Investigation on antioxidant interaction between isolated constituents from Dillenia excelsa leaves extract with Curcuma zedoaria roots extract

Medicinal plants have been mixed to augment the intended therapeutic effectiveness in treating diseases. One such combination is the roots of Curcuma zedoaria and the leaves of Dillenia excelsa , as both plants possess healing properties. This study investigated the antioxidant interaction between C. zedoaria and isolated compounds from D. excelsa extract. Seven compounds – diospyrolide, betulinic acid, 12-dien-3,28-dioic acid, platanic acid, afzelin, quercitrin and myricitrin were successfully isolated from D. excelsa for the first time. These isolated compounds displayed distinctive interactions when combined with C. zedoaria roots extract using different antioxidant approaches. The antioxidant capacity was assessed via oxygen radical absorbance capacity (ORAC), 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging activity, and ferric ion reducing antioxidant power (FRAP). The antioxidant results of the isolated compounds revealed that betulinic acid has the highest ORAC value (52.21 ± 1.63 µg Trolox equivalent/g of crude extract), quercitrin has the highest DPPH value (391.97 ± 0.19 mg gallic acid equivalent/g of crude extract), and myricitrin has both the highest FRAP and ABTS value (11.28 ± 0.48 mg Trolox equivalent/g and 39.14 ± 0.67 mg quercetin equivalent/g of crude extract, respectively). When the isolated compounds were mixed with C. zedoaria , all compounds showed synergistic effect via DPPH and ABTS except for 12-dien-3,28-dioic acid. These findings demonstrate the potential of combining C. zedoaria with compounds from D. excelsa extract to enhance antioxidant activity especially in radical scavenging capability, highlighting their promise for further development in therapeutic applications and natural antioxidant formulations, offering an optimistic outlook for future research and development.