Synthesis and Antioxidant Activity of Novel Thiazole and Thiazolidinone Derivatives with Phenolic Fragments

In this work, a series of thiosemicarbazones with phenol fragments were used as starting compounds for the synthesis of new effective antioxidants containing both a phenol substituent and a heterocyclic fragment: thiazole and thiazolidinone. To determine the most stable conformation of thiosemicarbazone, a potential energy scan was used, along with NOESY NMR spectroscopy data. A number of thiazole derivatives were obtained due the interaction of thiosemicarbazones with several bromoketones: bromoacetophenone, bromodimedone, and bromoacetylcoumarin. The product yields varied from 71 to 94%. Thiazolidinone derivatives were obtained through the reaction between thiosemicarbazones and chloroacetic acid or maleic anhydride with good yields of 82-95%. The antioxidant activities of all the products were determined in vitro: the radical cation scavenging activity was estimated using 2,2 '-azino-bis(3-ethylbenzothiazoline-6-sulfonate), while the ferric reducing capacity was determined using the ferricyanide/Prussian blue method. It was found that the antioxidant activity of most synthesized substances in both tests exceeds the activity of 4-methyl-2,6-di-tert-butylphenol, while derivatives with a fragment of 2,6-di-tert-butylphenol have the highest activity.