bluuebunny/crossref_metadata_2025 huggingface dataset:
Application of the gold(I)‐Catalyzed aldol reaction to a stereoselective synthesis of (2S, 3R, 4R, 6E)‐3‐Hydroxy‐4‐methyl‐2‐(methylamino)oct‐6‐enoic Acid ( = MeBmt), Cyclosporin's unusual amino acid
Authors: Togni Antonio , Pastor Stephen D. , Rihs Grety
Published: December 2004

The title compound 8 was prepared in three steps starting from the optically pure aldehyde (2R, 4E)‐2‐methyl‐hex‐4‐enal (3), thus constituting the shortest synthetic approach reported. Two of the three stereogenic centers in the product were generated in a coupling reaction of 3 with ethyl isocyanoacetate, catalyzed by a gold(I)/chiral ferrocenylphosphine system, giving the dihydrooxazole 5 in 85% diastereoselectivity (mismatchedcase). The weak effect of double stereodifferentiation in this reaction (matched case 90% ds) is discussed. N‐Methylation and hydrolytic ring opening of 5 gave the protected form 7 of MeBmt, The X‐ray diffraction study carried out on 7 confirms the absolute configuration of the two stereogenic centers formed in the gold(I)‐catalytic reaction.
Untersuchungen zur Thermochromie von Heterospiranen und Farbbildnern mit heterocyclischen Teilsystemen und O oder N als Ringschlussatom
Authors: Hellrung Bruno , Balli Heinz
Published: December 2004

Investigations on the Thermochromism of a Series of Spirocyclic Compounds and ‘Colourformers’ with Heterocyclic Parts and O or N as the ‘Key’ Atom.

The thermochromism of a series of spirocyclic compounds with heterocyclic parts and O or N as the ‘key’ atom and of ‘colourformers’ was investigated in different solvents such as benzyl alcohol, dimethyl phthalate, decaline, toluence, or xylene. Thermodynamic data for the involed equilibria (ΔH°, ΔS°, and ΔG°298k) and VIS‐spectroscopic data were determined and discussed in relation to the ones known spiropyrances. Compounds with O as ‘key’ atom behave very similary to the known spiropyrances, compounds with N as ‘key’ atom mostly are unstable undergoing irreversible bleaching. The ‘colour formers’ usually show only small thermochromic effects and very small equilibrium concentration of the coloured form.
Bildung von 5,6‐Dihydro‐1,3(4H)‐thiazin‐4‐carbonsäure‐estern aus 4‐Allyl‐1,3‐thiazol‐5(4H)‐onen
Authors: Jenny Christjohannes , Heimgartner Heinz
Published: December 2004

Formation of Methyl 5,6‐Dihydro‐l, 3(4H)‐thiazine‐4‐carboxyiates from 4‐Allyl‐l, 3‐thiazol‐5(4H)‐ones.

The reaction of N‐[1‐(N, N‐dimethylthiocarbamoyl)‐1‐methyl‐3‐butenyl]benzamid (1) with HCl or TsOH in MeCN or toluene yields a mixture of 4‐allyl‐4‐methyl‐2‐phenyl‐1,3‐thiazol‐5(4H)‐one (5a) and allyl 4‐methyl‐2‐phenyl‐1,3‐thiazol‐2‐yl sulfide (11; Scheme 3). Most probably, the corresponding 1,3‐oxazol‐5(4H)‐thiones B are intermediates in this reaction. With HCl in MeOH, 1 is transformed into methyl 5,6‐dihydro‐4,6‐dimethyl‐2‐phenyl‐1,3(4H)‐thiazine‐4‐carboxylate (12a). The same product 12a is formed on treatment of the 1,3‐thiazol‐5(4H)‐one 5a with HCl in MeOH (Scheme 4). It is shown that the latter reaction type is common for 4‐allyl‐substituted 1,3‐thiazol‐5(4H)‐ones.
The Photochemical Synthesis and Denitrogenation of 8,9‐diazadibenzo[c, e]isobullvalene
Authors: Burger Ulrich , Mentha Yves G. , Millasson Patricia , Lottaz Pierre‐André , Mareda Jiri
Published: December 2004

Starting from dibenzo[a, c]cyclooctene (4) and 4‐methyl‐3H‐1,2,4‐triazol‐3,5(4H)‐dione (MTAD), the strained skeleton of the title azo compound 1 is assembled in a tandem photo‐Diels‐Alder addition/di‐π‐methane rearrangement sequence. The synthesis is completed by a stepwise hydrolytic oxidation of the ensuing triazolidine‐dione 2 with nickel peroxide. Thermolysis of 1 in benzene solution is shown to be governed by an initial 1,3‐dipolar cycloreversion which leads, via an intermediate diazo compound 11, to cyclobuta[1]phenanthrene 8 and two further carbene‐derived C16H12 products. Photolysis of 1 at 350 nm leads in modest yield (12%), via a diazenyl diradical, to an unstable bridged bicyclobutane 10 (dibenzooctavalene). MNDO calculations suggest the latter to have a rapidly inverting, twisted structure of C2 symmetry.
Nucleotides. Part. XXXII. Synthesis of 2′–5′ Connected oligonucleotides. Prodrugs for antiviral and antitumoral nucleosides
Authors: Herdewijn Piet , Charubala Ramamurthy , De Clercq Erik , Pfleiderer Wolfgang
Published: December 2004

The cytotoxically and antivirally active compounds bvUd (1), flUd (4), acyclovir (7), and Aa (12) have chemically been combined with the appropriately protected (2′–5′)diadenylate 20 by the phosphotriester approach to give the 2′–5′ oligonucleotide trimers 21–24. The deprotection of the various blocking groups by chemical means afforded the 2′–5′ trimers 25–28, which can be regarded as new type of a potential prodrug form delivering nucleotides to the targets inside cells. In an analogous series of reactions, 9‐(3′‐azido‐3′‐deoxy‐β‐D‐xylofuranosyl)adenine was coupled with 7 to the 2′–5′ trimer 31. The antiviral screening of the oligonucleotides 25–27 and 31 showed biological activities closely related to the parent nucleosides, possibly indicating their release by enzymatic cleavage of the oligomers.
Allobetonicoside and 6‐O‐Acetylmioporoside: Two new iridoid glycosides from Betonica officinalis L.
Authors: Jeker Marianne , Sticher Otto , Çaliş İhsan , Rüedi Peter
Published: December 2004

A new allose‐containing iridoid diglycoside, allobetonicoside (1), and a new acyl iridoid glucoside, 6‐O‐acetylmioporoside (2) have been isolated from the aerial parts of Betonica officinalis L. in addition to two known iridoid glucosides, acetylharpagide (3) and reptoside (4). Their structures have been determined by spectroscopic methods as well as by means of chemical evidence.
Molecular‐Graphics Modelling of the Acid Strength in Zeolites: Influence of the Aluminium Distribution in Offretite
Authors: Goursot Annick , Fajula François , Figueras François , Daul Claude , Weber Jacques
Published: December 2004

Using extended Hückel wave functions, molecular electrostatic potentials (MEP's) have been calculated for several model clusters representative of zeolites of offretite type. The clusters studied, which are all made of a central unit comprising 2 AlO4 and 16 SiO4 tetrahedra, differ only by the relative positions of the Al‐atoms occupying the same crystallographic sites (T2) within the zeolite framework. using the MEP values as a color‐coded acidity index for the various clusters, three‐dimensional representations of their molecular surfaces are generated as solid models on a performing computer graphics system. Important differences in acidity are predicted for the clusters which can he classified into two types according to the distribution of Al‐atoms: the first one is characterized by nearly independent acid sites localized around the main channel of zeolite (Figs. 3 and 6) whereas the second one exhibits interacting acid sites located longitudinally along the channel of the same gmelinite cage (Figs. 4 and 5). The possible relationship between the structure of the clusters and their catalytic activity towards organic species is discussed.
1,2,3,4,4a,5,8,8a‐Octahydro‐4β,8aα‐dimethylnaphthalen‐4aβ‐ol ( = Dehydrogeosmin), a Novel Compound Occurring in the Flower Scent of Various Species of cactaceae
Authors: Kaiser Roman , Nussbaumer Cornelius
Published: December 2004

The 1,2,3,4,4a,5,8,8a‐octahydro‐4β8aα‐dimethylnaphthalen‐4aβ‐ol (= dehydrogeosmin; 1) has been identified as the olfactorily dominant compound in the flower scents of Rebutia marsoneri WERD., Dolichothele longimamma (DC.) BR. et R., and Sulcorebutia kruegeri (CARD.) RITT. The structure of 1, which might be of importance to the pollination biology of such Cactaceae, is based on spectral data and synthesis.
Total Syntheses of (−)‐Conduritol B ((−)‐1L‐Cyclohex‐5‐ene‐1,3/2,4‐tetrol) and of (+)‐Conduritol F((+)‐1D‐Cyclohex‐5‐ene‐1,2,4/3‐tetrol). Determination of the Absolute Configuration of (+)‐Leucanthemito
Authors: Le Drian Claude , Vionnet Jean‐Paul , Vogel Pierre
Published: December 2004

The ‘naked sugar’ (+)‐(1R,2R4R)‐2‐endo‐cyano‐7‐oxabicyclo[2.2.1]hept‐5‐sn‐2‐exo‐yl acetate ((+)‐4) was converted (7 steps, 45% overall) with high stereoselectivity into (−)‐(4R,5S,6R)‐4,5,6‐tris{[(tert‐butyl)dimethylsilyl]oxy}cyclohex‐2‐en‐1‐one ((−)‐11). Reduction of (−)‐1 with NaBH4‐ CeCl3 · 7 H2O, followed by deprotection of the silyl ether moieties gave (+)‐conduritol F ((+)‐1; 47%) whose characteristics were identical to those of natural (+)‐leucanthemitol. Reduction of (−)‐11 with DIBAH, followed by deprotection of the silyl ether moiety led to (−)‐conduritol B ((−)‐3; 51 %).
Synthesis and Complexation of 1,2‐Bis[(monoaza[15]crown‐5)‐N‐yl]glyoxime. Crystal Structure of (1,2‐Bis[(monoaza[15]crown‐5)‐N‐yl]glyoximato)palladium(II)
Authors: Ahsen Vefa , Musluoǧlu Emel , Gürek Ayşegül , Gül Ahmet , Bekâroǧlu Özer , Zehnder Margareta
Published: December 2004

A new vicinal dioxime ligand with two crown‐ether groups, 1,2‐bis[(monoaza[15]crown‐5)‐N‐Yl]‐glyoxime(LH2), has been prepared from cyanogen di‐N‐oxide and monoaza[15]crown‐5. Ni(II), Pd(II), and Pt(IV) complexes of LH2 with or without alkali‐metal ions bound to macrocyclic groups have been isolated. The high affinity of [Pd(LH)2] and [Ni(LH)2] for the K+ ion is observed in solvent extraction experiments. A single‐crystal X‐ray structure confirms the postulated geometry of [Pd(LH)2]‐ The Pd‐atom of the centro‐symmetric molecule has square‐planar PdN4 coordination where Pd–N distances range from 1.978(3) to 1.970(3) Å. The N–Pd–N intraligand angle is 79.9(1)°.
A Variable‐Pressure 2D 1H‐NMR Study of the Mechanism of Trimethyl Phosphate Intermolecular Exchange and cis/trains‐Isomerisation of Tetrachlorobis(trimethyl phosphate)zirconium(IV)
Authors: Frey Urban , Helm Lothar , Merbach André E.
Published: December 2004

In chloroform, [ZrCl4·2(MeO)3PO] exists in both cis‐ and trans‐isomeric forms. Three reactions can be envisaged in the presence of excess (MeO)3PO = L: (1) cis‐[ZrCl4·2L] + *L⇆cis‐[ZrCl4·L*L]+ L; (2) trans‐[ZrCl4·2L] + *L ⇆ trans‐[ZrCl4·L*L] + L; (3) cis‐[ZrCl4·2L]⇆ trans‐[ZrCl4·2L]. To distinguish between these possible reaction pathways, we have used 2D 1H‐NMR spectroscopy. For the first time, variable‐pressure 2D exchange spectra were used for mechanistic assignments. cis/trans‐Isomerisation was found to be the fastest reaction (in CHCl3/CDCl3), with a small acceleration at higher pressure: it is concluded to be an intramolecular process with a slightly contracted six‐coordinate transition state. The intermolecular (MeO)3PO exchange on the cis‐ and trans‐isomer are second‐order processes and are strongly accelerated by increased pressure: Ia mechanisms are suggested without ruling out limiting A mechanisms.
Blockcopolymers in microemulsions differential heats of solution and shift of the percolation temperature in W/O microemulsions
Authors: Eicke Hans‐Friedrich , Hilfiker Rolf , Xu Gu
Published: December 2004

Solutions of blockcopolymers (POE‐b‐PI‐b‐POE) in fluids of interacting aqueous nanodroplets (W/O microemulsions) are studied. The interaction strength between the (pseudo) two components is measured by the shift of the percolation temperature relative to that of the pure microemulsion. A quantitative measure of the interaction, the differential heat of solution, is thermodynamically related to the slopes of the equilibrium temperature of the system with varying monomeric nanodroplet concentration and the experimental percolation line in the presence of copolymer.
Cycloalkylations of N‐(ω‐Halogenoalkyl)‐substituted Macrocyclic Imides
Authors: Ognyanov Vassil I. , Hesse Manfred
Published: December 2004

With ω‐halogenoalkyl isocyanates, 2‐oxocyclododecane‐l‐carbonitrile is transformed under ring enlargement to 1‐(ω‐halogenoalkyl)‐2,14‐dioxo‐1‐azacyclotetradecane‐3‐carbonitriles. In the presence of base, these products undergo O‐ or C‐alkylation leading to bicyclic compounds. The C‐alkylation product 7 undergoes solvolysis to form a sixteen‐membered ring compound.
Synthesis of Aristotelia‐type alkaloids. Part V. Biomimetic synthesis of (±)‐aristomakine and (±)‐aristomakinine
Authors: Burkard Stefan , Borsehberg Hans‐Jürg
Published: December 2004

Biomimetic syntheses of racemic aristomakinine ((±)‐3) and aristomakine ((±)‐4), an unusual indole alkaloid bearing an N‐isopropyl group, are described. The key step is a Grob‐type fragmentation of anti‐15‐aristotelinyl methanesulfonate ((±)‐2) to the intermediate iminium ion I which, upon subsequent hydrolysis, furnished aristomakinine ((±)‐3). On the other hand, the same intermediate could be reduced in situ to aristomakine ((±)‐4). The controversial relative configurations of the two alkaloids have been firmly established by means of NOE difference experiments.
Effets de substituant, d'hétéroatome et de solvant sur les cinétiques de décoloration thermique et les spectres d'absorption de photomérocyanines en série spiro[indoline‐oxazine]
Authors: Pottier Eliane , Dubest Roger , Guglielmetti Robert , Tardieu Pascale , Kellmann Arlette , Tfibel Francis , Levoir Patrick , Aubard Jean
Published: December 2004

Substituent, Heteroatom, and Solvent Effects on the Thermal‐Bleaching Kinetics and Absorption Spectra of Photomerocyanines Issued from Spiro[indoline‐oxazines]

Quantitative information useful for the development of new photochromic systems is obtained from the study of heteroatom and substituent effects on the thermal‐bleaching kinetics and the absorption spectra of the photomerocyanines issued from spiro[indoline‐oxazines]. The effect on photochromic properties of the presence of N‐atoms either in the dimethine bridge or in the aromatic rings has been investigated through the comparison of spiro[indoline‐naphthopyrans] C with spiro[indoline‐naphthoxazines] A and with spiro[indoline‐quinolinoxazines] B. Besides the occurrence of biexponential thermal‐bleaching kinetics in non‐polar solvents is observed: a tentative explanation for this observation is given which involves the formation, in either sequential or parallel steps, of energetically distinct stereoisomers of the opened form.
Synthesis of 8‐Aza‐1,3‐dideaza‐2′‐deoxyadenosine and 5,6‐Disubstituted Benzotriazole 2′‐Deoxy‐β‐D‐Ribofuranosides via Nucleobase‐Anion Glycosylation
Authors: Kazimierczuk Zygmunt , Seela Frank
Published: December 2004

The synthesis of 8‐aza‐1,3‐dideaza‐2′‐deoxyadenosine (3a) as well as of 4‐ and 5,6‐substituted benzotriazole 2′‐deoxy‐β‐D‐ribonucleosides is described (Schemes 1–3). Glycosylation of benzotriazole anions is stereoselective in all cases (exclusive β‐D‐anomer formation), but regioisomeric N1, N2, and N3‐(2′‐deoxyribofuranosides) are formed. The distribution of the regioisomers is controlled by the nucleobase substituents. Anomeric configuration as well as the position of glycosylation are determined by UV and NMR in combination with 1D‐NOE‐difference spectroscopy. The unprotonated forms of 4‐aminobenzotriazoic 2′‐deoxy‐β‐D‐ribofuranosides 3a–c exhibit strong fluorescence.
Über Pterin‐Chemie 87. Mitteilung. Regiospezifische Synthese von (Polyhydroxypropyl)‐pterinen: Herstellung von D‐Anapterin und L‐Primapterin
Authors: Viscontini Max , Bosshard René
Published: December 2004

Regiospecific Synthesis of (Polyhydroxypropyl)‐pterins: Synthesis of D‐Anapterin and L‐Primapterin

Condensation of 2,5,6‐triaminopyrimidin‐4‐one(5) with the semicarbazone of pentoses proceeds regiospecifically with formation of 7‐(polyhydroxypropyl)pterins. D‐Anapterin (=7‐(D‐erythro‐1′,2′,3′‐trihydroxypropyl)pterin; D‐3) was obtained in 40% yield, and L‐primapterin (=7‐(L‐erythro‐1′,2′‐dihydroxypropyl)pterin; L‐4)in 10% yield.
Potential antipsychotic agents. Part 8. Antidopaminergic properties of a potent series of 5‐substituted (−)‐(S)‐N‐[(1‐ethylpyrrolidin‐2‐yl)methyl]‐2,3‐dimethoxybcnzaimides. Synthesis via common lithio intermediates
Authors: Högberg Thomas , Ström Peter , Hall Håkan , Ögren Sven Ove
Published: December 2004

A series of 5‐substituted (−)‐(S)‐N‐[(1‐ethylpyrrolidin‐2‐yl)methyl]‐2,3‐diniethoxybenzanndes were made by reaction of the corresponding benzoyl chlorides with (S)‐1‐ethylpyrrolidine‐2‐methylaruine (→ 14–16, 18–21). The acids required were prepared in a regiospecific manner from 5‐bromo‐2,3‐dimethoxybenzoic acid which was protected as dihydrooxazole (→ 4–8), metalated, reacted with various electrophiles (MeI, EtI, BuBr, CC13CCl3 or MeSSMe), and hydrolyzed (→9–13). Alternatively, (‐)‐(S)‐5‐bromo‐N‐[(1‐ethylpyrrolidin‐2‐yl)methyl]‐2,3‐di‐methoxybenzamide was treated with KH followed by BuLi and an electrophile (I2 or Me3SiCl) to give the 5‐iodo and 5‐(trimethylsilyl) derivatives 17 and 22, respectively. All 5‐substituted amides were highly potent inhibitors of [3H]spiperone binding in rat striatal membranes with IC50 values of 0.5 to 5 nM (Table 3). Thus, a relatively large steric bulk can be accomodated in the position para to the 2‐MeO group. This work also supports the notion that a positive as well as negative electrostatic potential can be located in this position. A selected number of derivatives were also investigated in vivo and found to inhibit apomorphine‐induced behavioural responses in the same dose range as haloperidol and raclopride (Table 4). This new group of benzamides is suitable for investigations of dopamine D‐2 receptors in labelled or unlabelled form.
Structure Determination of a New Spirobicyclic Triterpenoid from Iris foetidissima
Authors: Marner Franz‐Josef , Karimi‐Nejad Yasmin , Jaenicke Lothar , Wray Victor
Published: December 2004

The novel iridal 10 has been isolated from rhizome extracts of Iris foetidissima. Its structure was established by spectroscopic methods and oxidative degradation. Final proof of the spirobicyclic nature of the compound – a new feature in the triterpenoid field – was afforded by the correlations observed in the 2D‐HMBC‐ (1H‐detected multiple‐bond heteronuclear multiple‐quantum coherence) spectrum. The possible biogenesis of this unusual compound is discussed.
Further Studies on the Biosynthesis of Tabtoxin (Wildfire Toxin): Incorporation of [2,3‐13C2]Pyruvate into the β‐Lactam Moiety
Authors: Roth Patricia , Hädener Alfons , Tamm Christoph
Published: December 2004

[2,3‐13C2]Pyruvic acid (7) was synthesized and administered to cultures of Pseudomonas syringae pv tabaci. C(2) and C(3) of 7 were incorporated as an intact unit into the β‐lactam moiety of tabtoxin (1). The result suggests that the biosynthesis of 1 is proceeding in part along the lysine pathway. The labelling pattern in 1 and an incorporation experiment with α,α′‐dideuterated (±)‐2,6‐diaminopimelic acid (19) indicate that the branching in the biosynthesis of 1 occurs before lysine is formed.
N‐Acylureas in Peptide Synthesis: An X‐Ray Diffraction and IR‐Absorption Study
Authors: Toniolo Claudio , Valle Giovanni , Crisma Marco , Moretto Vittorio , Izdebski Jan , Pelka Jacek , Schneider Conrad H.
Published: December 2004

An X‐ray diffraction analysts of two N‐acyl derivatives of symmetrical dialkylureas, N‐[Nα‐(benzyloxycarbonyl)‐L‐valyl] ‐N, N′‐diisopropylurea (1) and N‐{Nα(tert‐butyloxy)carbonyl ‐L‐valyl}‐N‐N′‐dicyclohexylurea (2), and one N‐acyl derivative of an unsymmetrical N‐N′‐dialkylurea, N‐[Nα‐(benzyloxycarbonyl)‐L‐valyl] ‐N′‐(tert‐butyl)‐N‐ethylurea (3), has been performed. It was established that it is the least hindered O‐acylisourca N‐atom that attacks intramolecularly the carbonyl group of the Nα‐protected amino acid activated by the unsymmetrical carbodiimide to form the major rearrangement product. The occurrence and nature of intra‐ and intermolecularly Hbonded forms of the N‐acylureas in the crystal state were also assessed. It was also shown that soluble N‐acylureas may compete with intermolecular (peptide)NH…OC(peptide) H‐bonds in CH2Cl2.
Pteridine. Teil XCIV. Synthese und Eigenschaften von 5,6‐Dihydro‐6‐(1,2,3‐trihydroxypropyl)pteridinen: Kovalente intramolekulare Addukte
Authors: Soyka Rainer , Pfleiderer Wolfgang , Prewo Roland
Published: December 2004

Pteridines: Synthesis and Characteristics of 5,6‐Dihydro‐6‐(1,2,3‐trihydroxypropyl)pteridines: Covalent Intramolecular Adducts

Various 5,6‐diaminopyrimidines (1, 15, 24, 33) were condensed with the phenylhydrazones of L‐(2) and D‐arabinose (3) in acidic medium under N2 to give formal 5,6‐dihydro‐6‐(1,2,3‐trihydroxypropyl)pteridines (see, e.g., 4 and 5), the latter turned out to exist preferentially as intramolecular adducts, the hexahydropyrano‐[3,2‐g]pteridines 6, 7, 16, 17, 25, 26, and 34, formed subsequently by addition of the terminal OH group of the side‐chain to the C(7)N(8) bond of the pteridine moiety. Spectroscopically, the isomeric hexahydrofuro‐[3,2‐g]pteridines 10,11,18,19, and 35 were also detected as minor components in the equilibrium mixtures. In the 4‐amino‐2‐(methylthio)pteridine series, crystallization of 6 and 7 led to the stereochemically pure (3S,4R,4aR, 10aS)‐6‐amino‐3,4,4a,5,10,10a‐hexahydro‐8‐(methylthio)‐2H‐pyrano[3,2‐g]pteridine‐3,4‐diol (8) and its corresponding enantiomer 9, respectively Structure 8 was proven by X‐ray analysis. Acylation of the hexahydropyrano[3,2‐g]pteridines yielded the more stable tri‐, tetra‐, and pentaacetyl derivatives 12–14, 20–23, 27–32, and 37–39 which were characterized and of which the absolute and relative configurations were determined (1H‐ and 13C–NMR and UV spectra, chiroptical measurements, elemental analyses).
Stereoselective Coordination to Chiral Matrices. Cobalt(III). Chemistry of Simple Facially Coordinating Chiral Triamines
Authors: Comba Peter , Hörmann Aldo , Martin Lisandra L. , Zipper Luc
Published: December 2004

Chiral ligands coordinated to metal ions exert a selectivity towards the additional coordination of racemic substrates. Experimentally determined equilibria distributions of [Co(L3)2]3+ and [Co(L3)(L2)(X)]n+ are compared with calculated data based on strain‐energy minimization (L3: trap = propane‐1,2,3‐triamine; 1,2,4‐trab = butane‐1,2,4‐triamine; 1,2,3‐trab = butane‐1,2,3‐triamine; 1,3,4‐trpe = pentane‐1,3,4‐triamine; 1,3,4‐tmeb = 2‐methylbutane‐1,3,4‐triamine; 1,2,4‐trpe = pentane‐1,2,4‐triamine; L2: en = ethane‐1,2‐diamine; pn = propane‐1,2‐diamine; X: NH3, OH2, OH−). Equilibration of Co(III) complexes was achieved by oxygenation of aqueous solutions of Co(II) salts in presence of the ligands. Quantitative isomer distribution was investigated with HPLC, and quantitative analysis of the enantiomeric excess (ee) of the racemic substrate (present in a two‐fold excess) was studied, after chromatographical recovery, by 1H‐NMR analysis of its Mosher‐acid derivative. There is good agreement between calculated and experimental data. Systems with L = 1,2,4‐trab are, as expected, relatively poorly discriminating (ee([Co(1,2,4‐trab)2]3+) ∼ 5%; ee([Co(1,2,4‐trab)(pn)(X)]n+) ∼ 10%). Calculations indicate that Me substitution of the ligand backbone of 1,2,4‐trab (and trap) leads to an increased enantioselectivity (with practically constant isomer selectivity), and at the optimum site for substitution ∼ 90% ee is predicted.
A Short Synthesis of (±)‐Muscone
Authors: Rautenstrauch Valentin , Snowden Roger L. , Linder Simon M.
Published: December 2004

(±)‐Muscone ((±)‐1) has been synthesised in three steps from 2‐(2′‐methylprop‐2′‐enyl)cyclododecan‐1‐one (2). The synthesis involves two key transformations: a Lewis‐acid‐mediated intramolecular ene reaction (2→3) and the β‐cleavage of the bicyclic potassium alkoxide 3a′ to the macrocyclic enone (Z)‐11.
Analogues of Sialic Acids as Potential Sialidase Inhibitors Synthesis of 2‐C‐Hydroxymethyl Derivatives of N‐Acetyl‐6‐amino‐2,6‐dideoxy‐neuraminic Acid
Authors: Bernet Bruno , Murty A. R. C. Bulusu , Vasella Andrea
Published: December 2004

The intramolecular cycloaddition of the previously described azidoalkene 16, the related diacetates 7 and 13, and the monoacetate 8 led diastereoselectivity to the (2R)‐ and (2S)‐configurated hydropyridotriazoles 17, 9 and 11, 14 and 15, and 10 and 12, respectively (Scheme 1). Thermolysis of 16 gave also the aziridine 18, its proportion increasing with reaction time. The diastereoselectivity of the cycloaddition‐ is rationalized on the basis of steric interactions and of Hbonds in the transition state. Photolysis in benzene partially transformed 9 into the aziridine 19. Treatment of 9 with aqueous AcOH gave 19 and the tetrahydrofuran 20, with AcOH in benzene 20 and the triacetate 23, and with aqueous H2SO4 in THF, the primary alcohol 22 (room temperature) or 19 and 22 (0°). Deacetylation of 9 followed by reaction with pyridinium hydrochloride led to the tetrahydrofuran 21 and the chloride 24 (Scheme 2). The diacetate 22 and the triacetate 23 gave the tripl 25 which was deprotected to 26. Reduction of the keto‐aziridine 18 (NaBH4) gave the alcohols 27 and 29 which were acetylated to give 28 and 19, respectively (Scheme 3). Treatment of the aziridine 28 with AcOH in benzene followed by deacetylation gave 30 and hence 31. AcOH in benzene transformed the triazoline 15 first into the aziridine 32 and hence into 33, which was deprotected to give the triol 34 and hence 35. The 2‐(hydroxymethyl)piperidines 26, 31, and 35 inhibited Vibrio cholerae sialidase with K1 = 3.8 · 10−2 M, 3.4 · 10−3 M, and 1.5 · 10−4 M, respectively. The conformation of the glycerol side chain of these compounds and of the unbranched piperidines 2–4 deviates from the one of Neu5Ac (and Neu2en5Ac). This finding is rationalized by an H‐bond between OHC(8) and NHC(6). The conformations and the K1 values of 26, 31, and 35 correlate with each other.
Synthese der (3S,4R,3′S,4′R)‐ und (3S,4S,3′S,4′S)Crustaxanthine sowie weiterer Verbindungen mit 3,4‐Dihydroxy‐β‐Endgruppen
Authors: Buschor Daniel Jacques , Eugster Conrad Hans
Published: December 2004

Synthesis of (3S,4R,3′S,4′R)‐ and (3S,4S,3′S,4′S)‐Crustaxanthins and Further Compounds with 3,4‐Dihydroxy β‐End‐groups

Starting from 3, the enantiomerically pure title compounds were synthesized in eight steps. Spectra and HPLC systems are presented that allow a distinction between these isomers.
Photodissociation of Halonaphthalenes in Solution: Comparative Photochemistry of 1‐Iodo‐, 1‐Bromo‐, and 1‐Chloronaphthalenes
Authors: Haselbach Edwin , Rohner Yves , Suppan Paul
Published: December 2004

Fluorescence measurements have been used to follow the build‐up of photoproducts during the direct and benzophenone‐sensitized irradiation of the title compounds 1‐IN, 1‐BrN, and 1‐ClN (HN = naphthalene). Compounds 1‐IN and 1‐BrN react by homolytic dissociation through their lowest triplet and singlet excited states, respectively. Compound 1‐ClN does not undergo C–Cl bond fission, except through electron transfer in the presence of an amine A,

equation image

In the absence of this electron transfer, 1‐ClN reacts only through substitution and oxidation processes.
The Reaction of Singlet Oxygen with Adamantylideneadamantane Mediated by Rose Bengal
Authors: Jefford Charles W. , Estrada Manuel Jimenez , Barchietto Giacomo , Berclaz Théo , Geoffroy Michel
Published: December 2004

The photo‐oxygenation of adamantylideneadamantane (1) on siliceous supports using admixed granules of ion‐exchange resin fixed to methylene blue (MB) and rose bengal (RB) gave exclusively the corresponding dioxetane derivative 2 for the former sensitizer, while the latter gave 2 and traces of the epoxide 3. RB and the charge‐transfer complex produced from N‐ethylcarbazole and 2,4,5,6‐tetranitrofluoren‐9‐one both reacted with chemically generated singlet oxygen to give superoxide radical anion. Trapping of the latter with 5,5‐dimethyl‐1‐pyrroline 1‐oxide gave an adduct exhibiting a characteristic ESR spectrum. The treatment of 1 in MeOH with 30% aqueous H2O2 for 22 h at 60° gave 3 in 100% yield. Repetition of this experiment in the presence of 2,6‐di(tert‐butyl)‐p‐cresol caused no significant change. These results indicate that singlet oxygen reacts with 1, in the presence of RB, by two different processes. The first leads to dioxetane formation. The second process involves conversion of singlet oxygen by RB to superoxide radical anion which subsequently gives H2O2 so producing epoxide 3 from 1.
Synthese neuer Heptafulvene, Röntgenstrukturanalyse von ‘8,8‐(1′,4′‐Dioxotetramethylen)heptafulven’(2‐(Cyclohepta‐2,4,6‐trien‐1‐yliden)cyclopentan‐1,3‐dion)
Authors: Bönzli Peter , Neuenschwander Markus , Engel Peter
Published: December 2004

Synthesis of New Heptafulvenes; X‐Ray Analysis of ‘8,8‐(1′,4′‐Dioxotetramethylene)heptafulvene’ (2‐(Cyclohepta‐2,4,6‐trien‐1‐ylidene)cyclopentane‐1,3‐dione)

Experimental procedures for the synthesis of heptafulvene (3a), 8,8‐tetramethylene heptafulvene (3c) and ‘8,8‐(1′,4′‐dioxotetramethylene) heptafulvene’ (2‐(cyclohepta‐2,4,6‐trien‐1‐ylidene)‐cyclopentane‐1,3‐dion; 3d) are described. The most important sequences include a low‐temperature reaction of tropylium salts with lithium or Grignard carbenoids (Scheme 1) to give 3a and 3b as well as hydride abstraction from substituted cycloheptatrienes followed by deprotonation to give 3c and 3d. Limitations of these sequences are discussed. Two other heptafulvenes 3h and 3i are available by silylation of heptafulvenolates according to well‐known procedures. NMR‐Spectroscopic evidence as well as an X‐ray analysis of 3d are presented. Compound 3d is a relatively polar heptafulvene with a planarised seven‐membered ring as well as a partly delocalized π system.
Glycosylidene Carbenes. Part 2. Synthesis of O‐Aryl Glycosides
Authors: Briner Karin , Vasella Andrea
Published: December 2004

Phenol, 4‐methoxyphenol, 4‐nitrophenol, methyl orsellinate (1), and 2,6‐di(tert‐butyl)‐4‐methylphenol (BHT; 2) have been glycosylated by thermal reaction (20–60°) with various glycosylidene‐derived diazirines.

4‐Methoxyphenol reacted with the D‐glucosylidene‐derived diazirine 3 to give O‐glucosides (4 and 5, 69%, 3:1) and C‐glucosides (6 and 7, 16%, 1:1). Similarly, phenol yielded O‐glucosides (10 and 11, 70%, 4:1) and C‐glucosides (12 and 13, 13%, 1:1). 4‐Nitrophenol gave only O‐glycosides, 3 leading to 14 and 15 (75%, 3:2; Scheme 1), and the D‐galactosylidene‐derived diazirine 17 to 22 and 23 (52% (from 16), 65:35; Scheme 2). The reaction of phenol with 17 yielded 58% (from 16) of the O‐galactosides 18 and 19 (4:1) and 14% of the C‐galactosides 20 and 21 (1:1). From the D‐mannosylidene‐derived diazirine 25, we predominantly obtained the α‐D‐configurated 26 (38 % from 24). These results are interpreted by assuming that an intermediate (presumably a glycosylidene carbene) first deprotonates the phenol to generate an ion pair which combines to give O‐ and ‐ with electron‐rich phenolates ‐ also C‐glycosides. A competition experiment of 3 with 4‐nitro‐ and 4‐methoxyphenol gave the products from the former (14 and 15) and the latter phenol (4‐7) in almost equal amounts. Differences in the kinetic acidity of OH groups, however, may form the basis of a regioselective glycosidation, as evidenced by the reaction of 3 with methyl orsellinate (1) yielding exclusively the 4‐O‐monoglycosylated products 27 and 28 (78%, 85:15), although diglycosidation is possible (27→ 31 and 32; 67%, 4:3; Scheme 3). Steric hindrance does not affect this type of glycosidation; 3 reacted with the hindered BHT (2) to afford 33 and 34 (81 %, 4:1). The predominant formation of 1,2‐trans ‐configurated O‐aryl glycosides is rationalized by a neighbouring‐group participation of the 2‐benzyloxy group.
Conversion of Light into Electricity with Trinuclear Ruthenium Complexes Adsorbed on Textured TiO2 Films
Authors: Nazeeruddin Mohammad K. , Liska Paul , Moser Jacques , Vlachopoulos Nick , Grätzel Michael
Published: December 2004

A series of CN‐bridged trinuclear Ru complexes of the general structure [RuL2(μ‐(CN)Ru(CN)L2′)2] where L is 2,2′‐bipyridine‐4,4′‐dicarboxylic acid and L′ is 2,2′‐bipyridine (1)2,2′‐bipyridine‐4,4′‐dicarboxylic acid (2), 4,4′‐dimethyl‐2,2′‐bipyridine (3), 4,4′‐diphenyl‐2,2′‐bipyridine (4), 1,10‐phenanthroline (5), and bathophenanthrolinedisulfonic acid (6) have been synthesized, and their spectral and electrochemical properties investigated. The two carboxylic functions on the 2,2′‐bipyridine ligand L serve as interlocking groups through which the dye is attached at the surface of TiO2 films having a specific surface texture. The role of these interlocking groups is to provide strong electronic coupling between the π* orbital of the 2,2′‐bipyridine and the 3d‐wave‐function manifold of the conduction band of the TiO2, allowing the charge injection to proceed at quantum yields close to 100 %. The charge injection and recombination dynamics have been studied with colloidal TiO2, using laser photolysis technique in conjunction with time‐resolved optical spectroscopy. Photocurrent action spectra obtained from photo‐electrochemical experiments with these trinuclear complexes cover a very broad range in the visible, making them attractive candidates for solar light harvesting. Monochromatic incident photon‐to‐current conversion efficiencies are strikingly high exceeding 80% in some cases. Performance characteristics of regenerative cells operating with these trinuclear complexes and ethanolic triiodide/iodide redox electrolyte have been investigated. Optimal results were obtained with complex 1 which gave a fill factor of 75 % and a power conversion efficiency of 11.3% at 520 nm.
Kinetic Isotope Effects and exo/endo‐Face Selectivity in the Unimolecular Dehydrogenation of Norborneol Alkoxides in the Gas Phase
Authors: Dreyer Uwe , Sülzle Detlev , Schröder Detlel , Schwarz Helmut
Published: December 2004

The study of specifically labeled alkoxides generated in the gas phase by deprotonation of epimeric norbernols demonstrates, beyond any doubt, that ‘solvated’ hydride ions are formed as intermediates in the course of enolate formation. Kinetic isotope effects and exo/endo‐face selectivities for the dehydrogenation are discussed.
Coenzyme F430 from Methanogenic Bacteria: Oxidation of F430 Pentamethyl Ester to the Ni(III) Form
Authors: Jaun Bernhard
Published: December 2004

F430M, the pentamethyl ester of coenzyme F430, can be oxidized reversibly by one electron. The oxidation potential has been determined, and the electrolytically prepared oxidation product was characterized by its UV/VIS and ESR spectrum. The strongly anisotropic and nearly axial ESR spectrum is consistent with a S = ½ species with the unpaired‐electron spin density predominantly in a d‐type orbital of the central nickel ion. The properties of Ni(III)F430M are discussed in the context of two hypothetical mechanisms for the catalytic role of coenzyme F430 in methyl coenzyme M reductase, which catalyses the last step of methane formation in methanogenic bacteria.
New Synthetic Route to Polyhedral Organylsilsesquioxanes
Authors: Herren Daniel , Bürgy Heribert , Calzaferri Gion
Published: December 2004

Hydrosilation of methylenecyclohexane and hex‐1‐ene by octa(hydridosilsesquioxane) catalysed by hexachloroplatinic acid is a new route to polyhedral organylsilsesquioxanes. Quantitative yield of octa(cyclohexylmethylsilsesquioxane) is reached. This reaction opens a vast field of yet unknown polyhedral silsesquioxanes.
Rogiolenyne A, B, and C: The First Branched Marine C15 Acetogenins. Isolation from the Red Seaweed Laurencia microcladia or the Sponge Spongia zimocca of II Rogiolo
Authors: Guella Graziano , Pietra Francesco
Published: December 2004

It is shown here that the red seaweed Laurencia microcladia, collected off the torrent II Rogiolo, south of Livorno, contains rogiolenyne A (= (−)‐(1R*,2S*,3R*,5S*,7S*)‐2‐(bromomethyl)‐5‐[(Z)‐1‐chlorohex‐3‐en‐5‐ynyl]‐3‐ethyl‐4,8‐dioxabicyclo[5.1.0]octane; (−)‐1) while the sponge Spongia zimocca, which grows in the same small area, contains rogiolenyne B (= (−)‐(2R*3R*,4R*,5R*,7S*)‐3‐(bromomethyl)‐5‐chloro‐7‐[(Z)‐1‐chlorohex‐3‐en‐5‐ynyl]‐2‐ethyloxepan‐4‐ol; (−)‐4a) and its acetate, rogiolenyne C((−)‐4b). These structures, which are based on extensive NMR and MS data and on chemical transformation, are the first examples of branched marine C15 acetogenins. Biogenesis of (−)‐1 in L. microcladia is thought to involve C(12) extrusion form a C15 linear tetraen‐1‐yne precursor via H+‐induced cyclopropane ring closure, followed by Br+‐induced cyclopropane ring opening, aided by C–O− attack (Scheme 2). It is also proposed that transfer of (−)‐1 to S. zimocca is followed by epoxide ring opening by Cl− to give (−)‐4a and acetylation to give (−)‐4b.
Generation and Trapping of Cyclopropenes from 2‐Alkoxy‐1,1‐dichlorocyclopropanes
Authors: Müller Paul , Pautex Nicole
Published: December 2004

In presence of crown ether, 2‐alkoxy‐1,1‐dichlorocyclopropanes react with t‐BuOK/THF preferentially via ring opening to 2‐chloroalk‐2‐en‐1‐ones and alkynones or to chlorocyclopropenes. The latter may be intercepted with 1,3‐diphenylisobenzofuran, but in the absence of trapping agent, the rearrangement to vinylcarbenes does not occur.
Stereoselective Synthesis of Indazole 2′‐Deoxy‐β‐D‐ribonucleosides: Glycosylation of the Nucleobase Anion
Authors: Seela Frank , Bourgeois Werner
Published: December 2004

The glycosylation of indazolyl anions derived from 4a, b with 2‐deoxy‐3,5‐bis‐O‐(4‐methylbenzoyl)‐α‐D‐erythro‐pentofuranosyl chloride (5) is described. The reaction was Stereoselective – exclusive β‐D‐anomer formation – but regioisomeric N1‐ and N2‐(2′‐deoxy‐β‐D‐ribofuranosides) (i.e. 6a and 7a, resp., and 6b and 7b, resp.) were formed in about equal amounts. They were deprotected to yield 8a, b and 9a, b. Compound 1, related to 2′‐deoxyadenosine (3), and its regioisomer 2 were obtained from 8b and 9b, respectively, by catalytic hydrogenation. The anomeric configuration as well as the position of glycosylation were determined by 1D NOE‐difference spectroscopy. The first protonation site of 1 and 2 was found to be the NH2 group. The N‐glycosylic bond of 1H‐indazole N1‐(2′‐deoxyribofuranosides) is more stable than that of the parent purine nucleosides. Compound 1 is no substrate for adenosine deaminase.
On the Regioselectivity Control in the Palladium‐Catalyzed Hydro‐alkoxycarbonylation of α,β‐Unsaturated Esters
Authors: Consiglio Giambattista , Nefkens Sylvia C. A. , Pisano Carmelina , Wenzinger Fritz
Published: December 2004

The regioselectivity of the hydro‐alkoxycarbonylation of methyl acrylate, methacrylate, and crotonate catalyzed by [PdCl2L2] complexes (L = phosphine ligands) can be largely controlled by variation of the ligands. PPh3, promotes preferential carbonylation at the α‐position, whereas with [(2,2‐dimethyl‐1,3‐dioxolane‐4,5‐diyl)bis‐(methylene)]bis[diphenylphosphine] as ligand, the β‐position is overwhelmingly carbonylated.
Synthesis of 4‐{{[(Isopropyloxy)methylphosphoryloxy]imino}methyl}‐1‐methylpyridinium Iodide and Its Characterisation
Authors: Portmann Rudolf , Niederhaiiser Andreas , Hofmann Werner , Frey Alfred , Stoeckli‐Evans Helen
Published: December 2004

Oximes are used in the therapy of organophosphate poisoning. They form an interaction product with the organophosphate which is claimed to be more toxic than the organophosphate itself. We have synthesized one of these compounds which would be formed by the reaction of pyridine‐4‐carbaldehyde oxime methiodide with sarin (GB). Thus, reaction of oxime 1 with sarin chloridate (2), yielded 4‐{{[(isopropyloxy)methylphosphoryloxy]‐imino}methyl}‐1‐methylpyridinium iodide (4) which was characterized by NMR spectroscopy and X‐ray crystallography.
Synthesis of a Phosphonic Acid Analogue of N‐Acetyl‐2,3‐didehydro‐2‐deoxyneuraminic Acid, an Inhibitor of Vibrio cholerae Sialidase
Authors: Vasella Andrea , Wyler René
Published: December 2004

The synthesis of the phospha analogue 10 of DANA (2) is described. Bromo‐hydroxylation of the known 11 (→ 12 and 13) followed by treatment of the major bromohydrin 13 with 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) gave the oxirane 14 (Scheme 1). Depending on the solvent, TiBr4 transformed 14 into 16 or into a 15/16 mixture. Reductive debromination of 16 (→ 17), followed by benzylation provided 18. Oxidattve decarboxylation (Pb(OAc)4) of the acid, obtained by saponification of 18, yielded the anomeric acetates 19 and 20. While 19 was inert under the conditions of phosphonoylation, the more reactive imidate 22, obtained together with 23 from 19/20 via 21 (Scheme 2), gave a mixture of the phosphonates 24/25 and the bicyclic acetal 26. Debenzylation of 24/25 and acetylation led to the acetoxyphosphonates 27/28. Since β‐elimination of AcOH from 27/28 proved difficult, the bromide 34 was prepared from 27/28 by photobromination and subjected to reductive elimination with Zn/Cu (→ 35; Scheme 3). This two‐step sequence was first investigated using the model compounds 30 and 31. Transesterification of 35, followed by deacetylation gave 10, which is a strong inhibitor of the Vibrio Cholerae sialidase.
On the First Marine Stigmastane Sterols and Sterones Having a 24,25‐Double Bond. Isolation from the Sponge Stelletta sp. of Deep Coral Sea
Authors: Guerriero Antonio , Debitus Cécile , Pietra Francesco
Published: December 2004

The sponge Stelletta sp. (Astrophorida, Stellettidae), collected at −700 m in the Coral Sea, is shown to contain sterones and sterols of the stigmastane type with a C(24)C(25) bond for which there is no precedent in the sea. Structure elucidation of the second abundant of these steroids, stigmasta‐4,24(25)‐dien‐3‐one ((+)‐1), is based on 1D and 2D NMR spectra and chemical transformation to acetate (−)‐5. Stigmasta‐4,24(25)‐diene‐3,6‐dione ((−)‐3), present in trace amounts in the sponge, was obtained in sufficient quantity for NMR study by oxidation of the also present, inseparable, and abundant 4:1 mixture of stigmasta‐5,24(25)‐dien‐3β‐ol (6) and its 5,6‐dihydro derivative 7 (Scheme 1). This oxidation also afforded the ketone analogues (+)‐8 and (+)‐9, which could be separated, thus making structure elucidation possible. The 6β‐hydroxystigmasta‐4,24(25)‐dien‐3‐one ((+)‐4), also present in trace amounts in the sponge, was obtained in sufficient amount for NMR study, together with its C(6) epimer (+)‐11, by hydroperoxidation of (+)‐8 followed by deoxygenation (Scheme 2). The last trace steroid of the sponge, stigmasta‐4,6,24(25)‐trien‐3‐one ((−)‐2), was structurally elucidated using limited NMR data and comparison with the other stigmastanes. These stigmastanes, as the only steroids of this sponge, are likely to function as stabilizers of its cell walls; their phytosteroid structure, for a sponge which lives in the dark of deep waters, suggest origin through a complex food chain, possibly followed by bioelaboration in the sponge.
Transformations in the Isoxazole Series: Synthesis of Substituted 2‐Aminothiazoles
Authors: Pascual Alfons
Published: December 2004

Substitued N‐(isoxazol‐4‐yl)thioureas 1 undergo a transformation in the presence of hexacarbonylmolybdenum and acid to yield functionalized thiazoles 3 in a one‐pot reaction. In a few cases, 1,4,5‐trisubstituted dihydroimidazolethiones 4 are also isolated as side products. Mechanistic considerations are outlined and scope and limitations of this new methodology discussed.
4H‐Chromenone Glycosides from Eranthis hyemalis (L.) SALISBURY
Authors: Kopp Brigitte , Kubelka Erika , Reich Christian , Robien Wolfgang , Kubelka Wolfgang
Published: December 2004

Investigation of the tubers of Eranthis hyemalis (Ranunculaceae) afforded six chromenone glycosides. Their structures have been elucidated mainly by spectroscopic (FAB‐MS, 2D‐NMR techniques) and chemical methods (acidic and enzymatic hydrolysis) as 9‐{[(β‐D‐glucopyranosyl)oxy]methyl}‐8,11‐dihydro‐5‐hydroxy‐2‐methyl‐4H‐pyrano[2,3‐g][1]benzoxepin‐4‐one (1), 9‐{[(β‐D‐gentiobiosyl)oxy]methyl}‐8,11‐dihydro‐5‐hydroxy‐2‐methyl‐4H‐pyrano[2,3‐g][1]benzoxepin‐4‐one(2), 9‐{[(β‐D‐glucopyranosvl)oxy]melhyl}‐8,11‐dihydro‐5‐hydroxy‐2‐(hydroxy‐methyl)‐4H‐pyrano[2,3‐g][1]benzoxepin‐4‐one(3), 8‐{(2E)‐4‐[(β‐D‐glucopyranosyl)oxy]‐3‐methylbut‐2‐enyl}‐5,7‐dihydroxy‐2‐methyl‐4H‐1‐benzopyran‐4‐one (4), 8‐{(2E)‐4‐[(β‐D‐glucopyranosyi)oxy]‐3‐methylbut‐2‐enyl}‐5,7‐dihydroxy‐2‐(hydroxymethyl)‐4H‐1‐benzopyran‐4‐one (5), and 7‐{[(β‐D‐glucopyranosy1)oxy]methyl}‐2,3‐dihydro‐2‐(l‐hydroxy‐1‐methylethyl)‐4‐methoxy‐5H‐furo[3,2‐g][1]benzopyran‐5‐one (6). Compound 2 exhibited negative inotropic activity.
Lithium‐Salt Effects in Peptide Synthesis. Part I. Conditions for the Use of Lithium‐Salts in Coupling Reactions
Authors: Thaler Adrian , Seebach Dieter , Cardinaux Francis
Published: December 2004

The influence of Li‐salts on the course of peptide‐coupling reactions was investigated. As a model for segment couplings, Ac‐Phe‐OH was coupled to HCl·H‐Ala‐OMe using the mixed anhydride, DCC1, DCCl/HOBt, BOP‐Castro and TBTU‐Knorr methods. As a model for stepwise synthesis Z‐Phe‐OH was coupled with HCl·Ala‐O(t‐Bu), using symmetrical anhydrides and active esters. The effects of salt additives such as LiCl, LiBr, LiC104, and ZnCl2 on yields, side‐product formation, racemisation, and reaction rates are reported.
On the Methyl‐Transfer Reaction in Crystalline Methyl 2‐(Methylthio)benzenesulfonate: a Thermally Induced Non‐Topochemical Solid‐State Reaction
Authors: Venugopalan P. , Venkatesan K. , Klausen Jörg , Novotny‐Bregger Elisabeth , Leumann Christian , Eschenmoser Albert , Dunitz Jack D.
Published: December 2004

The rearrangement of methyl 2‐(methylthio)benzenesulfonate (1) to the zwitterionic 2‐(dimethyl‐sulfonium)benzenesulfonate (2) is known to proceed in solution by intermolecular Me transfers. The same rearrangement has been observed to occur in crystalline 1, but the crystal structure shows that the molecular packing is not conducive to intermolecular Me transfer. The reaction has been carried out with mixed crystals composed of 1 and deuteriomethylated (D6)‐l. By fast‐atom‐bombardment mass spectroscopy, it has been shown that the product consists of a 1:2:1 mixture of the non‐, tri‐, and hexadeuterated species, the mixture expected, if the solid‐state reaction proceeds by intermolecular Me transfers. From this result, together with the slower rates of conversion in the single crystal compared with the melt, it can be concluded that the reaction must occur not topochemically but rather at defects such as microcavities, surfaces, and other irregularities in the ordered crystal arrangement.
Synthesis of the Bretonins, Polyolefinic Esterified Glyceryl Ethers of an Unidentified Sponge from the North‐Brittany Sea: Absolute Configuration and Novel Structure Assignment
Authors: Mancini Ines , Guella Graziano , Pietra Francesco
Published: December 2004

The absolute configurations of acetylated bretonin A (= (+}‐(R)‐1‐[(acetoxy)methyl]‐2‐{[(4E,6E,8E)‐dodeca‐4,6,8‐trienyl]oxy}ethyl 4‐acetoxybenzoate; (−)‐1b) and isobretonin A (= (+)‐(S)‐3‐{[(4E,6E,8E)‐do‐deca‐4,6,8‐trienyl]oxy}‐2‐hydroxypropyl 4‐hydroxybenzoate; (+)‐2), previously isolated from an undetermined sponge of the North Brittany sea, were established by comparison with synthetic (+)‐lb and (+)‐2, obtained from the condensation of commerical (−)‐(R)‐2,2‐dimethyl‐1,3‐dioxolan‐4‐yl p‐toluenesuifonate ((−)‐(R)‐15) with a mixture of (4E,6E,8E)‐ (14e) and (4E,6Z,8E)‐dodeca‐4,6,8‐trien‐1‐ol (14z). This also allowed confirming the structure and configuration of bretonin B (= (S)‐2‐{[(4E,6Z,8E)‐dodeca‐4,6,8‐trienyl]oxy}‐1‐(hydroxy‐methyl)ethyl 4‐hydroxybenzoate; 3) which was also isolated from the same sponge, albeit in a too small amount for a complete study. As concerns the glyceryl ethers precursors of the bretonins, co‐occurrence of the usual (S)‐con‐figuration (from 1a) with the unusual (R)‐configuration (from (+)‐2)) poses intriguing biogenetic problems.
Stereo and Face Selectivity in Cycloadditions of 1,2,3‐Trichloro‐3‐fluorocyclopropenes to Acyclic Dienes and Furans
Authors: Müller Paul , Bernardinelli Gérald , Pfyffer Jean , Schaller Jean‐Pierre
Published: December 2004

The stereo and face selectivities of the cycloaddition of 1,2,3‐trichloro‐3‐fluorocyclopropene (1a) with acyclic dienes and furans has been re‐investigated by X‐ray determination and correlation of 19F‐NMR data. The isolated adducts of dienes exclusively have exo‐configuration, and exo‐Configuration predominates with furans. The Cl substituents of the resulting cyclopropane ring are cis‐oriented. The face selectivity of the reaction with both types of substrates is attributed to electrostatic interactions between the F and the bridgehead Cl substituents, which destabilize the F‐cis‐transition state (13 (F‐cis)) over 13 (F‐trans).