Indole alkoloids from Nauclea officinalis with weak antimalarial activity

Abstract

Five indole alkaloids (naucleofficines A– E) were isolated from the stems (with bark) of Nauclea officinalis: ( E)-2-(1-β- d-glucopyranosyloxybut-2-en-2-yl)-3-(hydroxymethyl)-6,7-dihydro-indolo[2,3-a]quinolizin-4(12 H)-one ( 1), ( E)-1-propenyl-12-β- d-glucopyranosyloxy-2,7,8-trihydro-indolo[2,3-a]pyran[3,4-g]quinolizin-4,5(13 H)-dione ( 2), ( E)-2-(1-hydroxybut-2-en-2-yl)-11-β- d-glucopyranosyloxy-6,7-dihydro-indolo[2,3-a]quinolizin-4(12 H)-one ( 3), ( E)-1-propenyl-4-hydroxy-2,4a,7,8,13b,14,14a-hepthydro-(4α,4aβ,13bα,14aβ)indolo[2,3-a]pyran[3,4-g]quinolizin-5(13 H)-one ( 4) and 1-(1-hydroxyethyl)-10-hydroxy-7,8-dihydro-indolo[2,3-a]pirydine[3,4-g]quinolizin-5(13 H)-one (10-hydroxyangustoline) ( 5), together with two known compounds, naucleidinal ( 6) and angustoline ( 7). All of the structures of the seven compounds above were elucidated by spectroscopic methods including use of 1 D- and 2 D-NMR spectroscopic analyses. Compounds 2 and 3 are rare examples of monoterpene indole alkaloids with a glucopyranosyloxy group attached to position C-12. In vitro activity screening of the above seven compounds showed weak to moderate inhibitory activity against Plasmodium falciparum.