Home About us Contact
|
Home About us Contact | ||
|
|
||
Syn Isomer (syn + isomer)
Selected AbstractsA New Entry to Bis-Tröger's BasesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 5 2004Thierry Mas Abstract This paper reports the use of p -phenylenediamine to prepare bis-Tröger's bases. The methyl,nitro-substituted bis-Tröger's base 5, already previously prepared by another procedure, was obtained in fewer steps, although with no improvement in the yield of the desired syn isomer. The symmetric dinitro-substituted bis-Tröger's base 17, which cannot be prepared by the older method, was then synthesized. Its structure was determined by mass spectrometry, 2D NMR spectroscopy, and, in the case of the syn isomer, by X-ray crystallography. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Preparation of a technetium-99m SPECT agent for imaging the sigma-2 receptor status of solid tumorsJOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 13 2001Robert H. Mach Abstract The synthesis and in vitro binding of a novel 99mTc-labeled radiotracer for imaging the sigma-2 (,2) receptor status of breast tumors is described. Structural characterization and in vitro binding studies were conducted using the corresponding rhenium surrogate, Re-2. X-ray crystallographic studies revealed that the complexation reaction gave exclusively the syn isomer. In vitro binding studies indicated that this complex has a high affinity for ,2 (Ki=13.7 nM) versus ,1 receptors (Ki=1125 nM). These data indicate that [99mTc]2 may be a promising agent for imaging the ,2 receptor status of tumors in vivo with the functional imaging technique, single photon emission computed tomography (SPECT). Copyright © 2001 John Wiley & Sons, Ltd. [source] Synthesis and In-Vitro Cytotoxicity Evaluation of Novel Naphtindolizinedione Derivatives, Part II: Improved Activity for Aza-AnaloguesARCHIV DER PHARMAZIE, Issue 2 2009Andrea Defant Abstract Our previous investigation on potential antitumor agents now got enriched by the evaluation of in-vitro activity against a full panel of NCI cancer cell lines for five new compounds. The concurrent presence in the molecular structure of a nitrogen atom in the aromatic system and a N,N -dimethylaminoethyl amide chain play a decisive role to enhance cytotoxicity. The N,N -anti compound 14 shows a higher activity than its N,N -syn isomer, exhibiting the best selective inhibition against the melanoma MALME-3M cell line, with a GI50 -value (= 30 nM) corresponding to a 330-fold increase in activity compared to the corresponding deaza-analogue. Compound 14 is efficiently synthesized by aminolysis of the ester obtained as a single regio-isomer by an one-pot three-component procedure involving metal-assisted cyclization under microwave irradiation conditions. [source] Regio- and Stereoselective Palladium-Pincer Complex Catalyzed Allylation of Sulfonylimines with Trifluoro(allyl)borates and Allylstannanes: A Combined Experimental and Theoretical StudyCHEMISTRY - A EUROPEAN JOURNAL, Issue 26 2006Olov A. Wallner Dr. Abstract Regio- and stereoselective palladium-pincer complex catalyzed allylation of sulfonylimines has been performed by using substituted trifluoro(allyl)borates and trimethylallylstannanes. The reactions provide the corresponding branched allylic products with excellent regioselectivity. The stereoselectivity of these processes is very high when trifluoro(cinnamyl)borate and trimethyl cinnamyl stannane are employed as allylic precursors; however, the reaction with trifluoro(crotyl)borate results in poor stereoselectivity. The major diastereomer formed in these reactions was the syn isomer, while the (previously reported) reactions with aldehyde electrophiles afforded the anti products, indicating that the mechanism of the stereoselection is dependent on the applied electrophile. Therefore, we have studied the mechanistic aspects of the allylation reactions by experimental studies and DFT modeling. The experimental mechanistic studies have clearly shown that potassium trifluoro(allyl)borate undergoes transmetallation with palladium-pincer complex 1,a affording an ,1 -allylpalladium-pincer complex (1,e). The mechanism of the transfer of the allyl moiety from palladium to the sulfonylimine substrate was studied by DFT calculations at the B3PW91/LANL2DZ+P level of theory. These calculations have shown that the electrophilic substitution of sulfonylimines proceeds in a one-step process with a relatively low activation energy. The topology of the potential energy surface in the vicinity of the transition-state structure proved to be rather complicated as nine different geometries with similar energies were located as first order saddle points. Our studies have also shown that the high stereoselectivity with cinnamyl metal reagents stems from steric interactions in the TS structure of the allylation reaction. In addition, these studies have revealed that the mechanism of the stereoselection in the allylation of aldehydes and sulfonylimines is fundamentally different. [source] Modes of Reactivity of Cyclic Diynes: Probing the syn/anti Selectivity of Tetrathiacycloalkadiynes and Mono(alkyne)cobalt ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 6 2003Christoph Benisch Abstract Cyclic tetrathiaalkadiynes in which two 1,4-dithiaalkyne units are connected with alkane bridges of length n and m [A(m.n)] were treated with [,2 -bis(tert -butylsulfonyl)acetylene]carbonyl(,5 -cyclopentadienyl)cobalt(I) (8a) and several substituted analogues (8b,8e) in order to probe the reactivity of electron-rich cyclic diynes. Both mono- [B(m.n)] and bis(cyclobutadiene) [C(m.n)] complexes were isolated as products of these reactions and the anti/syn ratio of C(m.n) was determined. For m, n < 4 the syn isomers dominate and this is attributed to the configuration of the intermediate metallacycle which is correlated with the conformations of the rings in the mono(cyclobutadiene) products B(m.n). This analysis was corroborated by X-ray structural investigations of the products. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] 9,10-Diarylanthracenes as Molecular Switches: Syntheses, Properties, Isomerisations and Their Reactions with Singlet OxygenCHEMISTRY - A EUROPEAN JOURNAL, Issue 36 2008Daniel Zehm Abstract A series of 9,10-diarylanthracenes with various substituents at the ortho positions have been synthesised by palladium-catalysed cross-coupling reactions. Such compounds exhibit interesting physical properties and can be applied as molecular switches. Despite the high steric demand of the substituents, products were formed in moderate-to-good yields. In some cases, microwave conditions further improved yields. Bis-coupling afforded two isomers (syn and anti) that do not interconvert at room temperature. These products were easily separated and their relative stereochemistries were unequivocally assigned by NMR spectroscopy and X-ray analysis. The syn and anti isomers exhibit different physical properties (e.g., melting points and solubilities) and interconversion by rotation around the aryl,aryl axis commences at <100,°C for fluoro-substituted diarylanthracenes and at >300,°C for alkyl- or alkoxy-substituted diarylanthracenes. The reactions with singlet oxygen were studied separately and revealed different reactivities and reaction pathways. The yields and reactivities depend on the size and electronic nature of the substituents. The anti isomers form the same 9,10-endoperoxides as the syn species, occasionally accompanied by unexpected 1,4-endoperoxides as byproducts. Thermolysis of the endoperoxides exclusively yielded the syn isomers. The interesting rotation around the aryl,aryl axis allows the application of 9,10-diarylanthracenes as molecular switches, which are triggered by light and air under mild conditions. Finally, the oxygenation and thermolysis sequence provides a simple, synthetic access to a single stereoisomer (syn) from an unselective coupling step. [source] | ||||||||||