Supplementary information: Isolation and Antioxidant Activity of Harmalol from Grewia villosa Willd. Stem and Root Bark

Abstract

Grewia villosa Willd. is a deciduous shrub found in arid parts of Kenya and used as
both food and medicine. The study aimed to isolate compounds present in Grewia
villosa stem and root bark extract and assess their antioxidant activity. Grewia
villosa stem and root bark were collected from Loitokitok, Kajiado County, Kenya.
They were dried in the shade, pulverized to fine powder, and extracted in
methanol/dichloromethane 1:1 mixture for 72 h. The solvent was removed by rotary
evaporation. The crude extract was subjected to column chromatography over silica
gel to obtain one pure compound. Analysis by mass spectrometry and nuclear
magnetic resonance spectroscopy identified the isolated pure compound as 1-
methyl-4,9-dihydro-3H-β-carbolin-7-ol (harmalol). Antioxidant activity was
performed using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) standard protocol.
Harmalol displayed significant antioxidant activity (115.22 μg/ml) comparable to
that of the methanol extract. This compound was previously isolated from the root
of G. villosa but was not fully characterized spectroscopically. This study is the first
report of NMR characterization of harmalol.
Keywords: Grewia villosa, isolation, harmalol, antioxidant