Bioactive steroidal alkaloids from Buxus macowanii Oliv.

• This is the first report on the phytochemical investigation of Buxus macowanii.
• The crude methanolic extract of this plant exhibited anti-AChE activity.
• A detailed phytochemical investigation of a bioactive fraction afforded five new and five known compounds (1–10).
• Compounds 1, 3, and 4 are members of a rare class of Buxus alkaloids containing Δ1,2 9(10 → 19) abeo triene system.
• All isolates exhibited moderate to weak anti-AChE activity.

Chemical investigation of the crude methanolic extract of Buxus macowanii resulted in the isolation of five new steroidal alkaloids, 31-hydroxybuxatrienone (1), macowanioxazine (2), 16α-hydroxymacowanitriene (3), macowanitriene (4), macowamine (5), along with five known steroidal bases, Nb-demethylpapillotrienine (6), moenjodaramine (7), irehine (8), buxbodine B (9) and buxmicrophylline C (10). Structures of compounds 1–10 were elucidated with the aid of spectroscopic methods including 1D and 2D NMR techniques and mass spectrometry. Compounds 1, 3, and 4 belong to a rare class of Buxus alkaloids having Δ1,2 9(10 → 19) abeo triene system. All isolates were evaluated for in vitro acetylcholinesterase (AChE) inhibitory activity and found to exhibit moderate to weak anti-AChE activity with IC50 values in the range of 10.8–98 μM. Compounds 1 and 6 were also moderately active in BACE1 inhibitory assay.

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