Taberdines L and M, two new alkaloids from Tabernaemontana divaricata

Abstract

Two new alkaloids, taberdines L (1) and M (2), together with six known alkaloids, were isolated from the twigs and leaves of Tabernaemontana divaricata. Taberdine L (1) represents the first optically active natural member of the allo iboga class of alkaloids with the ethyl side chain in a bridgehead position. Their structures including absolute configuration were elucidated by a combination of MS, NMR, and ECD calculation.The in vitro cytotoxic activities of 1 and 2 against five human cancer cell lines were also evaluated.

Two Novel Iboga-Type and an Oxindole Glucuronide Alkaloid from Tabernaemontana peduncularis Disclose Related Biosynthetic Pathways to Tabernaemontana divaricata

“…peduncularis , we found the exclusive accumulation of the javaniside epimers 4 [ 21 ] and 5 [ 21 ] in the methanolic leaf extract of T. divaricata together with the known alkaloids voacristine ( 7 ) [ 22 ], mehranine ( 8 ) [ 23 ], voafinidine epoxide ( 9 ) [ 24 ], voaphylline ( 10 ) [ 24 ], and apparicine ( 11 ) [ 23 ] ( Table 2 ). In the methanolic crude extract obtained from the stem bark of T. divaricata , we identified apparicine ( 11 ) [ 23 ] as well as tabernaemontanin ( 12 ) [ 25 ], dregamine ( 13 ) [ 26 ], 3-hydroxy coronaridine ( 14 ), ervatamine ( 15 ) [ 27 ], and 19–20 didehydroervatamine ( 16 ) [ 27 ]; the latter two were also present in the crude methanolic wood extract ( Figure S82 ). From the crude methanolic root extract of T. divaricata , the (seco)iridoids secologanoside ( 17 ) [ 28 ] and loganic acid ( 18 ) [ 29 ] could be isolated and identified.…”

“…It is unlikely that such a selective oxidation happened in a non-enzymatic way during the isolation and purification since we employed mild isolation procedures ( Figures S1–S5 ). Furthermore, such artifacts should have been earlier described for isolation procedures of other monoterpene indole alkaloids [ 1 , 2 , 3 , 4 , 5 , 6 , 8 , 9 , 10 , 13 , 18 , 19 , 20 , 21 , 22 , 23 ]. It seems possible, but very unlikely, that the glucose was oxidized after the formation of the indole alkaloid, as this would typically require a specialized enzyme for the oxidation of javaniside ( 4 ) or an alcohol oxidase with a very broad substrate spectrum.…”