bluuebunny/crossref_metadata_2025_split huggingface dataset:
Crystal Structures of the Lithium Cryptates of Two Macrobicyclic Ligands Containing Pyridine, Bipyridine, and Biisoquinoline Units
Authors: Cesario Michèle , Guilhem Jean , Pascard Claudine , Anklam Elke , Lehn Jean‐Marie , Pietraszkiewicz Marek 
Published: December 2004

AbstractThe crystal structures of the LiBr complexes of two macrobicyclic ligands, [py.py.bpy]1 and [py.biqi.biqi] 2, have been determined. They confirm the cryptate nature of these species. In 3, the Li+ cation is bound in the shallow cavity of a ligand of flattened shape, whereas in 4, it is buried inside the macrobicycle and surrounded by its three bridges.
Quantitative Formation in Water of [Ru(CO)(H2O)5]2+ from Hexaaquaruthenium(II) and Carbon Monoxide
Authors: Laurenczy Gábor , Helm Lothar , Ludi Andreas , Merbach André E. 
Published: December 2004

AbstractHigh‐pressure 17O‐ and 13C‐NMR show that [Ru(H2O)6]2+ reacts quantitatively with carbon monoxide (50 bar) in water to form [Ru(CO)(H2O)5]2+.
The Synthesis of 1,2,4‐Trioxan‐5‐ones
Authors: Jefford Charles W. , Currie Jane , Richardson Geoffrey D. , Rossier Jean‐Claude 
Published: December 2004

AbstractSeveral 3,6‐substituted 1,2,4‐trioxan‐5‐ones have been prepared in good yield by condensing aldehydes and ketones with trimethylsilyl α‐[(trimethylsilyl)peroxy]alkanoates in the presence of trimethylsilyl trifluoromethane sulfonate as catalyst.
Lagotoside: A New Phenylpropanoid Glycoside from Lagotis stolonifera
Authors: Çaliş İhsan , Taşdemir Deniz , Wright Anthony D. , Sticher Otto 
Published: December 2004

AbstractFrom the aerial parts of Lagotis stolonifera (Scrophulariaccae), a new phenylpropanoid glycoside, lagotoside (8), and the three known glycosides ehrenoside (5), verbascoside (= acteoside; 6), and plantamajoside (7) were isolated, together with the four known iridoid glucosides aucubin (1), catalpol(2), globularin (4), and lythantosalin (3). The structure of the new compound 8 was elucidated on the basis of chemical and spectral data as 2‐(3‐hy‐droxy‐4‐methoxyphenyl)ethyl O‐[α‐L‐arabinopyranosyl‐(1 → 2)]‐O‐[α‐L‐rhamnopyranosyl‐(1 → 3)]‐4‐O‐feruloyl‐β‐D‐glucopyranoside.
Madeiranes, a New Class of Pentacyclic Triterpenes: D‐Friedo‐madeir‐14‐en‐3β‐ol and ‐3‐one, D:C‐Friedomadeir‐7‐en‐3β‐ol and ‐3‐one
Authors: Ferreira Maria‐José Umbelino , Lobo Ana M. , O'Mahoney Caroline A. , Williams David J. , Wyler Hugo 
Published: December 2004

AbstractThe pentacyclic triterpenes 1a, b and 2a, b are isolated from extracts of Euphorbia mellifera Arr. Their structures, determined by X‐ray analysis, are supported in part by MS, NMR, and IR data. The skeleton differs from that of representatives of the lupane or hopane class by (i) an unusual arrangement of the substituents in the cyclopentane ring E, the Me group being on C(19) and the i‐Pr group in an angular position on C(17), and (ii) a cis D/E ring junction. We propose to name Die unknown pentacyclic parent ‘madeirane’, thus 1a, b and 2a, b are D‐friedomadeir‐14‐ene and D:C‐friedomadeir‐7‐ene derivatives. The biosynthesis of these compounds may be rationalized via ‘spirodammaranol’‐cation intermediates 5 and 5′ and madeiranol cation 6, as outlined in Scheme 2.
On the Stability of the Schiff Bases of Pyridoxal 5′‐Phosphate with Polypeptides Containing L‐Lysine
Authors: del Vado M. Angeles García , Echevarria Gerardo R. , Blanco Francisco García , Blanco José G. Santos , Vallejo José Laynez , de Paz José L. García 
Published: December 2004

AbstractWe determined the apparent equilibrium constant of formation, KpH, of the Schiff bases of pyridoxal 5′‐phosphate (PLP) and poly‐ and copolymers containing L‐lysine, as a function of pH at 25° and a constant ionic strength of 0.1 M. The KpH values obtained at acidic and neutral pH were larger that those reported for Schiff bases of PLP and hexylamine. We determined calorimetrically ΔH of formation of Schiff bases of PLP and poly(L‐lysine) (−4.5′kcal/mol), and PLP and hexylamine (−3.4 kcal/mol) at pH 7.00. Semi‐empirical theoretical calculations (INDO and AMI methods) of a model compound of Schiff base of PLP and polypeptide containing L‐lysine show the capability of specific interactions between groups of PLP and the peptide skeleton.
Stereochemical Studies on Homoterpene Biosynthesis in Higher Plants; Mechanistic, Phylogenetic, and Ecological Aspects
Authors: Gäbler Andreas , Boland Wilhelm , Preiss Ute , Simon Helmut 
Published: December 2004

AbstractIn higher plants, the two homotcrpenes 4,8‐dimethylnona‐l,3,7‐triene (1) and 4,8,12‐trimethyltrideca‐1,3,7,11‐teiracnc (2) originate from nerolidol (3) or geranyllinalool (4) by anoxidative cleavage of their C‐skele‐lons. The reaction proceeds with exclusive loss of H8–C(5) of 3 and formal production of a C4 fragment. The site specificity of the enzyme(s) is identical for all of the hitherto examined plant families (Agavaceae, Asclepiadaceae, Asteraceae, Leguminosae, Magnoliaceae, and Saxifragaceae). The enzyme tolerates a wide range of structural modifications at the polar head of 3. Instead of 3, also gcranylacclone 12 and the secondary alcohol 13 can be cleaved to the homoterpene 1 and as yet unidentified carbonyl fragments. The CC bonds within the aliphatic chain of 3 seem to be essential for the oxidative bond cleavage as well as for recognition and embedding of the substrate into the active center of the enzyme(s). The feed‐induced biosynthesis of 1 and 2 in leaves of the Lima bean Phaseolus lunatm infested with the spider mite Tetranychus urticae probably requires a preceding release of nerolidol (3) or geranyllinalool (4) from phylogenic glycosides prior to the fragmentation reaction. The microbial reduction of the trienoic acids 6 and 6ais the key stop for the synthesis of deuterium labelled nerolidol (3RS,5R)‐and (3RS,5S)‐9.
3J(H,H) Coupling Constants as a Simple Criterion for π Delocalization of Pentafulvenes and Pentafulvalenes
Authors: Neuenschwander Markus , Bönzli Peter 
Published: December 2004

AbstractA simple criterion for estimating the extent of π delocalization in the five‐membered ring of pentafulvenes and pentafulvalenes is described. It is based on the fact that changes of bond lengths (induced by exocyclic substituents R1‐R2 of 1) are reflected by systematic changes of 3J(H,H) values, so that linear correlations of σ vs, 3J(H,H)are obtained. Plots of that type (Fig. 1) are very useful for determining the extent of π delocalization of various pentafulvalenes 2–5 (Fig. 3) which show a very similar behavior to pentafulvenes. In principle, these plots could additionally be used for estimating substituent constants σ or for approximating the extent of π overlap between exocyclic substituents and the π system of pentafulvenes. Charge‐density effects of pentafulvenes and pentafulvalenes are observed by substituen‐induced shifts of the ring C‐atoms (Fig. 4).
Thiocyclosporins: Preparation, Solution and Crystal Structure, and Immunosuppressive Activity
Authors: Seebach Dieter , Ko Soo Y. , Kessler Horst , Köck Matthias , Reggelin Michael , Schmieder Peter , Walkinshaw Malcolm D. , Bölsterli J. Jakob , Bevec Dorian 
Published: December 2004

AbstractThe reaction of cyclosporin A (CsA) withLawesson's reagent under different conditions yields various thiocyclosporins, in which carbonyl O‐atoms and/or the hydroxy O‐atom of the MeBmt residue are replaced by an S‐atom. The position of the S‐atom is determined by NMR spectroscopy, and the conformations of the products are studied by NMR spectroscopy and X‐ray crystallography. Some of the thiocyclosporins show interesting conformational properties. Whereas one conformation strongly dominates for CsA in CDCL3, two conformers A and B, in a ratio 58:42 are found for [1ψ2, CS–NH]CsA. Extensive NMR studies including new 2D and 3D heteronuclear techniques and restrained MD calculations using ROE effects demonstrate that the major conformer A is identical to CsA, while the minor conformer B contains an additionalcispeptide bond between the Sar3and MeLeu4residues. [4ψ5, CSNH;7ψ8, CS–NH]CsA exhibits a conformation very similar to crystalline CsA. However, the D‐Ala8NH, MeLeu6Co γ‐turn H‐bond is not present in this dithio analogue. Also different is the MeBmt1side‐chain conformation, the dithio conformation showing a strong MeBmt1OH, Sar3COH‐bond. Immunosuppressive activities of thiocyclosporins are measured in IL‐2 and IL‐8 reporter gene assays. Their activities are discussed in relation to their conformations.
Convenient Synthesis of 2‐Azido‐2‐deoxy‐aldoses by Diazo Transfer
Authors: Vasella Andrea , Witzig Christian , Chiara Jose‐Luis , Martin‐Lomas Manuel 
Published: December 2004

AbstractDiazo transfer from trifluoromethanesulfonyl azide (TfN3) to 2‐amino‐2‐deoxy‐glycoses constitutes a high‐yielding, simple procedure for the preparation of partially protected or unprotected 2‐azido‐2‐deoxy‐aldoses. Thus, the D‐allosamine derivative 2 gave 93% of 3, while diazo transfer to D‐glucosamine, D‐mannosamine, and D‐galactosamine, followed by acetylation, yielded the azides 5, 7, and 9 in yields of 74–91, 65, and 70%, respectively.
Warum Pentose‐ und nicht Hexose‐Nucleinsäuren?? Teil I. Einleitung und Problemstellung, Konformationsanalyse für Oligonucleotid‐Ketten aus 2′,3′‐Dideoxyglucopyranosyl‐Bausteinen (‘Homo‐DNS’) sowie Betrachtungen zur Konformation von A‐ und B‐DNS
Authors: Eschenmoser Albert , Dobler Max 
Published: December 2004

Why Pentose and Not Hexose Nucleic Acids? Part I.
Introduction to the Problem, Conformational Analysis of Oligonucleotide Single Strands Containing 2′,3′‐Dideoxyglucopyranosyl Building Blocks (‘Homo‐DNA’), and Reflections on the Conformation of A‐ and B‐DNASummary in collaboration with Prof. Dr. C.E. Wintner, Haverford College, Haverford, PA 19041‐1392; academic guest, ETH, March and June/July, 1991.Chemical rationalization of the structure of a biomolecule can be sought through consideration of two criteria: first, the relationship between the structure and its biological function; and second, the structure's potential for constitutional self assembly. The latter criterion convers the judgment, by chemical reasoning, of the chance of its preformation, that is, a synthetic event which must have been undergone by any molecular structure in order to have been selected (or to have selected itself) to become a biomolecule. One way to further the task of rationalizing a biomolecule's structure by experimental means is the design, synthesis, and study of structural alternatives which might have become biomolecules on the basis of either criterion, but which do not, in fact, appear in Nature today.In the formation of sugar phosphates from glycolaldehyde phosphate under basic conditions, straightforward and selective formation of rac‐hexose 2,4,6‐triphosphates is observed in the absence of formaldehyde, while rac‐pentose 2,4‐diphosphates are dominant, when (0.5 equiv.) formaldehyde is present [1]. This and other observations indicate that hexose sugars should be regarded to have had a chance of preformation comparable with that of pentose sugars. Why, then, did Nature choose pentoses and not hexoses as the sugar building blocks of nucleic acids? The reason must be functional; it must be the case that pentose nucleic acids are biologically superior to potential hexose alternatives. To the extent that biological function is a consequence of molecular structure and reactivity, the origin of this superiority should be decipherable through chemical experiment, that is, through synthesis of hexose nucleic acids, systematic study of their chemical properties, and comparison of these properties with those of their natural counterparts. This has been the object of the present investigation, initiated in 1986. The paper introduces a series of papers which will describe the results of a model study, namely, the synthesis, pairing properties and structure of homo‐DNA oligonucleotides.
The Synthesis of a Novel Epoxycyclohexane from the Fungus Eutypa lata (Pers: F.) TUL
Authors: Defrancq Eric , Gordon John , Brodard André , Tabacchi Raffaele 
Published: December 2004

AbstractThe synthesis of the novel (1′R*,2′S*,3′R*, 4′S*,5′R*)‐1‐(3′,4′‐epxoy‐2′, 5′‐dihydroxycyclohexyl)‐3‐methyl‐but‐2‐enone (2), recently isolated from the culture medium of the fungus Eutypa lata, is described.
On the unusual propensity by the red seaweed Laurencia microcladia of II Rogiolo to form C15 oxepanes: Isolation of rogioloxepane A, B, C, and their likely biogenetic acyclic precursor, prerogioloxepane
Authors: Guella Graziano , Mancini Ines , Chiasera Giuseppe , Pietra Francesco 
Published: December 2004

AbstractIt is shown here that the red seaweed Laurencia microcladia KÜTZNING, collected in the Mediterranean off the torrent Il rogiolo, contains the C15 acetogenin rogioloxepane A ( = (+)‐(2R,7R)‐2‐(1‐bromopropyl)‐7‐[(Z)‐1‐chlorohex‐3‐en‐5‐ynyl]‐2,3,6,7‐tetrahydrooxepin; (+)‐3) besides its epoxy derivative rogioloxepane B ((+)‐4) and the rogioloxepane C ((+)‐5) derived from (+)‐4 by epoxide opening. Co‐occurring is an acyclic C15 acetogenin, perrogioloxepane ( = (7R,4Z,9Z,12Z)‐6‐chloropentadeca‐3,9,12‐trien‐1‐yn‐7‐ol; 9), which exists preferentially in a folded conformation as required to give, by intramolecular cyclization, rogioloxepane A (3TC) in its favored twist‐chair form. Molecular‐mechanics calculations support this view and help also to assign the relative configurations at the side chains, whereas the configurations at the seven‐membered ring are established via NMR spectroscopy and chemical correlations. The absolute configuration is established by Mosher's NMR method applied to the MTPA esters of (+)‐5 or 9.
Synthesis and Enzyme‐Inhibition Studies of Phenylsemicarbazones derived from D‐glucono‐1,5‐lactone and 2‐acetamido‐2‐deoxy‐D‐glucono‐1,5‐lactone
Authors: Wolk Diane R. , Vasella Andrea , Schweikart Fritz , Peter Martin G. 
Published: December 2004

AbstractThe carbohydrate‐derived lactone phenylsemicarbazones 3 and 4 were prepared from 5 and 8 (Scheme). Treatment with 4‐phenylsemicarbazide gave 6 and 7 (77:23) and 9 and 19 (76:24), respectively. Oxidation of 6 and 9 by CrO3–pyridine to 11 and 13, followed by deprotection, yeilded 3 and 4. The structure of 3 was established by X‐ray analysis. Enzyme‐inhibition studies using revealed that 3 is a competitive inhibitor with Ki = 23 μm. The activity of 4 was examined using N‐acetylglucosaminidase from bovine kidney, Aspergillus niger, and Artemia salina. compound 4 was found to be a competitive inhibitor of all three enzymes with Ki values of 0.13, 6.0, and 0.71 μm and KM/Ki values of 6910, 45, and 465, respectively.
Radical Anions of Cyclic Azoalkanes: An ESR, ENDOR, and TRIPLE‐Resonance Study
Authors: Ess Caspar H. , Gerson Fabian , Adam Waldemar 
Published: December 2004

AbstractRadical anions of ten monocyclic and bicyclic azoalkanes containing the azo group in (Z)‐conformation, have been fully characterized by their hyperfine data with the use of ESR, ENDOR, and general‐TRIPLE‐resonance spectroscopy. These azoalkanes are represented by 3,3,5,5‐tetramethyl‐1‐pyrazline (1), 2,3‐diazabicyclo[2.2.1]hept‐2‐ene (4), and 2,3‐diazabicyclo[2.2.2]oct‐2‐ene (9), as well as by their derivatives 2, 3, 5–8, and 10. For all radical anions \documentclass{article}\pagestyle{empty}\begin{document}$1^{- \atop \dot{}}-10^{- \atop \dot{}}$\end{document}, the 14N‐coupling constant, aN, is in the range of +0.83 to +0.97 mT; this finding indicates that the spin population is essentially restricted to the π system of the azo group. The 14N‐hyperfine anisotropy largely affects the width of ESR lines, particularly at low temperatures. Substantial coupling constants of 7Li‐, 23K‐, and 133Cs‐nuclei point to a close association of the radical anions with their alkakimetal counterions. With the exception of 39K, these nuclei give rise to readily observable ENDOR signals which appear along with those stemming from protons. The prominent hyperfine features of \documentclass{article}\pagestyle{empty}\begin{document}$1^{- \atop \dot{}}-10^{- \atop \dot{}}$\end{document} are discussed.
Reduction of Aldehydes and Ketones by Transition Metal Hydrides. Part 2. Reaction of trans,trans‐[WH(CO)2(NO)(PMe3)2] with pyridine, functionalized aldehydes, and ketones
Authors: Van Der Zeijden Adolphus A. H. , Berke Heinz 
Published: December 2004

AbstractThe reaction of trans,trans‐[WH(CO)2(NO)(PMe3)2] (1) with (pyridin‐2‐yl)‐substituted aldehydes and ketones, (pyridin‐2‐yl)C(O)R where R = H, Me, Ph, pyridin‐2‐yl, and with 6‐methylpyridine‐2‐carbaldehyde was studied. In all cases, facile insertion of the CO bond into the WH bond was observed, with rapid subsequent extrusionof a coordinated CO ligand affording O,N‐bidentate coordinated tungsten alkoxides. Only in case of pyridine‐2‐carbaldehyde and di(pyridin‐2‐yl) ketone, the initial n1 O‐bonded insertion product could be observed as unstable intemediates by low‐temperature NMR.
Synthesis of 3‐Adenyl‐ and 3‐Thyminylcyclobutane‐1,1‐dimethanols and Their Homo‐octameric Phosphodiesters
Authors: Henlin Jean‐Michel , Rink Hans , Spieser Erich , Baschang Gerhard 
Published: December 2004

AbstractStarting from 3‐(benzyloxy)cyclobutane‐1,1‐dimethanol, 3‐thyminyl‐ and 3‐adenylcyclobutane‐1,1‐dimethanol were synthesized by direct introduction of the heterocycles (Scheme 1). The mono‐O‐substituted methoxytrityl derivatives were separately converted to octameric phosphodiesters on an aminomethyl‐polystyrene carrier by the phosphotriester method. These oligomers of carba‐nucleosides were prepared in order to study their annealing behaviour towards ribo‐ and deoxyribo‐nucleic acids as well as their potential for homologous hybridization.
Isolation of Toxic and Potentially Toxic Sesqui‐ and Monoterpenes from the Tropical Green Seaweed Caulerpa taxifolia Which Has Invaded the Region of Cap Martin and Monaco
Authors: Guerriero Antonio , Meinesz Alexandre , D'Ambrosio Michele , Pietra Francesco 
Published: December 2004

AbstractThe green seaweed Caulerpa taxifolia (VAHL) C. AGARDH (Caulerpales), which, after its recent accidental introduction, is growing in the region of Cap Martin much more vigorously than in the tropics, is shown to contain the known sesquiterpenic toxins caulerpenyne (1) – in larger amounts than in tropical Caulerpales – and oxytoxin 1 (2). Novel, potentially toxic products isolated in small amounts from this seaweed include the sesquiterpenes taxifolial A ( = (5E)‐6,10‐dimethyl‐2‐[(E)2‐oxoethylidene]undeca‐5,9‐dien‐7‐ yne‐1,3‐diyl diacetate; 3), taxifolial B (= (1E,6E,10E)‐3‐[(Z)‐acetoxymethylidene]‐7, 11‐dimethyl‐12‐oxododeca‐1,6,10‐trien‐8‐yne‐1,4‐diyl diacetate; 4), 10,11‐epoxycaulerpenyne ( = (1E,6E)‐3‐[(Z)‐acetoxymethylidene]‐10,11‐epoxy‐7, 11‐dimethyldodeca‐1,6‐dien‐8‐yne‐1,4‐diyl diacetate; 1:1 diastereoisomer mixture; 5), and taxifolial C ( = (2Z,6E)‐3‐formyl‐7,11‐dimethyldodeca‐2,6,10‐trien‐8‐yne‐1,1, 4‐triyl triacetate; 6), besides, as the first example of a monoterpene from the Caulerpales, taxifolial D ( = (2Z)‐3,7‐dimethylocta‐2, 6‐dien‐4‐ynal; 7).
Nitrostyrene Derivatives of Adenosine 5′‐Glutarates as Selective Inhibitors of the Epidermal Growth Factor Receptor Protein Tyrosine Kinase
Authors: Peterli Stefan , Stumpf Regina , Schweizer Marc , Séquin Urs , Mett Helmut , Traxler Peter 
Published: December 2004

AbstractThe syntheses and biological activities of some nitrostyrene derivatives of adenosine 5′‐glutarates, a novel class of selective, bi‐substrate‐type inhibitors of the EGF receptor protein tyrosine kinase with IC50 values around 1 μM. Only marginal inhibition of the tyrosine kinases v‐able and c‐src and of the serine/threonine kinase PKC was observed. Compounds 8, 9, 11, and 12 – lacking the adenosine moiety – were ten times less active than the most potent derivatives, whereas 17 – lacking the nitrostyryl part – showed no inhibitory activity at all. Most of the compounds showed potent antiproliferative activity against an EGF‐dependent mouse keratinocyte cell line.
Synthesis of Dipeptides via Addition of N‐(Nitroacetyl)amino‐Acid Derivatives to Michael Acceptors: Scope, Stereoselectivity, and Absolute Configuration
Authors: Thomas Achamma , Manjunatha Sulur G. , Rajappa Srinivasachari 
Published: December 2004

AbstractMichael addition of N‐nitroacetyl derivatives 1 of proline esters using KF under phase‐transfer catalysis resulted in the formation of adducts 3–9 with chemical yields ranging from 40–90% (Scheme). Stereoselectivity of up to 51% was obtained on addition of benzyl N‐(nitroacetyl)‐L‐prolinate (1a). The absolute configuration at the newly created chiral centre was established in the case of 9 by carrying out a reductive acylation and comparing the product 10 with an authentic sample of ethyl N‐(O5‐ethyl N2‐acetyl‐L‐glutam‐1‐yl)‐L‐prolinate (L, L‐10).
Synthese von (6R, all‐E)‐Neoxanthin und verwandten Allen‐Carotinoiden
Authors: Baumeler Andreas , Eugster Conrad Hans 
Published: December 2004

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).
Reaktionen des 4‐Bromo‐1,6‐methano[10]annulen‐3‐carbaldehyds: Synthese von 3,4‐heteroanellierten 1,6‐Methano[10]annulenen
Authors: Neidlein Richard , Schröder Günter 
Published: December 2004

Reactions of 4‐Bromo‐1,6‐methano[10]annulene‐3‐carbaldehyde: Syntheses of 3,4‐Heteroanellated 1,6‐Methano[10]annulenesSimilarly to β‐chlorovinyl ketones, the title compound 1 reacts with dinucleophiles to give the 3,4‐heteroanellated 1,6‐methano[10]annulenes 2–4, 6, and 12–16, containing thiophene, pyrazole, pyrimidine, and thiazepine rings (Schemes 2 and 3). On reaction of 1 with tert‐butylhydrazin, an unusual Michael‐addition‐dehydrogenation sequence, resulting in 2,3‐anellation of a pyrazole ring (→5), is observed. Synthetic as well as some mechanistic aspects are briefly discussed.
Saponins with an Unusual Secoursene Skeleton from Sesamum alatum THONN.
Authors: Potterat Olivier , Hostettmann Kurt , Stoeckli‐Evans Helen , Saadou Mahamane 
Published: December 2004

AbstractThree new saponins, alatoside A–C (4a, 5, and 6a, resp.), with a 18,19‐secours‐12‐ene skeleton were isolated from the aerial parts of Sesamum alatum THONN. (Pedaliaceae) by preparative liquid chromatography. Their structures were elucidated by spectroscopic methods, including X‐ray diffraction analysis, and by chemical degradation (acidic and enzymatic hydrolyses). In addition, verbascoside (1) and two cyclohexylethanol derivatives, rengyol (2a) and isorengyol (3a), were isolated and identified.