Investigation of free radical scavenging activity by ESR for coumarins isolated from Tecoma radicans

Tecoma radicans (Campsis radicans (L.) Seem.), F. Bignoniaceae is a species that belongs to a tropical family but has been introduced in many countries as ornamental. Phytochemical investigation of the aerial parts of Tecoma radicans (L.) DC, indicates the presence of four coumarins, 2', 3'-epoxide alloimperatorin (I), pabulenone (II), pereflorin B (III) and 17–methylbothrioclinin (IV). One chromone was also isolated peucenin–7-methyl ether (V), and showed the violet colour with FeCl₃ directly while the four coumarins showed this violet after alkalinization with ammonia solution. They were isolated, purified and identified from their spectroscopic analysis and comparing with the published data [1]. When successive extracts of T. radicans and coumarin fraction were screened for cytotoxic activity in concentration of 100µg/0.1 mL DMSO, in vitro using a single tumour (Ehrlich ascites carcinoma cells) [2], they showed no cytotoxic activity. When the coumarin fraction and isolated compounds were examined for free radical scavenging activity, using the stable DPPH free radical [3] and recorded by ESR, using vitamin C as control, it was found that the whole coumarin fraction was the most active, Fig.1, (89. 06% inhibition of DPPH free radical), and the isolated components are 0, 25.9, 8.45, 13.85 and 50% respectively, Table 1.

Fig.1. ESR of control (DPPH) and coumarin extract of T.radicans

Table 1: Inhibition of DPPH radical by coumarins isolated from T. radicans.

Compound	Double integrationarea	Percentage inhibition
DPPH	638
Vitamin C	29.0	95.45
Coumarin ext.	69.0	89.2
Compound I	638	-
Compound II	472.7	25.9
Compound III	584	8.45
Compound IV	549.6	13.85
Compound V	319.0	50.0

References: 1. Murray, R.D.H., Mendez, J., Brown, S.A.. (1982), The Natural Coumarins, John Wiley and Sons Ltd., New York. 2. El-Hossary, G.A., Fathy, M.M. (2000), Bull. Fac. Pharm. Cairo Univ. 38: 87–97. 3. Acqua, S.D., Innocenti, G. (2004), Fitoterapia, 75, 592–595.