Alkaloids from the stem bark of Strychnos icaja

Abstract A comprehensive phytochemical study of the stem bark of Strychnos icaja was done for the first time and led to the isolation of two new monoindole alkaloids 15-hydroxyvomicine ( 1 ) and 12-methoxyicajine ( 2 ) along with 13 known alkaloids: the monoindoles N -methyl- sec - iso -pseudostrychnine ( 3 ), vomicine ( 4 ), icajine ( 5 ), 19,20-α-epoxy-12-methoxyicajine ( 6 ), 19,20-α-epoxy-12,15-dihydroxy-11-methoxyicajine ( 7 ), 19,20-α-epoxy-15-hydroxynovacine ( 8 ), 15-hydroxyicajine ( 9 ), 12-hydroxystrychnine ( 10 ), strychnine ( 11 ) and the tertiary bisindoles sungucine ( 12 ), isosungucine ( 13 ), strychnogucine C ( 14 ) and bisnordihydrotoxiferine ( 15 ). Apart from 10 and 11 , the other alkaloids were isolated for the first time from the stem bark of this plant. The hemisynthetic derivative, N b -chloromethosungucine ( 16 ) and the previously reported synthetic compound 3 were isolated from a natural source for the first time. Fractions and some isolated compounds were tested against the chloroquine-sensitive 3D7 strain of Plasmodium falciparum . The bisindole alkaloids were most active with IC 50 ranging from 0.72 to 3.41 μg/ml whilst the monomers 1 and 3 were slightly active (IC 50 39.92 and 40.27 μg/ml respectively) and 6 inactive. The structures of the compounds were determined based on the analysis of their spectral data. The full 1 H and 13 C NMR data of compounds 3 , 6 and 7 are also reported in the present work for the first time.