Free radical scavenging activity of sesquiterpene indole and caryophyllene- dominated leaf and stem essential oils of Secamone afzelii (Schult) K. Schum and Pergularia daemia (Forsk) Chiov (Asclepiadaceae)

Abstract

The chemical composition and free radical scavenging activities of leaf and stem essential oils of two Asclepiadaceae
species, Secamone afzelii and Pergularia daemia were investigated. They are claimed to be used in ethno-medicine for
the treatment of stomach problems, diabetes, colic, dysentery and kidney problems. Essential oils of the air-dried leaves
and stem of the plants were extracted by hydro-distillation using Clavenger-type apparatus. The oils were characterized
by Gas Chromatography and Gas Chromatography – Mass Spectrometry (GC-MS). The free radical scavenging activity
was determined using 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical method. Two antioxidant standards, ascorbic acid
and butylated hydroxy anisole (BHA) were used. GC and GC-MS analysis of the colourless essential oil of S. afzelii and
P. daemia leaves and stems showed the presence of 6, 12, 15 and 13 compounds of terpene origin representing 84.34%,
32.08%, 87.08% and 40.08% of the total essential oil respectively. The most abundant compounds are 1H-Indole, 1-methyl-
2-phenyl- (72.99%, S. afzelii leaf), ?-santalol (11.03%, S. afzelii stem), (E)-caryophyllene, (53.83%, P. daemia leaf) and
azulene (7.36%, P. daemia stem). The leaf essential oils of the two plants also showed good scavenging activity at 0.0625
mg/mL, 85.45% (S. afzelii) and 69.38% (P. daemia). S. afzelii leaf however showed better activity than the standards used.
It was therefore concluded that the scavenging activity of the leaves’ oil could be responsible for their use in ethno-
medicine and that intrinsic or genetic as well as extrinsic or environmental factors may have been responsible for the
variation in the oil constituents.