On the Concerted Ring Opening of Protonated Squalene Oxide and A-Ring Formation in the Biosynthesis of Lanosterol

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Title:On the Concerted Ring Opening of Protonated Squalene Oxide and A-Ring Formation in the Biosynthesis of Lanosterol
Creators:
Hess, B. Andes
Journal or Publication Title:
Collection of Czechoslovak Chemical Communications, 68, 1, pp. 202-210
Uncontrolled Keywords:Epoxides, Cyclizations, <i>Ab initio</i>, Terpenoids, Steroids, Reaction mechanism, DFT calculations, Biosynthesis

Abstract

Density functional calculations were performed on a model system of squalene oxide to study the mechanism of the formation of ring A in the biosynthesis of lanosterol from squalene. When (2<i>Z</i>)-6,7-epoxy-3,7-dimethyloct-2-ene was protonated, it was calculated to undergo a very facile ring opening of the oxirane in concert with the formation of the six-membered ring of the 4-(hydroxymethyl)-1,2,3,3-tetramethy1cyclohexyl cation. A study of the reaction pathway (IRC) indicates a very early transition structure in which the carbon- carbon double bond participates anchimerically in the ring-opening of the protonated oxirane. It is suggested that the primary role of the enzyme in this first step of the biosynthesis of lanosterol is protonation of the oxirane ring along with holding the substrate in the proper conformation for the concerted ring-closure to occur. The similarity between this mechanism and that recently proposed for concerted C-ring expansion and D-ring formation in the biosynthesis of lanosterol is discussed. <p>

Title:On the Concerted Ring Opening of Protonated Squalene Oxide and A-Ring Formation in the Biosynthesis of Lanosterol
Creators:
Hess, B. Andes
Uncontrolled Keywords:Epoxides, Cyclizations, <i>Ab initio</i>, Terpenoids, Steroids, Reaction mechanism, DFT calculations, Biosynthesis
Divisions:Life and Chemical Sciences > Institute of Organic Chemistry and Biochemistry > Collection of Czechoslovak Chemical Communications
Journal or Publication Title:Collection of Czechoslovak Chemical Communications
Volume:68
Number:1
Page Range:pp. 202-210
ISSN:0010-0765
E-ISSN:1212-6950
Publisher:Institute of Organic Chemistry and Biochemistry
Related URLs:
URLURL Type
http://dx.doi.org/10.1135/cccc20030202UNSPECIFIED
ID Code:2053
Item Type:Article
Deposited On:06 Feb 2009 17:15
Last Modified:06 Feb 2009 16:15

Citation

Hess, B. Andes (2003) On the Concerted Ring Opening of Protonated Squalene Oxide and A-Ring Formation in the Biosynthesis of Lanosterol. Collection of Czechoslovak Chemical Communications, 68 (1). pp. 202-210. ISSN 0010-0765

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