Isolation and Characterization of Curcumenotone, a Sesquiterpene from Curcuma aeruginosa Roxb as Antioxidant

Abstract

Antioxidant compounds are necessary to block the initiation of
oxidation chain reactions and inhibit the formation of ROS which are the cause
of various diseases. Natural antioxidants can be isolated from various sources:
one of which is Curcuma aeruginosa Roxb Rhizome. This study was aimed to
isolate and identify the antioxidant compounds from C. aeruginosa Roxb
rhizome. To isolate the active compound, the 2,2-diphenyl-1-picrylhidrazyl
(DPPH) free radical scavenging activity guide was used. Initially the C.
aeruginosa Roxb rhizome powder was macerated with 70% ethanol to
produce ethanol extract (EE). The EE was then fractionated gradually by
increasing the polarity of solvents to produce n-hexane (HF), ethyl acetate
(EAF), ethanol (EF) and insoluble (IF) fractions. EF as the active fraction, was
fractionated into 6 fractions (EF.a-f) based on their TLC images. Two
compounds (EF.a1 and EF.a2) were isolated from the active fraction (EF.a) by
preparative TLC. EF.a2 which appeared as white crystals demonstrated the
best activity as DPPH anti radical, having 96.24% purity (HPLC). EF.a2
appeared as a single peak in GC (Rt 12,78), and had a molecular weight of m/z
234. There were 2 absorbtion peaks at 226 nm and 260 nm in Uv-Vis
spectrophotometer and absorption bands at 3364, 3314, 2905 and 1653 cm
-1

on the FT-IR spectrum. Based on the spectroscopic data (
1
H-,
13
C-NMR) and the
reported data, the EF.a2 was identified as sesquiterpene, curcumenotone
(C
15
H
22
O
2
). The curcumenotone was shown to be a potent antioxidant in the
DPPH radical scavenging assay with an IC
50
of 53.24±1.51 µg/mL, ABTS radical
scavenging assay with an IC
50
of 41.33±3.15 µg/mL, and FRAP assay with an
IC
50
of 37,82±2.02 µg/mL.
Keywords: Bioassay-Guided Isolation, C. aeruginosa, Antioxidant,
Sesquiterpenes, Curcumenotone