The initial products of the oxidation process are concealed by secondary cyclization. Quassinoids or decanortriterpenoids Quassinoids occur only in the family Simaroubaceae. More than 120 compounds of this type have been described. The biosynthetic precursors of this series are similar to those of limonoids. D 7 -tirucallol appear to be involved.
Inadequate data exist to define clearly the pathway of biosynthesis.
This series of compounds have been isolated from members of the family Cneoraceae. Limonoids also are found in these plants. Many limonoids and quassinoids have powerful antifeedant properties. Probably the best known compound is azadirachtin from Azadirachta indica . This compound is active against a broad spectrum of insects.