bluuebunny/crossref_metadata_2025 huggingface dataset:
Dérivés de sucres benzimidazoliques et benzothiazoliques
Authors: Tronchet Jean M. J. , Gentile Bernard
Published: December 2004

Benzimidazole and benzothiazole sugar derivatives

Simple aldehydosugars such as 1 or 2, by reaction with o‐phenylenediamine, gave the corresponding benzimidazoles 3 and 4. Whereas the unperturbed α, β‐unsaturated aldehydosugar D gave the benzodiazepine E upon treatment with o‐phenylenediamine, the formyl‐bearing alkenyl acetals 5 and 8 led, in the same conditions, to the benzimidazoles 6 and 9 respectively or, on reaction with o‐aminothiophenol, to the benzothiazoles 7 and 10 respectively. This difference in reactivity is explained by the electrondonor ability of the oxygen atom of the alkenyl acetal function as shown by the 13C‐RMN. spectra.
24‐Isopropylcholesterol and 22‐Dehydro‐24‐isopropylcholesterol, Novel Sterols from a Sponge
Authors: Hofheinz Werner , Oesterhelt Gottfried
Published: December 2004

24‐Isopropycholesterol (1) and 22‐dehydro‐24‐isopropylcholesterol 2 have been isolated as the only sterols from an Australian sponge of the genus Pseudaxinyssa. Structures have been deduced from spectroscopic data.
Propellanes. L. Further support for control by secondary orbital overlap during Diels‐Alder reactions of certain propellanes,
Authors: Kaftory M. , Peled M. , Ginsburg D.
Published: December 2004

In contrast to the behavior of 4‐substituted‐1,2, 4‐triazoline‐3, 5‐diones which add to the syn‐face of the cyclohexadiene with respect to the hetero‐ring in propellanes of type 1, dienophiles containing a C, C double bond instead of an N, N double bond add exclusively to the anti‐face of the same substrates. This supports our thesis that these reactions are controlled by secondary orbital interaction between the N, N dienophiles and the hetero‐ring of the substrates, an interaction which cannot exist in the C, C dienophiles.
Polar Substituent Effects in the Solvolysis of Primary and Tertiary Alkyl Halides. Polar Effect IX
Authors: Grob Cyril A. , Waldner Adrian
Published: December 2004

When the Hammett‐Taft equation log (k/ko)=ρq · σ is applied to the solvolysis of the 3‐substituted propyl bromides 6a‐6i in ethanol/water 4:1 (v/v) log k correlates linearly with σ except in cases where R exerts an anchimeric effect. The reaction constant ρq for 6 is − 0.12 and is typical for a nucleophilic solvent‐assisted ks process at a primary C‐atom. The tertiary halides 1 and 3, however, which react with little or no nucleophilic solvent assistance, i.e. by kc processes, lead to larger ρq values of −0.71 and −1.14, respectively. The reaction constant pq is therefore a sensitive gauge for charge development in the transition state for solvolysis of saturated compounds.
Micellar Solubilization of Biopolymers in Hydrocarbon Solvents III. Empirical Definition of an Acidity Scale in Reverse Micelles
Authors: Smith Robert E. , Luisi Pier L.
Published: December 2004

This paper deals with the problem of defining, and measuring, the pH inside the water pool (which we define as pHwp) of reverse micelles, i.e. micelles formed by surfactants dissolved in apolar solvents in the presence of minimal amounts of water. The conceptual and experimental difficulties are discussed, and it is argued that no absolute determination of pHwp is possible, mostly because water in the water pools of reverse micelles is a new solvent, for which no standardization of acidity is available. The problem can be approached only on the basis of an empirical acidity scale.

An empirical acidity scale for water pools in reverse micelles of bis (2‐ethyl‐hexyl) sodium sulfosuccinate (AOT) in isooctane has been defined by measuring the 31P‐chemical shifts of phosphate buffers. The chemical shifts in bulk water were compared to those found in reverse micelles under the assumption that the pK of phosphate ion is the same in the two systems. It was found that in most cases there was little difference (less than 0.4 pH units) between pHwp and the pH of the starting buffer in bulk water (which we define as pHst). However, this difference between pHwp and pHst may become much larger in certain cases.

The difference (pHwp–pHst) is measured under a variety of conditions, and this permits the determination of an operational acidity in the micelle water pools as a function of the pHst with which the aqueous micelles are prepared. The significance of such data for interpreting the behaviour of enzymes confined in the micelles water pool is discussed. Based on the pHwp scale, the apparent pKa of phenol‐red and 4‐nitrophenol were determined in reverse micelles containing different buffers and different water content. The pKa values obtained were rather sensitive to changes of both these factors, which was taken to signify that organic dies have only a very limited applicability to measure the acidity of the water pools of reverse micelles.
Iodine Oxidation of S‐Trityl‐ and S‐Acetamidomethyl‐cysteine‐peptides Containing Tryptophan: Conditions Leading to the Formation of Tryptophan‐2‐thioethers
Authors: Sieber Peter , Kamber Bruno , Riniker Bernhard , Rittel Werner
Published: December 2004

Cystine peptides are conveniently prepared from S‐acetamidomethyl‐ or S‐trityl‐protected cysteine derivatives by direct oxidation with iodine. Since the reaction proceeds through the formation of sulfenyl iodides, these highly reactive groups may substitute the indole ring of tryptophan residues, resulting in the formation of 2‐thioethers. During the synthesis of the peptide hormone somatostatin, we investigated this possible side reaction. By‐products of the tryptophan‐2‐thioether type can be produced under conditions which lead to a marked retardation of the disulfide bond formation. The largest amount of these compounds were formed when the oxidation was carried out in 90% aqueous trifluoroethanol.

In model peptides in which tryptophan and cysteine residues were separated by 1 to 4 glycine residues, the ring size of the resulting thioether exerted a strong influence on the yield: in peptides with 1 and 2 glycines, only dimeric disulfides were formed. Incorporation of 3 and 4 glycine residues gave thioethers in yields of about 40% and 70% respectively. Conversely, under normal conditions of iodine oxidation, when disulfides are rapidly formed from the S‐acetamidomethyl‐ or S‐tritylcysteine residues, tryptophan‐2‐thioethers are produced only in insignificant amounts or not at all.
Synthese von (±)‐Diplodialid B und A
Authors: Shenvi Ashokkumar B. , Gerlach Hans
Published: December 2004

Synthesis of (±)‐Diplodialide B and A

Two steroid hydroxylase inhibitors, diplodialide B (1) and A (2) have been synthesized in the following way: The lithium enolate 5 of S‐t‐butyl thioacetate (4) was added to (E)‐7‐(2′‐tetrahydropyranoxy)‐2‐octen‐1‐al (8) and the newly formed 3‐hydroxy group in the product 9 was protected as t‐butyl‐diphenyl silyl ether followed by selective hydrolysis of the tetrahydropyranyl ether to give 10. Treatment with AgNO3/H2O cleaved the S‐t‐butyl ester group in 10 to give the corresponding hydroxy carboxylic acid which was converted into the S‐2‐pyridyl thioester by treatment with di(2‐pyridyl)disulfide and triphenyl phosphine and cyclized with AgClO4 to give the (4E,3,9‐trans)‐ and (4E,3,9‐cis)‐lactone 11 and 12 (Rt‐Bu(C6H5)2Si) in 67% yield. Chromatographic separation of 11 and 12 and cleavage of the t‐butyl‐diphenyl silyl ether with tetrabutyl ammonium fluoride yielded (±)‐diplodialide B (1) with (4E,3,9‐trans)‐configuration and the (4E,3,9‐cis)‐isomer 12 (RH). Both isomers could be oxidized to diplodialide A (2) with manganese dioxide. The synthesis described above has also been carried out via the intermediates 10, 11 and 12 with RCOOCH2CH2Si(CH3)3.
Photochemical High‐yield Preparation of Tricyclo [3.3.0.02,8]octan‐3‐ones. Potential Synthons for Polycyclopentanoid Terpenes and Prostacyclin Analogs. Preliminary Communication
Authors: Demuth Martin , Raghavan Palaykotai R. , Carter Charles , Nakano Koichi , Schaffner Kurt
Published: December 2004

Three‐step syntheses and the resolution into the enantiomers are reported for the tricyclo[3.3.0.02,8]octan‐3‐ones 7–9, which are destined to serve as synthons for polycyclopentanoid terpenes and prostacyclin analogs. Routine overall yields of ca. 75% for 7, 40% for 8, and 46% for 9 are obtained, with 2‐chloroacrylonitrile and 1,3‐cyclohexadiene (for 7) and 1‐methyl‐1,4‐cyclohexadiene (for 8 and 9) as the starting materials. The key step is the triplet‐sensitized oxadi‐π‐methane photorearrangement of the β,γ‐unsaturated ketones 1–3 which can be achieved in 80–90% yields of isolated product and quantum yields of 0.5–1.0. The racemates of both ketone 1 and its photoisomer 7 have been resolved via chromatographic separation of suitable diastereoisomeric acetal mixtures. On the other hand, sensitization of 1 with an optically active donor, (‐)‐14, gave only an impractical maximum enantiomeric excess of 10% (‐)‐7.
Methyl‐triisopropoxy‐titanium, a highly selective nucleophilic methylating reagent. Preliminary Communication
Authors: Weidmann Beat , Seebach Dieter
Published: December 2004

Replacement of lithium or magnesium by titanium can furnish nucleophilic organometallic reagents of high selectivity as exemplified by the title compound 1 (see Tables 1–3).
The Synthesis of Stereoisomers of Arteannuin B
Authors: Goldberg Ora , Deja Irena , Rey Max , Dreiding André S.
Published: December 2004

Die Synthese von Stereoisomeren des Arteannuins B

Wir beschreiben die Synthese von drei rac‐Diastereomeren 7A‐7C des Sesquiterpenlaktons Arteannuin B (I) auf dem in den Schemata 2 und 3 zusammengefassten Weg. Als Schlüsselstufe für den Aufbau des Ringsystems 6 wurde eine intramolekulare Reformatsky‐artige Reaktion verwendet, in der gleichzeitig ein Cyclohexanring und ein α‐Methylidenbutyrolaktonring gebildet werden (Schritte 3 und 6). Die Cyclisierung von 5A bzw. 5B oder von 9/10 führte vorwiegend zur cis, cis‐Verknüpfung der drei Ringe A/B/C, wie in 6A bzw. 6B. Daneben entstand aus 5B auch das trans, cis‐System 6C. Die Verlängerung der Seitenkette in 1A,B unter Ausbildung der für die Reformatsky‐artige Reaktion notwendigen Funktionalität (in 5 bzw. 9/10) wurde nach zwei Methoden ausgeführt, welche in den Schritten 1, 2 bzw. 5 beschrieben sind. Die Epoxydierung von 6A, 6B bzw. 6C zu 7A, 7B bzw. 7C (Schritt 4) war vollkommen regio‐ (an C(7′), C(8′)) und stereospezifisch. Die relative Konfiguration an den Zentren C(1′), C(4′), C(4a′) und C(8a′) der drei Diastereomeren A, B bzw. C von 6 und 7 wurde anhand der 1H‐NMR‐Spektren abgeleitet.
Microbial transformation of cannabinoids. Part 3: Major metabolites of (3R, 4R)‐Δ1‐tetrahydrocannabinol
Authors: Binder Michael , Popp Astrid
Published: December 2004

The metabolic transformations of the psychotropic cannabinoid (3R, 4R)‐Δ1‐tetrahydrocannabinol (5) (=Δ1‐THC) by cultures of Fusarium Nivale, Gibberella fujikuroi (both Ascomycetes) and Thamnidium elegans (Phycomycetes) were investigated. A number of metaboilites, 1–4 and 6–9 were isolated from the incubations, partly purified and their structures elucidated by combined gas chromatography/mass spectrometry. Four of these metabolites, 1″‐hydroxy‐Δ1‐THC (4) 2″‐hydroxy‐β1‐THC (1) 6Δ‐hydroxy‐ζ1‐THC (8) and 2″,6Δ‐dihydroxy‐Δ1‐THC (9) so far have not been reported as microbial transformation products of 5.
Mimulaxanthin, Hauptcarotinoid von Lamium montanum, und seine absolute Konfiguration; konfigurative Verknüpfung von Deepoxyneoxanthin mit Neoxanthin
Authors: Buchecker Richard , Eugster Conrad Hans
Published: December 2004

Mimulaxanthin, the Main Carotenoid in Lamium montanum, Determination of its Absolute Configuration. Absolute Configuration of Deepoxyneoxanthin by its Correlation with Neoxanthin

The carotenoid mixture isolated from the yellow flowers of Lamium montanum PERS. (Labiatae) consists of more than 75% of carotenoids with allenic end groups. Besides 32% of neoxanthin/neochrome we isolated 44% of mimulaxanthin (1a), a very rare carotenoid so far only found in Mimulus sp. (Scrophulariaceae). Its absolute configuration was determined by oxidative degradation to the known ketone 3 (‘grasshopper ketone’) and by spectroscopic and chiroptical comparisons with neoxanthin (6). Mimulaxanthin (1a) therefore is (3S, 5R, 6R, 3′S, 5′R, 6′R)‐6,7,6′,7′‐tetradehydro‐5,6,5′,6′‐tetrahydro‐β, β‐carotene‐3,5,3′,5′‐tetraol. Deep‐oxyneoxanthin, which was reisolated from Mimulus sp. is (3S, 5R, 6R, 3′R)‐6,7‐didehydro‐6,7‐dihydro‐β, β‐carotene‐3,5,3′‐triol (2), as shown by spectroscopic and chemical correlation with neoxanthin (6; de‐epoxydation by BuLi/FeCl3).
The Synthesis of 4‐Decarboxy‐4‐phosphono‐O‐2‐isooxacephems, ‐isopenams and ‐isooxacephems Containing Phosphorus at the 3‐Position
Authors: Hakimelahi Gholam Hosein , Just George
Published: December 2004

Two new types of iso‐oxacephems have been synthesized in which a phosphonate group replaces either the carboxyl group or C(3). The latter compound exists as a stable trialkoxyphosphonium ylide.

Potassium thioacetate and O2 in DMF are transformed in an autocatalytic, probably sulfur‐catalyzed process to CH3COOK and sulfur; the latter two reagents are sufficient to transform the methanesulfonate 7 to the isopenam 15.
High‐Pressure 17O‐NMR. Study of Vanadium (II) in Water: A Second Example of an Associative Interchange Mechanism (Ia) for Solvent Exchange on an Octahedral Divalent Transition‐Metal Ion
Authors: Ducommun Yves , Zbinden Donald , Murbach André E.
Published: December 2004

The water exchange of [V(H2O)6]Cl2 in aqueous solution has been studied as a function of temperature and pressure (up to 250 MPa), by measuring the 17O‐FT‐NMR. line‐widths of the free water resonance at 8.13 MHz. The kinetic parameters obtained are K = 87±4 s−1, ΔH* = +61.8 ± 0.7 kJ mo1−1 and ΔS* = −0.4±1.9 J mol−1 K−1. A pressure‐independent volume of activation ΔV* = −4.1±0.1 cm3 mol−1 is obtained, suggesting an associative interchange (Ia) mechanism for this early divalent metal ion.
Neue Synthesen von 1α,25‐Dihydroxycholesterin
Authors: Färst Andor , Labler Ludvik , Meier Werner
Published: December 2004

New Syntheses of 1α,25‐Dihydroxycholesterol

Five convergent syntheses of 1α,25‐dihydroxycholesterol (2) essentially achieved by combining 1α‐hydroxylated C21− and C22−steroids with C4− or C5−side‐chain building blocks, are described. The l,3‐bis(tetrahydropyranyloxy)pregnen‐21‐ol‐Ptoluenesulfonate (4) was used as a C22−unit in three approaches involving sulfone 24 as a C4−, sulfone 43 and 2‐propynyl ether 49 as C5−side‐chain building blocks. In a further preparation, the 1,3‐diacetoxypregnen‐21 ‐al 5 and the phosphorane 59, a C22− and a C5−unit, respectively, were connected. For the last one, the 1,3‐bis(tetrahydropyranyloxy)pregnen‐20‐one (6), a C2l−unit and the C5−phosphorane building block 66 were chosen. Furthermore, new routes for the preparation of the 3‐hydroxy‐27‐norcholestenone (29) and of 25‐hydroxycholesterol (3) are described for which the p‐toluenesulfonates 21 and 23 served as the steroidal units and the sulfones 24 and 43, respectively, as the side chain fragments. Finally, the 1,3‐diacetoxypregnen‐21‐al (5) and the C5‐phosphorane unit 60 gave a novel approach to 1α‐hydroxycholesterol (53).
Structural Characteristics of the Carboxylic Ester Group
Authors: Schweizer W. Bernd , Dunitz Jack D.
Published: December 2004

Average bond distances and bond angles in carboxylic esters with different substitution patterns have been derived by analyzing data from many crystal structures retrieved from the Cambridge Structural Database (CSD). Conformation‐al preferences in the attachment of substituents are found.
Synthese von 5,6‐Epimino‐5,6‐dihydro‐β‐jonon
Authors: Müller Ernst Peter
Published: December 2004

Synthesis of 5,6‐Ephnino‐5,6‐dihydro‐β‐ionone

In order to synthesize the title compound 5 the 2‐azidoalcohols 3 and 4 were treated with various nucleophilic phosphorus compounds. It was found that the course of the reaction depends strongly upon the kind of nucleophilic phosphorus derivative used.
Organization of Carotenoid‐Phospholipid Bilayer Systems. Incorporation of Zeaxanthin, Astaxanthin, and their C50 Homologues into Dimyristoylphosphatidylcholine Vesicles
Authors: Milon Alain , Wolff Geneviève , Ourisson Guy , Nakatani Yoichi
Published: December 2004

Four carotenoids (zeaxanthin 1, astaxanthin 2, and their C50 synthetic isoprene‐homologues 3 und 4) have been incorporated into bilayer unilamellar vescles of dimyristoylphospatidylcholine as proved by coelution on a Sepharose column. The incorporation into the bilayer proper has been proved by the sensitivity to phase transition of UV/VIS spectra and circular dichroism. The UV/VIS absorptions of the carotenoids are typical of a lipidic environment. At the temperature of phase transition occur both intermolecular phenomena (aggregation of carotenoid molecules) and intramolecular changes (conformational change). The relative solubilities of the various carotenoids in this phospholipid membrane can be fitted with molecular parameters (length of the lipophilic carotenoid segment vs. lipid bilayer thickness).
Synthesis and Properties of 1,5‐Dimethyltricyclo[3.3.0.02,8]octane‐ and 1,5‐Dimethyltetracyclo[3.3.0.02,804,6]octane Derivatives
Authors: Gleiter Rolf , Jähne Gerhard , Müller Georg , Nixdorf Matthias , Irngartinger Hermann
Published: December 2004

The synthesis of 1,5‐dimethyltricyclo[3.3.0.02,8]octane‐3,7‐dione (2), 1,5‐dimethyltetracyclo[3.3.0.02,804,6]‐octane‐3,7‐dione (3), the corresponding dienes 5 and 6 as well as the mixed enones 13–15 is reported. Using He(I) photoelectron spectroscopy (PE) as a tool, a considerable interaction between the n orbitals on the O‐atoms and the σ frame in 2 and 3 as well as of the double bonds in 5 and 6 and the σ frame is found. These interactions are also traced back by the electronic absorption spectra of these compounds. The molecular structures of 2 and 3 have been investigated by X‐ray analysis.
The Absolute Configurations and Biogenesis of Some New Halogenated Chamigrenes from the Sea Hare Aplysia dactylomela
Authors: Sakai Ryuichi , Higa Tatsuo , Jefford Charles W. , Bernardinelli GéRald
Published: December 2004

Four new halogenated chamigrenes have been isolated from the sea hare, the (E)‐ and (Z)‐9‐(bromomethylidene)‐1,2,5‐trimethylspiro[5.5]undeca‐1,7‐dien‐3‐ones (11 and 10, resp.) the structures of which were deduced by NMR spectroscopy and by comparison with a known relative, the (8R,9R)‐8‐bromo‐9‐chloro‐5,5,9‐trimethyl‐1‐methylidenespiro[5,5]undec‐3‐en‐2‐one (12), and its (11 R)‐11‐acetoxy‐substituted derivative 13. Their structures and absolute configurations were determined and deduced by X‐ray using the absolute‐structure parameter. The configurations were remarkable in being enantiomeric to those of the tertiary chlorochamigrenes isolated so far. Consequently, a more general scheme is proposed to account for their biogenesis.
An ESR Study of the Radical Cations of Tetrathiafulvalene (TTF) and Electron Donors Containing the TTF Moiety
Authors: Ćavara Luka , Gerson Fabian , Cowan Dwaine O. , Lerstrup Knud
Published: December 2004

Hyperfine data and g factors are reported for the radical cations of tetrathiafulvalene (TTF; 1) and of its derivatives 2–13. From the intense satellite spectra of 1+–13+ not only the coupling constants of the 33S isotopes in the TTF moiety could be determined, but also, in favourable cases, those of the 13C isotopes in the central double bond. The former values range from 0.370 (8+) to 0.470 mT (4+) and the latter from 0.255 (8+) to 0.360 mT (4+) in the radical cations of bis(ethylenedithio)‐TTF (8+) and tetracyano‐TTF (4+). The radical cation of TTF (1+) exhibits intermediate values, 0.425 for the 33S and 0.285 mT for the 13C isotopes. The spin population in 1+–13+ resides, to a large extent, in the central S2C  CS2 part of the π‐system. It tends to increase (decrease) by substitution with electron‐accepting (donating) groups in the 2,3,6,7‐positions of TTF.
Influence of N,N′‐Substituents on the FeCl3‐Catalyzed Photo‐oxidation of 2,5‐Dibenzylpiperazine‐3,6‐Diones
Authors: Barbier Michel
Published: December 2004

Reactions carried out on benzoyl (2) and hydroxybenzyl (10) derivatives of L‐phenylalanine‐cycloanhydride 1 lead to the conclusion that the structure 3, previously proposed for picroroccellin (a metabolite from the lichen Roccella fuciformis), should be revised to 6, While the FeCl3‐catalyzed photo‐oxidation of 1 gives 2, the N,N′‐dimethyl derivative 7 leads to N,N′‐dimethyl‐2‐benzylpiperazine‐3,5,6‐trione (9). N,N′ ‐diacetyl‐L‐phenylalanine‐cycloanhydride 11 remains unchanged. It is established that N,N′ ‐substitutions of 2,5‐dibenzylpiperazines‐3,6‐diones considerably influence their photo‐oxidations under the reported conditions.
Stoffwechselprodukte von Mikroorganismen. 233. Mitteilung. Danoxamin, der eisenbindende Teil des Sideromycin‐Antibioticums Danomycin
Authors: Huber Peter , Leuenberger Heinz , Keller‐Schierlein Walter
Published: December 2004

Danoxamine, the Iron‐Binding Moiety of the Sideromycin Antibiotic Danomycin

The antibiotic danomycin was separated into its components, danomycin A and B (1 and 2, resp.), by various methods. Danomycin A is a carbamate of danomycin B and can be transformed to the latter by boiling with H2O. Both danomycins can be hydrolyzed by alkali to the Fe‐containing moiety, danoxamine (3). The structure of the latter was determined by spectroscopy and chemical degradation as the Fe(III) complex of 5,16,27,32‐tetrahydroxy‐4,12,15,23,26‐pentaoxo‐5,11,16,22,27‐pentaaza‐dotriacontanoic acid. It belongs thus to the ferrioxamine family of siderophores. In the danomycins, this moiety is linked by an ester bond to a disaccharide moiety of unknown structure. One of the sugars is believed to be an aminohexane methyl ether. Chromatographically homogenous danomycins A and B are still mixtures of isomers, a neutral sugar being glucose or mannose.
Nucleophilic additions to N‐glycosylnitrones part IV Asymmetric synthesis of N‐hydroxy‐α‐aminophosphonic and α‐aminophosphonic acids
Authors: Huber Rolf , Vasella Andrea
Published: December 2004

The addition of phosphite anions and of tris(trimethylsilyl) phosphite (P(OSiMe3)3) to N‐glycosyl‐C‐arylnitrones was examined. While these nitrones proved inert towards the phosphite anions, they reacted with P(OSiMe3)3 under catalysis by Lewis acids. Thus, P(OSiMe3)3 reacted with the crystalline (Z)‐N‐glycosylnitrones 2 and 8 to give the optically active N‐hydroxy‐α‐aminophosphonic acids 4 and 10, respectively, and hence the α‐aminophosphonic acids 5 and 11 in yields up to 92% and with an enantiomeric excess (e.e.) up to 97% (Scheme 1). The absolute configuration of the phosphonates depend upon the nature and – in one case – upon the quantity of the catalyst (Figure). Upon catalysis by HCIO4 or Zn(OTF)2, p(OSiMe3)3 added to 2 to give, in both cases, the (+)‐(R)‐phenylphosphaglycine 5 (optical purity 79–84 and 90–93%, resp.). The optical purity (o.p.) was hardly influenced by the amount of these catalysts (0.02‐;1 equiv.). However, catalysis by ZnCl2 gave, with trace quantities of the catalyst, (–)‐(S)‐5 (o.p. 79%), while an equimolar amount of ZnCl2 yielded (+)‐(R)‐5 (o.p. 82%). The HClO4‐catalyzed addition of P(OSiMe3)3 to the nitrone 14 (Scheme 2) led to (+)‐(R)‐N‐hydroxyphosphavaline 15 (78%) and hence to (–)‐(R)‐phosphavaline 16 (71% from 14 e.e. 95%). Under conditions leading from the nitrones 2, 8, 14, and 20 (Schemes 1 and 2) predominantly to (R)‐α‐aminophosphonic acids, the addition of P(OSiMe3)3 to nitrone 18, possessing a benzyloxy substituent as an additional potential ligand for the catalyst, gave (S)‐phosphaserine 19. The addition of P(OSiMe3)3 to the nitrone 20, catalyzed by Zn(OTf)2, led to (+)‐(R)‐N‐hydroxyphosphamehionine 21 (71%, e.e. 77%) and hence to (–)‐(R)‐phosphamethionine 22 (77% from 20, e.e. 79%). Catalysis by trace quantities of ZnCl2 gave (+)‐(S)‐22 (85%, e.e. 61%). The enantiomerically pure aminophosphonic acids 5, 11, and 16 were obtained by recrystalliztion. The e.e. of the N‐hydroxyaminosphosphonic acids 10, 15, and 21 and the aminophosphonic acids 5, 11, 16, and 22 were determined by the HPLC analysis of the dimethyl N‐naphthoyl‐α‐aminophosphonats 7, 13, 17, and 23, on a chiral stationary phase.
Protonated diolefin complexes: Model systems for C;h activation via metal complexation
Authors: Piantini Umberto , Philipsborn Wolfgang Von , Salzer Albrecht , Buchmann Brigitte
Published: December 2004

On protonation of the diolefin complexes [M(C5R5)(diene)] (R = H, CH3; M = Co, Rh, Ir; diene = 2,3‐dimethylbutadiene, 1,3‐cyclohexadiene) with HBF4, cationic species are isolated which, at room temperature, show fluxional behaviour on the NMR time scale. Depending on R and M, three different ground states are observed for these cationic complexes in the NMR spectra at low temperatures. While for M = Ir a classical metal‐hydride structure M–H is observed, the Co and Rh complexes show ground states with ‘agostic’ H‐bridges M‥H‥C. The protonated species are characterized by 1H‐, 13C‐ and 103Rh‐NMR spectra. Total line‐shape analysis of the 1H and 13C spectra in the 298–154 K range gave the free enthalpies of activation ΔG ≠ for methyl rotation and 1, 4‐H shift in the agostic structures 2b, 2b′, 2c, and 2c′. The Rh complexes show the lowest ΔG± values for the 1,4‐H shift, and the strength of the agostic bond appears to decrease in the order CoC5H5 > CoC5Me5 > RhC5H5 > RhC5Me5. Only for R = H and M = Rh and in the presence of traces of Lewis bases (H2O, Pyridine, or acetone), variable amounts of coordinatively saturated allyl complexes competing with the agostic species are observable. Morethan equimolar amounts of basic solvents lead to irreversible deprotonation and recovery of the starting complexes. Stable allyl‐halide complexes are formed on reaction with HCI, while protonation with HBF4, in the presence of CO, gives high yields of complexes [M(CO)(allyl)(C5R5)] [BF4]. The different ground states observed for the protonated complexes and the dynamic behaviour in solution are compared with other hydride‐transfer reactions observed in organometallic chemistry, specifically with the β‐hydride elimination and the catalytic hydrogenation of olefins.
Über den Einfluss des Donor‐Teilchromophors bei Dimethinmerocyanin‐Farbstoffen auf das Aggregationsverhalten in wässriger Lösung
Authors: Kussler Manfred , Balli Heinz
Published: December 2004

On the Influence of the Donor Part of the Chromophor of Dimethinmerocyanine Dyes upon the Aggregation Tendency in Aqueous Solution

A series of novel long‐chain alkyl‐dimethinmerocyanine dyes containing the (rhodaninyl)benzenesulfonate or (cyanoacetoxy)alkanesulfonate group is synthesized in good yield and their aggregation tendency in H2O and/or in various organic solvents/H2O mixtures without addition of salt investigated. Except for the merocyanine 2h, all dyes give J‐aggregation in H2O or in organic solvents containing H2O. The Lambert‐Beer rule is proved for the solution of 3a(4) in H2O. The degree of aggregation of 3a(4) in H2O is investigated by ultracentrifugation. The kind of the aggregation (J‐ or H‐type) can be found out very quickly by dissolving the dye in H2O with the help of ultra‐sound.
Isolierung und Strukturaufklärung epimerer 1(5),6‐Guaiadiene aus Tolubalsam
Authors: Friedel Horst Dieter , Matusch Rudolf
Published: December 2004

Isolation and Structure Elucidation of Epimeric 1(5,)6‐Guaiadienes from Tolubalsam

Two epimeric 1(5),6‐guaiadienes, which have very similar spectroscopic properties, were isolated from tolubalsam. Their structures were elucidated by NMR spectroscopy, acid‐catalyzed isomerization of γ‐gurjunene, and Diels‐Alder reactions.
Acid‐Catalyzed Rearrangement of 3‐Aza‐8‐oxatricyclo[3.2.1. 02,4]octan‐6‐one Acetals. Highly Stereoselective Total Synthesis of 3‐Amino‐3‐deoxy‐D‐altrose and Derivatives
Authors: Nativi Cristina , Reymond Jean‐Louis , Vogel Pierre
Published: December 2004

Ethyl and tert‐butyl azidoformate added to 7‐oxabicyclo[2.2.1]hept‐5‐en‐2‐one dimethyl (5) and dibenzyl (6) acetals to give mixtures of regioisomeric triazolines. The latter gave the corresponding aziridines (6,6‐dialkoxy‐3‐aza‐8‐oxatricyclo[3.2.1.02,4]octane‐3‐carboxylates 15, 19, 23, and 27 and 31) on UV irradiation. In the presence of protic acids, the aziridines were rearranged into protected amines ([3‐endo‐alkoxy‐5‐oxo‐7‐oxabicyclo[2.2.1]hept‐2‐exo‐yl]carbamates 16, 20, 24, and 28 and 33). Using (+)‐(1R, 4R)‐5,5‐bis(benzyloxy)7‐oxabicyclo[2.2.1]hept‐2‐ene((+)‐6) derived from furan and l‐cyanovinyl (1S)‐camphanate, the method was applied to prepare 2‐O‐benzyl‐3‐[(tert‐butoxy)carbonyiamino]‐5‐O‐(3‐chlorobenzoyl)‐3‐deoxy‐β‐D‐altrofuranurono‐6,1‐lactone ((−)‐37). This compound was converted to methyl 3‐amino‐3‐deoxy‐α‐D‐altropyranoside hydrochloride (44) and several derivatives.
Photochemical Reactions 151st Communication. Photo‐oxygenation of (E)‐ and (Z)‐7‐Methyl‐β‐ionone
Authors: Nishio Takehiko , Mathies Peter , Job Kurt , Frei Bruno , Jeger Oskar
Published: December 2004

Photo‐oxygenation of (E)‐7‐methyl‐β‐ionone ((E)−1) and (E)‐8‐methyl‐β‐ionone ((E)−2) gave rise to the formation of the hydroperoxy‐enones (E)−10 and (E)−15, respectively, which, in part, underwent intramolecular epoxidation to the hydroxy‐epoxy‐ketones 11 and 16, respectively, The product distribution of the photo‐oxidation of (Z)−1 shows a marked influence of the skewed ground‐state conformation of the dienone chromophore. Thus, singlet oxygen (1O2) was added to C(γ) of the dienone chromophore leading to the spirocyclic peroxy‐hemiacetal 12 and to the endoperoxide 13. In addition, the tricyclic peroxide 14 was formed as a new type of product via primary addition of 1O2 to C(γ) of the dienone chromophore. The structure of 14 was established by X‐ray crystal‐structure analysis of the hemiacetal 22.
Notiz über Ellagitannine und Flavonol‐glycoside aus Rosenblüten
Authors: Nayeshiro Kyosuke , Eugster Conrad Hans
Published: December 2004

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.
A New Route to Crystalline Salts of the Hydrolytic Dimer of Chromium(III)
Authors: Merakis Thomas , Murphy Annette , Spiccia Leone , Beguin Alan , Marty Werner
Published: December 2004

Crystalline salts of the hydrolytic dimer of Cr(III), [Cr2(μ‐OH)2(H2O)8]X4·n H2O (X = p‐toluenesulfonate (tos) or mesitylene‐2‐sulfonate (dmtos)) have been prepared in good yields via a simple two‐step procedure: H+ oxidation of Cr metal to give Cr2+ (T ≈︁ 70°) followed by O2 oxidation, of Cr2+ to give the dimer (T ≈︁ 25°). The mechanism of conversion of Cr2+ into the dimer is discussed.
The Synthesis of Racemic Ambrox®
Authors: Büchi George , Wüest Hans
Published: December 2004

(±)‐Ambrox (10), the racemic form of (−)‐Ambrox®, the commercially most important ambergris odorant has been synthesized from a readily available bicyclic keto ester in five steps. The racemic ether retains the characteristic scent of fine‐quality ambergis, and the odor threshold of the racemate and the (−)‐enantiomer prepared from natural sclareol were found to be essentially identical.
Synthesis and NMD A Antagonistic Properties of the Enantiomers of 4‐(3‐phosphonopropyl)piperazine‐2‐carboxylic acid (CPP) and of the unsaturated analogue (E)‐4‐(3‐phosphonoprop‐2‐enyl)piperazine‐2‐carboxylic acid (CPP‐ene)
Authors: Aebischer Bernard , Frey Peter , Haerter Hans‐Peter , Herrling Paul L. , Mueller Werner , Olverman Henry J. , Watkins Jeffrey C.
Published: December 2004

The (R)‐ and (s)‐enantiomers of 4‐(3‐phosphonopropyl)piperazine‐2‐carboxylic acid (D‐ and L‐CPP, resp.; 15 and 16, resp.), and of its unsaturated analogue (E)‐4‐(3‐phosphonoprop‐2‐enyl)piperazine‐2‐carboxylic acid (D‐ and L‐CPP‐ene, resp.; 13 and 14, resp.) were prepared. The absolute configuration of the enantiomers was determined by a chemical correlation of the menthyl ester 7 with D‐asparagine. The affinity of these derivatives for the NMDA receptor was determined by displacement of [3H]CPP in rat cerebral cortical membranes. In two functional tests (the frog hemisected spinal cord preparation and the sodium efflux test from rat brain slices), D‐CPP‐ene appears to be the most potent, enantiomerically pure, competitive NMDA antagonist known to date.
Chloride Binding by Polyammonium Receptor Molecules: 35Cl‐NMR Studies
Authors: Hosseini Mir Wais , Kintzinger Jean‐Pierre , Lehn Jean‐Marie , Zahidi Assou
Published: December 2004

Binding of chloride anion by protonated polyamines was investigated by 35ClNMR spectroscopy. The presence of protonated macro(poly)cyclic polyamines caused downfield shifts and significant line broadening of the 53ClNMR signals. 35ClNMR spectroscopy was used for complex‐formation stoichiometry determination and revealed the formation of a binuclear chloride complex with the fully protonated ditopic hexaazamacrocyclic receptor 6. 35ClNMR spectroscopy was also applied in competition experiments between Cl and SO42− and demonstrated that the fully protonated macrocyclic hexaamine 4 forms a strong complex with SO4−2 with 1:1 stoichiometry.
Diastereoface Selectivity During Pthalimidonitrene Additions to (E)‐and (Z)‐configurated α, β‐unsaturated esters, induced by a chiral center in the γ‐position
Authors: Chilmonczyk Zdzislaw , Egli Markus , Behringcr Christoph , Dreiding AndréS.
Published: December 2004

In‐situ‐generated phthalimidonitrene was added to five α, β‐unsaturated esters containing a chiral secondary O‐function at C(γ). The additions were fully suprafacial, inasmuch as the (E)‐isomers 1 afforded only the trans‐aziridines 2 and 3 (J(β, γ) = 4.8−5.1 Hz) and the (Z)‐isomers 4 only the cis‐aziridines 5 and 6 (8.2−8.5 Hz). The products 2, 3, 5, and 6 where shown to possess the arabino‐, xylo‐, ribo‐, and lyxo‐ configuration, respectively, by X‐ray structure analysis of 2b, 2d, and 6a. The diastereoface selectivity of the nitrene additions, induced by the chiral substructure around C(γ), resulted in more 2 than 3 from 1, but more 6 than 5 from 4, which means that the preference of attack at the double bond switches from one side to the other depending on the C=C configuration. The preferences were higher at lower temperature. The aziridines 2a, 2d, and 3d exhibit 1H‐NMR‐visible isomerism at the ring N‐atom; the major (78−95 %)invertomer A is always the one with the phthalimido group in trans‐position to the (larger) substructure around C(γ). The other aziridines only show 1H‐NMR signals of one invertomer, which – by steric reasoning ‐ ought to be A; this is confirmed by a 1H‐NMR argument for 3a, 5a, 6a, 5c, and 6c.
An Eclipsed C(sp3)‐CH3 Bond in a Crystalline Hydrated Tricyclic Orthoamide: Evidence for CH…︁O hydrogen bonds
Authors: Seiler Paul , Dunitz Jack D.
Published: December 2004

Accurate, low‐temperature (81 K) X‐ray analyses have been made for two crystalline modifications of the tricyclic orthoamide 1b: a cubic trihydrate in space group Pa3 (Z = 8), where the molecule has crystallographic threefold rotation symmetry, and an anhydrous monoclinic form in space group P21/c (Z = 8) where two symmetry‐independent molecules have different configurations, one ail‐trans. (as in the cubic trihydrate), the other cis, cis, trans. In the cubic trihydrate, each orthoamide molecule is attached to a triad of H2o molecules by OH…︁N H‐bonds. A remarkable feature of this structure is the nearly eclipsed conformation about the central C‐CH3 bond. In the anhydrous crystal, both types of molecule have the normal staggered orientation of their Me groups. The reversal of the Me orientation in the trihydrate is attributed to CH…︁O H‐bonding, which must be much stronger and more directionally specific than has been previously assumed.
Dichotomy of Fe+‐Mediated Sequential Activation of CH/CC Bonds of Aldimines: A Case of Efficient Reaction Control by Chain‐Length Effects Preliminary Communication
Authors: Prüsse Tilmann , Schwarz Helmut
Published: December 2004

The metastable ions of Fe+ complexes of aldimines R1NCHR2 exhibit a unique behaviour in that sequential loss of olefin/H2 follows two distinct pathways: one corresponds to the familiar pattern of double remote functionalization, involving either alkyl chain R1 and R2. In addition, based on labeling studies, evidence is presented demonstrating that the consecutive elimination of C2H4/H2 from the Fe+ complex of C6H13NCHC3H7 involves exclusively the C6H13 part of the substrate. These and other Fe+‐mediated CH/CC bond activations of aldimines are controlled by chain‐length effects, reflecting the preferential formation of metallacyclic intermediates of particular ring sizes.
Determination of the Chemical Structure of Linden Ether
Authors: Blank Imre , Grosch Werner , Eisenreich Wolfgang , Bacher Adelbert , Firl Joachim
Published: December 2004

The chemical structure of the novel monoterpene 1, named ‘linden ether’ and isolated from linden honey and the blossoms of lime tree (Tilia cordata), was studied by two‐dimensional NMR spectroscopy, by high‐resolution MS as well as by hydrogenation experiments and by GC on a chiral phase. Thus, linden ether was identified as a racemic mixture, i.e. (7aRS)‐2, 4, 5, 7a‐tetrahydro‐3, 6‐dimethylbenzofuran.
Synthesis of Optically Active Bifunctional Isoprenoid Building Blocks by Rhodium(I)‐Catalyzed Asymmetric Allylamine to Enamine Isomerization
Authors: Schmid Rudolf , Hansen Hans‐Jürgen
Published: December 2004

The application of the known asymmetric allylamine to enamine isomerization methodology to bifunctional C5‐isoprenoid allylic amines of types IId and IIe (Scheme 1) is described. It is shown that a number of such substrates can be isomerized with enantioselectivities of > 90% ee. using cationie Rh1 complexes containing (6. 6′‐dimethylbiphenyl′2, 2′‐diyl)bis(dipheny phosphine) (BIPHEMP; 9) as asymmetry‐inducing ligand (Scheme 2, Tables 1 and 2). Synthetically most useful is the isomerization of the benzyloxy derivative 10a into the (E)‐enamine 11a. This isomerization proceeds with very high enantioselectivity (98‐99% ee) and affords, after enamine hydrolysis, the optically active 4‐(benzyloxy)‐3‐methylbutanals ((R)‐ or (S)‐12) in chemical yields of ca. 90%. In conjunction, a short synthetic route to the starting material 10a has been developed which has a Pd‐catalyzed amination of isoprene epoxide (30) as the key step. Thus, convenient and practical access to the optically active aldehydes (R)‐and (S)‐12 is now at hand. These aldehydes are useful optically active bifunctional building blocks for isoprenoid homologation.
A New Convergent Synthesis of Thiamine Hydrochloride
Authors: Contant Pierre , Forzy Liliane , Hengartner Urs , Moine Gérard
Published: December 2004

Thiamine hydrochloride (1a; 3‐[(4‐amino‐2‐methylpyrimidin‐5‐yl)methyl]‐5‐(2‐hydroxyethyl)‐4‐methylthia‐zolium chloride hydrochloride; vitamin B1) has been synthesized in excellent yield by condensation of 3‐mercapto‐4‐oxopentyl acetate (5a) with 3, 4‐dihydro‐7‐methylpyrimido[4, 5‐d]pyrimidine (4) in formic acid. The two intermediates 5a and 4 are prepared from 3‐chloro‐4‐oxopentyl acetate (3) and 4‐amino‐2‐methyl‐5‐(aminomethyl)‐pyrimidine (Grewe diamine; 2a), respectively.
Spectroscopical and Electrochemical Behavior of New Mixed‐Ligand Cyclometalated Rh(III) Complexes
Authors: Sandrini Diana , Maestri Mauro , Ciano Mauro , Maeder Urs , von Zelewsky Alex
Published: December 2004

The absorption spectra, luminescence spectra, excited‐state lifetimes, and electrochemical behavior of the cyclometalated [Rh(ppz)2bpy]+, [Rh(3‐Cl‐ppz)2(bpy)]+, [Rh(4‐NO2‐ppz)2(bpy)]+, [Rh(ppz)2(biq)]+ and [Rh(4‐NO2‐ppz)2(biq)]+ complexes (ppz−, 3‐Cl‐ppz−, and 4‐NO2‐ppz− are the ortho‐C‐deprotonated forms of 1‐phenylpyrazole, l‐(3‐chlorophenyl)pyrazole and l‐(4‐nitrophenyl)pyrazole, respectively) have been investigated. The results obtained have been compared with those concerning the free protonated ligands and some previously studied mixed‐ligand cyclometalated Rh(III) complexes. Luminescence originates from the lowest ligand‐centered (LC) excited state, which involves the diimine ligands in all cases except for [Rh(4‐NO2‐ppz)2(bpy)]+, where it involves the ortho‐metalating ligand. s. In the absorption spectra, LC and metal‐to‐ligand charge‐transfer (MLCT) bands, involving the diimine and/or the ortho‐metalating ligands, have been assigned, and correlations between spectroscopic and electrochemical data are discussed.
Chemie von α‐Aminonitrilen. Aziridin‐2‐carbonitril, ein Vorläufer von rca‐O3‐Phosphoserinnitril und Glycolaldehyd‐phosphat
Authors: Wagner Ernst , Xiang Yi‐Bin , Baumann Karl , Gück Jürgen , Eschenmoser Albert
Published: December 2004

Chemistry of α‐Aminonitriles. Aziridine‐2‐carbonitrile, a Source of Racemic O′‐Phosphoserinenitrile and Glycolaldehyde Phosphate

Racemic aziridine‐2‐carbonitrile (rac‐1) in MeCN solution reacts regioselectively (> 90%) with 2 equiv. of TsOH at room temperature to form the hydrotosylate of racemic O3‐tosylserinenitrile (rac‐2) via β‐ring opening (Scheme 2). A similar regioselective reaction takes place between rac‐l and H3PO4 to produce racemic O3‐phosphoserinenitrite (rac‐3) which is in turn a source of glycolaldehyde phosphate (=formylmethyl dihydrogenphosphate) under the conditions of a ‘retro‐Strecker’ reaction in aqueous solution (Scheme 6). These experiments document a close structural relationship between the simplest of the sugar phosphates and an α‐aminonitrile precursor. The English Footnotes (*) referring to Schemes 1‐7 are intended to provide an extension of this summary.
Elektrophile Substitutionsreaktionen des 1,1‐Difluoro‐1H‐cyclopropabenzols
Authors: Neidlein Richard , Kohl Matthias
Published: December 2004

Electrophilic Substitution Reactions of 1,1‐;Difluoro‐1H‐cyclopropabenzene

1,1‐Difluoro‐1H‐cyclopropabenzene (1) can be deprotonated with strong bases at C(2). The resulting 1,1‐di‐fluoro‐2‐lithio‐1H‐cyclopropabenzene (2) reacts with electrophiles to form C(2)‐substituted derivatives of 1. The Diels‐Alder reactions with electron‐poor dienes, characteristic for 1H‐cyclopropabenzene, do not occur with the 1,1‐difluoro analogue 1.
Eine Synthese methylierter Epoxyhydroazulenone durch intramolekulare [4 + 3]‐Cycloaddition einer aus 1,1‐Dichloro‐6‐(3‐methylfur‐2‐yl)hexan‐2‐on erzeugten Oxyallyl‐Zwischenstufe
Authors: Kaiser Roland , Föhlisch Baldur
Published: December 2004

A synthesis of Methylated Epoxyhydroazulenones by Intramolecular [4 + 3] Cycloaddition of an Oxyallyl Intermediate, Generated from 1,1‐Dichloro‐6‐(3‐methyl‐2‐furyl)hexan‐2‐one

(Z)‐3‐Methylpent‐2‐en‐4‐yn‐1‐ol (7) was transformed to 2‐(4‐chlorobutyl)‐3‐methylfuran (4b) and 2‐(but‐3‐enyl)‐3‐methylfuran (10a) by C‐alkylation and 5‐exo‐dig cyclization. The Grignard derivative formed from 4b gave 1,1‐dichloro‐6‐(3‐methylfur‐2‐yl)hexan‐2‐onc (1b) on reaction with dichloroacetyl chloride. This dichloromethyl ketone undergoes a base‐induced cyclization to form diastereoisomeric 7‐chloro‐1,2,3,6,7,8a‐hexahydro‐4‐methyl‐8H‐3a,6‐epoxyazulen‐8‐ones (3bα and 3bβ) by way of an intramolecular [4+3] cycloaddition of an oxyallyl intermediate 2b. By dechlorination and hydrogenation of 3bβ, the tricyclic hydroepoxyazulenones 18 and 19 have been synthesized.
Stereoelectronic Aspects of the Anomeric Effect in Fluoromethylamine
Authors: Irwin John J. , Ha Tae‐Kyu , Dunitz Jack D.
Published: December 2004

High‐level ab initio calculations have been made for fluoromethylamine to study structural and energetic effects of the relative orientation of the N lone pair to the CF bond. The anti‐conformer (N lone pair anti‐planar to the CF bond) corresponds to the global energy minimum. It has the longest CF distance, the shortest CN distance, and is 7.5 kcal·mol−1 more stable than the related perpendicular conformation (lone pair perpendicular to the CF bond). The syn‐conformation also shows hallmarks of the anomeric effect: long CF bond, short CN bond, and energetic stability when allowance is made for the two pairs of eclipsed hydrogens. The transition state for N inversion is close to the syn‐structure; rotation about the CN bond is strongly coupled with this inversion process. Small bond distance changes of ca. 0.02 Å between parallel and perpendicular conformations are associated with dissociation energy differences of ca. 30 kcal·mol−1. Various criteria for assessing the strength of the anomeric effect are discussed.
Enzyme‐Mediated Regioselective Acylations of Flavonoid Disaccharide Monoglycosides
Authors: Danieli Bruno , De Bellis Paolo , Carrea Giacomo , Riva Sergio
Published: December 2004

Flavonoid disaccharide monoglycosides have been acylated by the catalytic action of the protease subtilisin in anhydrous pyridine. The effects of the nature of the sugars and of the interglycosidic bonds on the regioselectivity of the reactions have been analyzed. The selectivity was excellent with rutin (1), hesperidin (2), naringin (6), and quercetin 3‐O‐[O‐(β‐D‐glucopyranosyl)‐(1→4)‐α‐L‐rhamnoside] (9), giving single monoesters on their glucose moieties (see la, 2a, 6a, and 9b, resp.); quite interestingly, in the last compound, acylation did not occur at the free primary OH group but at the secondary OHC(3‴). On the other hand, a mixture of mono‐ and diesters was obtained with the flavonoid peltatoside (7).
A Novel Type of Dimeric Secoiridoid Glycoside from Lisianthius jefensis ROBYNSet ELIAS
Authors: Hamburger Matthias , Hostettmanna Maryse , Stoeckli‐Evans Helen , Soils Pablo N. , Gupta Mahabir P. , Hostettmanna Kurt
Published: December 2004

A dimeric secoiridoid glucoside named lisianthioside (l) has been isolated from the roots of Lisianthius jefensis ROBYNS et ELIAS (Gentianaceae). The structure was established by spectroscopic analysis (UV, IR, 1H‐ and 13C‐NMR, DCI‐MS) of glycoside 1, peracetate 1a, aglycone 3 and the dimethoxy derivatives 4a–c. Lisianthioside (1) is the first representative of a novel type of dimeric secoiridoids. Biogenetically derived from two sweroside (2) moieties, the tricyclic aglycone features a symmetrical 12‐membered bislactone ring. In contrast to the moderately bitter sweroside (2), lisianthioside (1) is tasteless.
Circular Dichroism of Some 2‐(Phenylmethyl)pyridine Derivatives
Authors: Berova Nikolina , Eojadziev Stefan , Bresciani‐Pahor Nevenka , Ivanova Petko M. , Kojić‐Prodicć Biserka , Rakovska Rositza , Ružić‐Toroš ŽIva , Snatzke Günther
Published: December 2004

The absolute configuration of the 2‐(phenylmethyl)pyridine derivatives 1–9 had been established by X‐ray diffraction and chemical correlation. Their CD spectra have been studied in different solvents for the free and protonated forms. It has now been found that, from the sign of the strong CD couplet between 270 and 220 nm, which was observable for all these compounds besides 7 and 9, their absolute configuration can be determined much quicker.
Synthèse énantiospécifique du (+)‐(6S, 8R, E)‐2,3‐didéhydrononactate de méthyle
Authors: Deschenaux Pierre‐François , Jacot‐Guillarmod André
Published: December 2004

Enantiospecific Synthesis of (+)‐(6S,8R,E)‐Methyl 2,3‐Didebydrononactate

(+)‐(6S,8R,E)‐Methyl 2,3‐didehydrononactate (7) has been synthesised from (−)‐(3R)‐methyl 3‐hydroxy‐butanoate with an enantiomeric excess ≥95%. The known stereoselective hydrogenation of 7 affords (−)‐(2R,3R,6S,8R)‐methyl nonactate (8) as the major isomer, a chiral synthon for the synthesis of nonactin.