Indole alkaloids with in vitro antiproliferative activity from the ammoniacal extract of Nauclea orientalis.

Nine angustine-type alkaloids were isolated from ammoniacal extracts of Nauclea orientalis L. (Rubiaceae). Three of them, 10-hydroxyangustine and the two diastereoisomeric 3,14-dihydroangustolines, have not been described in the literature thus far. The structures of the isolates were determined with spectroscopic methods, mainly 1D- and 2D-NMR spectroscopy. The compounds were found to exhibit in vitro anti-proliferative activity against the human bladder carcinoma T-24 cell line and against EGF (epidermal growth factor)-dependent mouse epidermal keratinocytes. By using overpressure layer chromatography, it was shown that minor quantities of these alkaloids occur in dried Nauclea orientalis leaves. The use of ammonia in the extraction process results in a significant increase in the formation of angustine-type alkaloids from strictosamide-type precursors.