bluuebunny/crossref_metadata_2025_split huggingface dataset:
Bildung, Kristallstruktur und absolute Konfiguration von (−)‐N‐(Chloromethyl)galanthaminium‐chlorid
Authors: Matusch Rudolf , Kreh Mirko , Müller Ulrich 
Published: December 2004

Formation, X‐Ray Crystal Structure, and Absolute Configuration of (−)‐N‐(Chloromethyl)galanthaminium ChlorideThe acetylcholinesterase inhibitor galanthamine (1), main alkaloid of several Narcissus species, readily forms a quaternary ammonium salt by reaction with the solvent CH2Cl2. The structure and absolute configuration of (−)‐N‐(chloromethyl)galanthaminium chloride (2) were determined by X‐ray diffraction (R = 0.075 for 2775 observed independent reflexions) and NMR spectroscopy. The tetragonal crystals (space group P43) contain two crystallographically independent cations which do not differ significantly from one another. The CH2Cl group is attached to the quaternary N‐atom in stereospecific (R)‐configuration. In the crystal, the configurational position of the Me group at the N‐atom of 2 differs from that of the crystalline free base 1. Hydrogen bonding is observed from the OH group at C(3) of 2 to the Cl− anion or to the Cl‐atom of an adjacent cation.
Facile Preparation of (±)‐12‐Epiprostaglandins from 7‐Oxabicyclo[2.2.1]hept‐5‐en‐2‐one via an all‐cis‐formyllactone related to Corey lactone
Authors: Vionnet Jean‐Paul , Renaud Philippe 
Published: December 2004

AbstractThe bicyclic monoselenoacetal 7, easily obtained from (±)‐7‐oxabicyclo[2.2.1]hept‐5‐en‐2‐one (6) via a radical addition‐acyl migration sequence, was converted to racemic 12‐epiprostaglandins 3 and 4. The key intermediate was the all‐cis‐formyllactone 2b related to Corey lactone (see 12; Scheme 1). The presence of a (tert‐butyl)‐dimethylsilyl protective group for the 11‐OH substituent (prostaglandin numbering) was found to be crucial in avoidingβ ‐elimination and epimerization during the Wittig‐Horner reaction (Scheme 2). Epimerization at C(12) at the formyllactone stage (see 2b) was also possible and gave the known precursor 1b of naturally occurring prostaglandins and analogs.
Thermolysis and Chemiluminescence of Monocyclic 1,2,4‐Trioxan‐5‐ones
Authors: Jefford Charles W. , Josso Martin C. , da Graça H. Vicente Maria , Hagemann Hans R. , Lovy Dominique , Bill Hans 
Published: December 2004

AbstractThe 3,6‐substituted 1,2,4‐trioxan‐5‐ones 11–14, on heating to 170–200°, underwent unimolecular thermolysis to generate electronically excited singlet ketones with an efficiency of ca. 0.2%. The chemiluminescence quantum yields (ϕoSCL) depended on the nature of the 6‐substitutents and increased linearly with temperature. The Arrhenius activation energies were obtained by measuring the rate of decay of luminescence and determined as 22.9, 30.4, 35.6, and 34.2 kcal/mol for 11–14, respectively. Step analysis of the chemiluminescence of 14 afforded an average activation energy of 44.3 kcal/mol. This latter result is explicable in terms of two decomposition paths, higher and lower in energy, leading to excited and ‘dark’ products, respectively. The thermolysis of trioxanones 12–14 lacking a H‐atom at the 6‐position is interpreted as involving successive rupture of the peroxide bond, excision of ketone at the 3‐substituted end, and loss of CO2, to finally produce ketone originating from the 6‐position (see Scheme 4).
Fast‐Atom‐Bombardment Mass Spectra of Phloroglucinols from Dryopteris Ferns
Authors: Widén Carl‐Johan , Pyysalo Heikki , Reichstein Tadeus 
Published: December 2004

AbstractFast‐atom‐bombardment mass spectra of ten phloroglucinol derivatives containing two to six ring units were recorded. The mass spectral behavior of the compounds was quite similar under these conditions. Molecular‐weight information was readily available as well as sequential structural data due to extensive fragmentation. Sequential alterations due to the rottlerone change or other analogous decomposition reactions proved to be almost lacking in fast‐atom‐bombardment mass spectrometry. The negative‐ion spectra in general showed better signal‐to‐noise ratios and more distinct fragment ions.
An Efficient Synthesis of Optically Pure (R)‐ and (S)‐2‐(aminomethyl)alanine ((R)‐ and (S)‐ama) and (R)‐ and (S)‐2‐(aminomethyl)leucine ((R)‐ and (S)‐aml)
Authors: Obrecht Daniel , Karajiannis Helena , Lehmann Christian , Schönholzer Peter , Spiegler Clive , Müller Klaus 
Published: December 2004

AbstractAn efficient synthesis of enantiomerically pure (R)‐ and (S)‐2‐(aminomethyl)alanine ((R)‐ and (S)‐Ama) 1a and (R)‐ and (S)‐2‐(aminomethyl)leucine ((R)‐ and (S)‐Aml) 1b is described (Schemes 1 and 2). Resolution of the racemic amino acids was achieved using L‐phenylalanine cyclohexylamide (2) as chiral auxiliary. The free amino acids 1a, b were converted to the Nα‐Boc,Nγ‐Z‐protected derivatives 11a, b (Scheme 3) ready for incorporation into peptides. Based on the three crystal structures of the diastereoisomeric peptides 8a, 8b, and 9b, the absolute configurations in both series were determined. β‐Turn type‐I geometries were observed for structures 8b and 9b, whereas 8a crystallized in an extended backbone conformation.
Synthetic Studies towards Pseurotin A. Part 3. Synthesis of a related highly functionalized γ‐lactone
Authors: Su Zhuang , Tamm Christoph 
Published: December 2004

AbstractA new general concept for the total synthesis of pseurotin A (1), a secondary metabolite of Pseudeurotium ovalis STOLK, which possesses a highly substituted 1‐oxa‐7‐azaspiro[4.4]nonane skeleton, is presented. A key intermediate of the planned reaction sequence is the functionalized γ‐lactone 8. The corresponding protected compound 52 was prepared using (S)‐O,O‐isopropylideneglyceraldehyde (13) and the bromoacetal 14 as starting material. γ‐Lactone 52 was obtained in enantiomerically pure state in ten steps. It possesses the desired configuration.
Die Reaktion von 1‐Halogeno‐1‐Lithiocyclopropanen mit CuCl2: Konkurrenz zwischen ‘Carben‐Dimerisierung’ und oxidativer Kupplung
Authors: Borer Markus , Loosli Thomas , Minger Andrea , Neuenschwander Markus , Engel Peter 
Published: December 2004

The Reaction of 1‐Halogeno‐1‐lithiocyclopropanes with CuCl2: Competition between ‘Carbene Dimerization’ and Oxidative CouplingThe 1‐chloro‐1‐lithiocyclopropanes 2a–d react at low temperature with CuCl2 to give diastereoisomeric mixtures of oxidative‐coupling products 5a–d and of ‘carbene dimers’ 6a–d. The relative amount of 5a–d increases with CuCl2 concentration and reaction time. Diastereoselectivity of the reaction seems to be low, and separation as well as spectroscopic structure assignment of single diastereoselectivity of the reaction seems to be low, and separation as well as spectroscopic structure assignment of single diastereoisomers are difficult. The conformational behavior of 1,1′‐dichloro‐1,1′‐bi(cyclopropyls) 5c and 5d is discussed. Contrary to 2a–d, 1‐bromo‐1‐lithiocyclopropanes normally react with CuCl2 to give ‘carbene dimers’ 6 and no coupling products 5. So far the only exception is 1‐bromo‐1‐lithio‐2‐phenylcyclopropane 2e which in the presence of CuCl2 gives some percents of coupling products 5e besides carbene dimers 6b as main products. An X‐ray structure analysis of the predominant diastereoisomer 5e was performed.
Nucleosides. Part LIX. The 2‐(4‐nitrophenyl)ethylsulfonyl (Npes) Group: A New Type of Protection in Nucleoside Chemistry
Authors: Pfister Magdalena , Schirmeister Helga , Mohr Marion , Farkas Silke , Stengele Klaus‐Peter , Reiner Tilman , Dunkel Martin , Gokhale Surendra , Charubala Ramamurthy , Pfleiderer Wolfgang 
Published: December 2004

AbstractThe 2‐(4‐nitrophenyl)ethylsulfonyl (npes) group is developed as a new sugar OH‐blocking group in the ribonucleoside series. Its cleavage can be performed in a β‐eliminating process under aprotic conditions using 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) as the most effective base. Since sulfonates do not show acyl migration, partial protection of 1,2‐cis‐diol moieties is possible leading to new types of oligonucleotide building blocks. A series of Markiewicz‐protected ribonucleosides 1–10 is converted into their 2′‐O‐[2‐(4‐nitrophenyl)ethylsulfonyl] derivatives 29–38 in which the 5′‐OSi bond can be cleaved by acid hydrolysis forming 39–45. Subsequent monomethoxytritylation leads to 46–50, and desilylation affords the 5′‐O‐(monomethoxytrityl)‐2′‐O‐[2‐(4‐nitrophenyl)ethylsulfonyl]ribonucleosides 51–55. Acid treatment to remove trityl groups do also not harm the npes group (→56–58). Unambiguous syntheses of fully blocked 2′‐O‐[2‐(4‐nitrophenyl)ethylsulfonyl]ribonucleosides 96–102 are achieved from the corresponding 3′‐O‐(tert‐butyl)dimethylsilyl derivatives. Furthermore, various base‐protected 5′‐O‐(monomethoxytrityl)‐ and 5′‐O‐(dimethoxytrityl)ribonucleosides, i.e. 59–77, are treated directly with 2‐(4‐nitrophenyl)ethylsulfonyl chloride forming in all cases a mixture of the 2′,3′‐di‐O‐ and the two possible 2′‐ and 3′‐O‐monosulfonates 107–148 which can be separated into the pure components by chromatographic methods. The npes group is more labile towards DBU cleavage than the corresponding base‐protecting 2‐(4‐nitrophenyl)ethyl (npe) and 2‐(4‐nitrophenyl)ethoxycarbonyl (npeoc) groups allowing selective deblocking which is of great synthetic potential.
Intermediacy of Proton‐Bound Dimers and Ion/Dipole Complexes in the Unimolecular Decompositions of Dialkyl‐Peroxide Radical Cations: Evidence for a coupled proton and hydrogen‐atom transfer
Authors: Schalley Christoph A. , Schröder Detlef , Schwarz Helmut 
Published: December 2004

AbstractThe unimolecular fragmentation reactions of the radical cations of diethyl, diisopropyl, dipropyl, isopropyl propyl, and di(tert‐butyl) peroxide have been investigated by mass spectrometric and isotopic labeling techniques. Two competing pathways for unimolecular decomposition in the μs time regime (metastable ions) are observed: i) A combination of an α‐CC bond cleavage and a H migration gives rise to proton‐bound dimers of two ketone or aldehyde molecules. ii) Ion/dipole complexes of alkyl cations and alkylperoxy radicals are generated by C–O bond cleavage. These complexes either exhibit direct losses of alkylperoxy radicals, or they rearrange via a coupled proton and H‐atom transfer, this sequence of unprecedented isomerizations is completed by losses of alkyl radicals. Collisional activation experiments confirm that the ionic products of the latter process correspond to RR′COOH+; these ions can be regarded as protonated carbonyl oxides. In addition, we observe the elimination of alkenes leading to hydroperoxide radical cations and the expulsion of HO radicals. The latter process implies a CC bond formation step between the two alkyl fragments leading to higher alkyl cations.
Reactions of Enone Ethylene Ketals with Methyl Diazomalonate/Bis(acetylacetonato)copper(II)
Authors: Sezer özkan , Daut Ayşe , Anaç Olcay 
Published: December 2004

AbstractSeveral cyclic and acyclic enones and their ethylene ketals/acetals were reacted with dimethyl diazomalonate under bis(acetylacetonato)copper(II) catalysis. Cyclohex‐2‐en‐1‐one (1) yielded only C–H insertion products 2 and 3, whereas but‐3‐en‐2‐one gave a cyclopropane albeit in very low yield. The ethylene ketals 6 of cyclopent‐2‐en‐1‐one and cyclohex‐2‐en‐1‐one gave the corresponding cyclopropanes 7, which were in turn cleaved to the ketones 8. The acetals 9 and 10 of crotonaldehyde ((E)‐but‐2‐enal) and cinnamaldehyde ((E)‐3‐phenylprop‐2‐enal), respectively, yielded C–O insertion and [2,3]‐sigmatropic rearrangement products 11b, c and 12b, c, as well as cyclopropanes 11a and 11b, all of which are polyfunctional and synthetically useful compounds.
Leucascandrolide A, a New Type of Macrolide: The first powerfully bioactive metabolite of calcareous sponges (Leucascandra caveolata, a new genus from the coral sea)
Authors: D'Ambrosio Michele , Guerriero Antonio , Pietra Francesco , Debitus Cécile 
Published: December 2004

AbstractLeucascandrolide A ((+)‐1), a doubly O‐bridged 18‐membered macrolide of a new type, i.e., showing little C1‐branching vs. extensive 1,3‐dioxygenation and a peculiar side chain, was isolated from a calcareous sponge of a new genus, Leucascandra caveolata BOROJEVIC and KLAUTAU from the Coral Sea. Transesterification of (+)‐1 gave the methyl ester 3, derived from the side chain, and the 5‐hydroxy derivative (+)‐2, derived from the macrolide portion and with the natural configuration at C(5) (axial). Mosher's MTPA esters 4 and 5 obtained from (+)‐2 showed scattered Δδ = (δ(S) − δ(R)) data. However, inversion of the configuration at C(5) led, via ketone (+)‐6, to the less encumbered 5‐equatorial hydroxy derivative (+)‐7, whose MTPA esters 8 and 9 gave consistent Δδ data, allowing the assignment of the absolute configuration of (+)‐7, and hence of (+)‐1. The structural novelty of (+)‐1 and its powerful antifungal and cytotoxic activities are likely to renew interest in calcareous sponges, previously limited to scarcely biologically active 2‐aminoimidazoles.
Gas‐Phase Reactions of Aliphatic Alcohols with ‘Bare’ FeO+
Authors: Schröder Detlef , Wesendrup Ralf , Schalley Christoph A. , Zummack Waltraud , Schwarz Helmut 
Published: December 2004

AbstractIon/molecule reactions of ‘bare’ FeO+ with linear and branched aliphatic alcohols have been examined by Fourier‐transform ion‐cyclotron resonance mass spectrometry. Depending on the chain length of the alcohol, three different types of reactions can be distinguished: (i) Oxidation of the alcohols in the α‐positions, to yield the corresponding carbonyl‐Fe+ complexes, involves an initial OH bond activation of the alcohol resulting in the formation of ROFe+OH as the central intermediate. (ii) The formation of Fe(OH), concomitant by loss of the corresponding neutral alkenes, competes with the generation of neutral OFeOH and a carbocation R+. These couples point to the existence of an intracomplex acid‐base equilibrium and are connected with each other by a proton transfer from either acid to the other, e.g. i‐C3H + OFeOH⇄C3H6 + Fe(OH). The process is driven by the Lewis acidity of FeO+ and starts with the abstraction of a hydroxide anion from the alcohol. (iii) For longer alcohols, e.g. pentanol, functionalization of non‐activated CH bonds which are remote from the O functionality is observed. Here, the OH group of the alcohol serves as an anchor, which directs the reactive metal‐oxide cation toward a particular site of the hydrocarbon chain.
Synthesis of 4‐acetylcolchicine
Authors: Kouroupis Pavlos , Linden Anthony , Hansen Hans‐Jürgen 
Published: December 2004

AbstractThe synthesis of 4‐acetylcolchicine (1) by Swern dehydrogenation of the corresponding mixture of 4‐[(R)‐1‐hydroxyethyl]‐ and 4‐[(S)‐1‐hydroxyethyl]colchicine (3a and 3b, respectively) is described (cf. Scheme). The X‐ray analysis of 1 (cf. Fig.), crystallized from MeOH, showed the presence of MeOH in the crystals.
Synthesis of (15N2)[17O]Urea, (15N2)[O2, O4‐17O2]Uridine, and (15N3)[O2‐17O]Cytidine
Authors: Amantea Antonio , Henz Matthias , Strazewski Peter 
Published: December 2004

AbstractA general synthetic approach for the synthesis of 15N‐ and 17O‐doubly labelled pyrimidine nucleosides is described. The 15N isotopes in uridine and the 17O isotope in the urea‐derived carbonyl group of uridine and cytidine originate from (15N2)[17O]urea (5) which was synthesized from 15NH4Cl, thiophosgene (1), and H2[17O]. The third 15N isotope of cytidine in 4‐position stems from the substitution of the 1,2,4‐triazole moiety of (15N2)[O2‐17O]uridine derivative 8a/b with 15NH4OH. Hydrolysis of the same key intermediate 8a/b with Na[17O]H/H2[17O] introduced the second 17O isotope into the 4‐position of uridine. The 15N‐ and 17O‐NMR spectra of the target compounds 12 and 14 in phosphate‐buffered H2O serve as references for heteronuclear NMR spectra of labelled RNA fragments.
Ring‐Opening Reaction of a Dihydrozirconafuran (= 2,5‐Dihydro‐1,2‐oxazirconole): An equilibrium studied by NMR methods, and its chemical consequences
Authors: Baumann Wolfgang , Ohff Andreas , Ebener Michael 
Published: December 2004

AbstractThe dihydrozirconafuran 3 (2,2‐di(cyclopenta‐2,4‐dien‐l‐yl)‐2,5‐dihydro‐5,5‐dimethyl‐3,4‐bis(trimethylsilyl)‐1,2‐oxazirconole) is a valuable synthetic equivalent to the 14‐electron fragment Cp2ZrThroughout this paper, Cp=η5−C5H5
. The reactions of this metallacycle suppose an equilibrium with an ‘opened’ form [ZrCp2(RCCR)(acetone)], the latter paving the way to numerous ligand replacements. In a solution containing the dihydrozirconafuran and acetone, these reactions are reversible and degenerate, and can be studied by NMR methods: by two‐dimensional spectroscopy and by observation of the isotope‐induced chemical shifts that occur upon incorporation of (D6)acetone into the metallacycle. The findings give an indirect proof of the described equilibrium.
Ein alternativer Zugang zum PQQ‐Triester
Authors: Sicker Dieter , Stehfest Ekkehard , Wilde Horst , Martin Pierre 
Published: December 2004

An Alternative Approach to the PQQ‐TriesterA novel approach to triethyl 5‐methoxy‐1H‐pyrrolo[2,3‐f]quinoline‐2,7,9‐tricarboxylate (6), a close precursor of the redox cofactor PQQ of bacterial dehydrogenases, is described. Diethyl 2‐oxopent‐3‐ynedioate (5) was used as building block for the annelation of the quinoline unit. The annelation proceeds in two steps via the diastereoselective formation of diethyl (Z)‐4‐{[2‐(ethoxycarbonyl)‐5‐methoxyindol‐6‐yl]amiono}‐2‐oxopent‐3‐enedioate ((Z)‐7) followed by acid‐catalyzed cyclocondensation.
ESR Study of Nitroxide Radicals Generated from Triaz‐2‐en‐1‐ols
Authors: Omelka Ladislav , Vrábel Imrich , Erentová Katarína , Dauth Jochen , Deubzer Bernward , Weis Johann 
Published: December 2004

AbstractThe triazenols 4‐R1C6H4NNN(OH)R2 (1), oxidized with t‐BuO radicals, produced nitroxide radicals R1C6H4N(O⋅)NN(R2) +O− (5). The suggested radical structure was confirmed by 15N‐labeling. The reaction of triazenols 1 with PbO2 proceeded under N2 elimination, in which case nitroxides R1C6H4N(R2)O⋅(2) were observed as the final radical products. The intermediate R1C6H radicals were identified by spin‐trapping.
Synthese monodisperser linearer und cyclischer Oligomere der (R)‐3‐Hydroxybuttersäure mit bis zu 128 Einheiten
Authors: Lengweiler Urs D. , Fritz Monica G. , Seebach Dieter 
Published: December 2004

Monodisperse Linear and Cyclic Oligo[(R)‐3‐hydroxybutanoates] Containing up to 128 Monomeric UnitsUsing benzyl ester/(tert‐butyl)diphenylsilyl ether protection, (COCl)2/pyridine esterification conditions, and a fragment‐coupling strategy (with H2/Pd‐C debenzylation and HF · pyridine desilylation), linear oligomers of (R)‐3‐hydroxybutanoic acid (3‐HB) containing up to 128 3‐HB building blocks (mol. weight > 11 000 Da) are assembled (Schemes 1,2,5, and 6). In contrast to the previously employed protecting‐group combination, and due to the low‐temperature esterifying conditions, this procedure leads to monodisperse oligomers: all steps occur without loss of single 3‐HB units. The product oligomers with two, one, and no terminal protecting groups (mostly prepared in multi‐gram amounts) are characterized by all standard spectroscopic methods, especially by mass spectroscopy (Figs. 2 and 3), by their optical activity, and by elemental analyses. Cyclization of the oligo[(R)‐3‐hydroxybutanoic acids] with up to 32 3‐HB units, using thiopyridine activation and CuBr2 for the ring closure, produces oligolides consisting of up to 128 ring atoms (Scheme 7). Mixed oligolides containing 3‐HB and (R)‐3‐hydroxypentanoic units are prepared from the corresponding linear trimers, using Yamaguchi's method for the ring closure (Scheme 8 and Fig.4 (X‐ray crystal structures of two folded conformers)). Comparisons of melting points (Table 1), of [α] values (Tables 2 and 3), of 1H‐NMR coupling constants (Table 3), and of molecular volume/hydroxyalkanoate unit (Table 4) of linear and cyclic oligomer derivatives and of the high‐molecular‐weigh polymer show that the monodisperse oligomers appear to be surprisingly good models for the polymer. Besides this insight, our synthesis is supplying the samples to further test the role of P(3‐HB) (ca. 140 units) as a component of complexes forming channels through cell‐wall phospholipid bilayers.
Synthesen von 2,3‐Dioxoalkylphosphonaten und anderer neuartiger β‐Ketophosphonate sowie eines Phosphinopyruvamids ( = (Alkyloxyphosphinyl)pyruvamids)
Authors: Neidlein Richard , Feistauer Helmut 
Published: December 2004

Syntheses of 2,3‐Dioxoalkylphonates and Other Novel β‐Ketophosphonates As Well As of a Phosphinopyruvamide ( = (Alkyloxyphosphinyl)pyruvamide)The new 3‐(diethoxyphosphoryl)‐2‐oxopropanoates 5 and 6 and ‐propanamides 1–4 with various amino substituents at C(3) were prepared (Scheme 2). These compounds exist, depending on N‐substitution, as pure (E)‐enols (in the case of1 and 5) or as a mixture of three tautomeric forms (in the case of 1–4 and 6). The configuration could be unambiguously assigned from the 1H‐, 13C‐, and 31P‐NMR spectra. Phosphinopyruvamide ( = (alkyloxyphosphinyl)pyruvamide) 9 was prepared in a similar manner in spite of the instability of phosphinate derived carbanions. Some 3‐(ethoxyimino)‐2‐oxobutylphosphonates, 11–13 (Scheme 5), and various 3,3‐dimethoxy‐2‐oxoalkylphosphonates, 19–23 and 26–33 (Scheme 6), were available from the reaction of lithioalkylphosphonates with 2‐(ethoxyimino)propanoates and 2,2‐dimethoxyalkanoates, respectively. The 3,3‐dimethoxybutylphosphonates 20, and 26–30 were cleaved to give 2,3‐dioxobutylphosphonates 34–39 (Scheme 6). This method provides easy access to a new class of potentially pharmaceutically useful compounds.