Terpenes
Terpenes are a large and diverse class of organic compounds,
produced by a variety of plants, particularly conifers, though also by
some insects. They are often strong-smelling. They may protect the
plants that produce them by deterring parasites. The difference
between terpenes and terpenoids is that terpenes are hydrocarbons,
whereas terpenoids contain additional functional groups. When
terpenes are modified chemically, such as by oxidation or
rearrangement of the carbon skeleton, the resulting compounds are
generally referred to as terpenoids. Some authors will use the
term terpene to include all terpenoids. Terpenoids are also
known as isoprenoids. Terpenes and terpenoids are the primary
constituents of the essential oils of many types of plants and flowers.
Essential oils are used widely as natural flavor additives for food, as
fragrances in perfumery, and in medicine and alternative medicines
such as aromatherapy. Synthetic variations and derivatives of natural
terpenes and terpenoids also greatly expand the variety of aromas
used in perfumery and flavors used in food additives. Vitamin A is a
terpene
Isoprene structure
Terpenes General Structure
More than 30000 terpenes are known at present in the
literature. Their basic structure follows a general principle:
2-Methylbutane residues, less precisely but usually also
referred to as isoprene units, (C5)n , build up the carbon
skeleton of terpenes; this is the isoprene rule found by
RUZICKA and WALLACH. Therefore, terpenes are also
denoted as isoprenoids. In nature, terpenes occur
predominantly as hydrocarbons, alcohols and their
glycosides, ethers, aldehydes, ketones, carboxylic
acids and esters.
Depending on the number of 2-methylbutane (isoprene)
subunits one differentiates
between hemi- (C5), mono-
(C10), sesqui- (C15), di- (C20), sester- (C25), tri- (C30),
tetraterpenes (C40) and polyterpenes (C5)n with n > 8. The
isopropyl part of 2-methylbutane is defined as the head, and
the ethyl residues the tail. In mono-, sesqui-, di- and
sesterterpenes the isoprene units are linked to each other
from head-to-tail; tri- and tetraterpenes contain one tail-to-
tail connection in the center.
1-Hemiterpenes consist of a single isoprene unit. Isoprene itself is considered the only
hemiterpene, but oxygen-containing derivatives such as prenol and isovaleric acid are
hemiterpenoids.
2-Monoterpenes consist of two isoprene units and have the molecular formula C10H16. Examples
limonene, and myrcene, one of the main terpenes found in Cannabis Sativa plants.
3-Sesquiterpenes consist of three isoprene units and have the molecular formula C15H24.
4-Diterpenes are composed of four isoprene units and have the molecular formula C20H32.
5-Sesterterpenes, terpenes having 25 carbons and five isoprene units, are rare relative to the
other sizes. (The sester- prefix means half to three, i.e. two and a half.)
6-Triterpenes consist of six isoprene units and have the molecular formula C30H48. The linear
triterpene squalene, the major constituent of shark liver oil. Squalene is then processed
biosynthetically to generate either lanosterol or cycloartenol, the structural precursors to all the
steroids.
7-Sesquarterpenes are composed of seven isoprene units and have the molecular formula
C35H56. Sesquarterpenes are typically microbial in their origin. Examples of sesquarterpenoids
are ferrugicadiol and tetraprenylcurcumene.
8-Tetraterpenes contain eight isoprene units and have the molecular formula C40H64. Biologically
important tetraterpenes include the acyclic lycopene, the monocyclic gamma-carotene, and the
bicyclic alpha- and beta-carotenes.
9-Polyterpenes consist of long chains of many isoprene units. Natural rubber consists of
polyisoprene in which the double bonds are cis. Some plants produce a polyisoprene with trans
double bonds, known as gutta-percha.
Biosynthesis
1-Hemiterpenes
Cananga Tree (Cananga odorata)
Prenol, or 3-methyl-2-buten-1-ol, is a natural alcohol. It is one of
the most simple terpenes. It is a clear colorless oil that is
reasonably soluble in water and miscible with most common
organic solvents. It has a fruity odor and is used occasionally in
perfumery.
Prenol occurs naturally in citrus fruits, cranberry, bilberry,
currants(‫(الكشمش‬, grapes, raspberry, blackberry, tomato, white
bread, hop oil, coffee, cloudberry and passion fruit. It is also
manufactured industrially by BASF (in Ludwigshafen, Germany)
and by Kuraray (in Asia) as an intermediate to pharmaceuticals
and aroma compounds. Global production in 2001 was between
6000 and 13,000 tons.
2-Monoterpenes
I) Acyclic monoterpens
Humulus lupulus
‫جنجل‬
bitter orange(Citrus Vulgaris)
‫‪Basil‬‬
‫• الريحان أو الحبق‬
Geraniaceae)Pelargonium)
‫‪Bay‬‬
‫ورق الغار‬
Palmarosa
Lavender
Lemon Grass
Linalool is used as a scent in 60–80% of perfumed hygiene products and cleaning agents
including soaps, detergents, shampoos, and lotions.
It is also used as a chemical intermediate. One common downstream product of linalool is
Vitamin E.
In addition, linalool is used by pest professionals as a flea, fruit fly and cockroach insecticide.
Linalool is used in some mosquito repellent products.
Geraniol is a natural antioxidant. Geraniol has been suggested to help prevent cancer.
Carnesecchi S. et al demonstrated in his study "Geraniol, a component of Plant Essential
Oils, Inhibits Grwoth and Polyamine Biosyntehsis in Human Colon Cancer Cells", that
geraniol caused a 50% increase of ornithine decarboxylase activity, which is enhances during
cancer
growth.
Geraniol
inhibits
DNA
synthesis.
Burk YD concluded in his study "Inhibition of Pancreatic Cancer Growth by the dietary
isoprenoids farnesol and geraniol" (that geraniol, farnesol and perilll alcohol suppress
pancreatic
tumor
growth.
Other animal studies have also demonstrated the anticancer effects of geraniol.
Orchid Flowers
Cymbopogon Nardus
citronella •
Tagetes Glandulifera