bluuebunny/crossref_metadata_2025 huggingface dataset:
Copper(II) complexes of potentially terdentate N2‐[(R)‐2‐hydroxypropyl]‐ and N2‐[(S)‐2‐hydroxypropyl]‐(S)‐phenylalaninamide for chiral recognition: Synthesis of the Ligands and Formation Constants
Authors: Dallavalle Francesco , Folesani Giuseppina , Bertuzzi Terenzio , Corradini Roberto , Marchelli Rosangela
Published: December 2004

Copper(II) complexes of the ligands N2‐[(R)‐2‐hydroxypropyl]‐ and N2‐[(S)‐2‐hydroxypropyl]‐(S)‐phenylalaninamide performed chiral separation of N‐dansyl‐protected and unmodified amino acids in HPLC (reversed phase). With the aim of investigating which species are potentially involved in the discrimination mechanism, the two ligands were synthesized and their complexation equilibria with Cu2+ studied by potentiometry and spectrophotometry in aqueous solution up to pH 11.7. The formation constants of the species observed, [CuL]2+, [CuL2]2+, [CuLH–1]+, [CuL2H–1]+, [CuL2H–2], and [CuL2H–3]−, were quite similar for both compounds and were compared to those of (S)‐phenylalaninamide. Most probably, in [CuL2H–3]− the ligands behave as terdentate, with the deprotonated OH group occupying an apical position.
Dendrophanes: Water‐Soluble Dendritic Receptors. Preliminary communication
Authors: Mattei Sebastiano , Seiler Paul , Diederich FrançOis , Gramlich Volker
Published: December 2004

The dendritic cyclophanes (dendrophanes )1–3 containing a [6.1.6.1]paracyclophane as the initiator core embedded in dendritic poly(ether‐amide) shells of first (1), second (2), and third (3) generation were prepared and characterized. The X‐ray crystal‐structure analyses of esters 7 and 4, derivatives of cyclophane core 9 and first‐generation dendrophane 1, respectively, displayed open cavity binding sites suitable for the inclusion complexation of aromatic substrates. With their carboxylate surface groups, dendrophanes 1–3 were readily soluble in aqueous phosphate buffer (pH 8.0), and the complexation of naphthalene derivatives was investigated by 1H‐NMR and fluorescence titrations. The binding studies demonstrated that the cyclophane cavity remains open and accessible to appropriate substrates even at higher dendritic generations. The 1:1 complexes formed in aqueous buffer were of similar stability to those formed by the unbranched core 9 (Ka between 1000 and 10000 1 mol−1, 300 K). Investigations with the fluorescent probe 6‐(p‐toluidino)naphthalene‐2‐sulfonate (12) showed that the micropolarity at the dendrophane core decreases with increasing generation number.
Compounding Selectivity in Reactions of Diastereoisomeric Radical Intermediates. An experimental demonstration that the yield of a product from a diastereotopic‐group‐selective reaction can significantly exceed the level of group selectivity
Authors: Curran Dennis P. , Qi Hongyan
Published: December 2004

Reduction of a bis‐radical precursor, 6‐phenyl‐1,1‐bis[3‐(phenylselanyl)propyl]‐3a,4‐dihydro‐1H,3H‐cyclopenta[c]furan‐5‐one (6), with 3 equiv. of Ph3SnH provides mixtures of cis,cis‐ or cis,trans‐angular triquinane products (3aα,5aβ,8β,8aR*)‐ and (3aα,5aα,8β,8aR*)‐hexahydro‐3a‐propyl‐8‐phenyl‐5H‐dicyclopenta[b,c]furan‐7(8H)‐one (cis,cis‐12/cis,trans‐12), in yields that vary from 50%/50% to 91%/6% depending on the reaction concentration. A mechanistic model for this process is proposed that involves a non‐selective phenylselenium‐group abstraction step followed by successive kinetic resolutions of diastereoisomeric radical intermediates. This reaction shows how yields in group‐selective reactions can be compounded to levels above that ostensibly permitted by the level of the group‐selective step.
Regioselektive 1,3‐Dipolare Cycloadditionen eines ‘Thiocarbonyl‐methanids’ ((Alkylidensulfonio)methanids) mit aromatischen Sulfinen
Authors: Mlostoń Grzegorz , Linden Anthony , Heimgartner Heinz
Published: December 2004

Regioselective 1,3‐Dipolar Cycloadditions of a ‘Thiocarbonyl‐methanide’ ((Alkylidenesulfonio)methanide) with Aromatic Sulfines

Reaction of the spirocyclic 2,5‐dihydro‐1,3,4‐thiadiazole 7 and thiobenzophenone S‐oxide (6a) in THF at 45° yielded the spirocyclic 1,3‐dithiolane 1‐oxide 8, thiirane 9, and the diazane derivative 10 in a ratio of 61:15:23 (Scheme 2). The formation of 8 is rationalized by a 1,3‐dipolar cycloaddition of ‘thiocarbonyl‐methanide’ 1, generated from 7 by thermal elimination of N2, and the CS bond of sulfine 6a. Cyclization of intermediate 1 leads to thiirane 9. Under the same conditions, 7 and adamantane‐2‐thione S‐oxide (6b) or 2,2,4,4‐tetramethyl‐3‐thioxocyclobutanone S‐oxide (4) reacted to give only 9 and 10 but no cycloadduct of type 8 (Scheme 4). With the aim to favor the formation of 8, a mixture of 6a and 1.1 equiv. of 7 was heated to 45° without any solvent in a sealed tube. The ratio of products was only slightly different from that of the thermolysis in THF. An analogous experiment with 7 and 9H‐fluorene‐9‐thione S‐oxide (6c) yielded cycloadduct 13 and 9 (Scheme 5). It is most interesting that the 1,3‐dipolar cycloadditions of 1 and the sulfines 6a and 6c proceeded with different regioselectivity. A reaction mechanism for the unexpected formation of 10 is proposed in Scheme 7. The key step is the base‐catalyzed ring opening of 7 and the nucleophilic addition of the thereby formed thiolate 21 onto the sulfonium ion 19.
Formation of Cyclic Ketals from Hydroxyalkyl Enol Ethers, a stereoelectronically controlled endo‐trig‐cyclization process
Authors: Deslongchamps Pierre , Dory Yves L. , Li Shigui
Published: December 2004

Acid‐catalyzed cyclic ketal formation vs. hydrolysis of a series of hydroxyalkyl cyclic enol ethers in the presence of 1 equiv. of H2O, and acid‐catalyzed cyclic‐ketal formation (same ketals as above) vs. methanolysis of a series of mixed pent‐4‐enyl hydroxyalkyl ketals with N‐bromosuccinimide in the presence of 4 equiv. of MeOH led to the same result: the intramolecular cyclization processes occur at similar rates as the intermolecular H2O or MeOH attacks independently of the size of the rings formed (five‐, six‐, or seven‐membered), by cyclizations. These results can be explained by the facts that, due to stereoelectronic effects which impose a torsional strain to the sp2 hybridized O‐atom, the cyclization activation enthalpy decreases, as the length of the hydroxyalkyl chain increase (ease of cyclization: 7 > 6 > 5), whereas the entropy factor favors the cyclization in the reverse fashion (ease of cyclization: 5 > 6 > 7). The various reaction pathways have been examined using the semi‐empirical Hamiltonian AM1, and the results obtained confirm that large‐ring formation is enthalpically much favored over the cyclization processes leading to small rings (ease of cyclization: 7 > 6 > 5).
Enantioselektive Synthese von α‐Phosphinoketonen. Vorläufige Mitteilung
Authors: Enders Dieter , Berg Thorsten , Raabe Gerhard , Runsink Jan
Published: December 2004

Enantioselective Synthesis of α‐Phosphinoketones

The first asymmetric (CP)‐connective synthesis of α‐phosphinoketones in high enantiomeric purity (e.e.91–97%) is described. Key step is the highly diastereoselective phosphinylation of SAMP‐hydrazones (S)‐2 to produce α‐phosphinohydrazones (S,R)‐3, isolated as the more stable borane adducts. Subsequent ozonolysis afforded the title compounds (R)‐4, potential ligands for enantioselective homogeneous catalysis.
Total Synthesis of (+)‐Elacomine and (−)‐Isoelacomine, Two Hitherto Unnamed Oxindole Alkaloids from Elaeagnus commutata
Authors: Pellegrini Claudio , Weber Michael , Borschberg Hans‐Jürg
Published: December 2004

Racemic elacomine ((±)‐2), a hemiterpene spiro oxindole alkaloid from Elaeagnus commutata, was synthesized in five steps from 6‐methoxytryptamine (19) in 16% overall yield (Scheme 3). The final oxidative rearrangement of the corresponding β‐carboline precursor (±)‐21 furnished isoelacomine ((±)‐22) as a by‐product (6% overall yield). A more elaborate route that started from L‐tryptophan furnished (+)‐2 and (−)‐22 with optical purities of 76% (Scheme 4) and established the absolute configuration of these compounds. A reinvestigation of the alkaloidal content of the roots of E. commutata showed that both elacomine and isoelacomine occur naturally in racemic form.
New Triterpene Saponins from Herniaria glabra
Authors: Freiler Michaela , Reznicek Gottfried , Jurenitsch Johann , Kubelka Wolfgang , Schmidt Wolfram , Schubert‐Zsilavecz Manfred , Haslinger Ernst , Reiner Josef
Published: December 2004

Three new saponins 1–3 were isolated from Herniaria glabra by means of prep. HPLC and TLC. The structures were established mainly by a combination of 2D‐NMR techniques (COSY, TOCSY, ROESY, HMQC, and HMBC) as O‐α‐L‐rhamnopyranosyl‐(1→4)‐O‐β‐D‐glucopyranosyl‐(1‐→6)‐O‐[β‐D‐glucopyranosyl‐(1→2)]‐β‐D‐glucopyranosyl medicagen‐28‐ate (herniaria saponin 4; 1), O‐β‐D‐glucopyranosyl‐(1→3)‐O‐α‐L‐rhamnopyranosyl‐(1→2)‐O‐[β‐(3R)‐D‐apiofuranosyl‐(1→3)]‐β‐D‐4‐O‐acetylfucopyranosyl 3‐O‐(β‐D‐glucuronopyranosyl)‐16α‐hydroxymedicagen‐28‐ate (herniaria saponin 5; 2), and O‐α‐L‐rhamnopyranosyl‐(1→4)‐O‐β‐D‐glucopyranosyl‐(1→6)‐O‐[β‐D‐6‐O‐acetylglucopyra nosyl‐(1→2)]‐β‐D‐glucopyranosyl medicagen‐28‐ate (herniaria saponin 6; 3).
Nucleotides. Part XLVI. The synthesis of phospholipid conjugates of antivirally active nucleosides by the improved phosphoramidite methodology
Authors: Sigmund Harald , Pfleiderer Wolfgang
Published: December 2004

The application of the improved phosphoramidite strategy for the synthese of oligonucleotides using β‐eliminating protecting groups to phospholipid chemistry offers the possibility to synthesize phospholipid conjugates of AZT (6) and cordycepin. The synthesis of 3′‐azido‐3′‐deoxythymidine (6) was achieved by a new isolation procedure without chromatographic purification steps in an overall yield of 50%. Protected cordycepin ( = 3′‐de‐oxyadenosine) derivatives, the N6,2′‐bis[2‐(4‐nitrophenyl)ethoxycarbonyl]cordycepin (12) and the N6,5′‐bis[2‐(4‐nitrophenyl)ethoxycarbonyl]cordycepin (13) wre prepared by known methods and direct acylation of N6‐[2‐(4‐nitrophenyl)ethoxycarbonyl]cordycepin (9), respectively. These protected nucleosides and the 3′‐azido‐3′‐de‐oxythymidine (6) reacted with newly synthesized and properly characterized lipid‐phosphoramidites 21–25, catalyzed by 1H‐tetrazole, to the corresponding nucleoside‐phospholipid conjugates 26–38 in high yield. The deprotection was accomplished via β‐elimination with 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) in aprotic solvents to give analytically pure nucleoside‐phospholipid diesters 39–51 as triethylammonium or sodium salts. The newly synthesized compounds were characterized by elemental analyses and UV and 1H‐NMR spectra.
Synthesis of Tenuilobine, a Bis‐polyamine Alkaloid from Oncinotis tenuiloba, and Its Transamidation to Isotenuilobine
Authors: Doll Martin K.‐H. , Guggisberg Armin , Hesse Manfred
Published: December 2004

From the leaves of Oncinotis tenuiloba STAPF, a novel polyamine alkaloid, tenuilobine (9), was isolated. This paper presents the synthesis of 9, as well as the base‐catalyzed Zip reaction of 9, leading to the transamidation product isotenuilobine (10). The structure of 10 was further confirmed by 2D‐NMR correlation spectroscopy. For analytical purposes, the bis‐polyamines 9 and 10 were converted into their pentaacetyl derivatives 12 and 11, respectively, which were readily separable by reverse‐phase HPLC.
Further C‐Alkylations of Cyclotetrapeptides via Lithium and Phosphazenium (P4) Enolates: Discovery of a New Conformation
Authors: Seebach Dieter , Bezençon Olivier , Jaun Bernhard , Pietzonka Thomas , Matthews Jennifer L. , Kühnle Florian N. M. , Schweizer W. Bernd
Published: December 2004

Four cyclotetrapeptides containing one (1, 2) or two (3, 4) chiral amino acids have been C‐alkylated or C‐hydroxyalkylated through Li+ or phosphazenium (P4 · H+) enolates. The reactions are completely diastereoselective (by NMR or HPLC analysis) with respect to the newly formed backbone stereogenic centres (Tables 2 and 3). The reactivity of the polylithiated species responsible for these alkylations is such that only highly reactive electrophiles (MeI, BnBr, primary allylic halides, aldehydes, CO2) can be employed. It is shown that the position, and thus the chirality sense, of the newly formed stereogenic centre in a given cyclotetrapeptide backbone is controlled by the positioning of N‐methyl groups in the starting material (cf. cyclo(‐MeLeu‐Gly‐D‐Ala‐Sar‐) (3) and cyclo(‐Leu‐Sar‐MeDAla‐Gly‐) (4) in Scheme 1). With Schwesinger's phosphazene P4‐base, all NH groups are first benzylated and C‐benzylation then takes place at a sarcosine, rather than an N‐benzylglycine residue (Table 3). In contrast to open‐chain N‐benzyl peptides, the N‐benzylated cyclotetrapeptides could not be debenzylated under dissolving‐metal conditions (Na/NH3). Conformational analysis (NMR spectroscopy and X‐ray diffraction) shows that the prevailing species have cis/trans/cis/trans(ctct) peptide bonds (zigzag conformation of Ci backbone symmetry, Figs. 2–4). However, a hitherto unknown conformation of cyclotetrapeptides has been found in CDCl3 solutions of the hydroxyalkylated products 18–21 (obtained with EtCHO and PhCHO as electrophiles; Fig.4). The new conformation has four trans peptide bonds and is believed to result mainly from intramolecular H‐bond formation, involving the newly generated alkyl‐ or arylserine residue. This assumption has also been supported by modelling (TRIPOS force field, SYBYL, see Fig.5 and Table 6). The structure may be considered as a β‐turn mimic.
Nucleotides. Part IL. Synthesis and Characterization of Cordycepin‐Trimer‐Vitamin and ‐Lipid Conjugates Potential Inhibitors of HIV‐1 Replication
Authors: Wasner Marita , Pfleiderer Wolfgang , Suhadolnik Robert J. , Horvath Susan E. , Kon Ning , Guan Ming‐Xu , Henderson Earl E. , Adelson Martin E. , Henderson Earl E. , Suhadolnik Robert J.
Published: December 2004

The syntheses of biodegradable 2′‐ and 5′ ‐ester and 2′‐ and 5′ ‐carbonate conjugates of the antivirally active 3′‐deoxyadenylyl‐(2′–5′)‐3′‐deoxyadenylyl‐(2′–5′)‐3′‐deoxyadenosine (cordycepin‐trimer core) with the vitamins, E, D2, and A and the lipids 1,2‐di‐O‐palmitoylglycerol and 1,2‐di‐O‐hexadecylglycerol were achieved first by preparation of the trimeric educts 19–21 (Scheme 1). Secondly, these substances were condensed with the lipophilic residues via a succinate or carbonate linker and then deprotected by β‐elimination of the npeoc and npe protecting groups and acid treatment for detritylation without harming the ester and carbonate functions, respectively (Scheme 2). Metabolically stable cordycepin‐trimer‐vitamin and ‐lipid conjugates are a new class of bioconjugates that inhibit HIV‐1‐induced syncytia formation with IC50 values of 7, 18, and 24 m̈M for 39, 29, and 42, respectively, and inhibit HIV‐1 reverse transcriptase (RT) activity from 14 to 96% (see Table). Of the nine conjugates tested, inhibition of HIV‐1 replication by 28, 29, 32, 40, and 42 may be attributed in part to the activation of the RNase L/PKR antiviral pathways. Trimer conjugate 42 showed the greatest inhibition of HIV‐1 replication, i.e., a 120‐fold decrease in HIV‐1‐induced syncytia formation and an 88% inhibition of HIV‐1 reverse transcriptase (RT). This inhibition of replication of HIV‐1 by 42 can be attributed in part to the activation of recombinant, human RNase L. The inhibition of HIV‐1 replication by the cordycepin‐trimer‐vitamin and ‐lipid conjugates is significantly greater than that observed for the (2′–5′) A‐trimer core or cordycepin‐trimer core.
1,1,2,2‐Tetraethynylethanes: Synthons for Tetraethynylethenes and Modules for Acetylenic Molecular Scaffolding
Authors: Tykwinski Rik R. , Diederich François , Seiler Paul , Gramlich Volker
Published: December 2004

The synthesis of functionalized 1,1,2,2‐tetraethynylethanes (= 3,4‐diethynylhexa‐1,5‐diynes) as synthons for tetraethynylethenes (3,4‐diethynylhex‐3‐ene‐1,5‐diynes) and as building blocks for three‐dimensional acetylenic molecular scaffolding targeting the synthesis of the molecular carbon belts 3 and 4 is reported (Scheme 1). Reaction of diethyl oxalate and (trialkylsilyl)ethynyl Grignard reagents afforded the silyl‐protected 3,4‐diethynylhexa‐1,5‐diyne‐3,4‐ diols 7 and 8 which were transformed in high yields into the cyclic carbonate 9 and the cyclic orthoesters 10–13, respectively (Scheme 2). The solid‐state structures of 9 and 10 were elucidated by X‐ray crystallography. The alkyne protecting groups in 9, 10, and 12 were smoothly removed to give the free tetraynes 14–16 as relatively stable oils in nearly quantitative yields (Scheme 3). Orthoesters 15 and 16 underwent Pd‐catalyzed cross‐coupling with iodobenzene to give the tetraphenyl derivatives 17 and 18 (Scheme 4). Thermal acid‐catalyzed elimination of the orthoester moieties in 12 and 13 produced the silyl‐protected tetraethynylethenes 19 and 20 and concluded a novel, simple three‐step synthesis of these fully two‐dimensionally conjugated π‐chromophores (Scheme 5).
Synthesis of Carbocyclic C‐Nucleosides Containing Nonnatural Pyrimidine Bases
Authors: Hildbrand Stefan , Leumann Christian , Scheffold Rolf
Published: December 2004

A series of new carbocyclic C‐nucleosides with a cis‐4′‐(hydroxymethyl)cyclopent‐2′‐enyl sugar moiety and unnatural pyrimidine bases (2–6) were synthesized in racemic form in two steps starting from the easily accessible cyclic carbonate 1.
Isotactic and Atactic Copolymerization of Styrene and Carbon Monoxide Using Cationic Palladium‐Phosphino(dihydrooxazole) Complexes. Preliminary Communication
Authors: Sperrle Martin , Aeby Anton , Consiglio Giambattista , Pfaltz Andreas
Published: December 2004

Cationic palladium complexes 2 containing coordinated phosphino(dihydrooxazole) ligands 1 give catalytic systems which allow the production of alternating styrene‐carbon monoxide copolymers. Depending on the symmetry of the ligand, the copolymers are produced either with a highly isotactic or with an essentially completely atactic microstructure. Termination of the polymeric chain is mainly due to a β‐H‐elimination reaction. Both linear ((E)‐PhCHCHCO) and branched (CH2C(Ph)CO) unsaturated end groups were identified.
Reisolation of Carotenoid 3,6‐Epoxides from Red Paprika (Capsicum annuum)
Authors: Deli József , Molnár Péter , Matus Zoltán , Tóth Gyula , Steck Andrea
Published: December 2004

Cucurbitaxanthin A (= (3S,5R,6R,3′R)‐3,6‐epoxy‐5,6‐dihydro‐β,β‐ carotene‐5,3′‐diol; 5), cucurbitaxanthin B (= (3S,5R,6R,3′S,5′R,6′S)‐3,6,5′, 6′‐diepoxy‐5,6,5′,6′‐tetrahydro‐β,β‐carotene‐5,3′‐diol; 6), the epimeric cucurbitachromes 1 and 2 (= (3S,5R,6R,3′S,5′R,8′S)‐ and (3S,5R,6R,3′S,5′R,8′R)‐3,6,5′, 8′‐diepoxy‐5,6,5′,6′‐tetrahydro‐β,β‐carotene‐5,3′‐diol, resp.; 9/10), cycloviolaxanthin (= (3S,5R,6R,3′S,5′R,6′R)‐3,6,3′, 6′‐diepoxy‐5,6,5′,6′‐tetrahydro‐β,κs‐carotene‐5,5′‐diol; 8), and capsanthin 3,6‐epoxide (= (3S,5R,6R,3′S,5′R)‐3,6‐epoxy‐5,6‐dihydro −5,3′‐dihydroxy‐β,κ‐caroten‐6′‐one; 7) were isolated from red spice paprika (Capsicum annuum var. longum) and characterized by their 1H‐ and 13C‐NMR, mass, and CD spectra.
An Unexpectedly Stable Chiral Hydrido‐Solvent Complex of RuII: A mechanistic link in the enantioselective hydrogenation of pyrones. Preliminary communication
Authors: Currao Antonio , Feiken Nantko , Macchioni Alceo , Nesper Reinhard , Pregosin Paul S. , Trabesinger Gerald
Published: December 2004

The ligand (6,6′‐dimethoxybiphenyl‐2,2′‐diyl)bis[3,5‐di(tert‐butyl)phenylphosphine] (1) forms an unexpectedly stable hydrido‐bis‐solvento complex of composition [RuH(isopropanol)2(1)]BF4, (2) under the conditions used in the enantioselective hydrogenation of pyrones. The structure of 2, determined by X‐ray diffraction, represents the first well‐characterized chiral five‐coordinate bis‐phosphine ruthenium‐hydride complex stable as a solvento complex, and provides a structural link in the enantioselective pyrone hydrogenation cycle catalyzed by [Ru(OAc)2(1)]. Using the arene complex [RuH(p‐cymene)(1)]BF4 (3), the chiral pocket of coordinated 1 is shown to be relatively rigid, via NMR spectroscopy. This is reflected in restricted rotation about one of the four P–[3,5‐di(tert‐butyl)phenyl] PCipso bonds at room temperature.
Detection of Noncovalent Complexes of Hydroxamic‐Acid Derivatives by means of electrospray mass spectrometry
Authors: Bigler Laurent , Baumeler Andreas , Werner Christa , Hesse Manfred
Published: December 2004

The complexes of isolated benzoxazinone derivatives with FeIII were investigated by means of electrospray ionization mass spectrometry. The hydroxamic‐acid derivatives could be differentiated from the lactam or the methyl‐hydroxamate derivatives by the formation of FeIII complexes with two or three ligands. These complexes or adducts of them have been identified in the mass spectra. Moreover, the mass‐spectral behavior of these complexes was not markedly influenced by the presence of a β‐D‐glucopyranosyloxy substituent.
Carbenoid Reactions of Dimethyl Diazomalonate with Aromatic Thioketones and 1,3‐Thiazole‐5(4H)‐thiones
Authors: Mlostón Grzegorz , Heimgartner Heinz
Published: December 2004

Dimethyl diazomalonate (4) and thiobenzophenone (2a) do not react in toluene even after warming to 50°. After addition of catalytic amounts of Rh2(OAc)4, a smooth reaction under N2 evolution afforded a mixture of thiiranedicarboxylate 5 and (diphenylmethylidene)malonate 6 (Scheme 2). A reaction mechanism via an intermediate ‘thiocarbonyl ylide’ 7, formed by the addition of the carbenoid species 8 to the S‐atom of 2a, is plausible. Similar reactions were carried out with 9H‐xanthene‐9‐thione (2b), 9H‐thioxanthene‐9‐thione (2c, Scheme 4), and 1,3‐thiazole‐5(4H)‐thione 18 (Scheme 6). In the cases of 2b and 2c, spirocyclic 1,3‐dithiolanetetracarboxylates 14a and 14b, respectively, were obtained as the third product. Reaction mechanisms for their formation are proposed in Scheme 5: S‐transfer from intermediate thiirane 12 to the carbenoid species yielded thioxomalonate 15 which underwent a 1,3‐dipolar cycloaddition with ‘thiocarbonyl ylide’ 16. An alternative is the formation of ‘thiocarbonyl ylide’ 17 via carbene addition to 15, followed by 1,3‐dipolar cycloaddition with 2b and 2c, respectively.
Protein‐Loop Mimetics: A Diketopiperazine‐Based Template to Stabilize Loop Conformations in Cyclic Peptides Containing the NPNA and RGD Motifs
Authors: Bisang Christian , Weber Christoph , Robinson John A.
Published: December 2004

We explore here an approach to mimic the structures and biological functions of protein loops in small synthetic molecules, by grafting the loop of interest onto an organic template comprising a bicyclic diketopiperazine, prepared by the formal coupling of (2S,4S)‐4‐aminoproline (Pro(NH2)) and aspartic acid (Asp). The Fmoc‐protected template 4 is used to prepare cyclo(‐Ala1‐Asn2‐Pro3‐Asn4‐Ala5‐ Ala6‐Temp‐) (5) and cyclo(‐Ala1‐Arg2‐Gly3‐Asp4‐Temp‐) (6) (where Temp = template derived from 4), containing the Asn‐Pro‐Asn‐Ala (NPNA) and Arg‐Gly‐Asp (RGD) motifs. The conformational properties of these molecules are studied in aqueous solution by NMR and simulated‐annealing methods. The NPNA motif, an immunodominant epitope on the circumsporozoite surface protein of the malaria parasite Plasmodium falciparum, is shown to adopt a stable type‐I β‐turn in 5. The template in 5 adopts a preferred conformation with Pro(NH2)χ1 ≈︁ −35° and the Asp moiety χ1 ≈︁ 70°. A different template conformation is inferred for 6, with Pro(NH2)χ1 ≈︁ 0°, but the ARGD loop appears by NMR to undergo rapid conformational averaging. Solid‐phase binding assays reveal that 6 displays modest antagonist activity towards both the integrin αIIbβ3 and αvβ3 receptors.
Synthesis and Crystal Structure of Tricaesium Heptaphosphide–Ammonia(1/3) Cs3P7·3 NH3
Authors: Korber Nikolaus , Daniels Jörg
Published: December 2004

Recrystallization of Cs3P7 from liquid NH3 yields the triammoniate Cs3P7·3 NH3, which loses the weakly bound NH3 of crystallization below 253 K. A low‐temperature crystal‐structure analysis shows that Cs3P7· NH3 consists of a framework of heptaphosphanortricyclane anions P and Cs+ cations with NH3 molecules completing the coordination of the cations. The framework is built from Cs3P7 layers connected by only few Cs…︁P interactions, the interlayer gap being filled by a two‐dimensional network of NH3. The Cs7P7 part of the structure completes a family of alkali‐metal‐polyphosphide substructures which range from [RbP7]2− or [CsP11]2− chains over [Cs2Pn]− layers (n = 7, 11) to now [Cs3P7] frameworks.
Synthesis and Structure of Functionalized Cyclododecadiynes and ‐dienes
Authors: Boss Christoph , Keese Reinhart
Published: December 2004

The cyclododecadiynes 3b–d, 8b–d, and 10b–c with functionalities in two propargylic positions, as well as the monofunctionalized diyne 13b have been prepared from simple open‐chain building blocks. In the DMPU ( = N,N'‐dimethylpropyleneurea)‐assisted ring‐closing alkylation of 1,7‐diynes, the twelve‐membered ring compounds have been prepared in yields of 16–55%. The preparation of the diene‐diyne 15 and the cyclododeca‐5,11‐diyne‐1,4‐dione 18 are described.
A Tricyclic Template Derived from (2S,4R)‐4‐Hydroxyproline for the Synthesis of Protein Loop Mimetics
Authors: Beeli Reto , Steger Mathias , Linden Anthony , Robinson John A.
Published: December 2004

A tricyclic diketopiperazine, formally derived by coupling (2S,4S)‐4‐aminoproline (Pro(NH2)) and (2S,4R)‐4‐(carboxymethyl)proline (Pro(CH2COOH)), is synthesized starting from readily available (2S,4R)‐4‐hydroxyproline. The resulting tricyclic template has carboxy and amino groups to which a peptide chain may be attached. The Fmoc‐protected template 5 is incorporated into the cyclic molecule cyclo(‐Ala1‐Asn2‐Pro3‐Asn4‐Ala5‐) (6) where Pro(NH2)7 = Pro(CH2COOH)8 represents the template, using solid‐phase peptide synthesis with cyclization in solution. The molecule is shown by NMR and dynamic simulated annealing methods to adopt a preferred conformation in aqueous solution, which includes an extended backbone at the residues Asn2‐Pro3‐Asn4, and a type‐Iβ‐turn at . These studies show that this novel template may be used in the synthesis of cyclic peptide and protein mimetics having defined secondary structure in aqueous environments.
Naphthopyranquinone Antibiotics: Novel enantioselective syntheses of frenolicin B and some of its stereoisomers
Authors: Masquelin Thierry , Hengartnerb Urs , Streith Jacques
Published: December 2004

Two new enantioselective syntheses of the naphthopyranquinone antibiotic frenolicin B (1), of its enantiomer 2, and of its diastereoisomers 3 and 4 were accomplished using two different routes from optically active β‐Hydroxy esters (R)‐ and (S)‐11 and 18. β‐Hydroxy esters (R)‐ and (S)‐11 were prepared stereoselectively from optically active sulfenylacetates (S)‐ and (R)‐10, respectively (Scheme 2, Method A). Alternatively, compound 18 was obtained in excellent yield by enantioselective hydrogenation of the corresponding β‐keto ester 17, using a chiral ruthenium‐complex catalyst (Scheme 3, Method B). Subsequently, compounds (S)‐11 and 18 were transformed into frenolicin B (1). In analogy, Stereoisomers 2–4 were prepared from (S)‐ and (R)‐11 in good yields.
Synthesen neuer Phosphono‐Analoga von Pantethein‐derivaten
Authors: Neidlein R. , Li S.
Published: December 2004

Syntheses of New Phosphono Analogues of Pantetheine Derivatives

The phosphono analogues 5 and 13 of pantothenate 4′‐(dibenzyl phosphate) and pantetheine 4′‐(dibenzyl phosphate), respectively, are prepared as intermediates for the synthesis of a coenzyme‐A phosphono analogue (Schemes 1 and 2). The synthesis of phosphono analogues 20 and 21 of oxapantetheine, which are structurally similar compounds to the phosphono analogue of pantetheine, is also described (Scheme 3).
Nucleotides. Part L. Aglycone protection by the (2‐dansylethoxy)carbonyl (= {2‐{[5‐(dimethylamino)naphthalen‐l‐yl]sulfonyl}ethoxy}carbonyl; dnseoc) group a new variation in oligodeoxyribonucleotide synthesis
Authors: Wagner Thomas , Pfleiderer Wolfgang
Published: December 2004

The (2‐dansylethoxy)carbonyl (= {2‐{[5‐(dimethylamino)naphthalen‐l‐yl]sulfonyl}ethoxy}carbonyl; dnseoc) group was employed for protection of the amino functions of the aglycone residues. The lactam function of 2′‐deoxyguanosine was on the one hand unprotected and on the other hand alkylated at O6 of the aglycone with the 2‐(4‐nitrophenyl)ethyl (npe) and 2‐(phenylsulfonyl)ethyl (pse) group, respectively. The syntheses of monomeric building blocks, both phosphoramidites and nucleoside‐ functionalized supports, are described for the three common 2′‐deoxynucleosides (2′‐deoxycytidine, 2′‐deoxyadenosine, 2′‐deoxyguanosine). As kinetic studies with the tritylated nucleosides showed, the dnseoc group is more labile towards DBU cleavage than the corresponding 2‐(4‐nitrophenyl)ethyl‐(npe) and [2‐(4‐nitrophenyl)ethoxy]carbonyl(npeoc)‐protected analogues (see Table 2). These results were confirmed by the very fast deprotection rate of the dnseoc groups at some oligonucleotides.
The Absolute Configuration of 3‐Methylpyrrolidine Alkaloids from Poison Glands of Ants Leptothoracini (Myrmicinae)
Authors: Koob Robert , Rudolph Christiane , Veith Hans Jiirgen
Published: December 2004

The absolute configuration of 3‐methylpyrrolidine alkaloids isolated from the poison gland of ants Leptothoracini was determined as (3R). The enantiomeric separation by chiral gas chromatography and unambiguous structural assignment of the target compounds are described.
An Unexpected Isomerization of N‐Aryl‐3‐amino‐4‐nitroisothiazol‐5(2H)‐imines to 2‐(Benzothiazol‐2‐yl)‐2‐nitroethene‐l, l‐diamines
Authors: Argilagos Dally Moya , Trimiño María I. García , Cabrera Arturo Macías , Linden Anthony , Heimgartner Heinz
Published: December 2004

The syntheses of several N‐aryl‐3‐amino‐4‐nitroisothiazol‐5(2H)‐imines 12 from 3, 3‐diamino‐2‐nitro‐thioacrylamides 11 are reported (Scheme 3). In polar solvents, a spontaneous isomerization of some of the prepared isothiazol‐5(2H)‐imines 12 yielded benzothiazoles 13 (Scheme 4). In the case of 2‐alkyl‐substituted derivatives of type 12, the isomerization occurred only at higher temperatures. Electronic influences of different substituents on the rate of the isomerization were studied, and a polar reaction mechanism is proposed in Scheme 6. The structures of 12e and 13e were established by X‐ray crystallography. Conformational analyses of 3‐(methylamino)‐2‐nitro‐N‐phenyl‐3‐(pyrrolidin‐1‐yl)thioacrylamide (111) by NMR and X‐ray methods were performed with the aim of explaining the distinct behavior of this amide towards Br2 or diethyl azodicarboxylate.
Isolation, Structure, and Biological Activities of Long‐Chain Catechols of Plectranthus sylvestris (Labiatae)
Authors: Juch Mathias , Rüedi Peter
Published: December 2004

Antioxidant activity guided fractionation of extracts of the aerial parts of the title plant and HPLC separation yielded a series of oxygenated long‐chain alkylcatechols. Their structures were inferred by spectroscopic methods and chemical transformations to be the novel 4‐[(2S,4R,6S)‐4‐(acetyloxy)tetrahydro‐6‐pentyl‐2H‐pyran‐2‐yl]benzene‐1,2diol (1a), 4‐[(2S,4R6S)‐tetrahydro‐4‐hydroxy‐6‐pentyl‐2H‐pyran‐2‐yl]benzene‐1,2‐diol (1b), 4‐[(3S,5S)‐5‐(acetyloxy)‐3‐hydroxydecyl]benzene‐1,2‐diol (2a), 4‐[(3S,5S)3‐(acetyloxy)‐5‐hydroxydecyl]benzene‐1,2‐diol (2b), (3S,13Z)‐1‐(3,4‐dihydroxyphenyl)‐3‐hydroxydocos‐13‐en‐5‐one (3a), (Z)‐1‐(3,4‐dihydroxyphenyl)docos‐13‐en‐5‐one (4), besides the known l‐(3,4‐dihydroxyphenyl)icosan‐5‐one (5). The absolute configurations of the optically active compounds which are structurally related to the [n]‐gingerols (6) and ‐diols (7) were established by the high‐field 1H‐NMR application of Mosher's method. All compounds are in vitro potent antioxidants, inhibiting the Fe2+‐catalysed autoxidation of linoleic acid in the same order of magnitude as the commercial antioxidant 2,6‐di(tert‐butyl)‐4‐methylphenol (BHT). The dose‐dependent inhibitory effects on soybean‐lipoxygenase are in the μmol range, that of the most effective compound (3a) in the nmol range, hence being significantly more potent than the Known anti‐inflammatory and analgesic drugs indomethacin and nordihydroguaiaretic acid.
Variants of Solid‐State and Solution Structures of (η3‐Allyl)‐ {2‐[2′‐(diphenylphosphino)phenyl]‐4,5‐dihydrooxazole‐P,N}palladium(II) hexafluorophosphates and tetraphenylborates
Authors: Schaffner Silvia , Macko Ludwig , Neubufger Markus , Zehnder Margareta
Published: December 2004

Crystal and solution structures of the enantiomerically pure and the racemic pairs of (η3‐allyl) {2‐[2′‐(diphenylphosphino)phenyl]‐4,5‐dihydro‐4‐phenyloxazole}palladium(II) hexafluorophosphates (1, and rac‐1, resp.) and tetraphenylborates (2, and rac‐2, resp.) as well as (η3‐allyl){2‐[2′‐(diphenylphosphino)phenyl]‐4,5‐dihydro‐4‐isopropyloxazole}palladium(II) tetraphenylborate (3) were characterized by X‐ray crystallography and 1H‐NMR spectroscopy. In the solid state, rac‐1 and rac‐2 proved to be disordered with both diastereoisomeric complexes in the crystal. The complexes 2 and 3 exist only in the ‘exo’ form. The X‐ray structures show that the [PdII(η3‐allyl)] moiety may adopt different configurations between a nearly symmetrical three‐electron PdII(π3‐allyl) system and an asymmetrical allyl group with a η1‐ and a η2‐bonding to the metal center. The [PdII(η3‐allyl)] system of rac‐1 and of ‘endo’ rac‐2 is closer to the former, and that of 2, ‘exo’‐rac‐2, and 3 closer to the later geometry. The 1H‐NMR spectra of the hexafluorophosphates 1 and rac‐1 show two sets of signals of the allylic protons in an ‘exo’/‘endo’ ratio of 2:3. The tetraphenylborates 2, rac‐2, and 3 give only one set of broad signals of the allylic protons.
Synthesis and Structure of a Macrocyclic Europium Complex and its possible role as a catalyst for phosphodiester transesterification
Authors: Haner Robert , Hall Jonathan , Rihs Grety
Published: December 2004

The synthesis and X‐ray crystal structure of a europium macrocyctic complex 1, an important catalyst used for the sequence‐specific cleavage of RNA, is reported. The role of this metal complex in facilitating phosphate transesterification is discussed.
Photochemistry of Tetraalkyl‐2H‐thietes
Authors: Mergenhagen Thomas , Margaretha Paul
Published: December 2004

The 3‐alkyl‐2,2‐dimethyl‐4‐(tert‐butyl)‐2H‐thietes 9a–c were obtained in several steps from the corresponding, newly synthesized, 3‐alkyl‐2‐(tert‐butyl)thiophenes 5a–c. Irradiation (254nm) of these tetraalkylated four membered S‐heterocycles leads to a photostationary equilibrium with enethiones 10a–c (thiete/enethione 3:1).
Some Unusual Products from the Thermal Reaction of Azulenes with Dimethyl Acetylenedicarboxylate
Authors: Magnussen Anette , Hansen Hans‐Jürgen
Published: December 2004

The thermal reaction of azulene‐1‐carbaldehydes 5 and 6 with excess dimethyl acetylenedicarboxylate (ADM) in decalin leads mainly to the formation of (1 + 1) and (1 + 2) adducts arising from the addition of ADM at the seven‐membered ring of the azulenes (cf. Schemes 2 and 4). The (1 + 2) adducts are formed in a homo‐Diels‐Alder reaction of ADM and isomeric tricyclic carbaldehydes which are derived from the primary tricyclic carbaldehydes by reversible [1s5s]‐C shifts (cf. Schemes 3 and 5). The thus formed pentacyclic carbaldehydes seem to undergo deep‐seated skeletal rearrangements (cf. Scheme 7) which result finally in the formation of the formyl‐tetrahydrocyclopenta[bc]acenaphthylene‐tetraesters 12 and 19, respectively. In other cases, e.g., azulene‐1‐carbaldehydes 7 and 8 (cf. Scheme 8), the thermal reaction with excess ADM furnishes only the already known tetracycfic (1 + 2) adducts of type anti‐26 to ‘anti’‐29. The thermal reaction of 1,3,4,8‐tetramethylazulene (9) with excess ADM in decalin resulted in the formation of two (1 + 2) and one (1 + 3) adduct in low yields (cf. Scheme 9). The latter turned out to be the 2,6‐bridged barrelene derivative 32. There are structural evidences that 32 is formed by similar pathways as the formyl‐tetrahydrocyclopenta[bc]acenaphthylene‐tetraesters (cf. Schemes 7 and 11). [2H3]Me‐Labelling experiments are in agreement with the proposed mechanisms (cf. Scheme 13).
Photoreduction of Triplet Benzophenone by Tertiary Amines: Amine molecular structure and ketyl radical yield
Authors: Raumer Markus Von , Suppan Paul , Haselbach Edwin
Published: December 2004

The photoreduction of triplet benzophenone by 14 tertiary amines was investigated. The ketyl radical yields do not correlate with the quenching rate constants, nor with the electron donor propensity of the amines. Individual structural features of the amines seem to determine the photoreduction yields.
Molecular Recognition of NADP(H) and ATP by Macrocyclic Polyamines Bearing Acridine Groups
Authors: Fenniri Hicham , Hosseini Mir Wais , Lehn Jean‐Marie
Published: December 2004

The macrocyclic polyamine‐based receptor BA bearing two acridine units makes use of combined electrostatic and stacking interactions for the binding of nucleotide polyphosphates and for the recognition of ATP and of NADPH (ka > 3 · 108 M), with a high selectivity for NADPH vs. NADP (ca. 103) and NAD(H) (> 106). The binding properties of this receptor towards a variety of substrates led to its in vitro application as a fluorescent probe for ATP. BA also interacts strongly with nucleic acids as shown by spectrophotometric, spectrofluorimetic, and electrophoretic mobility methods.
Selective N3‐ and 5′‐O‐Alkylation of 2′,3′‐O‐isopropylideneuridine with methyl iodide
Authors: Hovinen Jari
Published: December 2004

The 2′,3′‐O‐isopropylideneuridine (1) reacts with MeI in the presence of an excess of NaH in THF giving 2′,3′‐O‐isopropylidene‐5′‐O‐methyluridine (2). Prolonged reaction time gives rise to 2′,3′‐O‐isopropylidene‐3,5′‐O‐dimethyluridine (4). The use of an equimolar amount of base and alkylating agent results predominantly in methylation at N(3) (→ 3).
Metal Complexes with Macrocyclic Ligands. Part XLIV Kinetics of the Cu2+ incorporation into a macrocyclic ligand conjugated to proteins: Model studies for the d‘post‐labeling’ technique
Authors: Manzetti Matthias , Macko Ludwig , Neuburger‐Zehnder Margareta , Kaden Thomas A.
Published: December 2004

The kinetics of the Cu2+ complexation by macrocycles 1 (4‐[(l,4,8,11‐tetraazacyclotetradec‐1‐yl)methyl]‐benzoic acid) and 2 (N‐propyl‐4‐[(1,4,8,11‐tetraazacyclotetradec‐1‐yl)methyl]‐benzamide) as well as by macrocycle 1 conjugated to bovine serum albumin (bsa) and to ribonuclease A (rnase) were studied by stopped flow techniques. For 1 and 2, the kinetics were followed in the mM range monitoring the d‐d* absorption band of the Cu2+ complex. From the pH dependence of kobs, the rate law is v = [Cu2+] (kLH[LH] + k[LH2]), where kLH and k are the bimolecular rate constants for Cu2+ with the diprotonated (LH2) and monoprotonated (LH1) form of the ligand, respectively. The values are k = 1.7(1) M−1s−1 and kLH = 2.3(1) 105 M−1s−1 for 1, and k, = 0.28(9) M−1s−1 and kLH = 2.0(1) 105 M−1s−1 for 2. The kinetics of the Cu2+ incorporation into 1,2 and 1 conjugated to bsa and rnase, i.e., 3 and 4, respectively, were also followed using nitroso‐R salt as a metal indicator in the μM range, i.e., under conditions typical for the ‘post‐labeling’ technique to give radiolabeled monoclonal antibodies. In these cases, the reaction takes place between the 1:1 complex of Cu2+ with nitroso‐R‐salt and the macrocycle. At pH 6.5, the rates are very similar to each other indicating that the complexation properties of the macrocycle attached to a protein are not very different from those of the free ligand under comparable conditions.
Nucleotides. Part LII. Synthesis and biological activity of new base‐modified (2′–5′)oligoadenylate trimers
Authors: Kvasyuk Evgeny I. , Kulak Tamara I. , Tkachenko Olga V. , Sentyureva Svetlana L. , Mikhailopulo Igor A. , Suhadolnik Robert J. , Horvath Susan E. , Henderson Earl E. , Guan Ming‐Xu , Pfleiderer Wolfgang
Published: December 2004

Some new (2′–5′)oligoadenylate trimers, i.e., 22–28, containing the antiviral nucleoside ribavirin (= 1‐(β‐D‐ribofuranosyl)‐1H‐1,2,4‐triazole‐3‐carboxamide; 7) and the synthetic cytokine 6‐(benzylamino)purine riboside (= N6‐benzyladenosine; 1) in different positions of the trimer, have been synthesized by the phosphotriester method. The selectively blocked nucleosides 2–6 and 8–11 and the 2′‐phosphodiesters 13 and 14, used for the oligonucleotide syntheses, were synthesized from the corresponding unprotected ribonucleosides 1 and 7, and isolated by silica‐gel column chromatography. The fully deblocked trimers 22–28 were purified by ion‐exchange chromatography on DEAE‐Senacell 23‐SS. The newly synthesized compounds were characterized by physical means. The ability of synthesized trimers to inhibit HIV‐1 replication and to improve RNase L activation were investigated. Some of the synthesized trimers showed also biological inhibition of HIV‐1 reverse transcriptase and HIV‐1‐induced syncytia formation. It was shown that AdoBn‐containing trimers inhibited HIV‐1‐induced syncytia formation > 1500‐fold, independently of the position of the AdoBn residue in the oligomer chain.
Glyconothio‐O‐lactones. Part III. Thermolysis of a 4,5‐Dihydro‐1,2,3‐ and a 2,5‐Dihydro‐1,3,4‐thiadiazole
Authors: Bernet Bruno , Mäder Thomas , Vasella Andrea
Published: December 2004

Addition of CH2N2to 2,3:5,6‐di‐O‐isopropylidene‐1‐thio‐mannono‐1,4‐lactone (1) gave the 2,5‐dihydro‐1,3,4‐thiadiazole2and the 4,5‐dihydro‐1,2,3‐thiadiazole3. First‐order kinetics were observed for the thermolysis of3(Scheme 3) at 80–110° in C6D5Cl solution and of 2 (Scheme 3) at 20–35° in CDC13, respectively. The 1,2,3‐thiadiazole3led to mixtures of the thiirane9, the starting thionolactone1, the thiono‐1,5‐lactone8, and the enol ether7, while the isomeric 1,3,4‐thiadiazole2led to mixtures of the anomeric thiiranes9and12, the O‐hydrogenS,O,O‐ortholactone α‐D‐14, theS‐methyl thioester15, theS,S,O‐ortholactone13, and the 2,3:5,6‐di‐Oisopropylidene‐mannono‐1,4‐iactone (16). Pure products of the thermolysis were isolated by semipreparative supercritical fluid chromatography (SFC), whereas preparative HPLC led to partial or complete decomposition. Thus, the β‐D‐mannofuranosyl β‐D‐mannofuranoside10, contaminated by an unknown S species, was isolated by preparative HPLC of the crude product of thermolysis of3at 115–120° and partially transformed in CD3OD solution into the symmetric di(α‐D‐mannofuranosyl) tetrasulfide11. Its structure was evidenced by X‐ray analysis. Similarly, HPLC of the thermolysis product of2gave the enethiol17, the sulfide19, and the mercapto alcohol18as secondary products. Thermolysis of the thiirane9at 110–120° (Scheme 4) led to the anomeric thiirane12which was transformed into mixtures of the enethiol17and the enol ether7.Addition of H2O to17and7gave the corresponding hemiacetals18and20.The mechanism of the thermolysis of the dihydrothiadiazoles2and3, and the thiiranes9and12is discussed.
Rate Constants for the Addition of 2‐Hydroxy‐2‐propyl Radicals to Alkenes in Solution studied by laser flash photolysis
Authors: Martschke Rainer , Farley Robert D. , Fischer Hanns
Published: December 2004

Absolute rate constants for the addition of the highly nucleophilic 2‐hydroxy‐2‐propyl radical to eight fast‐reacting 1‐ and 1,1‐disubstituted alkenes in MeOH at room temperature have been determined by laser flash photolysis. Also the absorption spectra of the 2‐hydroxy‐2‐propyl and the benzylic and alkyl‐type adduct radicals are presented. The rate constants were obtained using various methods for the analysis of the kinetic traces and support earlier findings.
Changes in the Leaf Surface Chemistry of Apium graveolens (Apiaceae) stimulated by jasmonic acid and perceived by a specialist insect
Authors: Stanjek Volker , Herhaus Christian , Ritgen Ulf , Boland Wilhelm , Städler Erich
Published: December 2004

Treatment of celery leaves (Apium graveolens, cv. secalinum) with Jasmonic acid (JA, 1) or analogues of amino‐acid conjugates of Jasmonic acid such as the leucine conjugate with 1‐oxoindan‐4‐carboxylic acid (IN‐ILE, 2) stimulated the biosynthesis of the furanocoumarins psoralen (6), xanthotoxin (8), bergapten (7), and isopimpinellin (9). Besides the increase of the compounds within the leaf, a significant amount (ca. 20%) of the total furanocoumarins was deposited on the surface of the leaf. The two monomethoxy furanocoumarins, 7 and 8, began to increase steadily and simultaneously within the leaf and on the leaf surface ca. 40 h after the onset of the jasmonic‐acid stimulus. Within the leaf, the ratio 7/8 was ca. 1.3:1.0, while among the surface lipids 8 dominated (7/8 0.8:1.0), indicating that the export of the compounds to the surface is not a simple diffusive translocation along the oil‐ducts. Females of the carrot fly (Diptera, Psilidae) responded with an increased oviposition to the altered leaf surface chemistry of the JA‐treated celery plants. The effect shown for total leaves was corroborated by surrogate leaves treated with leaf‐surface extracts of JA‐induced leaves. Based on the known stimulation of oviposition by furanocoumarins, we conclude that the enhanced amount of furanocoumarins on the surface can explain the insects' preference for the JA‐stimulated plants. This is the first report of a JA‐induced change of the surface chemistry of a plant and an increase of the acceptability of treated leaves for a specialist insect, like the carrot fly.
Stereoselective Ring Opening of Electronically Excited Cyclohexa‐2, 4‐dienones: Cause and effect
Authors: Quinkert Gerhard , Scherer Stefan , Reichert Dietmar , Nestler Hans‐Peter , Wennemers Helma , Ebel Andreas , Urbahns Klaus , Wagner Klaus , Michaelis Klaus‐Peter , Wiech Gerhard , Prescher Günter , Bronstert Bernd , Freitag Bernd‐Jürgen , Wicke Ilka , Lisch Dietmar , Belik Pavel , Crecelius Thorsten , Hörstermann Dirk , Zimmermann Gottfried , Bats Jan W. , Dürner Gerd , Rehm Dieter
Published: December 2004

The two conformers of a cyclohexa‐2, 4‐dienone with different substituents at C(6) on irradiation are believed to undergo ring opening stereospecifically affording a mixture of two configurationally isomeric diene‐ketenes (and descendents thereof)‐ Exceptions are generally found for those dienones with one C and one O substituent or even with two C substituents, if one of them carries a polar group at a site able to interact through space with the ring CO group. In these cases, only one of the two anticipated diene‐ketenes (and descendents thereof) is produced. A thorough investigation of the photochemistry of a series of structurally different cyclohexa‐2, 4‐dienones on analytical as well as on preparative scale extends our mechanistic knowledge of the various routes from diene‐ketenes into a variety of compound classes. Novel compound classes accessible to diene‐ketenes are seven‐membered carbocycles (by intramolecular aldolization of the zwitterion of appropriately substituted, transiently formed diene‐(N, O)‐ketene acetals) and β‐lactams (by Staudinger reaction).
The Structure of an Isomeric Pair of a (Tetraamine)copper(II) Compound in the solid state and in solution
Authors: Comba Peter , Hilfenhaus Peter , Nuber Bernhard
Published: December 2004

The template condensation of [Cu(3, 2, 3‐tet)]2+ (3, 2, 3‐tet = N, N″)‐(ethane‐1, 2‐diyl)propane‐1, 3‐diamine with CH2O and en (en = ethane‐1, 2‐diamine) affords the copper(II) compounds of two isomeric tricyclic ligands in high yield. The strikingly different UV/VIS and EPR spectroscopic behavior of these two compounds, [Cu(‘syn’‐L)](CIO4)2 and [Cu(‘anti’‐L)](ClO4)2 · 1/2 H2O (L = 1, 4, 8, 10, 13, 15‐hexaazatricyclo [13.3.1.14, 8]icosane), is analyzed by angular overlap model (AOM) calculations based on the experimentally determined solid‐state structures (powder spectra) and a combination of molecular mechanics and AOM calculations (MM‐AOM) for the solution‐structure behavior.