The Meliaceae family is rich sources of limonoid (meliacin), which are well know for their antifeedant activity and bitterness. Although their existence also could be found in Rutaceae, Cneoraceae, Ptaeroxylaceae, and Simaroubaceae family, they are especially abundant and structurally diversified in the Meliaceae family. Structurally, they are highly oxygenated and modified nortriterpenoids either containing or derived from a precursor with a 4,4,8-trimethyl-17-furanylsteroid skeleton. Nearly three decades ago, Taylor divided so far found three hundreds of the meliacins from the Meliaceae family into protolimonoids and nine classes of limonoids based on which of the four triterpenoid skeleton rings have been oxidatively opened. From then on, much progress has been made on the field. Up to very recently, approximately 1300 limonoids, exhibiting more than 35 different carbon frameworks have been observed from the four families.
Consider the complex structures and broad biological activity of limonoids, however, their chemical synthesis is rather rare. Recently, there were several reports on partly and total synthesis of limonoids, in which a currently successful total synthesis of azadirachtin marked a breakthrough.
This review covers the chemistry of limonoids of Meliaceae before July 2009. It mainly focuses on the identification of novel skeletons and ring system, and provides a new expanded category and corresponding biosynthetic relationship map of limonoids aiming at expanding and deepening the understanding of this type complex compound. The progress in limonoid synthesis is also reviewed for the first time.
Keywords: Biosynthesis, biosynthetic evolution, chemical synthesis, limonoid, meliaceae, natural product, Balsamodendron pubescens (Burseraceae), Flacourtia jangomas (Flacourtiaceae), Microula sikkimensis (Boraginaceae), Croton jatrophoides (Euphorbiaceae), delevoyin, secomahoganin, cipadonoid, cipadesin, 30-nortrijugin, ecuadorin, dukunolide, abeo phragmalin, khayalactone