Twenty-six alkaloids, including the new taberines A−I (1−9), were obtained from Tabernaemontana corymbosa. The structures and absolute configurations were elucidated via MS, NMR, and ECD spectroscopic data analyses. Alkaloids 1−4 are new vobasinyl-ibogan alkaloids, and 1 is characterized by an unusual 1,3-oxazinane moiety. Alkaloids 4 and 16 exhibited moderate cytotoxic potency against various human cancer cell lines, while 4, 10, 11, 13, 14, and 16 showed attenuation of lysosomal acidification activity (EC 50 : 12.9−29.8 μM), thereby inhibiting autophagic flux.
Two new monoterpenoid indole alkaloids, tabervarines A (1) and B (2), along with seven known monoterpenoid indole alkaloids, were isolated from the methanol extract of the twigs and leaves of Tabernaemontana divaricata. The structures including the absolute configurations of the new alkaloids were elucidated based on MS, NMR, and ECD calculation. The in vitro cytotoxic activities of the isolated alkaloids against several human cancer cell lines were also evaluated.
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