Isolation and Characterization of Anti- Sickling Bioactive Compounds from Seeds of Picralima Nitida Stapf (Apocynaceae)
Felix N. Osuala, Uchenna E. Odoh
Aim: To isolate and Characterize the anti-sickling bioactive compounds of Ethanol fraction of Picralima nitida seeds. Methods: The fresh matured fruits (8 kg) of P. nitida were cut into transverse section to expose the seeds, The seeds were air-dried and then pulverized into a homogenous powder, The organoleptic properties (taste, colour, odor, texture) of the powdered P. nitida were determined using the sensory organs. A 2.5 kg pulverized seeds were extracted with methanol and concentrated in a rotary evaporator to yield a dried residue. The methanol extract of Picralima nitida was then defatted using n-hexane. The extract was successively fractionated with different solvents, chloroform, dichloromethane, ethyl acetate and 50% ethanol in increasing order of polarity to obtain the chloroform fraction (CF), dichloromethane fraction (DCMF), ethyl acetate fraction (EF) and ethanol fraction. Antisickling activity tests were carried out on all the fractions at the same time, comparing their antisickling activities with that of p-hydroxybenzoic acid (positive control). The Ethanol Fraction which has the greatest anti sickling activity was subjected to further fractionation using silica gel column chromatography. The fractions based on bioactivity-guide, were eluted with gradient mixtures followed by a preparative TLC using EtOAc:MeOH (2:3) as solvent system to get compounds 1 and 2.The structures of the isolated active compounds were elucidated using spectrophototropic analyses. Result: The two compounds were identified as (19 )-16, 17- didehydro-19-methyl-oxayohimbin-16-Carboxylic acid methyl ester (Ajmalicine) and (19 )-19-methyl-2-oxoformosanan-16-carboxylic acid methyl ester (Ajmalicine Oxindole B). Ajmalicine showed significant antisickling effect (97 %) when compared to the standard drug (50 %). Ajmalicine Oxindole B Showed (90 %) antisickling effect at concentration 2.5 mg/ mL at 90 minutes incubation in HbSS blood. Conclusion The seeds of Picralima nitida possesses antisickling effect and could serve as a lead to produce further antisickling drug.
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