TERPENOIDS

Terpenoids (or isoprenoids), a subclass of the prenyllipids (terpenes, prenylquinones, and sterols), represent the oldest group of small molecular products synthesized by plants and are probably the most widespread group of natural products.

Terpenoids can be described as modified terpenes, where methyl groups are moved or removed, or oxygen atoms added. Inversely, some authors use the term "terpenes" more broadly, to include the terpenoids.

During the 19th century, chemical works on turpentine led to name "terpene" the hydrocarbons with the general formula C₁₀H₁₆ found in that complex plant product. These terpenes are frequently found in plant essential oils which contain the "Quinta essentia", the plant fragrance.

They are universally present in small amounts in living organisms, where they play numerous vital roles in plant physiology as well as important functions in all cellular membranes. 

 They may be defined as a group of molecules whose structure is based on a various but definite number of isoprene units (methylbuta-1,3-diene, named hemiterpene, with 5 carbon atoms).  

Terpenoids are extraordinarily diverse but they all originate through the condensation of the universal phosphorylated derivative of hemiterpene, isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP) giving geranyl pyrophosphate (GPP). 

In higher plants, IPP is derived from the classic mevalonic acid pathway in the cytosol but from the methylerythritol phosphate pathway in plastids. It is generally accepted that the cytosolic pool of IPP serves as a precursor of sesquiterpenes, triterpenes, sterols and polyterpenes whereas the plastid pool of IPP provides the precursors of mono-, di- and tetraterpenes.

A rational classification of the terpenes has been established based upon the number of isoprene (or isopentane) units incorporated in the basic molecular skeleton:

 

	Terpenes	Isoprene units	Carbon atoms
1	Monoterpenes	2	10
2	Sesquiterpenes	3	15
3	Diterpenes	4	20
4	Sesterpenes	5	25
5	Triterpenes	6	30
6	Carotenoids	8	40
7	Rubber	> 100	> 500

Mono-, sesqui-, di-, and sesterpenes contain the isoprene units linked in a head to tail fashion. The triterpenes and carotenoids (tetraterpenes) contain two C15 and C20 units respectively linked head to head. 

 Many terpenes are hydrocarbons, but oxygen-containing compounds such as alcohols, aldehydes or ketones are also found. These derivatives are frequently named terpenoids.Mono- and sesquiterpenes are the chief constituents of the essential oils while the other terpenes are constituents of balsams, resins, waxes, and rubber.

General nature of terpenoids

• The physical properties of terpenoids are:
1) In the fresh state is a colorless liquid, but if the color will be dark oxidized
2) Having a characteristic odor
3) high refractive index,
4) The most optically active
5) lower density than water
6) soluble in organic solvents: ether and alcohol

• chemical
1) unsaturated compounds (open-chain or cyclic)
2) isoprenoid form khiral and occurs in two forms enantiomer.

Synthesis of terpenoid

In general, the terpenoid biosynthesis of three basic reactions, namely:

1. Formation of active isoprene derived from acetic acid via mevalonic acid.

2. Melting head and tail isoprene units to form mono-, seskui-, di-, Sester-, and poly-terpenoids.

3. The incorporation of the tail and the tail unit C-15 or C-20 produces triterpenoids and steroids.

acetic acid after being activated by coenzyme A produced acid asetoasetat type Claisen condensation. Compounds produced by the condensation of acetyl coenzyme A produced aldol branched carbon chains of type as found in acid mevanolat. Reactions phosphorylation is, the elimination of phosphoric acid and subsequent decarboxylation produces IPP to DMAPP by the enzyme isomerase berisomerisasi. IPP as isoprene units active joined to the queue with DMAPP and this fusion is the first step of the polymerization of isoprene to produce terpenoids.

  

This fusion occurs because electrons attack the double bond carbon atoms of IPP to DMAPP ison electron deficient followed by removal of pyrophosphate. These attacks to geranyl pyrophosphate (GPP), which is an intermediate for all monoterpenes compounds.

Subsequent incorporation between IPP and GPP units, with the same mechanism of IPP and DMAPP, produce farnesyl pyrophosphate (FPP), which is an intermediate compound for all sesquiterpene compounds. Compounds derived diterpene geranyl geranyl pyrophosphate (GGPP) derived from the condensation between the units or IPP and GPP with the same mechanism as well.

When organic reactions are listed in Figure 2 to be explored, it turns out that the synthesis of terpenoids by a very simple nature. In terms of the theory of the reaction of organic synthesis is only using some basic types of reactions. Subsequent reactions of the compounds between GPP, FPP and GGPP for the production of terpenoid compounds one by one involves only a kind of secondary reactions. These secondary reactions are typically hydrolysis reactions, cyclization, oxidation, reduction and spontaneous that can easily be done in a neutral atmosphere and at room temperature, such as isomerization, dehydration, decarboxylation, and so on.

From the above equation shows that the formation of compounds monoterpenes and compounds derived from the incorporation of 3.3 dimethyl allyl terpenoida pyrophosphate with isopentenyl pyrophosphate.