1-Methylidenesqualene and 25-Methylidenesqualene as Active-Site Probes for Bacterial Squalene:Hopene Cyclase
摘要:
1-Methylidenesqualene and 25-methylidenesqualene were converted to 30-methylidenehop-22(29)-ene by squalene:hopene cyclase from Alicyclobacillus acidocaidarius. It was remarkable that both analogues generated the same product. The hopanyl intermediate cation, stabilized by the methylidene residue, enabled a rotation of the isobutenyl group at C-21 prior to the final proton elimination. In contrast, in the formation of hop-22(29)-ene, the final proton abstraction takes place regiospecifically from the Z-methyl group, which was verified by cyclization of (1,1,1,24,24,24-H-2(6))squalene into (23,23,23,30,30,30-H-2(6))hop-22(29)-ene.