Limonoids are phytochemicals abundant in citrus fruit and other plants of the families Rutaceae and Meliaceae. Citrus fruits contain the limonoids limonin, nomilin and nomilinic acid, while both neem seeds and leaves contain the limonoid azadirachtin with insecticidal activity. Chemically, the limonoids consist of variations of the furanolactone core structure. The prototypical structure consists of four six-membered rings and a furan ring. Limonoids are classified as tetranortriterpenes.