TERPENES

INTRODUCTION,CLASSIFICATION,BIOSYNTHESIS AND IMPORTANCE

BY NAVEED UL MUSHTAQ

SECONDARY METABOLITES

• Plants produce a large, diverse array of organic compounds that appear to have no direct function in growth, development, photosynthesis, respiration, solute transport, translocation, protein synthesis, nutrient assimilation differentiation, or the formation of carbohydrates.

• These substances are known as secondary metabolites, secondary products, or natural products.

• Secondary metabolites also differ from primary metabolites in having a restricted distribution in the plant kingdom.

Secondary Metabolites Are Divided intoThree Major Groups

• Plant secondary metabolites can be divided into three chemically distinct groups:

Terpenes(25,000 types)Phenolics (8,000 types) andNitrogen- containing compounds• The terpenes, or terpenoids, constitute the

largest class of secondary products.• Terpenoids - oxygen-containing terpenes.

Pie chart representing the major groups ofplant secondary metabolites

TERPENES

• The term terpenes originates from turpentine (lat. balsamum terebinthinae). Turpentine, the so-called "resin of pine trees", is the viscous pleasantly smelling,insoluble in water which flows upon cutting or carving the bark and the new wood of several pine tree species (Pinaceae).

• Turpentine contains the "resin acids" and some hydrocarbons, which were originally referred to as terpenes.

Terpenes are Formed by the Fusion of Five-Carbon Isoprene Units

• All terpenes are derived from the union of five-carbon elements that have the branched carbon skeleton of isopentane.

• The basic structural elements of terpenes are sometimes called isoprene units because terpenes can decompose at high temperatures to give isoprene.

• All terpenes are occasionally referred to as isoprenoids.

CLASSIFICATION OF TERPENES

• Terpenes are classified by the number of five-carbon units they contain.

• Ten-carbon terpenes, which contain two C5 units, are called monoterpenes

• 15-carbon terpenes (three C5 units) are sesquiterpenes

• 20-carbon terpenes (four C5 units) are diterpenes. • Larger terpenes include triterpenes (30 carbons),

tetraterpenes (40 carbons),and poly terpenoids ([C5]n carbons, where n > 8).

There Are Two Pathways for Terpenes Biosynthesis

• Terpenes are biosynthesized from primary metabolites in at least two different ways. In the well-studied mevalonic acid pathway, three molecules of acetyl-CoA are joined together stepwise to form mevalonic acid.

• This key six-carbon intermediate is then pyrophosphorylated, decarboxylated, and dehydrated to yield isopentenyl diphosphate (IPP).

• IPP is the activated five-carbon building block of terpenes.

Biosynthesis

• IPP also can be formed from intermediates of glycolysis or the photosynthetic carbon reduction cycle via a separate set of reactions called the methylerythritol phosphate (MEP) pathway

• It operates in chloroplasts and other plastids• Glyceraldehyde-3-phosphate and two carbon

atoms derived from pyruvate appear to combine to generate an intermediate that is eventually converted to IPP.

Squalene has a natural and vital part in the synthesis of all plant and animal sterols, including cholesterol, steroid hormones, and vitamin D in the human body

Lycopene is responsible for the red color in tomatoes and watermelon

-carotene is the compound that causes carrots and apricots to be orange14

Lycopene's conjugated double bonds give it its deep red color and are responsible for its antioxidant activity.

IMPORTANCE• Biologically, the monoterpenes have been found to possess a

variety of biological effects, including antibacterial, sedative, antitumor, cytotoxic, anti-inflammatory, insecticidal, molluscidal and others.

• They have historically been important ingredients individually in medicinal and economic products including cosmetics and other fragrant products.

• One of the best known and most often used monoterpenes is menthol which has been used as a topical antipruritic, a counterirritant in external analgesic preparations, as antiseptic and as a flavoring agent in chewing gums, toothpaste and tobacco products such as cigarettes.

IMPORTANCE

• In drug discovery research reports, linalool, a monoterpene alcohol found in the essential oils from many aromatic plants was determined to be able to moderately inhibit cell proliferation.

• Miliusol, miliusate and miliusane demonstrated potent cytotoxic activity against a panel of cancer cell lines.

• Horticulturally, the pyrethrins from Pyrethrum cinerariaefolium flowers have been used as potent natural insecticides.

IMPORTANCE

• Cumene is a terpene that has been used in bioremediation studies