*3.1.2 Works done on terpenoids*

*Bioactive Compounds - Biosynthesis, Characterization and Applications*

adhesion, and communication [40].

**3. Biosynthesis of plant origin**

sign that this is indeed the case [41].

**3.1 Biosynthesis of terpenoid compounds**

The reaction catalyzed by HMGR is the rate-limiting step of cholesterol biosynthesis. Mevalonate is then activated by three successive phosphorylations, yielding 5-pyrophosphomevalonate. Phosphorylation mevalonate and successive reactions

Different plants not only synthesize different aromatic secondary metabolites

Some terpenoids play an important role in plant growth and development, such as gibberellin, as plant hormones regulate plant development. Other terpenoids play a role in the interaction between plants and the environment, such as participating in plant defence systems as phytoalexins and interspecies competition as interspecific sensing compounds. Terpenoids make up one of the largest and structurally diverse groups of naturally occurring compounds [42]. Mevalonic acid is mostly employed as a terpenoid synthetic racemate; however, mevalonic acid dimethoxy acetal may be resolved as its quinine salt. The acetates of the individual enantiomers of mevalonolactone are much less soluble than the racemate, and these may determine the purity and chirality of biosynthetic mevalonate. The steric course of many terpenoid biosynthetic processes has been followed using the stereospecifically deuterated and tritiated 2R,3R- [2-'H]-, 2S,3R- [2-3H]-, 3R,4R- [4–3 H] -, 3R,4S- [4- HI-, and 3R,5R- [S 3 H]-mevalonate. Several routes for preparing 5S- [5-3H] mevalonate have been described. [l-3H] Isopentenal is a substrate for liver alcohol dehydrogenase and this affords 1 s- [l-3H] isopentenyl, which may then be converted into mevalonic acid. Alternatively, [5-3H] mevalonic acid can be reduced enzymatically with mevalonate reductase to afford 5S-[5-3H] mevalonic acid. The hemithioacetal of mevalonate and coenzyme-A is reduced by 3-hydroxy-3-methylglutaryl COA reductase." The steric course of this reduction is now known and they can also adapt this to afford 3R,5S- [5-3H] mevalonic acid. They have reported a mevalonate kinase assay [13]. An enzyme system capable of forming the mono- and pyro-phosphates of mevalonic acid, isopentenyl pyrophosphate and dimethylallyl pyrophosphate has been isolated 'From orange-juice vesicles and shown to convert isopentenyl pyrophosphate and dimethylallyl pyrophosphate into linalool [42].

Antitumour, [43] anti-inflammatory, antibacterial effects, cardiovascular effects, antimalarial, hypoglycemic effect, and transdermal absorption promotion have been investigated to give such pharmacological activities. Other activities apart

but also synthesize varying amounts of them at specific times and in specific subcellular compartments. One would expect that regulation of the differential biosynthesis of sometimes very complex molecular structures might involve regulation of the supply of the precursors influencing the rate-limiting step for carbon flow through the shikimate pathway. Recent data on transgenic potatoes give some

maintain their solubility since otherwise, these are insoluble in water [40]. Cholesterol from both diet and synthesis is utilized in the formation of membranes and the synthesis of the steroid hormones and bile acids, regulating membrane fluidity and permeability as a cell membrane structural component, formatting lipid rafts with sphingolipid to mediate cell-to-cell recognition,

**12**

*3.1.1 Pharmacology of terpenoids*

They have conducted several studies on terpenoids and their outcomes are promising. For antitumour activity, they have shown that perillyl alcohol which contains terpenoids plays a preventive and therapeutic role in cancer. The results showed that the administration of perillyl alcohol in rats can significantly reduce the incidence and multiplicity of colonic invasive adenocarcinoma caused by the injection of carcinogen azomethane [43]. Paeoniflorin which is a monoterpene glycoside compound isolated from the root of *Paeonia lactiflora* gave significant levels of anti-inflammatory activity. It could also dose-dependently inhibit the production of inflammatory factor nitric oxide (NO), interleukin-6 (IL-6) and tumour necrosis factor-alpha (TNF-α) induced by lipopolysaccharides (LPS) [44]. Besides, menthol, which is a cyclic monoterpene, has been shown to have antibacterial activity [45], they found that menthol showed significant inhibitory activity of biofilm when studying the effects of plant-derived terpenoids on *Candida albicans*. Several studies have also shown that terpenoids, particularly artemisinin which is a sesquiterpene lactone compound isolated from *Artemisia annua* Linn, has an effective antimalarial activity and currently in use [3]. The latest findings suggest that tanshinone IIA (TS) which is a terpenoid can prevent the formation of atherosclerosis and the damage and hypertrophy of the heart. This is because of its ability to inhibit the oxidation of low-density lipoprotein and the expression of proinflammatory factors, and TS also has certain activity and potential to stabilize atherosclerotic plaque [46].
