Formation of ring A in the biosynthesis of hopanoids from squalene. A density functional study

摘要

Density functional calculations were carried out on the ring closure of the 2,6-dimethyloct-6-en-2-yl cation to a chair conformer of the 1,2,3,3-tetramethylcyclohexyl cation as a model for the first step in the biosynthetic cyclization of squalene to the triterpene hopanoids. The concerted reaction was found to have an activation energy of 4.6 kcal/mol and to be exothermic by 11.5 kcal/mol.