Electronic circular dichroism studies of pentacyclic oxindole alkaloids and flavonoids from Malaysian Uncaria longiflora var. pteropoda (MIQ.) RIDSD. / Dr Rohaya Ahmad

This study was performed with the aim of establishing the absolute configuration of six new chiral constituents comprising five pentacyclic oxindole alkaloids and a flavonoid isolated from Uncaria longiflora var. pteropoda. The absolute configurations of the new chiral compounds were established by comparing the cotton effects (CEs) of the experimental ECD spectra to the simulated ECD values, as well as to the ECD spectra of six known related compounds in hand. The known alkaloids were isopteropodine, pteropodine, Uncarine F and speciophylline while the known flavonoids were epi-catechin and epi-afzelechin. The POAs rauniticine-allo-oxindole B ULSl and rauniticinic- allo acid B ULS2 were both established to have the 3S, 7R, 15S, 19R, 20S stereochemistry. The absolute configuration of three other new alkaloids were also determined: 2-oxosecologanine ULL5 possess a 4S, 8R, 9S configuration while isoformosaninol ULL6 and formosaninol ULL7 exhibited a 3S, 7S, 15S, 16R, 17R, 19R, 20R and a 3S, 7R, 15S, 16R, 17R, 19R, 20R stereochemistry, respectively. The new flavonoid, uncariechin ULL14 was established to possess a 2R, 3R configuration.