Discovery of Unusual Ajmaline‐Macroline Type Bisindole Alkaloids from <i>Alstonia macrophylla</i> by Building Blocks‐Based Molecular Networking
Ziwei Li, Chun‐Lin Fan, Sun Biao, Lan Huang, Ziqi Wang, Xiao‐Jun Huang, Shiqing Zhang, Wen‐Cai Ye, Zhen‐Long Wu, Xiao‐Qi Zhang
Abstract
Three unusual ajmaline-macroline type bisindole alkaloids, alsmaphylines A-C, together with their postulated biogenetic precursors, were isolated from the stem barks and leaves of Alstonia macrophylla via the building blocks-based molecular network (BBMN) strategy. Alsmaphyline A represents a rare ajmaline-macroline type bisindole alkaloid with an S-shape polycyclic ring system. Alsmaphylines B and C are two novel ajmaline-macroline type bisindole alkaloids with N-1-C-21' linkages, and the former possesses an unconventional stacked conformation due to the presence of intramolecular noncovalent interactions. The chemical structures including absolute configurations of alsmaphylines A-C were established by comprehensive spectroscopic analyses, electronic circular dichroism (ECD) calculations, and single-crystal X-ray crystallography. In addition, a plausible biosynthetic pathway of these bisindole alkaloids as well as their ability to promote the protein synthesis on HT22 cells were discussed.