Photochemical synthesis of cyclic peptide models from phthalimido acetamides and phthaloyl dipeptide esters

Synthesis and Investigation of Flavanone Derivatives as Potential New Anti-Inflammatory Agents

Flavonoids are polyphenols with broad known pharmacological properties. A series of 2,3-dihydroflavanone derivatives were thus synthesized and investigated for their anti-inflammatory activities. The target flavanones were prepared through cyclization of 2'-hydroxychalcone derivatives, the later obtained by Claisen-Schmidt condensation. Since nitric oxide (NO) represents an important inflammatory mediator, the effects of various flavanones on the NO production in the LPS-induced RAW 264.7 macrophage were assessed in vitro using the Griess test. The most active compounds were flavanone (4G), 2'-carboxy-5,7-dimethoxy-flavanone (4F), 4'-bromo-5,7-dimethoxy-flavanone (4D), and 2'-carboxyflavanone (4J), with IC50 values of 0.603, 0.906, 1.030, and 1.830 µg/mL, respectively. In comparison, pinocembrin achieved an IC₅₀ value of 203.60 µg/mL. Thus, the derivatives synthesized in this work had a higher NO inhibition capacity compared to pinocembrin, demonstrating the importance of pharmacomodulation to improve the biological potential of natural molecules. SARs suggested that the use of a carboxyl-group in the meta-position of the B-ring increases biological activity, whereas compounds carrying halogen substituents in the para-position were less active. The addition of methoxy-groups in the meta-position of the A-ring somewhat decreased the activity. This study successfully identified new bioactive flavanones as promising candidates for the development of new anti-inflammatory agents.

On the large apparent Stokes shift of phthalimides

The photophysics of N-methylphthalimide (MP) in solution (cyclohexane, ethanol, acetonitrile, and water) was characterized by steady state as well as time resolved fluorescence and absorption spectroscopy. In all solvents the compound exhibits an unusually large Stokes shift of ∼10 000 cm-1. It is attributed to an ultrafast (<100 fs) depletion of the initially excited state, which results in the population of a weakly emitting state. Quantum chemical computations (DFT-MRCI) support this. They identify two energetically low-lying singlet ππ* excitations of different oscillator strength. Whereas the Stokes shift and thereby the ultrafast depletion of the initial excitation are hardly affected by the solvent later processes respond strongly. The fluorescence lifetime varies from ∼10 ps (cyclohexane) to ∼3 ns (water). This is attributed to a varying energetic accessibility of nπ* excitations.

Recent Advances in Photodecarboxylations Involving Phthalimides

Owing to their favourable photophysical and electrochemical properties, phthalimides undergo a variety of highly efficient photodecarboxylation reactions. These transformations have been applied to the synthesis of macrocyclic compounds as well as bioactive addition adducts. N-Acetoxyphthalimides are versatile precursors to imidyl and alkyl radicals through photodecarboxylation and have subsequently been used for a variety of coupling reactions. The generally mild reaction conditions make these reactions attractive for green chemical applications. The process protocols were successfully transferred to novel photoreactor devices, among these falling film or continuous flow reactors.