Helical Conformational Dynamics and Photoisomerism of Alternating Pyridinedicarboxamide/m-(Phenylazo)azobenzene Oligomers
摘要:
Alternating sequences of pyridine-2,6-dicarboxamides and meta-(phenylazo)azobenzenes have been assembled into oligomers composed of four (8) and eight (9) azobenzene linkages. X-ray crystallography confirmed that oligomer 8 adopts a two-turn helical conformation with a helical pitch of approximately 3.4 angstrom in the solid state. The presence of a two- and four-turn helical conformation of 8 and 9, respectively, in polar and nonpolar solvents was elucidated by the anisotropic upfield shifting of protons located within the helices, NOE enhancements between protons oriented toward the helix interior, and the diastereotopicity of the terminal benzyloxycarbonyl (CBz) methylene protons. H-1 NMR line shape analysis of the CBz methylene hydrogens at the chain ends revealed a dynamic equilibria interconverting M and P helical conformations with energetic barriers (Delta G(double dagger)) of 11.1 (AS(double dagger) = -19.4 +/- 1.6 cal mol(-1) K-1; Delta H-double dagger = 6.5 +/- 0.4 kcal/mol) for 8 and 13.8 kcal/mol (Delta S-double dagger = -6.6 +/- 6.2 cal mol(-1) K-1; Delta H-double dagger = 11.8 +/- 1.8 kcal/mol) for 9. Irradiation of the oligomers with 350 nm light induces an E -> Z isomerization of the azo linkages that decreases in efficacy at longer helix lengths. The suppression of E -> Z isomerization is a consequence of the contrasting behavior of the azo linkages located at the helix termini, which afford Z/E ratios similar to those of model compound 7d, and the internal azo groups, which undergo significantly lower Z/E conversion ratios compared with 7e.
This disclosure describes compositions and methods for delivering and localizing repair cells, such as mesenchymal stem cells (MSCs) to the sites of tissue injuries, including cartilage injuries. This disclosure also describes methods for chondrogenic differentiation of MSCs in pellet compositions.
phthalimide derivatives (compounds 3a–3m) were synthesized through the reaction of phthalicanhydride and various derivatives of aniline in toluene solvent (Reflux, 24 h). Antiepileptic activity of synthesized compounds (3a–3m) was investigated using two experimental models namely, maximal electroshock (MES) and pentylenetetrazole (PTZ), and the obtained results were compared with diazepam as reference drug
Catalyst-Free, Eco-Friendly, One-Pot Syntheses of 2-(3H-imidazo[4,5-b] pyridine-2-yl)-N-arylbenzamides in Water
作者:Y. Reddy、P. Kumar、B. Devi、Ch. Reddy、P.K. Dubey
DOI:10.2174/1570178611666140813205658
日期:2014.11.17
Eco-friendly, one-pot three-component syntheses of 2-(3H-imidazo[4,5-b]pyridine-2-yl)-N-arylbenzamides have been developed by combining phthalic anhydride with anilines and pyridine-2,3-diamine in water without any catalyst. These reactions involves easy workup, provide good yields and use of water as solvent which were the merits of this preparation.
A facile synthesis of phthalimides from <i>o</i>-phthalaldehyde and amines <i>via</i> tandem cyclocondensation and α-C–H oxidation by an electrochemical oxygen reduction reaction
Electrochemical synthesis of phthalimides from o-phthalaldehyde and amines via tandem cyclocondensation and α-C–H oxygenation of isoindolinone was achieved. The α-C–H oxidation proceeded with molecular oxygen via an oxygen reduction reaction (ORR) on the cathode under electrochemical conditions. The synthetic utility of this protocol was successfully demonstrated by employing gram-scale synthesis and obtaining