Potential antioxidants of secondary metabolite isolates ethyl acetate fraction Coleus amboinicus Lour. Leaves.

Abstract

The aim of the study was to isolate and characterize secondary metabolites that have the potential as antioxidants from the ethyl acetate fraction of the leaves of Coleus amboinicus, L. (C. amboinicus).
 Materials and methods. Purification of the ethyl acetate fraction of C. amboinicus using gravity column chromatography with a stationary phase (silica gel, Merck) and a mobile phase with a solvent ratio of n-hexane (Merck) and ethyl acetate (Merck). Examining isolates includes physical (colour, shape, and melting point). Qualitative purity detection by TLC at 254 nm and 366 nm wavelengths. Structural analysis of metabolites with UV-Vis spectrometer (Spectronic 3000, Genesis 10, Japan), FT-IR(KBr) (Shimadzu IR Prestige-21, Japan), NMR spectrometer (JEOL spectrometer, Japan) operating at 500 MHz (1H-NMR) and 125 MHz (13C-NMR), and Shimadzu's GC-MS (QP-2010S Shimadzu, Japan) and determination of potential antioxidant activity using the DPPH method.
 Results. The secondary metabolite compounds were isolated in the form of yellow crystals with a melting point of 232-233 °C and Rf values of 0.86 and 0.56, which TLC monitored at a solvent ratio of n-hexane and ethyl acetate 6:4 and 8:2. Spectronic analysis with a UV-Vis Spectrometer showed two electron absorbances, namely a wavelength of 210 nm indicating methanol solvent and 272 nm isolate. The absorbance of functional groups at wave numbers 3379 cm-1 (-OH; hydroxy), 2931 cm-1 (-CH; aliphatic), 1735 cm-1 (-C=O; carbonyl ketone), 1234 cm-1 (-CO-; methoxy) and 1643 cm-1 (-C=C-; alkene). GC-MS analysis obtained two absorbance peaks, (1) the first retention time of 6.658 minutes (3.95 %) and (2) the second retention time of 9.001 minutes (96.05 %). Structural analysis with 1H&13C-NMR showed 28 types of protons and 22 types of carbon. The antioxidant activity potential test showed an activity value (IC50) of 338.54 ppm.
 Conclusion. The structure of the isolated secondary metabolite compound is 16-acetoxy-7α-hydroxyroyleanone (syn. 16-acetoxyhorminone) and has the potential as an antioxidant.