH which produced a full initial response failed to prolong the effect, whereas 1.2·10−8M hormone caused irreversible stimulation. It appears that only about 10% of the initially occupied receptors were covalently labelled because the log dose response curve was shifted to ∼ 10x higher concentration after a 200 min wash period: EC50 immediately after photolysis was 6 · 10−10M; after 200 min EC50 increased to ∼8·10−9M.
Dediazoniation of Arenediazonium Ions. Part XX. Secondary deuterium isotope effects in reactions of benzenediazonium tetrafluoroborate
Authors: Szele Ivanka , Zollinger Heinrich 
Published: December 2004

AbstractSecondary deuterium isotope effects were measured for the dediazoniation of [2,4,6‐2H3]‐benzenediazonium tetrafluoroborate ([2H3]‐1), and were found to be (kH/kD3)s = 1.46 in 2,2,2‐trifluoroethanol (TFE) and 1.51 in 1, 1, 1, 3, 3, 3‐hexafluoro‐2‐propanol (HFIP), respectively. These values are in agreement with the previously proposed rate determining formation of the phenyl cation (Eqn. 1), and are similar to the results obtained by Swain et al. in other solvents. The Nα‐Nβ rearrangement Eqn. 2) of β‐15N labelled 1 was studied in TFE. The percent of rearrangement after 70% dediazoniation was found to be 8.18, which corresponds to a rate constant for the rearrangement kr=4.02 · 10−6S−1. Thus the secondary deuterium isotope effect in the rearrangement in TFE (kH/kD3)r was calculated to be 1.42. The fact that the isotope effect in the rearrangement is, within experimental error, the same as that observed during dediazoniation, definitely excludes the formation of benzenespirodiazirine cation 3, which has repeatedly been discussed as an intermediate in the rearrangement. The size of the deuterium isotope effect in the rearrangement is in accordance with the rearrangement proceeding via a phenyl cation/N2 molecule pair (2).
Trennung und Charakterisierung von β‐Carotin‐Isomeren
Authors: Vecchi Max , Englert Gerhard , Maurer Res , Meduna Vladimir 
Published: December 2004

Separation and Characterization of the cis‐Isomers of β,β‐CaroteneA stable HPLC. system is described allowing the excellent separation of 11 different cis‐isomers of β,β‐carotene from the all‐trans compound. The system is applied to the analysis of cis/trans mixtures obtained from plant extracts and by photoisomerization of the all‐trans isomer. Al2O3 is used as the stationary phase while hexane with controlled H2O content is utilized as the mobile phase. With the aid of the optimum conditions 8 sufficiently stable cis isomers were isolated and their structures shown to be the 9‐, 13‐ and 15‐cis, the 9,9′‐, 9, 13‐, 9, 13′‐ and 13,13′‐di‐cis and, tentatively, the 9,13,13′‐tri‐cis β,β‐carotenes by application of 270‐MHz‐FT.‐1H‐NMR. spectroscopy.
The mass spectra of organic compounds. 6th Communication.. The Ring Opening Reaction of Isomeric Cyclanones C8H14O\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{+ \atop \dot{}} $\end{document} in metastable and collisional‐activation spectra
Authors: Gäumann Tino , Schwarz Helmut , Stahl Daniel , Tabet Jean‐Claude 
Published: December 2004

AbstractThe molecular ions from three isomeric cyclanones isomerize to the ethyl‐2‐cyclohexanone ion prior to C2H4 elimination. With D‐ and 18O‐labelled compounds it is shown by Mass Analyzed Ion Kinetic Energy Spectroscopy (MIKES.) that both isomerization and C2H4 loss are specific processes. By high resolution collisional activation spectra it is shown that the resultant fragment ion [C6H10O]\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{+ \atop \dot{}} $\end{document} (m/z = 98) differs in structure from the cyclohexanone molecular ion.
Asymmetric induction in Diels‐Alder reactions to acrylates derived from chiral sec‐alcohols. Preliminary communication
Authors: Oppolzer Wolfgang , Kurth Mark , Reichlin Daniel , Chapuis Christian , Mohnhaupt Martin , Moffatt Frank 
Published: December 2004

AbstractStarting from the enantiomerically pure monoterpenes (+)‐pulegone (3), (+)‐limonene (7), (−)‐β‐pinene (9), (+)‐ and (−)‐camphor (13) or (+)‐cholestenone (11) the chiral alcohols 4, 5, 6, 8, 10, 12, 14, 15, 16, 17 et 18 were prepared; their acrylates II underwent a TiCl4‐promoted Diels‐Alder addition to cyclopentadiene (Scheme 3, Table) giving in a predictable manner either the (2R)‐ or the (2S)‐adducts III with 63 to 88% asymmetric induction.
Synthesis and Absolute Configuration of New Trichloro Steroids with Cyclopropane‐Containing Side Chains
Authors: Lang Robert W. , Djerassi Carl , Strong Phyllis D. , Swenson Dale C. , Duax William L. 
Published: December 2004

AbstractThe determination of the absolute configuration of the trichloro steroids 2a and 2c (cf. Scheme 1) by means of two X‐ray crystal structure analyses is reported and applies also to the determination of the absolute configurations of several derived steroidal cyclopropanes [1]. The preparation of the chlorinated derivatives 2a‐c is described and the spectroscopic properties of 1 and 2 are summarized.
Lipophilic Synthetic Monoamides of Dicarboxylic Acids as Ionophores for Alkaline Earth Metal Cations
Authors: Maj‐Zurawska Magdalena , Erne Daniel , Ammann Daniel , Simon Wilhelm 
Published: December 2004

AbstractN, N‐Dioctadecyl‐substituted lipophilic monoamides of certain dicarboxylic acids have been prepared. It is shown that they induce a transport of alkaline earth metal cations through solvent polymeric membranes coupled to a counter transport of hydrogen ions or K+. They proved to be suitable components for ion‐selective electrodes.
Strukturaufklärung eines Dimethylfulven‐Trimeren. Hinweis auf eine [6 + 4]‐Cycloaddition von 6, 6‐Dimethylfulven
Authors: Uebersax Beat , Neuenschwander Markus , Engel Peter 
Published: December 2004

Structure Elucidation of a Dimethylfulvene‐trimer. Evidence for a [6+ 4]‐Dimerization of 6, 6‐DimethylfulveneThermal reaction of pure 6, 6‐dimethylfulvene (1c) at 60° gives an oligomeric mixture consisting mainly of fulvene‐trimers. The structure of the main product 3c is partially elucidated by 1H‐NMR. investigations at 400 MHz and definitely confirmed by X‐ray analysis. The formation of 3c is explained in terms of a [6+4] dimerization, followed by a 1, 5‐proton‐shift and a final Diels‐Alder reaction.
Total Synthesis and Electrophysiological Properties of Natural (−)‐Perhydrohistrionicotoxin, its Unnatural (+)‐Antipode and their 2‐Depentyl Analogs
Authors: Takahashi Kimio , Witkop Bernhard , Brossi Arnold , Maleque Mohammed A. , Albuquerque Edson X. 
Published: December 2004

AbstractNatural (−)‐perhydrohistrionicotoxin (6a), its unnatural (+)‐antipode 6b, (−)‐2‐depentylperhydrohistrionicotoxin (7a) and its (+)‐antipode 7b have been prepared and characterized. Kishi's lactam 8 reacted with optically active iso‐cyanates, and the mixture of diastereomeric carbamates so obtained was separated and hydrolyzed yielding the optical antipodes of Kishi's lactam in optically pure form. Reduction with LiAlH4 yielded the optically active 2‐depentyl analogs, while another sequence already developed in the racemic series afforded the natural toxin and its (+)‐antipode. Some electrophysiological properties of these compounds are presented.
Stoffwechselprodukte von Mikroorganismen. 211. Milteilung. Röntgenstrukturanalyse von Elaiophylin
Authors: Neupert‐Laves Katarina , Dobler Max 
Published: December 2004

AbstractThe X‐ray crystal structure analysis of the antibiotic elaiophylin (1), monoclinic, a = 9.927, b = 10.105, c = 31.183 Å, β = 93.20°, space group P21, confirms the constitution elucidated by spectroscopic methods and chemical degradation. In the crystal the two chemically equivalent halves of the molecule are related by an approximate twofold rotation axis.
The Reaction of 3‐Formylchromone with ortho‐Substituted Anilines. Preparation of a Tetraaza [14]annulene
Authors: Sigg Ivo , Haas Georges , Winkler Tammo 
Published: December 2004

AbstractThe reactions of 3‐formylchromone (1) with 1, 2‐phenylenediamine, 2‐amino‐diphenylamine and 2‐aminophenol were reinvestigated and shown to yield 1, 8‐dihydro‐6, 13‐di (2‐hydroxybenzoyl)‐dibenzo [b, i]‐l, 4, 8, 11‐tetraazacyclotetradeca‐ 4, 6, 11,13‐tetraene (7), 3‐[2‐(1‐phenyl)benzimidazolyl]chromone (10b) and 3‐(2‐hydroxyphenyl)iminomethylchromone (4), respectively at variance with earlier reports. Compound 4 reacts with ethanol to give 2‐ethoxy‐3‐[(2‐hydroxyphenyl)‐aminomethylidene]chroman‐4‐one (5b). Dehydrogenation of 7 produces 3‐(2‐benz‐imidazolyl)chromone (10a), also at variance with earlier reports. The structures have been elucidated with the aid of NMR. and mass spectra. The reaction mechanism is discussed.
On the Absolute Configuration of (+)‐Indane‐1‐carboxylic Acid
Authors: Hansen Hans‐Jürgen , Slewka Hans‐Richard , Hug Werner 
Published: December 2004

AbstractThe (R)‐configuration, attributed to (+)‐indane‐1‐carboxylic acid ((+)‐1) by Fredga [1], is unequivocally confirmed (Scheme 1). Configurational doubts, raised by an erroneous ORD. curve of (−)‐1‐methylindane ((−)‐4) published by Brewster & Buta [2], are unfounded (cf. the following paper of Brewster[3] and the corrections in (4)). This was further verified by preparing deuteriated 1‐methylindanes starting with (−) (R)‐3‐phenylbutyric acid ((−)‐(R)‐5) as well as with (+)‐(R)‐1 or (−)‐(S)‐1 (Scheme 2). The ORD. curves of the optically active 4 thus obtained were (disregarding deuteri‐um isotope effects) identical or antipodal, respectively (of. Fig. 1, 2, and 7a–e).Optically active methyl indane‐1‐carboxylates ((−)‐(R)‐14 or (+)‐(S)‐[l‐2H]‐14) show a strong solvent dependence of their ORD. and CD. spectra with a sign inver‐sion occuring in going from isooctane to methanol or benzene. The observed changes can be explained by a change in the population of conformations where the ester carbonyl group is eclipsed either with the C(1), C(2)‐ or C(1), H‐bond, with the n, π* ‐transition having a slightly different energy and the ester group an essentially enantiomeric environment with respect to its orientation relative to the benzene moiety.
Zum stereochemischen Verlauf der Biosynthese von 2‐Oxo‐pantolacton: Synthese von stereospezifisch indiziertem Pantolacton aus Äpfelsäure
Authors: Wasmuth Daniel , Arigoni Duilio , Seebach Dieter 
Published: December 2004

Abstract(+)‐Pantolactone1 (13) has been synthesized from (−)‐(S)‐dimethyl malate (7) in 40% yield in a short sequence involving double alkylation (7 → 10 → 11), selective hydrolysis (11 → 12) and subsequent reduction (12 → 13). Through variation of the alkylating agents and preparation of the two diastereomeric 3‐ethyl‐3‐methyl malates 14 and 15 it was possible to show that the diastereoselectivity of the second alkylation step is brought about by preferential attack from the Re‐face of the critical enolate (9, see also Scheme 1). This knowledge, in turn, has been exploited for the synthesis of a sample of pantolactone specifically enriched with 13C in its Si‐methyl group. Analysis of the 13C‐NMR. spectrum of this sample together with the results of biosynthetic experiments previously reported by Aberhart demonstrates that the biological hydroxymethylation of 2‐oxoisovaleric acid (3) to 2‐oxopantoic acid (4), an important step in the biosynthesis of pantothenic acid, takes place in a retention mode (of. Scheme 2).
Synthesis of optically pure compounds by enantiotopically differentiating monoacetalization of prochiral diketones
Authors: Duthaler Rudolf O. , Maienfisch Peter 
Published: December 2004

AbstractReaction of 9‐methyl‐cis‐decalin‐1,8‐dione (2) and of its trans‐isomer (3) with (2R,3 R)‐2,3‐butanediol (8) gives in both cases the monoacetals in high yield. While no enantiotopic differentiation is found for 3, a strong preference for the (9S,10 R)‐monoacetal 9 is found for the cis‐decalin‐dione 2. The differentiation, reaching a maximal ratio of 9:1, is found to increase by conditions, which slow down the rate of reaction, e. g. lowering the temperature, the concentration of the acid catalyst, or by using a sterically encumbered catalyst. The use of this procedure for the preparation of optically active compounds is exemplified by the transformation of monoacetal 9 (obtained in 76% yield from 2) into (9 R, 10 R)‐9‐methyl‐1‐decalone (12). The differing behaviour of diketones 2 and 3 is discussed in terms of steric and electronic effects.
Intramolecular Carbonyl Group Site Exchange in Symmetrically Substituted (n‐1, 3‐Diene)tricarbonyliron Complexes Short Communication
Authors: Bischofberger Pius , Hansen Hans‐Jürgen 
Published: December 2004

AbstractActivation parameters have been determined for the intramolecular site exchange of the carbonyl groups in tricarbonyliron complexes of 1,4‐ and 2,3‐disubstituted 1,3‐butadienes, of 1,3‐cycloalkadienes and of 1,2‐dimethylidene‐cycloalkanes by temperature‐dependent 13C‐NMR. spectroscopy (see Table 1). The variations of the activation parameters are discussed in terms of a turnstile‐type mechanism for the exchange process and of the differences in the ground state and transition state stability of the complexes. A VB‐model of the complexes is used to explain the difference in the stabilities.
Face Selectivity of the Diels‐Alder Additions of Exocyclic Dienes Grafted onto 7‐Oxabicyclo[2.2.1]heptanes
Authors: Mahaim Cyril , Vogel Pierre 
Published: December 2004

AbstractStereoselective syntheses of 2exo, 3exo‐bis (chloromethyl)‐5‐[(Z)‐chloromethylidene]‐ (9), 2exo, 3exo‐bis (chloromethyl)5‐[(E)‐chloromethylidene]‐ (10) and 2exo, 3exo‐bis(chloromethyl)‐5‐[(E)‐methoxymethylidene]‐6‐niethylidene‐7‐oxa‐bicyclo[2.2.1]heptane (13) are presented. Double elimination of HCI from 9, 10 and 13 yielded 2‐[(Z)‐chloromethylidene]‐ (14), 2‐[(E)chloromethylidene]‐ (15) and 2‐[(E)‐methoxymethylidene]‐3,5,6‐mmethylidene‐7‐oxabicycio[2.2.1]heptane (18), respectively, without loss of the olefin configuration. Ethylene tetracarbonitrile (TCE) and N‐phenyltriazolinedione (NPTAD) added to these new exocyclic dienes and tetraenes preferentially onto their exo‐face. The same face selectivity was observed for the cycloadditions of TCE to the (Z)‐ and (E)‐chlorodienes 9 and 10, thus realizing a case where the kinetic stereoselectivity of the additions is proven not to be governed by the stability of the adducts. The exo‐face selectivity of the Diels‐Alder additions of dienes grafted onto 7‐oxabicyclo [2,2.1]heptanes contrasts with the endo‐face selectivity reported for a large number of cycloadditions of dienes grafted onto bicyclo[2.2.1]heptane skeletons.
Synthese und Circulardichroismus optisch aktiver Carotinoidmodelle
Authors: Buchecker Richard , Marti Urs , Eugster Conrad Hans 
Published: December 2004

Synthesis and Circular Dichroism of Optically Active Carotenoid ModelsThe synthesis of the following optically active carotenoidic model compounds are described: (—)‐(3,S,3′S)‐3,3′‐diisopropenyl‐16,17,18,16′,17,18′‐hexanor‐β,β‐carotene (1), (3R,3′R)‐19,20,19′,20′‐Metranor‐zeaxanthin (2) and (6R,6′R)‐19,20, 19′,20′‐tetranor‐ε,ε‐carotene (3). These compounds were synthesized for the following reasons: (1) the presence of methyl groups at C(1), C(1′), C(5), C(5′) of cyclic carotenoids profoundly affects the torsional angle of the C(6), C(7)‐ and C(6′), C(7′)‐bonds. Sign and magnitude of this angle are, according to recent theories [4] [5], responsible for a helical chromophore and for strong conservative [4] Cotton effects. CD. measurements of 1 give experimental support to these state‐ 1 exhibits weaker and less temperature dependent Cotton effects. Of more significance, the shape of the curve is no longer conservative, as expected. This constitutes experimental evidence for the contention that the β‐endgroups and the polyene chain indeed form an inherently dissymmetric chromophore in optically active β, β‐carotene derivatives; (2) the slightly S‐shaped form of the polyene chain of carotenoids, shown by X‐ray analyses [12] [13], is mainly ascribed to the presence of the methyl groups in the chain. Models 2 and 3 therefore are assumed to be linear. CD. studies of these compounds should consequently give information about the influence of deviation from Linearity and planarity of the polyene on the CD. spectra of carotenoids. CD measurements of 2 and 3 show that the lack of methyl groups does not alter the general type of the curve. Only the intensity and to some extent the position of the Cotton effects are influenced. Carotenoids with the ε‐endgroup possess inherently symmetric but asymmetrically distorted chromophores.The assumption that non‐conservative CD. spectra could become conservative upon cooling [4] is experimentally confirmed by model 3.The rule stating that pairs of all‐(E) and mono‐(Z) isomers of carotenoids with only one cyclic endgroup should have CD. spectra with the same sign [5] is disproved by the CD. spectra of four stereoisomeric rubixanthins (s. Fig. 5).The UV./VIS. spectrum of 3, λmax 447 (ε 216000), 418 (ε 189000) exhibits the highest molecular extinction ever reported for a carotenoid.