Two new indole alkaloids from Nauclea officinalis and their evaluation for cytotoxic activities

Two new indole alkaloids, naucleamide H (1) and (±)-19-O-butylangustoline (8), along with seven known alkaloids, 3,14-dihydroangustine (2), (-)-naucleofficine D (3a), (+)-naucleofficine D (3b), nauclefine (4), angustidine (5),19-O-ethylangustoline (6) and angustine (7) were isolated from the water extract of Nauclea officinalis. The structures of these compounds were established by spectroscopic analysis. Among them, the cytotoxicity of 1, 2, 6 and 8 were evaluated against six human cancer cell lines (HepG-2, SKOV3, HeLa, SGC 7901, MCF-7 and KB) in vitro for the first time with 5-fluorouracil as a positive control drug. The new compound 1 had a strong inhibitory effect on the proliferation of HepG-2 with an IC₅₀ value of 19.59 μg/mL. The new compound 8 had a strong inhibitory effect on HepG-2, SKOV3, HeLa, MCF-7 and KB, IC₅₀ value was 5.530, 23.11, 31.30, 32.42 and 37.26 μg/mL, respectively.