Napthoquinone

• Naphthoquinones are yellow or orange coloured pigments, mainly found in Angiosperm families such as Ebanaceae, Droseraceae and Bignoniaceae.

• They are generally 1,4- naphthoquinones and rarely 1,2-naphthoquinones.

• They are bacterial and fungal product and also obtained from secondary metabolism of higher plants. Few examples are lawsone, juglone and plumbagin occurs most widely in nature.

• Naphthoquinones are cytotoxic, antibacterial, antifungal, antiviral, insecticidal, antiinflammatory and antipyretic in nature.

• It also possesses pharmacological effect on cardiovascular and reproductive system.

• Their mechanism is quite large and complex. They bind with DNA and inhibit the replication process. They interact with enzymes and create disturbance in cell and mitochondrial membranes.

• They also interfere with electrons of respiratory chain in mitochondrial membranes.

• The plants containing naphthaquinone widely used in China and South America for malignant and parasitic disease treatment. Free quinones are water insoluble.

• It can be extracted with common organic solvents and can be separated by chromatography.

• Naphthoquinones are obtained from steam distillation.

• They are fairly stable but artefacts are formed e,g. 7-methyljuglone upon oxidation by silica gel yields methylnaphtharizin and its dimer or methoxylation of naphthaquinones by using methanol.

• One of the most appropriate constituents is juglone (5-hydroxy-1,4-naphthalenedione), which naturally occurs in the leaves, roots, husks, and bark of the plants of Juglandaceae family, especially in black walnut (Juglans nigra).

• It is toxic or growth stuntingfor many types of plants. It is used as a herbicide, cloth dye and inks, and a colouring agent in foods and cosmetics.

• Juglone is a type of allelopathic compounds that is synthesised by one type of plant and affects the growth of another plant.

Chemical Test:

1. Juglone test: Take chloroform extract (2 ml) and treat it with ethyl ether (2 ml) with dilute ammonia solution. Pink colour develops which indicates the presence of naphthoquinones.

2. Dam-karrer test: Add potassium hydroxide solution (10%) into chloroform extract (2 ml) of drug, blue colour appears, indicates the presence of naphthaquinones.