bluuebunny/crossref_metadata_2025_split huggingface dataset:
Isolierung und Struktur von langkettigen Alkylphenolen und ‐pyrocatecholen aus Plectranthus albidus (Labiatae)
Authors: Bürgi Christoph , Rüedi Peter 
Published: December 2004

Isolation and Structure of Long‐Chain Alkylphenols and ‐catechols from Plectranthus albidus (Labiatae)From the title plant, a series of even‐numbered long‐chain, phenol‐ or pyrocatechol‐derived 1‐arylalkan‐5‐ones was isolated by classical chromatography and preparative reversed phase HPLC. By chemical and spectroscopic methods, including coupled chromatographic techniques (GC/MS/FT‐IR, HPLC/MS), their structures were established to be 1‐(4′‐hydroxyphenyl)tetradecan‐5‐one (2a), 1‐(4′‐hydroxyphenyl)hexadecan‐5‐one (2b), 1‐(4′‐hydroxyphenyl)octadecan‐5‐one (2c), and (Z)‐1‐(4′‐hydroxyphenyl)octadec‐13‐en‐5‐one (2d); (E,E)‐1‐(3′,4′‐dihydroxyphenyl)deca‐1,3‐dien‐5‐one (1a), 1‐(3′,4′‐dihydroxyphenyl)dodecan‐5‐one (3a), 1‐(3′,4′‐dihydroxyphenyl)‐tetradecan‐5‐one (3b), 1‐(3′,4′‐dihydroxyphenyl)hexadecan‐5‐one (3c), 1‐(3′,4′‐dihydroxyphenyl)octadecan‐5‐one (3d), 1‐(3′,4′‐dihydroxyphenyl)icosan‐5‐one (3e), and (Z)‐1‐(3′,4′‐dihydroxyphenyl)octadec‐13‐en‐5‐one (3f). In vitro, the compounds show significant antioxidant activity, the inhibitory concentration of the most potent one, 1a, being slightly lower than for 2‐(tert‐butyl)‐4‐methoxyphenol (BHA) and 2,6‐di(tert‐butyl)‐4‐methylphenol (BHT) in the Fe2+‐catalysed autooxidation of linoleic acid, whereas the acitivities of phenols 2a–d are in the same order of magnitude as α‐tocopherol.
Hetero‐Diels‐Alder cycloadditions of α,β‐unsaturated acyl cyanides. Part 2. Reactions with N,N‐dimethyluracils, a new route to 5‐substituted uracil derivatives
Authors: Zhuo Jin‐Cong , Wyler Hugo 
Published: December 2004

AbstractThe [4 + 2] cycloadditions of 2‐oxobut‐3‐enenitrile (1a), 2‐oxopent‐3‐enenitrile (1b), and ethyl 4‐cyano‐4‐oxobut‐2‐enoate (1c) with 1,3‐dimethyluracil (2), 1,3, 6‐trimethyluracil (9), or 1,3,5‐trimethyluracil (16) were investigated. The reactions of 1a with 2 or with 9 lead to bicyclic adducts 3 and 10, respectively. These hexahydro‐cis‐pyranopyrimidines undergo ring opening under acidic conditions, restoring in 4 and 11, respectively, an uracil system comprising 2‐hydroxybut‐2‐enenitrile as a side chain at C(5). The surprisingly stable enols tautomerize slowly to the corresponding acyl cyanides 6a and 13a, respectively. Reacting 1b or 1c with 2 and with 9 does not afford cycloadducts; instead the uracil derivatives 6b, c and 13b, c, respectively, show up, carrying at C(5) α‐oxobutanenitrile side chains. Cleavage of the acyl cyanide functions in 6a–c and 13a–c with nucleophilic agents produces various acids, esters, or amides, i.e. derivatives 8a–c and 15–c, respectively. The methyl esters 8a (X  MeO, R  H) and 15a (X  MeO, R  H) are also formed directly from the adducts 3 and 10, respectively, with acid or base catalysis in presence of MeOH. The cycloadducts 17a and 17c, resulting from the reaction of 1a and 1c with 16, respectively, have a Me group at the ring junction C(4a) and are stable. The structure of 17c proves that this hetero‐Diels‐Alder addition of inverse electron demand follows the endo‐mode.
Synthesis and NMR‐Spectroscopic Structure Determination of Novel 7,7′‐Diphenyl‐7,7′‐diapocarotenoids
Authors: Hand Elli S. , Belmore Kenneth A. , Kispert Lowell D. 
Published: December 2004

AbstractWittig reaction of crocetindial (1) and benzylidenetripenylphosphorane (2) gave (7E, 7′Z)‐7,7′‐diphenyl‐7‐7′‐diapocarotene (3), instead of the previously reported (7E, 7′E)‐isomer. Similar reaction of 8,9‐didehydrocrocetindial (4) with 2 yielded the three acetylenic isomers 5a–c which differ in the configuration of the terminal double bonds. Structures were established by 1D‐ and 2D‐NMR studies. Illustrative spectra and their interpretation are presented. Most chemical shifts of corresponding protons in 3 and 5 and nearly identical, but 13C shifts differ considerably.
Catalytic Cyclophanes. Part VIII. Cytochrome P‐450 activity of a porphyrin‐bridged cyclophane
Authors: Benson David R. , Valentekovich Robert , Tam Suk‐Wah , Diederich François 
Published: December 2004

AbstractFollowing a known synthetic procedure, the porphyrin‐cyclophane 1 having a porphyrin attached by two straps to an apolar cyclophane binding site was prepared. Upon metallation, the ZnII and FeIII derivatives 2 and 3, respectively, were obtained in good yields. Treatment of 3 with base yielded the μ‐oxo dimer 4 in which the two oxo‐bridged porphyrins moieties are both capped by cyclophane binding sites. All compounds 1–4 are freely soluble in protic solvents such as MeOH and CF3CH2OH, and the FeIII derivatives 3 and 4 are active cytochrome P‐450 mimics in these protic environments. Strong inclusion complexation of polycyclic aromatic hydrocarbons by 1 and 3 in alcoholic solvents was observed and quantified by 1H‐NMR and UV/VIS titrations. Acenaphthylene binds in an ‘equatorial’ orientation which locates its reactive 1,2‐double bond near the porphyrin center, whereas phenanthrene binds ‘axially’ with the reactive 9,10‐double bond oriented away from the porphyrin. The reduction potential of 3 was not significantly altered by substrate binding. In the unbound form, the FeIII center in porphyrin 3 was found by ESR and 1H‐NMR to prefer a high‐spin state (S = 5.2). In CF3CH2OH, using iodosylbenzene as O‐transfer agent, the FeIII derivative 3 catalyzed the oxidation of acenaphthylene to acenaphthen‐1‐one (14). Phenanthrene inhibited the reaction, possibly as a result of strong but nonproductive binding. Under similar conditions, isotetralin (18) was aromatized with high turnover to 1,4‐dihydronaphthalene. The μ‐oxo dimer 4 also showed high activity in the oxidation of acenaphthylen in MeOH, a result which provides strong evidence for efficent supramolecular catalysis. Due to as yet unknown reaction channels leading to polymeric products, poor mass balances were generally obtained in the oxidations effected in MeOH and CF3CH2OH in the presence of PhIO.
Preparation of optically active flowery and woody‐like odorant ketones via Corey‐Chaykovsky oxiranylation: Irones and analogues
Authors: Chapuis Christian , Brauchli Robert 
Published: December 2004

Abstractα‐, β‐, and γ‐Irones and analogues have been prepared from optically active ketones (+)‐1, (+)‐6a,b, and (+)‐17, via a Corey‐Chaykovsky oxiranylation (Me2S, Me2SO4, Me2SO, NaOH) followed by isomerisation (SnCl4 or MgBr2). (+)‐Dihydrocyclocitral (19a), obtained from (−)‐citronellal, and analogue (+)‐19b, were condensed with various ketones to afford (+)‐21a–f, and after hydrogenation (+)‐22a–f. A mild oxidative degradation of aldehydes (+)‐trans‐and (−)‐cis‐8a,b, to ketones (−)‐16a,b, as well as olfactive evaluations, 13C‐NMR assignments, and absolute configurations of the intermediate epoxides, aldehydes, and alcohols are presented.
Reactions of Nucleosides with 1,8‐Diazabicyclo[5.4.0]undec‐7‐ene (DBU). Syntheses of N(3)‐Methylene‐Bridged Bis‐uridines and Secouridine‐Dinucleoside Analogs
Authors: Čaplar Vesna , Škarić Vinko 
Published: December 2004

AbstractDiasteroisomeric secouridine derivatives, appropriately protected and activated, served as starting compounds in the reactions with 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) in various solvents (CH2Cl2, MeCN, or dimethylformamide (DMF)). Reactions with DBU/CH2Cl2 gave N(3)‐methylene‐bridged bis‐secouridines and bis‐uridines (Scheme 3), while the reactions with DBU in non‐alkylating solvents resulted in formation of secdinucleosides as the result of intermolecular ‘dimerizations’ (Scheme 2).
Sponge‐Derived Polyunsaturated C16 Di‐ and Tribromocarboxylic Acids
Authors: Ichiba Toshio , Scheuer Paul J. , Kelly‐Borges Michelle 
Published: December 2004

AbstractOne previously described and two new bromo‐substituted polyunsaturated C16 fatty acids were isolated from an Indonesian sponge, Oceanapia sp. Their common structural feature is an (13E, 15Z)‐14,16‐dibromodiene terminus. They differ in their C(5) to C(10) portions in unsaturation and halogenation. All three compounds are unstable oils. The mixture exhibits mild cytotoxicity against KB cells.
Cationic RhI Complexes of Azulenes and Their Catalytic Activity on the Formation of Heptalene‐1,2‐dicarboxylates from Dimethyl Acetylenedicarboxylate and Azulenes
Authors: Rippert Andreas Johannes , Linden Anthony , Hansen Hans‐Jürgen 
Published: December 2004

Abstract[Rh1(η5‐azulene)(cod)]+BF complexes 3a–g (cod = (Z,Z)‐cycloocta‐1,5‐diene) have been synthesized by reaction of [Rh1(cod)]+BF in THF with the corresponding azulenes 1a–g (Table 1). The structure of [Rh1(cod)(η5‐guaiazulene)]+BF (3a) has been determined by X‐ray diffraction analysis (Fig. 1 and 2). The Rh‐atom is oriented above the five‐membered ring of the azulene with almost equal RhC distances to all five C‐atoms of the ring. The (Z,Z)‐cycloocta‐1,5‐diene ring occurs in two enantiomorphic distorted (C2v → C2) tub conformations in the crystals (Fig. 3). In CDCl3 solution, the cod ligand in the complexes 3 shows a dynamic behavior on the 1H‐NMR time scale which is best explained by rotation of the cod ligand relative to the azulene ligands around an imaginary codRhazulene axis. The new complexes 3 catalyze the formation of heptalene‐1,2‐dicarboxylates 2 from dimethyl acetylenedicarboxylate (ADM) and the corresponding azulenes 1 just as effectively as [RuH2(PPh3)4] and the analogous [RhH(PPh3)4] complex in MeCN solution (Table 3). On grounds of simplicity, 3 can be generated in situ, when [RhCl(cod)]2 is applied as catalyst (Table 3).
Intramolecular Site Exchange of Carbonyl Ligands in the Cluster Compounds Nonacarbonyl{μ3‐[η3‐(1,3,5‐trithiane)]}triruthenium ([Ru3(CO)9{μ3‐(η3‐C3H6S3)}]) and (tert‐Butyl Isocyanide)octacarbonyl‐{μ3‐[η3‐(1,3,5‐trithiane)]}triruthenium ([Ru3(t‐BuNC)(CO)8{μ3‐(η3‐C3H6S3)}])
Authors: Laurenczy Gábor , Merbach Andrée. , Moullet Bertrand , Roulet Raymond , Hoferkamp Lisa , Süss‐Fink Georg 
Published: December 2004

AbstractVariable‐temperature and ‐pressure 13C‐NMR studies of the 1,3,5‐trithiane‐capped triruthenium clusters [Ru3(CO)9{μ3‐(η3‐1,3,5‐trithiane)}] (1) and [Ru3(t‐BuNC)(CO)8{μ3‐(η3‐1,3,5‐trithiane)}] (2) revealed that CO site exchanges occur via an intramolecular merry‐go‐round process, involving a transition state mostly dissociative in character.
Synthese und Eigenschaften der Furo‐ und Thieno‐Analogen von PQQ‐Triester
Authors: Martin Pierre , Winkler Tammo 
Published: December 2004

Synthesis and Characterization of the Furo and Thieno Analogues of the Triester of PQQWe report here the synthesis and properties of the furo and thieno analogues of 4,5‐dihydro‐4,5‐dioxo‐1H‐pyrrolo[2,3‐f]quinoline‐2,7,9‐ tricarboxylic acid ( = PQQ), i.e. the furo‐ and thieno[2,3‐f]quinoline‐4,5‐quinone (FQQ and TQQ, resp.) derivatives B and C, obtained as triesters. The triester of PQQ derivative A is much more stable than the triesters of B or C, and only the triester of A shows strong activity in nonenzymatic catalytic oxidations.
Metal complexes with macrocyclic ligands. Part XXXVI. Thermodynamic and kinetic studies of bivalent and trivalent metal ions with 1,4,7,10‐tetraazacyclododecane‐1,4,7‐triacetic acid
Authors: Cai Hui‐Zhi , Kaden Thomas A. 
Published: December 2004

AbstractNMR, potentiometric, and UV/VIS measurements were run to study the protonation and the In3+ and Cu2+ stability constants of 1,4,7,10‐tetraazacyclododecane‐1,4,7‐triacetic acid (do3a, L). The protonation of do3a follows the typical scheme with two high and several low log KH values. Between pH 11 and 13, the protonation mainly occurs at the N‐atom, which is not substituted by an acetate side chain. The In3+ complex is not appreciably protonated even at low pH values (pH ⋐ 1.7), whereas [CuL] can add up to three protons in acidic solution to give the species [CuLH], [CuLH2], and [CuLH3], the stability of which was determined. The formation rates of the Y3+, Gd3+, Ga3+, and In3+ complexes with do3a were measured using a pH‐stat technique, whereas that of Cu2+, being faster, was followed on a stopped‐flow spectrophotometer. In all cases, the reaction scheme implies the rapid formation of partially protonated intermediates, which rearrange themselves to the final product in the rate‐determining process. ([MLH])in, an intermediate, in which the metal ion probably is coordinated by two amino acetate groups, proved to be the reactive species for Y3+, Gd3+, and Ga3+. The formation of [Cu(do3a)] was interpreted by postulating that either ([CuLH])in or ([CuLH])in, and ([CuLH2])in are the reactive complexes. The rates of dissociation of the Y3+, Gd3+, and Cu2+ complexes with do3a were studied spectrophotometrically. For Y3+ and Gd3+, arsenazo III was used as a scavenger, whereas for Cu2+ the absorption associated with d‐d* transition was followed. For [Y(do3a)] and [Gd(do3a)], the rate law follows the kinetic expression kobsd  k0 + k1[H+]. The dissociation of [Cu(do3a)] goes through the proton‐independent dissociation of [CuLH3], which is the main species at low pH.
Enantioselective Formation of Bicyclic Lactones by Rhodium‐Catalyzed Intramolecular CH‐insertion reactions
Authors: Müller Paul , Polleux Philippe 
Published: December 2004

AbstractThe decomposition of cyclohexyl diazoacetate (5a) in the presence of the chiral [Rh2{(2S)‐mepy}4] catalyst leads to a 3:1 cis/trans mixture of bicyclic lactone 6a with an enantiomeric excess of 95–97% (cis) and 90% (trans). The conformationally rigid tert‐butyl derivatives 5b and 5c afford, in the presence of the same catalyst, 6b and 6c, respectively, via insertion into the equatorial CH bonds exclusively, with ee's of ca. 95%. A remarkable degree of induction (92–95%) results in the lactone 6g upon decomposition of 1‐isopropyl‐2‐methylpropyl diazoacetate (5g). The diazoacetates derived from 1‐methylcyclohexanol, cyclopentanol and 1‐methylcyclopentanol (5d–f) afford under similar conditions insertion products with higher diastereoselectivity, but significantly lower enantioselectivity. Other dirhodium catalysts are less efficient.
Synthesis of a New Bivalent Hirudin Analog (hirufos), which includes a stable 4′‐phosphono‐L‐phenylalanine mimic of (L‐tyrosine O4‐sulfate)‐63
Authors: Thurieau Christophe , Guyard Christel , Simonet Serge , Verbeuren Tony J. , Fauchère Jean‐Luc 
Published: December 2004

AbstractThe synthesis on solid phase of a new derivative of the anticoagulant protein hirudin is described (see Scheme and Fig.1, I). The henicosapeptide is a bivalent conjugate of the C‐terminus of hirudin and of the active‐site‐binding tetrapeptide D‐Phe‐Pro‐Arg‐Pro linked via a tetraglycine spacer. The peptide, for which the name hirufos was coined, incorporates a stable phosphono derivative of L‐phenylalanine which, combined with the other structural modifications, leads to a potent anticoagulant agent. Synthesis was readily achieved by the (9H‐fluoren‐9‐yl)‐methoxycarbonyl (Fmoc) strategy followed by acidolytic cleavage from the resin and deprotection, including the liberation of the crucial phosphonic group on L‐phenylalanine.
Solvent Isotope Effect on the Rate Constants of Singlet‐Oxygen Quenching by edta and Its Metal Complexes
Authors: Hessler Diane P. , Frimmel Fritz H. , Oliveros Esther , Braun André M. 
Published: December 2004

AbstractThe reactivity of singlet oxygen (O2(1Δg)) with edta and its metal complexes with Al3+, Cu2+, Fe3+, and Mn2+was investigated. The emission of singlet oxygen at 1270 nm in D2O was measured in order to determine the quenching efficiency of edta and edta‐metal complexes for different metal/edta ratios. The sum of the rate constant (kr+kq) of the chemical reaction between singlet oxygen and the acceptor (kr) and of the physical quenching of singlet oxygen by the acceptor (kq) was obtained by aStern‐Volmeranalysis. Measurements of the oxygen consumption in H2O were used to determine quantum yields of the sensitized photooxidation, and the combined results of these experiments allowed the determination ofkrandkqseparately. A strong isotope effect was observed between the deuterated and the hydrogenated solvents. This effect was shown to be independent of the analytical procedure used. The isotope effect, as well as the reactivity of edta and its metal complexes, depend markedly on the complexed metal ion.
Xenicane Diterpenes Revisited: Thermal (E)→(Z) isomerization and conformational motions. A unifying picture
Authors: Guella Graziano , Chiasera Giuseppe , N'Diaye Ibrahima , Pietra Francesco 
Published: December 2004

AbstractKinetic and equilibrium studies show that typical xenicanes such as dictyolactone (1) and 4‐hydroxydictyolactone (3) undergo slow conformation medium‐ring flipping between the predominant trans‐(1a or 3a; Me(20) trans to H–C(3)) and the minor cis‐conformers (1b or 3b; Me(20) cis to H–C(3); see Scheme 1). The formation of the latter is inhibited in heterocyclic‐ring‐opened congeners such as 18‐acetoxy‐4‐hydroxydictyo‐19‐al (7). Molecular‐mechanics calculations suggest that typical‐xenicane cis‐conformers are disfavoured by mainly C(4)–C(5) torsional strain. This is confirmed by the observation of two sizably populated cis‐and trans‐conformers for the unnatural 4‐oxoxenicanes 10–12. Unusually facile thermal (E)→(Z) isomerization of xenicanes 1,3,10–12, and 7 is also observed (→ 13–17 and 9, resp.; Scheme 3), reflecting great strain relief in the transition state. Conflicting results in the literature now fit into this scheme which provides a basis for unravelling recognition phenomena with these biologically active systems.
Synthesis, Crystal Structure, and Thermal Behaviour of Some New Copper Complexes with tridentate β‐iminoketone ligands
Authors: Becht Michael , Gerfin Tobias , Dahmen Klaus‐Hermann 
Published: December 2004

AbstractThe reaction of Cu(AcO)2 · H2O and tridentate β‐iminoketone ligands yielded four new copper complexes: acetato{4‐{[2‐(dimethylamino)ethyl]amino}pent‐3‐en‐2‐onato}copper(II) (1), triacetato{4‐{[3‐(dimethylamino)‐propyl]amino}pent‐3‐en‐2‐onato}dicopper(II) (2), {4‐{[2‐(dimethylamino)ethyl]amino}‐1,1,1‐trifluoropent‐3‐en‐2‐onato}( trifluoroacetato)copper(II) (3), and pentaacetato{4‐{[3‐(dimethylamino)propyl]amino}‐1,1,1‐trifluoropent‐3‐en‐2‐ onato}tricopper(II) (4). All compounds were coloured and air‐stable solids. The crystal structures of 1 and the dioxane adduct of 3, μ‐(1,4‐dioxane)bis{{4‐{[2‐(dimethylamino)ethyl]amino}‐1,1,1‐trifluoropent‐3‐ en‐2‐onato}(trifluoroacetato)copper(II)} (3a), were determined. Complex 1 consists of dimeric units [{Cu(AcO)L}2] in the solid state (L = β‐iminoketonato ligand). In 3a, two [Cu(CF3COO)L] are linked via the O‐atoms of the coordinated solvent 1,4‐dioxane. Compound 1 crystallized in the monoclinic space group P21/n with a formula unit in a cell having the dimensions a = 11.152(6)Å, b = 10.104(3)Å, c = 11.805(7)Å, and β = 99.02(4)Å, and compound 3a crystallized in the triclinic space group P1 with a formula unit in a cell having the dimensions a = 8.709(3)Å, b = 9.439(4)Å, c = 12.395(3)Å, α = 67.57(3)°, β = 77.01(2)°, and β = 84.17(3)°. Mass spectra (MS), thermal analysis (DTA/TG), and evaporation‐rate measurements are reported for all compounds. The influence of fluorination on the structure and volatility will be discussed.
Efficient Synthesis of Methyl 2‐(tert‐Butyl)acrylate and Analogous Esters
Authors: Xu Long‐He , Kündig Ernst Peter 
Published: December 2004

AbstractThe title products are prepared via an efficient three‐step synthesis which involves hydroalumination of methyl propiolate and Lewis‐acid‐promoted reaction with acetone in the presence of BF3 followed by two highly selective SN2′ reactions. The key step is the reaction of 2‐(chloromethyl)acrylates with R2CuLi/ZnCl2 reagents which takes place with complete allylic rearrangement.
Radical Arylation Reactions of 4, 6, 8‐Trimethylazulene
Authors: Briquet Anne Andrée Sophie , Hansen Hans‐Jürgen 
Published: December 2004

AbstractThe synthesis of 1‐ and 2‐aryl‐substituted (aryl = Ph, 4‐NO2C6H4, and 4‐MeOC6H4) 4, 6, 8‐trimethylazulenes (4 and 3, respectively) in moderate yields by direct arylation of 4, 6, 8‐trimethylazulene (8) with the corresponding arylhydrazines 13 in the presence of CuIIions in pyridine (see Scheme 4) as well as with 4‐MeOC6H4Pb(OAc)3 (16) in CF3COOH (see Scheme 5) is described. With 13, also small amounts of 1, 2‐ and 1, 3‐diarylated azulenes (see 14 and 15, respectively, in Scheme 4) are formed. The 4‐methoxyphenylation of 8 with 16 yielded also the 1, 1′‐biazulene 17 in minor amounts (see Scheme 5). 4, 6, 8‐Trimethyl‐2‐phenylazulene (3a) was also obtained as the sole product in moderate yields by the reaction of sodium phenylclopentadienide (1a) with 2, 4, 6‐trimethylpyrylium tetrafluoroborate (2) in THF (Scheme 1). The attempted phenylation of 8 as well as of azulene (9) itself with N‐nitroso‐N‐phenylacetamide (10) led only to the formation of the corresponding 1‐(phenylazo)‐substituted azulenes 12 and 11, respectively (Scheme 3).
X‐Ray Crystal Structure of the 2‐Phenyladamant‐2‐yl Cation
Authors: Laube Thomas , Hollenstein Sandro 
Published: December 2004

AbstractThe crystal structure of the Sb2F11 salt of the 2‐phenyladamant‐2‐yl cation, 1 · Sb2F11, was determined at 183 K (P21/c, R1 = 0.0652, σ(CC) = 0.02 Å), because earlier published results indicated a charge delocalization from the cationic C(2) into the σ framework (CC hyperconjugation) and a bending of the C(2) bridge. In the structure of 1, a displacement of the C(2) bridge by 7.8(12)° from the symmetrical position and CC bond‐length deviations from expectation values were found which are in agreement with preferential CC hyperconjugation on one face of C(2). The interactions of 1 with two Sb2F11 counterions nearest to C(2) also indicate different behaviour of the two faces of C(2). The benzylic resonance in 1 is confirmed.
Syntheses of Bile Pigments. Part 18. Synthesis and conformational studies of oxa‐ and thia‐deaza‐biliverdin analogues
Authors: Nesvadba Petr , Ngoc‐Phan Do , Nydegger Fredy , Ferao Arturo Espinosa , Gossauer Albert 
Published: December 2004

AbstractFollowing the conventional methodology used for the synthesis of bile pigments, some oxa‐ and thia‐deazabiliverdin analogues were synthetized for the first time. Both UV/VIS spectroscopic and 1H{1H}‐NOE difference studies reveal that the oxa‐deaza‐biliverdin analogue 8a occurs in apolar solvents in a partly ‘stretched’ conformation, whereas the corresponding thia derivative 8b behaves rather like a genuine bile pigment. Unexpectedly, the helical‐shaped conformation is also preponderant in a trioxa‐trideaza‐biliverdin analogue, which could be only characterized in its protonated form 14.
Imidazolone and Imidazolidinone Artifacts of a Pivotal Imidazolthione, Zyzzin, from the poecilosclerid sponge Zyzza massalis from the coral sea. The first thermochromic systems of marine origin
Authors: Mancini Ines , Guella Graziano , Pietra Francesco , Debitus Cécile , Duhet Daniel 
Published: December 2004

AbstractDry acetone extracts of the freeze‐dried, deep‐red powder of the poecilosclerid sponge Zyzza massalis (DENDY) from the Coral Sea gave the orange alkaloid zyzzin (= 4‐(1H‐indol‐3‐yl)‐1,5‐dihydro‐5‐thioxo‐1H‐imidazol‐2‐one 14), which underwent exchange of the 5‐thioxo for the 5‐oxo group during aqueous chromatographic workup, giving yellow 13. Both 13 and 14 added hydroxylic solvents at C(4)=N giving colourless, racemic products, 3 and 8, respectively, by incorporation of MeOH and 10 and 11, respectively, by incorporation of H2O. On warming 3 or 10 in DMSO, 13 was recovered, thus furnishing a novel thermochromic system. Optically active (+)‐12, which may be viewed to derive from enzymatic reduction of 14 at C(4)=N followed by S→O exchange, was also isolated from this sponge, along with the linear amides 16 and 19. Compound 3 proved to have antibacterial and antifungal activities.