Steglich esterification of oleic acid with curcumin and toxicity test of its products against Daphnia magna

Oleic acid is an unsaturated fatty acid that has been known to have therapeutic activities such as antimicrobial, anti-inflammatory, antidiabetic, and anticancer. In this study, the synthesis of oleic acid ester compounds with curcumin was carried out by Steglich esterification using DCC as a coupling reagent and DMAP as a catalyst. Thin layer chromatographic analysis was performed to identify the product and showed that the Rf value of oleic acid was 0.70, dioleic-curcumin ester was 0.92, monooleic-curcumin ester was 0.78, and curcumin was 0.49. The product was then purified using silica gel column chromatography with n-hexane:ethyl acetate (12:1, v/v) as the eluent. Characterization using FT-IR showed that there was a new absorption of the C=O ester functional group at wave numbers 1760 cm-1 - 1735 cm-1. There were also absorption peaks for carboxyl ketone C=O functional group at 1640 cm-1-1620 cm-1, aromatic C=C functional group at 1650 cm-1 - 1566 cm-1, aromatic C-O functional group at 1310 cm-1 - 1250 cm-1, and C-O-C at 1075 cm-1 - 1020 cm-1. The results of the toxicity test against Daphnia magna showed that the LC50 value of the dioleic-curcumin ester compound product was 189.91 mg/L and monooleic-curcumin was 98.68 mg/L. Based on the LC50 value, the monooleic-curcumin ester was categorized as very toxic and had the potential as a bioactive compound.