bluuebunny/crossref_metadata_2025_split huggingface dataset:
1H‐ und 13C‐NMR.‐Spektren von 6‐(p‐X‐Phenyl)fulvenen. Kurzmitteilung
Authors: Otter Albin , Mühle Hansueli , Neuenschwander Markus , Kellerhals Hans Peter 
Published: December 2004

1H‐ and 13C‐NMR.‐spectra of 6‐(p‐X‐phenyl)fulvenesThe 1H‐ and 13C‐NMR.‐spectra of a series of 6‐(p‐X‐phenyl)fulvenes 3, measured at 9.39 T (93.9 kgauss), have been analyzed. In these compounds, electronic effects due to the substituent X clearly exert changes in chemical shifts as well as in coupling constants in the 5‐membered ring. Small changes in bond length are observed by comparison of the vicinal 1H, 1H‐coupling constants, whereas changes in charge densities linearly influence the chemical shifts of C(5), C(2) and C(3).
Analogues de la lincomycine. I. Allongement de la chaîne du di‐O‐isopropylidène‐1,2:3,4‐α‐D‐galacto‐hexodialdopyrannose‐1,5
Authors: Tronchet Jean M. J. , Massoud Mohammed A. M. 
Published: December 2004

Lincomycin analogues. I. Chain‐extensions of [1,2:3,4]‐di‐O‐isopropylidene‐α‐D‐galacto‐hexodialdo‐1,5‐pyranoseThe title aldehydosugar 1 treated with Wittig reagents led in good to excellent yields to the unsaturated sugar derivatives 3–7 and 10–15, 8 having been prepared by condensation of 1 with malonic acid. The configuration (Z or E) of each compound obtained has been established by 1H‐NMR. These chain‐extensions constitute the first synthetic step towards the preparation of lincomycin analogues.
Photochemische Reaktionen. 104. Mitteilung [1]. Zur Photospaltung der C,C‐Oxiranbindung konjugierter γ, δ‐Epoxy‐enone: Photolyse von 4‐Methyliden‐5,6‐epoxy‐5,6‐dihydro‐β‐jonon
Authors: Frei Bruno , Wolf Hans Richard , Jeger Oskar 
Published: December 2004

The photoinduced cleavage of the C,C‐oxirane bond of γ, δ‐epoxy‐enones: UV.‐irradiation of 4‐methylidene‐5,6‐epoxy‐5,6‐dihydro‐β‐iononeOn 1n, π*‐excitation (λ ≥ 347 nm, pentane) 5 gives the isomeric bicyclic ether 10 in 75% yield (s. Scheme 2). In methanol the photoconversion of 5 to 10 is strongly reduced (12%) in favour of the formation of the methanol adduct 11 (43%). On photolysis in aqueous acetonitrile 5 is converted to the bicyclic ether 10 (9%), the dihydrofurane 12 (18%) as well as to the triketones 13A and 13B (7%), and 14 (23%).On 1π, π*‐excitation (λ = 254 nm) in pentane no 10 is formed, but 5 isomerizes to the tricyclic cyclopropyl compound 16 (59%), the allenic product 17 (10%), and the cyclopropene compound 18 (12%; s. Scheme 3). Photolysis in methanol furnishes 11 (63%), and 18 (4%), but no tricyclic cyclopropyl compound 16. In a secondary photoreaction (λ = 254 nm) the dihydrofurane 12 is isomerized to the bicyclic cyclopropyl compound 20.Evidence is given that the products 11 and 13 are formed by solvent addition to an intermediate ketonium ylide b (s. Scheme 12). The presence of b is further proven by the formation of 12, a product of an electrocyclization of b. On photofragmentation of b carbenoids d and e are presumably formed (s. Scheme 14). 1,2‐Hydrogen shift in d yields the allene derivative 17, and cyclization of d gives the cyclopropene compound 18. On the other hand, e cyclizes to the non isolated cyclopropene compound 69 which is transformed to 16 by an intramolecular [4 + 2]‐cycloaddition.The present investigation shows that the photochemistry of 5 is determined by photoinduced C,C‐bond cleavage of the oxirane ring. This is in sharp contrast to the photochemistry of conjugated γ, δ‐epoxy‐enones without the additional double bond in ε, ζ‐position, where selective photocleavage of the C(λ), O‐bond is observed.
Chemistry of Succinyl Succinic Acid Derivatives. Part V. On the transesterification of succinyl succinates
Authors: Sinnreich Joel , Batzer Hans 
Published: December 2004

AbstractThe unique stabilization of the ester link in dialkyl succinyl succinates is explained and a facile route to known as well as to hitherto inaccessible succinyl succinates is suggested. New representatives of this series are described.
Enantioselektive 1,4‐Additionen von metallorganischen Verbindungen an konjugierte Systeme im chiralen Medium DDB
Authors: Langer Werner , Seebach Dieter 
Published: December 2004

Enantioselective 1,4‐additions of organometallic compounds to conjugated systems in the chiral medium DDBDDB = 1,4‐Dimethylamino‐2,3‐dimethoxybutan (= 2,3‐Dimethoxy‐N,N,N′,N′‐tetramethyl‐1,4‐butandiamin).
The chiral methoxyamine DDB is used as a cosolvent to add achiral Li‐, Cu‐, and Zn‐organic compounds enantioselectively to prochiral β‐carbon atoms of α, β‐unsaturated aldehydes, ketones, nitro compounds and ketene‐thioacetals (Tables 1 and 2). The selectivity generally ranges from 55:45 to 63:27, in one case (9b) an enantiomeric excess of 43% was obtained.
On the Position of the Intramolecular Equilibrium between Opened and Aromatic‐Ring Stacked Forms in Ternary Complexes Composed of Adenosine 5′‐triphosphate, Mg2+ or Zn2+, and L‐Tryptophanate, and in Related Ternary Systems
Authors: Mitchell Paul R. , Prijs Bernard , Sigel Helmut 
Published: December 2004

AbstractThe intramolecular and dimensionless equilibrium constant, K′, for the equilibrium between open and aromatic‐ring stacked isomers of ternary complexes formed between adenosine 5′‐triphosphate, inosine 5′‐triphosphate, or uridine 5′‐triphosphate, Mg2+ or Zn2+, and L‐tryptophanate, 2,2′‐bipyridyl (bipy), or 1,10‐phenanthroline (phen) have been estimated by 1H‐NMR. shift measurements in D2O (I = 0.1M, NaNO3; 27°). The approximate equilibrium constants K′ are ≥ 20, ≥ 20, 1.2, 0.9, 0.7, 0.5, and 0.3 for the ternary complexes Zn (phen) (ATP)2−, Mg (phen) (ATP)2−, Zn (bipy) (ATP)2−, Zn (bipy) (ITP)2−, Zn (bipy) (UTP)2−, Zn (trp) (ATO) 3−, and Mg (trp) (ATP)3−, respectively. The percentages of the stacked isomers decrease in the order Zn (phen) (ATP)2− (≥ 95%) ≫ Zn (bipy) (ATP)2− (55%) > Zn (bipy) (ITP)2− (48%) > Zn (bipy) (UTP)2− (∼ 40%), which coincides with the order of stability of the binary metal‐free adducts (phen) (ATP)4− > (bipy) (ATP)4− ≃ (bipy) (ITP)4− > (bipy) (UTP)4−; the corresponding stability constants are K = 28.2 ± 4.7, 8.1 ± 2.6, 8.8 ± 1.8, and ∼ 1 (M−1), respectively (D2O; I = 0.1 M, NaNO3; 27°): these series reflect the decreasing size of the aromatic‐ring systems forming the stacks. The indole moiety of tryptophan resembles 2,2′‐bipyridyl rather than 1,10‐phenanthroline and K = 6.2 ± 1.8 M−1 for (trp) (ATP)4−. Implications with respect to the stability of ternary complexes, and to biological systems are indicated briefly.
Pyrazolo [1,5‐a]indole. 10. Mitteilung über metallogranische reaktionen und folgeprodukte
Authors: Marxer Adrian , Siegrist Max 
Published: December 2004

Pyrazolo[1,5‐a]indolesTreatment of 1‐(2‐heteroaroyl or aroyl‐phenyl)‐pyrazoles (3) with potassium hydroxide in 95% ethanol or with sodium ethanolate in ethanol produces a novel ring closure to new 4‐hydroxy‐4‐(4‐heteroaryl or aryl)‐4H‐pyrazolo [1,5‐a]indoles 5 and 6 (Table 1). A 2, 3, or 4‐pyridyl at position 4 is easily reduced yielding the 4‐(2, 3, or 4‐piperidyl)‐derivatives 7 and 8 (Table 2). Water is split off from these piperidyl‐derivatives 7 or 8 to give the piperidylidene derivatives 9 or 10 (Table 3) which may be considered as heterocyclic analogues to known tricyclic psychopharmaceuticals with antidepressant or neuroleptic activities.
Über Reaktionen Oxygenierter Kobalt (II)‐Komplexe. X. 1,4,7,10‐Tetraazadecan‐kobalt (II) und 4, 7‐dimethyl‐1,4,7,10‐tetraazadecan‐kobalt (II) als sauerstoffträger
Authors: Mäcke H. , Zehnder M. , Thewalt U. , Fallab S. 
Published: December 2004

Reactions of oxygenated cobalt (II) complexes. X. 1,4,7,10‐tetraazadecanecobalt (II) and 4,7‐dimethyl‐1,4,7,10‐tetraazadecanecobalt (II) as dioxygen carriersIX: siehe [1].
Oxygenation of cobalt (II) chelates with fourdentate amines such as 1,4,7,10‐tetraazadecane (= tad) in aqueous solution yields μ‐peroxo‐μ‐hydroxo‐dicobalt (III) complexes. Due to facultative ligand disposition of the amine, 8 different diastereoisomers are possible. Introducing methyl groups in positions 4 and 7 of tad destabilizes the isomers with β‐configuration. A crystallized perchlorate, obtained by oxygenation of 4, 7‐dimethyl‐1,4,7,10‐tetraazadecanecobalt (II) (= dmtad) in alcaline solution, proved to be of the expected μ‐peroxo‐μ‐hydroxo type. The ligand configuration is and lattice constants a (ΔΔ/ΛΛ). The X‐ray structure was solved by Patterson's method and refined to R = 0.093. The crystals are orthorhombic with space group Pna21 and lattice constants a = 14.632 (4), b = 17.525 (5), c = 12.888 (5) Å. In its UV./VIS. absorption spectrum and its solution reactivity the binuclear cation is closely related to oxygenation products obtained with the chelate of unsubstituted tad. The kinetic parameters of the decomposition reaction of the μ‐peroxo complexes in acidic solution are compared. The binuclear cations with 4, 7‐dimethyl‐1,4,7,10‐tetraazadecane as ligand are generally more reactive. In slightly alcaline solution isomerization of the μ‐peroxo‐μ‐hydroxo complexes has been observed.
Anil‐Synthese. 21. Mitteilung. Über die Herstellung von stilbenyl‐derivaten des pyrazols
Authors: Palmberg Roger B. , Siegrist Adolf Emil 
Published: December 2004

Preparation of Stilbenyl Derivatives of PyrazolesSchiffs bases derived from 1‐, 3‐ and 5‐(p‐formylphenyl)phenylpyrazoles and p‐chloroaniline are reacted with various p‐tolyl substituted aromatic heterocycles in the presence of dimethylformamide and potassium hydroxide or potassium t‐butoxide to yield the corresponding heterocyclic substituted stilbenes (anil synthesis). Introduction of a chloro substituent in the 4‐ and 4,5‐positions of the pyrazole system causes a decrease in yield and a hypsochromic shift in the absorption and fluorescence maxima of the title compounds.
Carbocyclische Verbindungen aus Monosacchariden. I. Umsetzungen in der glucosereihe
Authors: Bernet Bruno , Vasella Andrea 
Published: December 2004

Carbocyclic Compounds from Monosaccharides. 1. Transformations in the Glucose SeriesA method for the preparation of pentasubstituted cyclopentanes from monosaccharides is presented, involving two crucial steps, viz. the reductive fragmentation of 5‐bromo‐5‐deoxyglucosides (such as 10, 17 and 23, see Scheme 3) with Zn or butyl lithium yielding 5,6‐dideoxy‐hex‐5‐enoses (such as 11 and 24, see Schemes 3 and 4), and the subsequent cyclization of these hexenoses with N‐methyl‐ or N‐(alkoxyalkyl)hydroxylamines (via the corresponding nitrones) to form cyclopentano‐isoxazolidines (see Scheme 2). Thus, the glucosides 17 and 23 were converted diastereoselectively and in good yields into the cyclopentano‐isoxazolidines 27 and 45 (Schemes 5 and 7), which were characterized by their transformation into various derivatives. 27 and 45 were correlated through the common derivative 62. The configuration of the cyclization products were established by pyrolysis of the N‐oxide 65 to the enol ether 67 (Scheme 10).
Préparation de phosphonates de sucres ramifiés par addition nucléophile conjuguée. Communication préliminaire
Authors: Tronchet Jean M. J. , Neeser Jean‐Richard , Gonzalez Luis , Charollais Etienne J. 
Published: December 2004

Preparation of unsaturated sugars phosphonates using nucleophilic conjugate additionDifferent types of phosphorus nucleophiles underwent conjugate addition reaction with one of the branched‐chain sugars 4, 5 or 11 the addition taking place either on the endo or the exo face of the furanose ring (or on both faces in the case of 11). The configuration at C(3) of these new phosphorus‐bearing types of sugars as well as the configuration at the phosphorus atom of the cyclic phosphinates 9 and 10 was established by NMR. (3JP,H–C(2), 3JP,C(1)). Small amounts (7%) of the spiro enol phosphonate 16 were formed when 11 reacted with trimethyl phosphite.
Ergosta‐5,7,9(11), 22‐tetraen‐3β‐ol and its 24ξ‐Ethyl Homolog, Two New Marine Sterols from the Red Sea Sponge Biemna fortis
Authors: Delseth Claude , Kashman Yoel , Djerassi Carl 
Published: December 2004

AbstractThe steroidal components of a Red Sea sponge, Biemna fortis, were fractionated through reversed phase HPLC. and analyzed by a combination of physical methods, including high resolution GC./MS. and 360 MHz 1H‐NMR. The sponge contains five conventional Δ5‐sterols, 1a–c, 1e, 1g, which comprise about 25% of the mixture and 2,5% of gorgosterol (1h), a sterol never found before in Porifera. Three Δ5,7,22‐sterols were also present as major components in the mixture (∼70%): cholesta‐5,7,22‐trien‐3β‐ol (2a), ergosta‐5,7,22‐trien‐3β‐ol (2c) and (24R)‐ethylcholesta‐5,7,22‐trien‐3β‐ol (2e) whereas two new tetra‐unsaturated sterols were identified in minor amounts (2%): ergosta‐5,7,9(11),22‐tetraen‐3β‐ol (3c) and 24ξ‐ethylcholesta‐5,7,9 (11), 22‐tetraen‐3β‐ol (3e or 3f). NMR. spectroscopy made possible the assignment of a 24R configuration for all the C(24) substituted sterols isolated in sufficient amount from the mixture. The possible symbiotic, dietary or biosynthetic origins of these sterols are discussed.
Preparative Scale Separation of Xanthones and Iridoid Glycosides by Droplet Counter‐Current Chromatography
Authors: Hostettmann Kurt , Hostettmann‐Kaldas Maryse , Sticher Otto 
Published: December 2004

AbstractDroplet counter‐current chromatography (DCCC.) has been used for the preparative scale separation of pure constituents from crude medicinal plant extracts. Xanthones and the bitter principles have been isolated from North‐American Gentiana species. From a crude extract of Ajuga pyramidalis L. (Labiatae), several hundred mg of iridoid glycosides were obtained within eight hours. The total volume of mobile phase employed for the elution was less than 150 ml. All the separations were achieved far more readily than by conventional chromatography. In addition, some general rules for solvent system selection are proposed.
Reaktion oxygenierter Kobalt (II)‐Komplexe. XII. Über einen binuclearen μ‐Peroxodikobalt (III)‐Komplex mit makrocyclischem Brückenring
Authors: Zehnder Margareta , Thewalt Ulf , Fallab Silvio 
Published: December 2004

Reactions of oxygenated cobalt(II) complexes. XII. A binuclear μ‐peroxodicobalt(III) complex with a macrocyclic bridging ringXI: siehe [1].
Singly bridged [(tren) (NH3) CoO2(NH3) (tren)]4+ reacts with excess tren by replacement of NH3 in cis‐position to the peroxo group and formation of a new type of doubly bridged μ‐peroxo complex. An X‐ray structure determination of [(tren)‐Co(O2, tren)Co(tren)] (ClO4)4 · 2 H2O showed that the additional tren forms a macrocyclic bridging ring. The conformation of the CoOOCo group is transoid with a dihedral angle of 20°. The crystals are monoclinic with space group P21/c. The lattice constants are a = 9,798, b = 26,385, c = 16,385 Å, β = 110,2° with four formula units in the cell. The final R value is 0,124. ClO anions are disordered.The reactions of [(tren)Co(O2, tren)Co(tren)]4+ in aqueous solution are compared with those of [(tren) (NH3) CoO2Co (NH3tren)]4+. In acidic solution the new complex mainly decomposes to CoII and O2. In alcaline medium the bridging tren is replaced by an OH bridge, forming the well characterized doubly bridged [(tren)‐Co(O2, OH)Co(tren)]3+. Differing from the singly bridged bis (ammino) complex, the reactions of which show no pH dependency at all, the decomposition of the tren bridged complex is H+‐catalyzed. The kinetic data have been interpreted as (i) preceding fast protonation step which is followed by a conformational change of the bridging ring, (ii) acid hydrolysis of a Co‐μ‐tren bond and (iii) fast cleavage of the Co‐OO bond which is labilized by coordinated H2O.
Fragmentation of Energy Selected Butadiyne‐ and 1,3‐Pentadiyne Radical Cations
Authors: Dannacher Josef , Heilbronner Edgar , Stadelmann Jean‐Pierre , Vogt Jürgen 
Published: December 2004

AbstractMonomolecular fragmentations of butadiyne‐ and 1,3‐pentadiyne radical cations in their electronically excited states have been investigated by use of the photoelectron‐photoion coincidence technique. Breakdown curves for the molecular and various fragment ions have been recorded over the ionization energy range of 9 to 17 eV. These breakdown curves reveal the extent of the competition between the radiative relaxation (ion fluorescence) and the non‐radiative internal conversion followed by fragmentation for the decay of the first excited electronic states. Extensive hydrogen scrambling and/or ionic‐carbon‐skeleton isomerization takes place prior to fragmentation, as revealed by the breakdown curves obtained for the site specifically deuteriated 1,3‐pentadiynes.
Cycloadditionen von 3,4‐Dimethoxyfuran an Dienophile
Authors: Iten Peter Xaver , Hofmann Alfred André , Eugster Conrad Hans 
Published: December 2004

On cycloaddition reactions with 3,4‐dimethoxyfuranWe describe new cycloadditions of 3,4‐dimethoxyfuran (3,4‐DF, 1) with various dienophiles. In contrast to furan, the reaction of 3,4‐DF with maleic anhydride gives exo‐ and endo‐adducts at approximately the same rate. The thermodynamically more stable product is again the exo‐product. Less active dienophiles lead also to mixtures of exo‐ and endo‐adducts, except for citraconic anhydride (methylmaleic anhydride) which forms only the adduct with an endo‐methyl group. Dimethylmaleic anhydride could not be reacted with 3,4‐DF.All adducts with 3,4‐DF contain a hidden 1,2‐dicarbonyl group in the form of an endiolether. Its pronounced nucleophilic character allows a series of further additions. Noteworthy are the stereospecific cis‐additions of halogens and the preparation of several acetals. Ozonolysis of the enolether in 4 allows the preparation of the hitherto unknown 2r, 3trans, 4trans, 5cis‐tetrahydrofuran tetracarboxylic acid and derivatives thereof (5 and 6).
Cycloadditionen von 3,4‐Dimethoxyfuran an Benzochinone
Authors: Hofmann Alfred André , Wyrsch‐Walraf Ingeborg , Iten Peter Xaver , Eugster Conrad Hans 
Published: December 2004

Cycloadditions of 3,4‐dimethoxyfuran with benzoquinonesCycloaddition of 3,4‐dimethoxyfuran (3,4‐DF, 1) with 1,4‐benzoquinones furnishes isolable (2 + 4)‐adducts in high yield. The crystalline products with benzoquinone, 2‐methyl‐benzoquinone, 2,3‐dimethoxy‐benzoquinone have endo‐configuration, whereas 2,3‐dimethyl‐benzoquinone gives the exo‐adduct 4c exclusively. Halogens (Cl2, Br2) add rapidly across the highly nucleophilic double bond of 3 or 4 in stereospecific cis‐manner, and exclusively from the exo‐side. The product 5c shows no sign of enolization to the hydroquinone; but with 3a and 3d the hydroquinones 6 were found. Methanolysis of 5 leads to the stable acetals 7 and 8. On oxidation of the hydroquinones 7 the thermolabile quinones 10 were obtained. Preparative pyrolysis of 10a under relatively mild conditions (N2, 200°, 0.1 Torr) gives tetramethoxy ethene (11) and isobenzofuran‐4,7‐quinone 12, a yellowish, crystalline and stable compound.
Lithium‐ und Kupfer‐Derivate von α,α‐doppeldeprotonierten Nitroalkanen. – Erzeugung, Eigenschaften und Umsetzungen mit Alkyl‐ und Allylhalogeniden
Authors: Seebach Dieter , Lehr Friedrich 
Published: December 2004

Lithium‐ and copper‐derivatives of α,α‐doubly deprotonated nitroalkanes. Generation, properties and reactions with alkyl‐ and allylhalidesAus der Dissertation von F.L., ETH Zürich, 1979; Nr. 6356. Die Arbeiten wurden teilweise am Institut für Organische Chemie der Justus‐Liebig‐Universität Giessen durchgeführt.

Vorläufige Mitteilungen siehe [1] und [2].
Primary nitroalkanes are deprotonated twice in the α‐position when treated with two mol‐equiv. of butyllithium at −78° to −100° in THF containing HMPT to give dilithium derivatives 15 (the compound with R = C2H5 is stable up to −30°). The acidity of the nitronate proton of 13 is estimated to be in the same range as that of diisopropylamine. The C‐nucleophilicity of the novel reagents 15 is dramatically increased as compared with that of simple nitronates 5: C,C‐bond‐forming reactions readily take place with alkylhalides (→22c–e,g,h,j–m) and benzylbromide (→22b,f,i); allylations are possible via nitroalkycopper‐lithium‐derivatives (→27–29).
Stereospezifische Synthese von 6β,7β‐Methylen‐20‐spirox‐4‐en‐3,21‐dion (Prorenon). Über Steroide. 235. Mitteilung
Authors: Wieland Peter 
Published: December 2004

Stereospecific synthesis of 6β,7β‐methylene‐20‐spirox‐4‐ene‐3,21‐dioneA stereospecific synthesis of the highly active 6β,7β‐methylene‐20‐spirolactone 4 (Prorenone) is described.
The Four Diastereomeric Thio‐Analogues of (±)‐Muscarine
Authors: Giannella Mario , Pigini Maria , Rüedi Peter , Eugster Conrad Hans 
Published: December 2004

AbstractDie vier diastereomeren Thioanalogen des (±)‐MuscarinsIm Zusammenhang mit pharmakologischen Arbeiten über die chemische Natur des cholinergischen Rezeptors haben wir die reinen (±)‐Thiomuscarinjodide 4a–d hergestellt und ihre relativen Konfigurationen an C(2), C(3) und C(5) an den nor‐Basen 3a–d in 1H‐NMR.‐Spektren mit Lanthanidverschiebung aufgeklärt. Auf der Stufe der 3‐Hydroxymide 2 wurden die vier Diastereomere chromatographisch voneinander getrennt.
Aktivierte Chinone: O‐ versus C‐Addition von Phenolen; eine neue, regiospezifische Synthese von Xanthonen, Thioxanthonen und N‐Methyl‐9‐acridonen
Authors: Müller Peter , Venakis Thomas , Eugster Conrad Hans 
Published: December 2004

Activated quinones: O‐ versus C‐addition of phenols. New regiospecific syntheses of xanthones, thioxanthones and N‐methyl‐9‐acridonesThe acid catalyzed reaction of phenols with activated quinones, e.g. 2‐methoxycarbonyl‐1, 4‐benzoquinone or 2‐acetyl‐1, 4‐benzoquinone, leads to substituted biphenylderivatives (C, C‐addition) as has been previously described [1]. O, C‐Addition of phenols has now been achieved by using 2‐methoxypyridin or 4‐dimethyl‐aminopyridin [4] as basic catalysts. The resulting substituted diphenylethers can serve as convenient starting materials for regiospecific syntheses of substituted xanthones, especially for 1, 4‐dimethoxyxanthones.Arylthiols and N‐methyl‐N‐arylamines also react readily with activated quinones to give substituted di‐aryl‐thioethers and N‐methyl‐N, N‐diarylamines respectively; both types of compounds are convenient materials for regiospecific syntheses of substituted thioxanthones and N‐methyl‐9‐acridones.
Divergent Melanophore‐Dispersing and Tyrosinase‐Stimulating Activity of Synthetic Leucine9‐α‐melanotropin
Authors: Eberle Alex , Schwyzer Robert 
Published: December 2004

AbstractLeucine9‐α‐melanotropin ([Leu9]α‐MSH) was synthesized in homogeneous solution by a fragment condensation approach, and it was assayed for its melanophore‐dispersing and its tyrosinase‐stimulating activity with a reflectometricin vitrofrog skin assay and with cultured mouse melanoma cells, respectively. In both assay systems, parallel log dose‐response curves were obtained for ([Leu9)]α‐MSH and α‐MSH; however, in the frog skin assay the activity of the title compound was 1 middot; 1010Units/mmol,i.e.25% of the activity of α‐MSH, whereas its tyrosinasestimulating potency was only 1% compared to α‐MSH (EC50= 2.5 · 10−7M). This indicates a major difference in the recognition/stimulation process of the receptors of the two cell types.