We have developed a strategy for the stereoselective synthesis of cyclolignans related to podophyllotoxin and its derivatives. The crucial step of the synthesis is the photocyclization of a chiral atropoisomeric 1,2-bisbenzylidenesuccinate amide ester, which can be prepared from suitable aromatic aldehydes, diethyl succinate and l-prolinol. The photocyclization was found to be more efficient when irradiation was performed in a home-built continuous flow photochemical reactor. The in-flow irradiation also allowed us to perform the reaction on a multigram scale. The chiral auxiliary was removed by reductive cleavage with the Schwartz's reagent to give the cytotoxic 1R,2R-cis-podophyllic aldehyde, which in turn could be easily reduced to the corresponding alcohol, completing the formal synthesis of (-)-podophyllotoxin.

The first total synthesis of (+)-epigalcatin was completed in a highly stereoselective manner starting from piperonal, 3,4-dimethylbenzaldehyde, and diethyl succinate. l-Prolinol was used as a chiral auxiliary. The crucial step in this procedure involves the construction of the cyclolignan framework by continuous-flow photocyclization of a chiral atropisomeric 1,2-bisbenzylidenesuccinate amide ester.

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This study aimed to determine the antioxidant properties of the sulfate monoesters of ferulic, caffeic, dihydroferulic and dihydrocaffeic acids, the main metabolites of chlorogenic acids. These compounds are not commercially available, so they were synthesized in the laboratory. The LC-MS/MS analysis allowed for the full characterization of these derivatives, which has made them reliable standards for further research. Purified metabolites including ferulic acid-4-O-sulfate, caffeic acid-4-O-sulfate and caffeic acid-3-O-sulfate, dihydrocaffeic acid-4-O-sulfate and caffeic acid-3-O-sulfate were examined for their antioxidant capacities and compared to their precursor compounds using Folin–Ciocalteu, CUPRAC (cupric ion—reducing) and DPPH• (2,2-diphenyl-1-picrylhydrazyl) methods. This study shows that hydrogenation of caffeic and ferulic acids into dihydrocaffeic and dihydroferulic acids has a positive influence on their reducing properties. Moreover, all synthesized sulfate monoesters exhibited very weak antioxidant properties compared to precursor compounds. The presented results show that the transformation of phenolic acids via sulfation leads to the inhibition of antioxidant properties due to the blockage of hydroxyl groups.

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