The chemistry and biology of securinega alkaloids.

Securinega alkaloids have attracted immense attention from the phytochemical, synthetic, and pharmacological communities owing to their structural diversity and intriguing biological activities. Predominantly found in the genera Flueggea, Phyllanthus, Margaritaria, and Zygogynum, these alkaloids display a remarkable range of molecular architectures derived from the monomeric tetracyclic core consisting of the α,β-γ,δ-unsaturated ester moiety and the tertiary alkyl amine group. Their biosynthetic elaboration through oxidation, rearrangement, and oligomerization gives rise to an extraordinary chemical diversity spanning monomeric, dimeric, trimeric, and even higher oligomeric forms with varying oxidation states. This chapter provides a comprehensive overview of the isolation and structure elucidation of securinega alkaloids and recent (2014-2025) discoveries related to their biosynthesis, chemical synthesis, and biological evaluations. Particular emphasis is placed on recent discoveries, including the synthesis of oxidized, rearranged, and dimerized congeners, and newly uncovered biosynthetic enzymes that illuminate the molecular logic underlying scaffold assembly. The chapter also summarizes emerging insights into their pharmacological properties, including cytotoxic, neurotropic, and anti-inflammatory activities. Collectively, these advances not only clarify the intricate biogenetic origins and chemical synthesis of the securinega family but also establish a foundation for future exploration of their chemical biology and potential therapeutic applications.