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 substitutes. 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 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 i ...

located in plant cell

plastids The plastid (Greek: πλαστός; plastós: formed, molded – plural plastids) is a membrane-bound organelle found in the cells of plants, algae, and some other eukaryotic organisms. They are considered to be intracellular endosymbiotic cy ...

, which produces

isopentenyl pyrophosphate Isopentenyl pyrophosphate (IPP, isopentenyl diphosphate, or IDP) is an isoprenoid precursor. IPP is an intermediate in the classical, HMG-CoA reductase pathway (commonly called the mevalonate pathway) and in the ''non-mevalonate'' MEP pathway of i ...

(IPP) and

dimethylallyl pyrophosphate Dimethylallyl pyrophosphate (DMAPP; or alternatively, dimethylallyl diphosphate (DMADP); also isoprenyl pyrophosphate) is an isoprenoid precursor. It is a product of both the mevalonate pathway and the MEP pathway of isoprenoid precursor biosynt ...

(DMAPP). IPP and DMAPP are converted to

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

(GGDP), which is the precursor of many diterpenoids, by GGDP synthase. GPDP is made into a

cyclic compound A cyclic compound (or ring compound) is a term for a compound in the field of chemistry in which one or more series of atoms in the compound is connected to form a ring. Rings may vary in size from three to many atoms, and include examples where ...

, 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 NADP ...

. 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