Voacafrines A-N, aspidosperma-type monoterpenoid indole alkaloids from Voacanga africana with AChE inhibitory activity

摘要

Fourteen undescribed monoterpenoid indole alkaloids, voacafrines A-N, along with 7 known monoterpenoid indole alkaloids were isolated from the seeds of Voacanga africana Stapf. Among them, voacafrines A-G were aspidosperma-aspidosperma type bisindole alkaloids, while voacafrines H-N were aspidosperma-type monomers. Their structures and absolute configurations were elucidated by a combination of NMR, MS, and ECD analyses. Voacafrines A-C were characterized by an acetonyl moiety at C-5', while voacafrine H possessed a methoxymethyl moiety at C-14 within aspidosperma-type alkaloids. The acetylcholinesterase (AChE) inhibitory activity and cytotoxicity of voacafrines A-N were evaluated. Voacafrines A-C and E-G were bisindole alkaloids that exhibited AChE inhibitory activity with IC50 values of 4.97-33.28 mu M, while voacafrines I and J were monomers that showed cytotoxicity against several human cancer cell lines with IC50 values of 4.45-7.49 mu M.