Rotenoid diversity, distribution and evolution in plant lineages

Covering upto 2025Rotenoids are angular hybrid isoflavonoids mainly characterized by an additional six-membered ring between the B and C rings of flavonoids. The extra ring introduces further chemical diversity to the densely substituted precursors, isoflavonoids, making rotenoids a significant group of compounds within the plant kingdom. Early biosynthesis studies by L. Crombie, Nat. Prod. Rep., 1984, 1, 3-19, and subsequent revisions housed rotenoids into three groups, based on the oxygenation pattern of the bridge carbons between rings B and C. Since then, many more new structures of rotenoids have been discovered, prompting a need to revisit this classification as key structural traits of rotenoids might contribute to phylogenetic relationships and lineage diversification of plants. The new classification builds upon previous considerations, but also incorporates the defining feature of rotenoids, the additional carbon at the C-6 position, leading to nine distinct classes (Types I-IX). Types I and VII were found with the most representatives, predominantly distributed across the Pentapetalae clade, but also found in a few monocots. Rotenoids were found in phylogenetically distant lineages within the clade, raising intriguing questions about the evolutionary pathways that led to their biosynthesis and how their occurrences could inform plant taxonomy. The review addresses these questions and provides a thorough understanding of rotenoids and their chemotaxonomy significance.