Photochemical Transformations of Diverse Biologically Active Resveratrol Analogs in Batch and Flow Reactors.

Previous biological tests have shown that some resveratrol analogs exhibited significant antioxidative and cholinesterase inhibitory potential, as evidenced by lower IC50 values compared to the established standards, resveratrol and galantamine, respectively. Photochemical transformations were made in parallel on these compounds in the presence of porphyrin photocatalysts in batch and microreactor, showing the significant advantage of flow photochemistry concerning productivity, selectivity, and yields. In this research, the products of photocatalysis and direct irradiation (photolysis) of resveratrol analogs were compared to elucidate how the types and ratios of the products depend on the excitation energy, to reveal the effects of the substituent on the photoinduced reactions and to rationalize experimentally and computationally the nature and ratio of the obtained products. Thus, two main paths were computed in agreement with the experimental results: isomerization with the participation of triplet state intermediates to yield the experimentally detected cis-isomers and subsequent cyclization following a pathway not available for the trans-isomers. The investigation of five model compounds confirmed the advantages of the flow photoreactor in the photochemical reactions of heterocyclic resveratrol analogs.

Synthesis, crystal structure and spectroscopic and Hirshfeld surface analysis of 4-hy-droxy-3-meth-oxy-5-nitro-benzaldehyde.

The title compound, C8H7NO5, is planar with an r.m.s. deviation for all non-hydrogen atoms of 0.018 Å. An intra-molecular O-H⋯O hydrogen bond involving the adjacent hy-droxy and nitro groups forms an S(6) ring motif. In the crystal, mol-ecules are linked by O-H⋯O hydrogen bonds, forming chains propagating along the b-axis direction. The chains are linked by C-H⋯O hydrogen bonds, forming layers parallel to the bc plane. The layers are linked by a further C-H⋯O hydrogen bond, forming slabs, which are linked by C=O⋯π inter-actions, forming a three-dimensional supra-molecular structure. Hirshfeld surface analysis was used to investigate inter-molecular inter-actions in the solid state. The mol-ecule was also characterized spectroscopically and its thermal stability investigated by differential scanning calorimetry and by thermogravimetric analysis.