Degraded limonoids: biologically active limonoid fragments re-enhancing interest in Meliaceae and Rutaceae sources

Abstract Phytochemical studies on the roots, twigs and leaves of Meliaceae and Rutaceae family plants have revealed the presence of non-complex terpenes derived from limonoid fragmentation. The occurrence and chemical structure of these degraded limonoids isolated from 1930 to March 2022 are reported in this review. Particular attention is given to the degradation levels in these compounds and their absolute configuration to discover presumable deconstruction pathways from more complex limonoids. Plausible intermediates have been postulated for most of them that would explain their origin from limonoids. The total or semi-synthesis of the most isolated degraded limonoids or analogues remains undescribed. This review focuses on the bioactivity of these fragmented limonoids and their synthesized analogues. Based on pharmacological and agrochemical studies, degraded limonoids appear to be excellent structural leads to consider for the total or semi-synthesis of more potent derivatives with the aim of discovering new hits and clarifying their modes of action.