Triterpene (C30) Classes
Ring configuration
The basic structure is 4 carbon rings, cyclopenta[a]phenanthrene, gonane, or sterane.
The rings B/C are always trans in all natural steroids. If the rings C/D are trans, it is called gonane. If its stereochemistry is unspecified, it is called sterane.
Most steroids take gonane form, but in cardenolides and bufanolides, the rings C/D are cis.
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Cyclopenta[a]phenanthrene
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Gonane
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The majority of steroids have methyl groups sticking out from the bridgehead positions C-10 and C-13.
When these methyl groups (or hydrogens) stand above the plane, they are called β-configuration.
Those below the plane are called α-configuration. If the configuration at any site is unknown, it is indicated as ξ (Greek Xi).
By default, hydrogen atoms or substituents at the positions C-8, 9, 10, 13, and 14 are assumed to be
8β, 9α, 10β, 13β, and 14α configurations. C-5 is a special position, because there are as many 5α steroids as 5β are.
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cholestane backbone
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5α-configuration
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5β-configuration
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Biosynthesis
The starting point is squalene, which is formed by joining two FPPs tail-to-tail.
Bacterial cyclases use squalene directly, but those of the other species use
2,3-oxidosqualene for cyclization.
- In bacteria, squalene is cyclized via the 17α-deoxydammarenyl cation to hopene and other triterpenes[1].
- In eukaryotes, 2,3-oxidosqualene is cyclized via the protosteryl cation to lanosterol (animals and fungi) or cycloartenol (plants) by a series of 1,2-hydride and methyl shifts (Wagner-Meerwein shifts).[2]
- In plants, various triterpenes arise from the dammarenyl cation.
- ↑ Bacterial squalene cyclases can accept oxidosqualene as their substrates, but oxidosqualene usually does not exist in bacteria
- ↑ A trace amount of phytosterols comes from lanosterol. Ohyama K, Suzuki M, Kikuchi J, Saito K, Muranaka T (2009) Dual biosynthetic pathways to phytosterol via cycloartenol and lanosterol in Arabidopsis Proc Natl Acad Sci USA 106(3):725-730
- ↑ The most accessible enzyme among oxidosqualene cyclases.
Ref. Corey EJ, Russey WE, Ortiz-de-Montellano PR (1966) 2,3-Oxidosqualene, an intermediate in the biological synthesis of sterols from squalene J Am Chem Soc 88:4750-1
- ↑ The rings of protosteryl cation are chair-boat-chair configuration. The C-17 chain is β-configuration, not α.
Ref. Corey EJ, Virgil SC (1991) An experimental demonstration of the stereochemistry of enzymic cyclization of 2,3-oxidosqualene to the protosterol system, forerunner of lanosterol and cholesterol. J Am Chem Soc 113:4025-6
- ↑ The rings of dammarenyl cation are all-chair configuration. The C-17 chain is β-configuration.
Ref. Xiong Q, Rocco F, Wilson WK, Xu R, Ceruti M, Matsuda SPT (2005) Structure and reactivity of the dammarenyl cation: configuration transmission in triterpene synthesis. J Org. Chem. 70:5362-75
Useful Reviews:
- Xu R, Fazio GC, Matsuda SPT (2004) On the origins of triterpenoid skeletal diversity. Phytochemstry 65:261-291 PMID 14751299
Design of Tri-terpene ID numbers ID番号の設計
12-DIGIT
- x ... species information
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- y ... backbone structure (母核構造)
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Symbol at y |
Carbons |
Steroids |
Backbone Structure
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GN
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C17
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gonane
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ES
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C18
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estrane
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AD
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C19
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androstane
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PG
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C21
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pregnane
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CA
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C24
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cholane
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CL
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C27
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cholestane
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CM
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C28
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campestane
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EG
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C28
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ergostane
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SG
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C29 (4 rings)
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stigmastane
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PR
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C29 (4 rings)
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poriferastane
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Symbol at y |
Carbons |
Triterpenoids |
Backbone Structure
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PS
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C30
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protostane
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EU
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C30
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euphane
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LN
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C30
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lanostane
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CY
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C30
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cycloartane
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FS
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C29
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fusidane
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HP
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C30 (5 rings)
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hopane
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FN
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C30 (5 rings)
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fernane
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CC
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C30
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cucurbitane
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DM
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C30
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dammarane
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BC
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C30
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baccharane
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HL
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C30
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holostane
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PF
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C29 (5 rings)
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pfaffane
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LP
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C30 (5 rings)
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lupane
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OL
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C30 (5 rings)
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oleanane
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FD
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C30 (5 rings)
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friedelane
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TR
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C30 (5 rings)
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taraxastane
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UR
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C30 (5 rings)
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ursane
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SR
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C30 (5 rings)
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serratane
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- r ... number of major rings (環構造数)
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Click above categories to see details.
- h ... hydroxylation pattern (水酸基数)
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Click above categories to see details.
- g ... glycosylation pattern(糖修飾パターン)
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Click above categories to see details.
- n ... number of sugars (修飾糖数)
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Click above categories to see details.
- c ... serial number (通し番号)
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