ABSTRACT
Aims: This study investigated the antisickling and radical scavenging activities of different morphological parts of nine plants, belonging to six families. A bioassay-guided fractionation was carried out on Mitracarpus villosus (Sw.) DC. Cham, which was one of the most active plants. Place and Duration of Study: Drug Research and Production Unit, Faculty of Pharmacy, Obafemi Awolowo University (OAU), Ile Ife, Nigeria between May 2013 and June 2016. Methodology: Plant materials were collected from OAU campus and Ile-Ife town, identified and voucher specimen deposited at IFE herbarium, OAU for future reference. In-vitro radical scavenging and antisickling (by haemoglobin polymerization inhibitory test) activities of extracts and isolated compounds were performed using ascorbic acid and vanillic acid as positive controls respectively. Bioassay-guided fractionation was achieved by combination of various chromatographic procedures and bioassay techniques to isolate the active constituents. Structural elucidation of the isolated compounds was by spectroscopic techniques including NMR and MS. Results: Six of the nine plant extracts showed considerable antisickling and antioxidant activities. Extracts of Emilia praetermissa and M. villosus, were however the most active. Extracts or compound which demonstrated strong radical scavenging activity were also found to demonstrate significant antisickling effects. Bioassay-guided fractionation of M. villosus resulted in the isolation of psychorubrin, quercetin and a mixture consisting of stigmasterol and an unidentified terpene. Quercetin was the most active antisickling and radical scavenging compound with percentage inhibition of 96.46±0.3 and 87.99±0.18 respectively. Conclusion: Mitracarpus villosus ranked second best in activity among the tested plants. Antisickling activity of its isolated compounds was found to increase with increase in the antioxidant capability of the compounds. Quercetin was the most active compound while the non-antioxidant terpenoidal mixture had very weak polymerisation inhibitory effect.