Oxidosqualene radical cyclization

The following syntheses of natural products were based on the use of substo-ichiometric quantities of Cp2TiCl to catalyze different cyclization processes initiated by homolytic epoxide opening. They have been classified according to the type of cyclization process employed. Section 4.4 has been reserved for the Cp2TiCl-catalyzed radical cyclization of 2,3-oxidosqualene due to the biological importance of this terpenoid and steroid precursor. 

In this context, Hoshino et al. have recently reported the cyclization of (3S)-2,3-oxidosqualene catalyzed by a Gly600-deletion mutant (AG600SHC) of the enzyme squalene-hopene cyclase (SHC) from Alicyclobacillus acidocal-darius (Scheme 31) [108]. The enzymatic biotransformation gave monocyclic (9) and tricyclic triterpenoids (38 and 44-47), but no detectable bicychc products [108]. Despite the authors biogenetic proposal of a conventional carbocationic pathway, the skeletal profile of products reported closely resembles that expected for a radical-type cyclization. 

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