Bousmekines A-E, New Alkaloids from Two Bousigonia Species: B.angustifolia and B. mekongensis

Abstract

Four new monoterpenoid indole alkaloids, bousmekines A-D (1-4), and one new pyranopyridine alkaloid, bousmekine E (5), were isolated from the twigs and leaves of Bousigonia angustifolia and Bousigonia mekongensis. Their structures including absolute configurations were elucidated by a combination of MS, NMR, ECD calculation, and single-crystal X-ray diffraction analysis. Compound 2 was an eburnea-type MIAs characterized by a rare chlorine atom while 5 possessed a novel pyranopyridine moiety. Their cytotoxicities against several human cancer cell lines were evaluated and compound 1 exhibited significant cytotoxicity with IC₅₀ values of 0.8-7.4 μM.

Keywords: B. angustifolia; B. mekongensis; Bousigonia; Bousmekines A-E; Monoterpenoid indole alkaloids.

Fig. 1

Structures of compounds 1–5

Fig. 2

Key HMBC (arrow) and ¹H-¹H COSY (bold) correlations of compounds 1–5

Fig. 3

Key ROESY correlations of compounds 1, 3, and 5

Fig. 4

Experimental and calculated ECD of 1

Fig. 5

X-ray crystal structure of 2