The structure and bioactivities of Stemona alkaloids and alkaloids with [1,2-α] azepine nucleus (2009–2021)

Stemona alkaloids with a unique skeleton of pyrrolo[1,2-a]azepine, pyrido[1,2-a]azepine, pyrido[1,2-a]azonine or indolizidine core are obtained only from the Stemonaceae family. And some plants from this family have been used for treating respiratory diseases and as antihelmintic in China for thousands of years. In addition, some alkaloids with [1,2-a]azepine nucleus have also been isolated from plants of the Flueggea (Euphorbiaceae), Securinega (Phyllanthaceae), Phyllanthus (Phyllanthaceae) and Cephalotaxus (Cephalotaxaceae) genera. These alkaloids are named as Securinega alkaloids or Cephalotaxus alkaloids. A total of 94 new Stemona alkaloids, 51 new Securinega alkaloids, and 24 new Cephalotaxus alkaloids were obtained from 2009 to 2021. The absolute configurations of Stemona, Securinega, and Cephalotaxus alkaloids are usually determined using NOESY, biogenic synthesis, and data comparison methods during structural analysis. Based on an in-depth analysis of these structures, we found that the above methods are not rigorous. This article raises some problems in the structure determination of these alkaloids and summarizes the rules of nuclear magnetic resonance data of Securinega and Cephalotaxus alkaloids, which can also make the structure analysis more rigorous. In this review, we describe the isolation, structures, NMR rules, biogenic synthetic pathway and biological activities of these Stemona alkaloids, as well as the structure-related alkaloids isolated from the genera Flueggea, Securinega, Phyllanthus, and Cephalotaxus. This review also provides significant reference for the structural analysis, biogenic pathways, and pharmacological activities of Stemona, Securinega, and Cephalotaxus alkaloids.

Graphical Abstract