(Photos: Limonin, Lemon and Simarouba(Laxmi-taru)
We all are familiar with , though unknowingly, these compounds. The delayed bitterness of the juices from various Citrus spp., which were considered as the culprits lowering the juice quality, is due to limonoids. The word “Limonoids’ is derived from “limonin” the first bitter principle isolated from lemon. Limonoid aglycones that cause bitterness in numerous citrus fruits are converted into tasteless limonoid glucosides during fruit maturation. More than 50 limonoid aglycones and glucosides have been identified from various Citrus species. Over 300 limonoids have been isolated to date and about one-third are generated from neem (Azadirachta indica) and Chinaberry (Melia azedarach). These compounds are characteristically present in the order “Rutales” consisting of Rutaceae, Meliaceae, Simaroubaceae and Cneoraceae (Daniel, 2009).
Both Limonoids and Quassinoids are formed by the loss of a few carbon atoms from C30 triterpenoids and thus known as nor-triterpenoids. Most of the limonoids are C26 compounds, having 4 carbons less than the triterpenoids and thus are named “Tetra-nor- triterpenoids”. With loss of more carbon atoms (up to 10-11), Quassinoids are formed. They are C20/C19 compounds named after the plant Quassia.
The Limonoids are characteristic to the families Rutaceae, Meliaceae and Cneoraceae, whereas quassinoids are seen in the Simaroubaceae. Limonoids are tetra-nor-triterpenoids formed by the conversion of 8-carbon side at C17 to a furan ring with subsequent loss of four atoms. Five groups of Limonoids are recognized 1). Tirucallane group has an intact triterpenoid skeleton (C¬30) where there is no reduction in carbon number, 2) Azadirone group, 3) Gedunin group, 4) Azadirachtin group which are well-known antifeedant compounds, 5). Toonafolin group, 6) Tricoccin group, 7)Surenolactone group and 8) Penta-nor-triterpenoids (C¬¬25) All the various types of limonoids (expect for the last group of C25) are seen in members of Meliaceae. The limonoids of Rutaceae belong mostly to the 3rd and 6th group i.e. A and D ring cleaved (seco-limonoids). Quassinoids possess C20 or C19 skeletons though a few possess C25 skeleton. All the quassinoids are heavily oxygenated lactones. Altogether five groups are recognized here.
1. Medicinal properties of limonoids and quassinoids .
Limonoids have a large number of pharmacological activities like, anticancer, antimicrobial(against fungal, bacterial and parasitic infections like eczema, ringworm, scabies, Mycobacterium tuberculosis (in vitro)), antiviral measles virus (in vitro) and fowl pox, antihistaminic, antimalarial (Plasmodium falciferum), antiarthritic and anti-inflammatory, hypoglycemic (diabetes) and hepatoprotective, hypotensive and anxiolytic properties. It is also used against atherosclerosis and heart attack.
Limonoids have been shown to inhibit proliferation of the cancers of the stomach, colon, breast, skin, and pancreas. Nimbolide, the most potent neem limonoid was found to inhibit the growth of myriad cancer cell lines including 143B TK osteosarcoma, HL-60, U-937 and THP-1 leukemic, B16 melanoma, SMMC 7721, A-549, MCF-7 breast, MD-MBA-231, HT-29, SW-620, SW-480, HOP-62, A-549, prostate PC-3, choriocarcinoma (BeWo), leukemic (HeLa) and WiDr and HCT-116 colon adenocarcinoma and ovarian OVCAR-4,5,8 cell lines [9,13–17,34–36]. Studies also indicated that the anticancer properties of limonoids can be correlated to the induction of glutathione S-transferase, a major detoxifying enzyme system.
The medicinal plants containing quassinoids are Picrasma excelsa Planch. (Quassia),(Pikra = bitter, alluding to bitter leaves and wood), Quassia amara L. and Brucea javanica Merril (B. amarissima Desv., B. antidysenterica Merril
Biopesticidal properties
Limonoids and quassinoids form a group of best biopesticides, non-toxic to man and animals. A broad spectrum of biological activities of limonoids has been reported, ranging from insecticidal, insect antifeedant and growth regulatory activities on insects. It is known that neem limonoids (azadirachtin) or derivatives have the potential to effectively control more than 200 insect species without harming the environment. Azadirachtin and other limonoids isolated from other species of plants have adverse effects on larvae of mosquitoes and flies.
Biopesticidal plants
1. Aglaia basiphylla. A. Gray and A. gracilis A. C. Smith and many other species of Aglaia. Azadirachta indica A. Juss, Cedrela sinensis Juss. Guarea grandiflora A.D.C.
4. Lansium domesticum Corr. (Lansone)
5. Melia azedarach Linn. (Bakum-nimb, Persian Lilac)
6. Swietenia humilis Zucc.
7. Toona ciliata Roem. (Cedrela toona Roxb.-Indian Mahogany)
8. Trichilia emetica Vahl (Natal Mahogany)
9. Walsura trifoliolata Harms (W. piscida Roxb.)
10. Ailanthus excelsa Roxb. (Ardusa, Tree of heaven).
11. Hannoa undulata Planch. (Quassia undulata D. Dietr)
12. H. klaineana Pierre & Engl.
13.. Picrasma excelsa
14.. Quassia amara Linn.
Due to the insect-repellant and insecticidal limonoids, the woods of this family are very strong and are commercially much exploited. For eg. 1. Swietenia mahagoni Jacq. (Mahogany) Cedrela odorata Linn. (Spanish Cedar) and C. toona Roxb. (Moulmein Cedar), and Khaya senegalensis are the important timber trees known for their stability towards insect and pest attacks.
Natural Dyes are prepared from Azadirachta indica A. Juss., Chukrasia tabularis A. Juss., will keep clothes resistsnt to mosquitos and other insects.
References:
1. Taxonomy: Evolution at Work. M. Daniel, (2009) Alpha Science International Ltd, Oxford, U. K. Pages 467.
2. Useful Herbs of the Planet Earth, M. Daniel, (2012), Scientific Publishers, Jodhpur, Pages 710,
Mammen Daniel
