Modification of Flavonoids from Surface Exudate of Polygonum senegalense

Surface exudate of Polygonum senegalense contains flavonoids of the chalcone and flavanone
types. Our interest is in the anti-plasmodial activities of synthetically modified flavonoids and
chalcones in comparison with the starting natural compounds.
New compounds were produced by structural modification via environmentally benign reactions.
The reactions undertaken involved the transformation of 2’, 6’-Dihydroxy-4’-methoxychalcone
into 5-hydroxy-7-methoxyflavanone using base catalysis, sodium hydroxide solution, in purely
aqueous medium.
The product was then reacted with ethyl amine and methyl amine at room temperature yielding
5-hydoxy-4-ethylimino-7-methoxyflavanone and 5-hydroxy-7-methoxy-4-methyliminoflavanone
respectively.
The reduction of the above imines to the respective amines was achieved by reaction with
NaBH4 after dissolution of the imines in ethanol. Nitration of 2’-hydroxy-4’,6’-
dimethoxydihydrochalcone at temperatures below room temperature led to the production of
three nitro derivatives as indicated by TLC analysis. Determination of the structures was via
spectroscopic evidence (1H, 13 C NMR) and the products formed were tested to assess their in
vitro anti-plasmodial activities.