Further evidence that the polycyclization reaction by oxidosqualene-lanosterol cyclase proceeds via a ring expansion of the 5-membered C-ring formed by Markovnikov closure. On the enzymic products of the oxidosqualene analogue having an ethyl residue at the 15-position

The incubation of the substrate analogue, (3S)-(6E,10E,14E,18E)-15-ethyl-2,6,19,23-tetramethyl-2,3- epoxytetracosa-6,10,14,18,22-pentaene (-)-1 with 2,3-oxidosqualene-lanosterol cyclase from pig liver gave products 2 (a lanosterol homologue) and 3 (a tricyclic product), definitively demonstrating that the cyclization of oxidosqualene proceeds via the expansion reaction from a 5- to a 6-membered ring for the C-ring formation of lanosterol.