bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stereochemistry of the Inhibition of δ‐Chymotrypsin with Optically Active Bicyclic Organophosphates: 31P‐NMR studies
Authors: Ganci Walter , Meier Eric J. M. , Merckling Franco A. , Przibille Georg , Ringeisen Urs , Rüedi Peter 
Published: December 2004

AbstractThe inhibition of δ‐chymotrypsin with optically active, axially and equatorially substituted trans‐3‐(2,4‐dini‐trophenoxy)‐2,4‐dioxa‐3λ5‐phospbubicyclo[4.4.0]decan‐3‐ones ( = hexahydro‐4H‐1,3,2‐benzodioxaphosphorin 3‐oxides) was investigated. Their inhibitory power was determined by kinetic measurements, and the stereochemical course of the reaction of stoichiometric amounts of the enzyme and inhibitor was monitored with 31P‐NMR spectroscopy at pH 7.8. The irreversible inhibitors show significant enantioselectivity (the (Sp)‐enantiomer reacting faster) and yield diastereoisomeric, covalently phosphorylated derivatives of δ‐chymotrypsin.31P‐NMR Spectroscopic studies of the inhibition by the axially substituted inhibitor revealed for the racemic (±)‐2a first a resonance at –4.4 ppm and later, while inhibition proceeded, a second one at –4.5 ppm. The reaction with optically active (+)‐2a showed only one signal at –4.4 ppm and its enantiomer (–)‐2a only one signal at –4.5 ppm. Using the equatorially substituted racemic epimer (±)‐2b, we observed the main resonance at –5.3 ppm and two minor ones at –4.4 and –4.5 ppm. The optically active compound (+)‐2b showed two peaks at –4.5 and –5.3 ppm, whereas its antipode (–)‐2b revealed two signals at –4.4 and –5.3 ppm.Comparing the 31P chemical shifts of the corresponding covalent phosphoserine derivatives 4a (‐5.7 ppm, axial) and 4b (‐4.5 ppm, equatorial) shows the inhibition with the axial compounds 2a to proceed via neat inversion of the configuration at the P‐atom, whereas the equatorial epimers 2b with a higher conformational flexibility seem to follow a different stereochemical pathway which results in both inversion and retention.
Lipophilicity Behavior of Model and Medicinal Compounds containing a suilfide, sulfoxide, or sulfone moiety
Authors: Caron Giulia , Gaillard Patrick , Carrupt Pierre‐Alain , Testa Bernard 
Published: December 2004

AbstractThis study was designed to unravel lipophilicity changes associated with the oxidation state of the S‐atom in model compounds, drugs, and metabolites, special attention being given both to intermolecular and intramolecular effects. The methods used were experimental (potentiometry, CPC, and shake‐flask techniques to measure lipophilicity, 13C‐NMR spectroscopy to investigate tautomeric equilibria) and computational (quenched molecular dynamics and molecular lipophilicity potential). Simple, monofunctional model compounds were used to assess intermolecular forces, as revealed by the Δlog Poct–alk and Δlog Poct–chf parameters. Drugs and their metabolites proved to be good probes to study intramolecular effects in both neutral and anionic forms, as revealed by the difference between calculated and experimental log Poct values (the diff(log Pexp–calc) parameter). Sulindac and its metabolites showed a normal partitioning behavior, whereas the lipophilicity of sulfmpyrazone and its metabolites' was markedly affected by tautomeric and conformational equilibria.
Elektronentransfer und Ionenpaar‐Bildung. 46. Mitteilung. Titrationen von Tetracyanethen mit Alkali‐ und Erdalkalimetallen in aprotischen Lösungen
Authors: Bock Hans , Kleine Markus 
Published: December 2004

Electron Transfer and Ion‐Pair Formation: Titrations of Tetracyanoethene by Alkaline and Alkaline Earth Metals in Aprotic SolutionFor alkaline and earth alkaline metal ‘titrations’ of the π‐acceptor tetracyanoethene in aprotic (c(H⊕) < 0.1 ppm) solution, UV/VIS and ESR spectra have been measured in a sealed glas apparatus. Isosbestic points prove uniform but differing metal‐mirror reduction processes for [Li]x, [Na]x, and [K]x vs. [Cs]x. The formation of solvent‐shared or solvent‐separated contact ion pairs detected is supported by subsequent crystallization and structure determination. For the tetracyanoethene radical anion, semiempirical PM3 calculations with limited configuration interaction allow to reproduce the structural data as well as the long‐wavelength charge transfer excitation.
An Efficient Synthesis of Enantiomerically Pure Δ‐ and Δ‐Ruthenium(II)‐Labelled Oligonucleotides
Authors: Meggers Eric , Kusch Dirk , Giese Bernd 
Published: December 2004

AbstractThe synthesis of a novel tris(bidentate ligand)ruthenium(II) complex 7 and its efficient tethering to the 5′‐end of Oligonucleotides is described. The resulting Δ‐ and Δ‐isomeric ruthenium(II)‐labelled Oligonucleotides 10a‐‐c and 11a‐‐d were separated either by reversed‐phase HPLC or by polyacrylamide gel electrophoresis. The diastereoisomerically pure isomers were fully characterized by UV/VIS and CD spectroscopy, mass spectrometry, and enzymatic digestion with base analysis. We also investigated the thermal denaturation of the hybridized double strands.
Properties and Reactions of Substituted 1,2‐Thiazetidine 1,1‐Dioxides: Synthesis ofN‐Substituted 4,4‐dimethyl‐1,2‐thiazetidin‐3‐one 1,1‐dioxides, and a new base‐catalyzed rearrangement to thiazolidin‐4‐one 1,1‐dioxides
Authors: Glasl Dietmar , Otto Hans‐Hartwig , Rihs Grety 
Published: December 2004

AbstractAlkylation of 3‐oxo‐1,2‐thiazetidine 1,1‐dioxide 2 yields theN‐alkylated 3‐oxo‐β‐sultams3a‐i. Solvolysis with NaOH or NH3selectively opens the NS bond forming the sulfonate carboxamides4and the sulfonamidocarboxamides7, respectively. Furthermore, the hitherto unknown compounds of type5are prepared, representing a strained four‐membered ring with a diacylated, sulfonated N‐atom. Depending upon the reaction conditions,3b‐dand3gare rearranged by base‐catalyzed reactions into the substituted 4‐oxothiazolidine 1,1‐dioxides9or10.Structures are elucidated by spectroscopic methods, established by crystal‐structure analyses, and a possible way of formation is proposed. Furthermore, some side reactions and transformations are reported.
Synthesis of Chiral Bicyclic Bis‐lactam Components for the controlled self‐assembly of hydrogen‐bonded arrays
Authors: Brienne Marie‐JosèPhe , Gabard Jacqueline , Leclercq Martine , Lehn Jean‐Marie , Chevé Michel 
Published: December 2004

AbstractThe chiral biyclic bis‐lactams of structures 3 and 4 were synthesized from the key intermediate 2′b, the N,N′‐bis(4‐methoxybenzyl) derivative of 2 (X = MeO) (Scheme 6). The synthesis of this intermediate involved two key steps: (1) a double condensation of glyoxylic acid/anisamide (= oxoacetic acid/4‐methoxybenzamide) adduct 11c with veratrole (1,2‐dimethoxybenzene; 10) allowed the introduction of two glycine units at the 4,5‐positions of the veratrole ring to give 18c (Schemes 3 and 4); (2) in order to circumvent the hydrolysis of 4‐methoxybenzoyl protective groups which proved to be unfeasible, these groups were transformed into 4‐methoxybenzyl groups through a sequence involving thiocarbonylation followed by reduction (Scheme 5). Thereafter, the double intramolecular cyclization of the resulting diamino diester 22c proceeded easily to afford 2′b. This intermediate may be transformed via the tetrol 2′g or the diol 2′h into the N‐protected derivatives of 2 (X = OR) and of 3 (X = OCOR). Cleavage of the 4‐alkuxybenzyl groups was achieved by ceric ammonium nitrate. However, when the aromatic ring bore ether functions (N‐protected 2), this normal reaction was accompanied by the oxidative ring cleavage to give the diene‐diester structure 4 (Schemes 5 and 6).
Molecular Recognition and Enantiomer Separations on a novel chiral stationary phase based on a 9,9′‐spirobi[9H‐fluorene]‐derived molecular cleft
Authors: Cuntze Jens , Diederich François 
Published: December 2004

AbstractAn optically active molecular cleft incorporating a 9,9′‐spirobi[9H‐fluorene] spacer and two N‐(5,7‐dimethyl‐1,8‐naphthyridin‐2‐yl)carboxamide: (CONH(naphthyr)) moieties as H‐bonding sites was covalently bound to silica gel to provide the new chiral stationary phase (CSP) (R)‐16 (Scheme 2). Previous solution‐binding studies in CDCl3 had shown that the anchored molecular cleft was capable of complexing optically active dicarboxylic acids with differences in free energy of the formed diastereoisomeric complexes (Δ(ΔG0)) between 0.5 and 1.6 kcal mol−1 (T = 300 K). The optical resolution of racemic dicarboxylic acids, that are bound with a high degree of enantioselectivity in the liquid phase, was now achieved by HPLC on the CSP (R)‐16. The order of enantiomer elution was as predicted from the solution studies, and the separation factor α varied between 1.18 and 1.24. A series of 1,1′‐binaphthalene‐2,2′‐diol derivatives were also resolved on the new CSP, in some cases with baseline separation. The order of enantiomer elution under normal‐phase chromatographic conditions was rationalized by computer modeling of the association between the solute enantiomers and the immobilized molecular cleft. HPLC Separations with eluents of different polarity suggested that the attractive interactions between solute and immobilized chiral selector are a combination of H‐bonding, which prevails in apolar eluents, and aromatic π‐‐π stacking, which dominates in polar eluents.
Synthesis of Medium‐ and Large‐Ring Compounds Initiated by Photochemical Decarboxylation of ω‐Phthalimidoalkanoates
Authors: Griesbeck Axel G. , Henz Andreas , Kramer Wolfgang , Lex Johann , Nerowski Frank , Oelgemöller Michael , Peters Karl , Peters Eva‐Maria 
Published: December 2004

AbstractThe synthesis of a variety of hydroxylactams from ω‐phthalimidoalkanoates using a triplet‐sensitized photodecarboxylation reaction initiated by intramolecular photo electron transfer is described. Ring sizes available by this method span from 4 (benzazepine‐1,5‐dione 7) to 26 (cyclodipeptide 26e). Ground‐state template formation is proposed as the explanation for the high efficiency of this reaction and for the decrease in reactivity in the presence of organic bases instead of metal carbonates. The crucial step in this macrocyclization reaction seems to be the protonation of the intermediary ketyl radials (Scheme 4). Spacer groups investigated were alkyl chains (C3‐C11: 5c‐h, 11a, 12), ether (16, 18), ester (20, 22), and amide (26a‐f) linkages. Within the detection limits, no dimeric (= decarboxylative coupling) products were observed, indicating the high preference for intra‐vs. intermolecular photoelectron transfer. The C,C radical combination step proceeds with low stereoselectivity (cf, products 11 and 12) in contrast to comparable singlet reactions. Except for the lactones 22, all products were stable under the photolysis conditions. Prolonged irradiation of 22 led to the formation of the spiro compounds 23, probably via an intermediary acyliminium betaine (Scheme 8). One serious limitation of the decarboxylative macrocyclization is its incompatibility with the glycine spacer (as in 27a and 27b), probably the consequence of a strong intramolecular H‐bond (Scheme 10).
Nucleotides. Part LIII. 6‐Aminohexanoyl‐linked conjugates of monomeric and trimeric cordycepin
Authors: Wasner Marita , Pfleiderer Wolfgang , Suhadolnik Robert J. , Horvath Susan E. , Kon Ning , Guan Ming‐Xu , Henderson Earl E. , Adelson Martin E. 
Published: December 2004

AbstractTo improve cell permeability, monomeric 3′‐deoxyadenosine (cordycepin) and antivirally active trimeric 3′‐deoxyadenylyl‐(2′–5′)‐3′‐deoxyadenylyl‐(2′–5′)‐3′‐deoxyadenosine (2′–5′)d3 (A‐A‐A); (cordycepin‐trimer core) were modified at the 2′‐O‐ or 5′‐O‐position by myristic, cholic, and folic acid = tetradecanoic, 3α, 7α, 12α ‐trihy‐droxy‐5β‐cholan‐24‐oic, and N‐{4‐{[(2‐amino‐3,4‐dihydro‐4‐oxopteridin‐6‐yl)methyl]amino}benzoyl}‐L‐glutamic acid, resp., linked by a 6‐aminohexamoyl spacer. Syntheses of the trimeric educts 21, 27, and 28 were performed by phosphoramidite chemistry, using β‐eliminating 2‐(4‐nitrophenyl)ethyl (npe), 2‐(4‐nitrophenyl)ethoxycarbonyl (npeoc) and (9H‐fluoren‐9‐yl)methoxycarbonyl (fmoc) groups which allow a deprotection by DBU in an aprotic solvent without harming the ester‐bounded conjugates, to give the products 24–26 and 31–33. The metabollically stable (2′–5′)A derivatives 26 and 33, covalently linked to folic acid either at the 2′‐terminus or at the 5′‐terminus of (2′–5′)d3′(A‐A‐A), respectively, are a new class of the anti‐HIV‐1 compounds. Inhibition of HIV‐1 reverse transcriptase (RT) activity by 26 and 33 was 45 and 81%, respectively. Only 33 activated recombinant, human RNase L by 35%.
Rhodium(II)‐Catalyzed CH Insertions with {[(4‐Nitrophenyl)sulfonyl]imino}phenyl‐λ3‐iodane
Authors: Nägeli Ivo , Baud Corine , Bernardinelli GéErald , Jacquier Yvan , Moraon Mary , Müllet Paul 
Published: December 2004

AbstractThe [Rh2(OAc)4]‐catalyzed decomposition of {[(4‐nitrophenyl)sulfonyl]imino}phenyl‐λ3‐iodane (NsNIPh) resulted in formal insertions into CH bonds, activated by phenyl or vinyl groups, or by O‐substituents. Scope and limitations of the reaction were investigated. Yields of up to 84% were achieved in the most favorable cases. Yields were enhanced by electron‐releasing substituents and decreased by steric hindrance. Aziridination competed with allylic insertion with olefinic substrates. The insertion reaction proceeded with retention of configuration. With chiral RhII catalysts, a modest asymmetric induction was observed. A mechanism involving direct insertion by a Rh‐complexed nitrene into the CH bond is proposed.
Fluorescence Quenching of 2,2′‐Bithiazole‐Containing Calix[4]arenes by Copper(I). Access to the corresponding [ML2], [ML], and [M2L] copper(I) complexes
Authors: Pellet‐Rostaing Stephane , Regnouf‐de‐Vains Jean‐Bernard , Lamartine Roger , Meallier Pierre , Guittonneau Sylvie , Fenet Bernard 
Published: December 2004

AbstractThe complexing behaviour of 2,2′‐bithiazole‐containing calix[4]arenes towards Cu1 was investigated. The extinction of the intrinsic blue fluorescence of the free ligands upon addition of stoichiometric amounts of the metallic salt was used as complexation probe. This extinction was directly related to the chelation of the metal and allowed the controlled synthesis of new mono‐ and dimetalic complexes which were fully characterized.
Photochemistry of Isothiocoumarin (= 1H‐[2]benzothiopyran‐1‐one)
Authors: Bethke John , Kopf Jürgen , Margaretha Paul , Pignon Bernard , Dupont Léon , Christiaens Léon E. 
Published: December 2004

AbstractIrradiation (λ = 350 nm) of 1H‐[2]benzothiopyran‐1‐one (2) in the solid state affords selectively and in good yield 6aα, 6bα, 12bα, 12cα ‐tetrahydrocyclobuta[1, 2‐c:4, 3‐c′]bis([2]benzothiopyran)‐5, 8‐dione (3), the head‐to‐head (HH) cis‐cisoid‐cis‐cyclodimer of 2, X‐Ray analysis of 2 confirms that this reaction proceeds according to the well‐established topochemical principles. The same dimer 3 is obtained in low yields on irradiation of 10−1 M solutions of 2 in either MeOH or MeCN, while no conversion at all is observed in benzene. On irradiation of 2 in MeCN in the presence of tetrachloroethene, the [2 + 2] photocycloadduct 4 is formed in good yield, the conversion 2 → 4 being efficiently quenched by naphthalene. In contrast, no reaction is observed ‐on irradiation of 2 in the presence of 2, 3‐dimethylbut‐2‐ene, neither in polar nor in apolar solvents.
Pyranosyl‐RNA: Further Observations on Replication
Authors: Bolli Martin , Micura Ronald , Pitsch Stefan , Eschenmoser Albert 
Published: December 2004

AbstractReplication (single‐turnover) of pyranosyl‐RNA (= p‐RNA) sequences can be accomplished reliably by template‐directed ligation of 2′, 3′‐cyclophosphates of short oligomers. The ligation process was studied using (mostly) octamers as templates and tetramers as ligands. The transcription of the sequence pr(GGGCGGGC) into the (antiparallel) complementary sequence pr(GCCCGCCC) by ligation of two molecules of pr(GCCC)‐2′, 3′‐cp was investigated in detail; In aqueous 1.5M LiCI solution of pH 8.5 at room temperature (0.45 mM ligand, 0.15 m,M template), the reaction proceeds in up to 60% yield within a week. It is limited by concomitant hydrolysis of cyclophosphate groups of both reactand and ligation product as the only efficient side reaction, the latter occurring ca. three times more slowly than ligation. No ligation at all is observed in the absence of template. The reaction is highly regioselective: the (4′ → 2′) phosphodiester junction is formed exclusively; no isomeric (4′ → 3′) junctions are found. For ligation to occur, template and ligand must be homochiral and must have the same sense of chirality; with chiro‐diastereoisomeric tetramer‐2′, 3′‐cyclophosphates containing a single enantio‐ribopyra‐nosyl unit, no ligation is observed, except to a minor extent in the case of the diastereoisomer that has that unit at the 4′‐end. Observations made in experiments involving six different octamer templates containing isomeric base sequences indicate that the ligation process does not tolerate a mismatch at ligation sites. However, ligation still takes place when a mismatch occurs at either end of the (octamer) template. Ligation efficiencies differ widely, depending on the nature, as well as the sequence, of participating bases. These differences can be understood qualitatively by considering the relative stability of ternary pre‐ligation complexes, together with the differences in interstrand base stacking at ligation sites, Dominance of the latter over intrastrand base stacking is the feature of the p‐RNA structure that appears to determine most of the characteristic properties of p‐RNA.As regards the etiological context of our work on nucleic‐acid alternatives, it is essential that the chemical properties found for p‐RNA be compared with the corresponding properties of RNA. In the RNA series, the two ligations of the replicative cycle r(GGGCGGGC) ⟺ r(GCCCGCCC) using the corresponding ribofuranosyl‐te‐tramer 2′, 3′‐cyclophosphates as ligands are found to proceed also, though somewhat less efficiently than in the p‐RNA series; however, the ligation step produces exclusively the unnatural (5′ → 2′) phosphodiester junctions instead of the natural (5′→ 3′) junctions. This is in sharp contrast to p‐RNA, where template‐controlled 2′, 3′‐cyclophosphate ligations produce the ‘correct’ phosphodiester junctions.
‘Three‐Component Reaction’ with aromatic thioketones, phenyl azide, and dimethyl fumarate
Authors: Mlostoń Grzegorz , Romański Jaroslaw , Linden Anthony , Heimgartner Heinz 
Published: December 2004

AbstractThe reaction of thiobenzophenone (= diphenylmethanethione; 8a) or 9H‐fluorene‐9‐thione (8b) and methyl fumarate (9) in excess PhN3 at 80° yields a mixture of diastereoisomeric thiiranes 10 and 11 (Scheme 1). A mechanism involving the initial formation of 1‐phenyl‐4, 5‐dihydro‐1H‐1, 2, 3‐triazole‐4, 5‐dicarboxylate 12 by 1, 3‐dipolar cycloaddition of PhN3 and 9 is proposed in Scheme 2. The diazo compound 13, which is in equilibrium with 12, undergoes a further 1, 3‐dipolar cycloaddition with thioketones 8 to give 2, 5‐dihydro‐1, 3, 4‐thiadiazoles 14. Elimination of N2 yields the thiocarbonyl ylide 15 which cyclizes to the corresponding thiirane. Desulfurization of the thiiranes 10 and 11 with hexamethylphosphorous triamide leads to the olefinic compounds 16 (Scheme 3). The crystal structures of 10a, 11a, and 16b were determined.
β‐Loop, γ‐loop, and helical peptide conformations in cyclopeptides containing a steroidal pseudo‐amino acid
Authors: Albert Dieter , Feigel Martin 
Published: December 2004

AbstractThe steroidal pseudo‐amino acids 3ã‐amino‐5β‐cholan‐24‐oic acid (2a), 12ã‐acetoxy‐3ã‐ammonia‐5β‐cholan‐24‐oic acid (2b), and 7ã,12ã‐diacetoxy‐3ã‐amino‐5β‐cholan‐24‐oic acid (2c) are used as rigid spacers in the backbone of the cyclic peptides cyclo(–2a–Phe‐Phe–)2 (1a), cyclo(–2b–Phe‐Phe–)2 (1b), and cyclo(–2c‐Phe‐Phe–)2 (1c). A homogeneous β‐loop conformation is found in the peptide chains of 1a and 1b, while 1c exists as a mixture of ã‐helical and γ‐loop conformations. The structure and homogeneity of the conformations are established by several NMR techniques and are supported by molecular‐dynamics calculations. The peptide conformations depend on the distance and attraction of the two large and lipophilic steroidal parts of the cyclic molecules.
Hybridnaturstoffe: Synthese cyclischer Hydroxamsäuren der Estra‐1,3,5(10)‐trien‐Reihe
Authors: Scherlitz‐Hofmann Ina , Dubs Manuela , Krieg Reimar , Schönecker Bruno , Kluge Michael , Sicker Dieter 
Published: December 2004

AbstractAn approach to a new class of cyclic hydroxamic acids is described leading to a formal combination of a benzoxazine subunit related to some natural aglucones occurring in plants with the steroidal skeleton from two members of the estra‐1,3,5(10)‐triene series. The annelation procedure for a 4‐hydroxy‐1,4‐oxazine moiety to the aromatic A‐ring in estrone (1) and 1‐hydroxy‐4‐methylestra‐1,3,5(10)‐trien‐17‐one (7), used as steroidal precursors, proceeds in four or three steps, respectively (Schemes 1 and 2, resp.). First, a 2‐nitro group is introduced regioselectively by a novel nitrosation‐oxidation procedure or by conventional nitration (→ nitrophenols 2 and 8). Reaction of the phenolic unit of 2 and 8 with methyl bromoacetate or ethyl chlorooxoacetate gives rise to the nitro esters 3, 4, 9, and 10, which are subjected to reductive cyclization either by means of Zn dust in ammonium chloride solution (for the acetates) or of H2/Pt(S)/C (for the sensitive oxalates). Hence, the novel cyclic hydroxamic acids 5, 6, 11, and 12 of the estra‐1,3,5(10)‐triene series are obtained.
Glycosylidene Carbenes. Part 25. Glycosidation of ginkgolides B and A
Authors: Weber Martin , Vasetla Andrea 
Published: December 2004

AbstractGinkgolide B (1b) has been glucosylated in THF with the glucosylidene‐derived diazirine 2 under thermal or photochemical conditions. Depending on the amount of 2, we obtained either monoglucosides (5–8), diglucosides (13–17), or triglucosides (21–23). In keeping with earlier results, the use of THF as solvent led mostly to β‐D‐glucosides. The modest regioselectivity in the formation of the monoglucosides, glucosylated either at OC(1) or OC(10), is rationalized on the basis of the relative kinetic acidity of the intra‐ and intermolecularly H‐bonded OH groups of 1b. The tertiary HOC(3) of the monoglucosides was more readily glucosylated than the secondary HOC(1) or HOC(10) (H‐bonded). Glucosidation with 3.5 equiv. of 2 led to triglucosides, with the tri‐β‐D‐glucoside 21 (42%) as the major product. Catalytic hydrogenation afforded the free glucosides 9–12, 18–20, and 24. The di‐ and triglucosides are readily soluble in H2O. Glucosidation with 2 of the ginkgolide‐A‐derived tertiary alcohol 25 yielded 93% of the β‐D‐anomeric glucoside 26. Similarly, glycosidation of 25 with the lactosylidene‐derived diazirine 34 proceeded with a very high stereoselectivity, yielding 92% of the β‐D‐lactoside 35, that was deprotected to the H2O soluble acetate 36.
Methyl and Phenylmethyl 2‐Acetyl‐3‐{[2‐(dimethylamino)‐1‐(methoxycarbonyl)ethenyl]amino}prop‐2‐enoate in the Synthesis of heterocyclic systems: Preparation of 3‐amino‐4H‐pyrido‐[1,2‐a]pyrimidin‐4‐ones
Authors: Selič Lovro , Grdadolnik Simona Golič , Stanovnik Branko 
Published: December 2004

AbstractMethyl 2‐acetyl‐3‐{[2‐(dimethylamino)‐1‐(methoxycarbonyl)ethenyl]amino}prop‐2‐enoate (4) and phenyl‐methyl 2‐acetyl‐3‐{[2‐(dimethylamino)‐1(methoxycarbonyl)ethenyl]amino}prop‐2‐enoate (5) were prepared in three steps from the corresponding acetoacetic esters, and used as reagents for the preparation of N3‐protected 3‐amino‐4H‐pyrido[1,2‐a]pyrimidin‐4‐ones 10–12, 5H‐thiazolo[3,2‐a]pyrimidin‐5‐one 13, 4H‐pyrido[1,2‐a]‐pyridin‐4‐one 19 and 2H‐1‐benzopyran‐2‐ones 20–23. Free 3‐amino‐4H‐pyrido[1,2‐a]pyrimidin‐4‐ones 24–26 were prepared from 10–12 by removal of the 2‐(methoxycarbonyl)‐3‐oxobut‐1‐enyl or 3‐oxo‐2‐[(phenyl‐methoxy)carbonyl]but‐1‐envl as N‐protecting group by various methods.