Steviol is a diterpene first isolated from the plant '' Stevia rebaudiana'' in 1931. Its chemical structure was not fully elucidated until 1960. Steviol occurs in the plant as steviol glycosides, sweet compounds that have found widespread use as

sugar substitute A sugar substitute is a food additive that provides a sweetness like that of sugar while containing significantly less food energy than sugar-based sweeteners, making it a zero-calorie () or low-calorie sweetener. Artificial sweeteners may be d ...

s. The aglycon is prepared by enzymatic hydrolysis, since upon acid treatment steviol will undergo Wagner-Meerwein rearrangement to the very stable isosteviol.

Biosynthesis

In ''Stevia rebaudiana'', the

biosynthesis Biosynthesis is a multi-step, enzyme-catalyzed process where substrates are converted into more complex products in living organisms. In biosynthesis, simple compounds are modified, converted into other compounds, or joined to form macromolecules. ...

of steviol is confined to green tissues. The precursors of steviol are synthesized via the

non-mevalonate pathway The non-mevalonate pathway—also appearing as the mevalonate-independent pathway and the 2-''C''-methyl-D-erythritol 4-phosphate/1-deoxy-D-xylulose 5-phosphate (MEP/DOXP) pathway—is an alternative metabolic pathway for the biosynthesis of the is ...

located in plant cell plastids, which produces isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP). IPP and DMAPP are converted to

geranylgeranyl diphosphate Geranylgeranyl pyrophosphate is an intermediate in the biosynthesis of diterpenes and diterpenoids. It is also the precursor to carotenoids, gibberellins, tocopherols, and chlorophylls. It is also a precursor to geranylgeranylated proteins, whi ...

(GGDP), which is the precursor of many

diterpenoids Diterpenes are a class of chemical compounds composed of four isoprene units, often with the molecular formula C20H32. They are biosynthesized by plants, animals and fungi via the HMG-CoA reductase pathway, with geranylgeranyl pyrophosphate bein ...

, by GGDP synthase. GPDP is made into a cyclic compound, copalyl diphosphate (CDP), by CDP synthase, after which kaurene is produced by another cyclization catalyzed by kaurene synthase. The kaurene is then transferred to the

endoplasmic reticulum The endoplasmic reticulum (ER) is, in essence, the transportation system of the eukaryotic cell, and has many other important functions such as protein folding. It is a type of organelle made up of two subunits – rough endoplasmic reticulum ( ...

, where it is oxidized to

kaurenoic acid Kaurenoic acid (ent-kaur-16-en-19-oic acid or Kauren-19-oic acid) is a diterpene with antibacterial activity against Gram-positive bacteria. However its low solubility and blood lytic activity on erythrocytes might make it a poor pharmaceutical c ...

by kaurene oxidase in a reaction that uses up oxygen and

NADPH Nicotinamide adenine dinucleotide phosphate, abbreviated NADP or, in older notation, TPN (triphosphopyridine nucleotide), is a cofactor used in anabolic reactions, such as the Calvin cycle and lipid and nucleic acid syntheses, which require NAD ...

. Then steviol is produced by hydroxylation. The steviol is subsequently glycosylated in the cytoplasm. Bio synthesis of steviol glycoside 01

References

{{cite journal , author1=Dolder, Fred , author2=Lichti, Heinz , author3=Mosettig, Erich , author4=Quitt, Peter , title = The structure and stereochemistry of steviol and isosteviol , journal = Journal of the American Chemical Society , year = 1960 , volume = 82 , pages = 246–247 , doi = 10.1021/ja01486a054

External links

PubChem summary of steviol molecule
Diterpenes Cyclopentanes Vinylidene compounds