Most of us are familiar with the ubiquitous plastoquinones, ubiquinones and tocopherols and vitamin K. But Quinones, the aromatic diketones, form the largest class of natural colouring matters and of the total 800 and more compounds known, about 50% occur in higher plants and of the rest, a large percentage are known form fungi. A number of quinones from higher plants are widely used in medicine.
Quinones may be benzo, naphtho or anthraquinones depending on the mono-, bi- or tri-cyclic ring systems they possess.
a. Benzoquinones
These compounds possess an aromatic ring with or without an aliphatic side chain. A few of them are medicinally important, e.g., embelin. The physiologically active representatives of this group are Plastoquinones are believed to act as redox carriers in photosynthesis; ubiquinones as hydrogen carriers in respiratory chain and tocopherols as antioxidants or growth regulators.
b. Naphthaquinones
Most of the naphthaquinones are yellow or red plant pigments. A few like chimaphilin, plumbagin and eleutherin are toxins or antimicrobial agents; while some others like lapachol are important dye stuffs. Vitamin K and related compounds are having very specific roles in electron transport systems. Arnebin, another naphthaquinone isolated from the roots of Arnebia nobilis roots, is a potent anticancer agent.
c. Anthraquinones
Of this large group of quinones about 50% are distributed in higher plants especially, Rubiaceae, Rhamnaceae and Polygonaceae, and the rest in fungi. This group provides some important dyestuffs and many purgatives.
The hydroxylated anthraquinones occur as glycosides. The common compounds are dihydroxy phenols like chrysophanol and alizarin, trihydroxy derivatives such as emodin and aloe-emodin or methoxylated compounds like physcion. Carboxylated anthraquinones such as rhein also are reported. But the pharmacologically active anthraquinones are found to be anthranols that are formed as a result of slow hydrolysis of the glycosides during storage. Anthranols also, in course of time, get oxidised to anthraquinones. The pharmacological action of anthraquinone is due to its conversion to anthranols by intestinal bacteria (Fairburn, 1964).
The important plants containing quinones are as follows.
1. Vavding, Embelia (Embelia ribes Burm.f. - Myrsinaceae)
The fruits, the drug, contain benzoquinones, embelin (2,5-diOH-3-undecyl-1,4- benzoquinone), vilangin, embelinol, embeliaribyl ester and embeliol. Leaves also are found to contain embelin.
Embelin and embelia are well-known anthelmintics esp. for tapeworm. The fruits are effective in cystic and abdominal tumours.
2. Ratanjot (Arnebia nobilis Rachinger - Boraginaceae)
The roots, which are generally covered by several layers of thin scaly bark, yield up to 2.5% of a red dye consisting of seven napthaquinones, arnebins 1-7.
The roots are used for dyeing clothes such as wool and silk as also as a food color. Arnebins are known to possess anticancer activity in that the crude extract/arnebin-1/arnebin-3 is found to inhibit Walker Carcino-Sarcoma tumour cells.
3. Patala (Stereospermum suaveolens DC. - Bignoniaceae)
The bark yields a gum and all parts contain a napthaquinone, lepachol. The roots contain dinatin and beta-sitosterol also. The wood contains lepachonone also. Seeds yield a fatty oil and -sitosterol. All the parts are used in medicine. Roots form a component of “Dasamula” (Ten roots) which is a general tonic.
4. Chitrak (Plumbago indica Linn.- Plumbaginaceae)
Root bark contain a napthaquinone, plumbagin (0.91%), sitosterol, and tannins.
Roots are highly valued for their curative action on leucoderma and other skin diseases. They are digestive stimulants, diuretic, germicidal, vesicant and abortifacient. Chitrak is also used for haemorrhoidal inflammation of anus, diabetes, diarrhoea and elephantiasis.
5. Indian Aloe, Kumari (Aloe barbadensis Mill. - Liliaceae)
The leaves contain mucilage, anthraquinones and chromones. The quinones present near the skin of leaves are barbaloin and isobarblonin (c-glycosides) and their aglycone, aloe-emodin. Alocutin A and B are lectins found useful in cancer and inflammation.
6. Coffee senna, Kasamarda (Cassia occidentalis Linn.- Caesalpiniaceae)
The leaves are found to contain anthraquinones such as chrysophanol, emodin (and their glycosides), physcion etc.
All parts of this plant exhibit similar medicinal properties such as purgative, tonic, febrifugal, diuretic and for skin diseases. A bark infusion is given in case of diabetes.
7. Sickle senna, Chakramarda (Cassia tora Linn. .- Caesalpiniaceae)
The stem bark contains emodin, rhein, euphol, -sitosterol and basseol. The leaves also contain emodin, kaempferol d-mannitol stachydrine and choline. Seeds contain cassiamide, rhein, emodin, aloe emodin etc. The whole plant is purgative, anthelmintic and exceeding useful in eczema, ringworm and other skin diseases.
8. Alexadrian/Tinnevelly Senna, Sonamukhi (Cassia senna Linn)
The leaves and the shells of fruits contain sennosides and related anthraquinnones. Shells contain 3-5% of these compounds whereas the leaves have 2.5 – 4%. The various sennosides are sennoside A.B.C and G as well as three sennidins. The leaves and shells are used as tonics in Ayurvedic and Unani Systems of medicine as an efficient purgative, as a febrifuge, in splenic enlargements, anemia, jaundice, rheumatism, tumours, and bronchitis and against skin diseases.
9. Indian Laburnum, Amaltas (Cassia fistula Linn)
The bark contains flavonoids such as catechin, epicatechin, fistacacidin, fistucacidin, kaempferol, procyanidin, propelargonidin and rhein glycoside. The leaves and fruits yield sennosides A and B, chrysophanol, physcion, rhein etc. The bark is used as a tonic and against dysentery and skin diseases.
10. Senna, Hindisana (Cassia angustifolia Vahl - Caesalpiniaceae)
The leaflets yield about 2% quinones consisting of aloe-emodin, rhein, sennosides A, B, C & D and many other heterodianthrones. Also present in the drug are flavonols like kaempferol, sterols, mucilage and resins. Senna is widely used as a purgative. It is preferred over rhubarb because it does not produce the astringent after effect of the latter.
11. Rhubarb (Rheum palmatum Linn.- Polygonaceae)
This plant, a native of Hong Kong, are widely cultivated in China.
The drug yields a variety of anthraquinones, which occur as glycosides or aglycones. They are: (1) dihydroxy phenols such as chrysophenol; trihydroxy phenols like emodin, (2) Carboxylated anthraquinones, e.g., rhein (cassic acid) and glucorhein. (3) Anthrones (4) Heterodianthrones. The drug is used as a bitter stomachic and in the treatment of diarrhoea because of the purgative action of anthrones and the astringency of tannins.
R. emodi Wall. R. webbianum Royle, or other species of Rheum native to India are known in commerce as Indian Rhubarb. They contain up to 2.2% anthraquinones.
12. Cascara bark (Rhamnus purshiana DC. - Rhamnaceae)
The bark contains about 6-9% anthraquinones mostly as glycosides. The C-glycosides, cascarosides, barbaloin, emodin etc. Cascara is a purgative having an action very similar to that of senna. Aloe-emodin isolated from the seeds of R. frangula Linn. exhibited anticancerous property in that, it showed significant inhibitory activity when tested in mice against the P-388 lymphocytic leukemia.
13. Alder Buckthorn bark, Frangula bark (Rhamnus alnus Mill. - Rhamnaceae)
Glycosides form the major group of the 2-5% anthraquinones present in the purple bark. The principal compound in the drug is a pair of isomers frangulosides A & B,
Alder buck thorn bark is used as a cathartic. R. cathartica L. and R. carnifolia B & H. also possess active quinones and so are used as cathartics.
14. Chrysarobin, Goa powder (Andira araroba Aguiar. - Fabaceae)
The yellowish brown powder found in large lacunae of the stem wood forms the drug. This powder, which is scraped off, contains 50-75% chrysarobin, The drug is extensively used in fighting skin diseases.
15. Indian madder, Manjishta (Rubia cordifolia Linn. - Rubiaceae)
Plant contains various chemical constituents like anthraquinones, iridoids (6-methoxy geniposidic acid); hexapeptides Mangishta is one of the acclaimed blood purifiers and used as an alterative, tonic and for diseases of blood, skin and urino-genital system.
16. Red sandalwood, Raktachandan (Pterocarpus santalinus Linn.- Fabaceae)
Wood contains a quinone, santalin (santalic acid, 16%) and desoxy santalin ( a napthaquinone). Raktachandan is a reputed remedy to remove pimples, scars and other skin diseases. It purifies the blood and is an antipyretic, diaphoretic and febrifuge. It is also useful in haemophilic disorders and inflammations. Both pterolinus K, and a chalcone, pterolinus L are found to be cytotoxic. The wood is hypoglycemic also.
For more details kindly refer the
Source:
1. Medicinal Plants: Chemistry and Properties. M. Daniel, (2006) Science Publishers, New Hampshire, USA. Indian Edition published by and Oxford & IBH Publishers, Delhi. Can be downloaded free from internet
Mammen Daniel
