Isomerization of E-Cinnamamides into Z-Cinnamamides Using a Recycling Photoreactor.

The photocatalytic synthesis of thermodynamically less-stable Z-alkenes has received considerable research attention in recent years. In this study, a recycling photoreactor was applied to the photoisomerization of E-alkenes (cinnamamide and Weinreb amide derivatives) to produce Z-alkenes. The closed-loop recycling system comprises an immobilized photosensitizer to achieve rapid photoisomerization and a high-performance liquid chromatography instrument for separation of the Z/E diastereomers. After 4-10 cycles, the desired pure Z-alkenes were obtained efficiently. In the photoreactor system, a photosensitizer (thioxanthone) was covalently immobilized on silica gel via amide bonding, which led to an enhanced photocatalytic activity compared to the parent thioxanthone. This recycling photoreactor shows promise as an alternative system for the production of Z-alkenes.

Photoisomerization of Sulindac and Ozagrel Hydrochloride by Vitamin B2 Catalyst Under Visible Light Irradiation.

PURPOSE: Photoisomerization of the E/Z-alkene structures of drugs is a matter of concern as it could result in potency loss and adverse side effects. This study focused on light-induced isomerization of sulindac and ozagrel hydrochloride catalyzed by concomitant vitamin B2 under light-emitting diode (LED) or fluorescent light. METHODS: In the presence of 0.05/0.03 equivalents of vitamin B2/flavin adenine dinucleotide (FAD), sulindac or ozagrel hydrochloride was irradiated with LED light (405 nm) or fluorescent light. The photoisomerization in CD3OD and D2O was monitored by 1H NMR spectroscopy. RESULTS: Sulindac and ozagrel hydrochloride isomerized in the presence of a catalytic amount of vitamin B2 or FAD under irradiation of 405 nm LED light and fluorescent light. Irradiation with LED light was found to be more effective than fluorescent light irradiation. The rate of photoisomerization was affected by the solvent, and the reaction in CD3OD proceeded faster than in D2O. Furthermore, ozagrel hydrochloride was more prone to isomerization than sulindac. CONCLUSION: The catalytic activity of vitamin B2 or FAD was demonstrated in the photoisomerization reaction of sulindac and ozagrel hydrochloride. Considering that the rate of photoisomerization in D2O is very slow, the possibility of the occurrence of photoisomerization during clinical use is low. However, this study suggests that the interfusion of vitamin B2 or FAD under excessive light exposure should be avoided as a caution during intravenous administration of sulindac or ozagrel hydrochloride.