Synthesis of rigidified flavin-guanidinium ion conjugates and investigation of their photocatalytic properties.

Flavin chromophores can mediate redox reactions upon irradiation by blue light. In an attempt to increase their catalytic efficacy, flavin derivatives bearing a guanidinium ion as oxoanion binding site were prepared. Chromophore and substrate binding site are linked by a rigid Kemp's acid structure.

Thiourea-enhanced flavin photooxidation of benzyl alcohol.

Upon irradiation, flavin oxidises 4-methoxybenzyl alcohol to the corresponding aldehyde using aerial O(2) as the terminal oxidant. We have observed that this reaction is significantly accelerated by the presence of thiourea. A series of thiourea-functionalised flavins has been prepared from flavin isothiocyanates and their photocatalytic efficiencies have been monitored by NMR.