Cyclization of 2,3-oxidosqualene through a protosteryl cation intermediate generates lanosterol and
cycloartenol, the structural precursors to all the steroids, while cyclization through a dammarenyl,
baccharenyl and lupenyl cation intermediates generates lupeol and α/-amyrin [20], the precursors of
the Centella pentacyclic triterpenoid saponins. The α/AS enzymes cyclize oxidosqualene via the
dammarenyl cation and allow further ring expansion and some rearrangement before deprotonation to
α-amyrin and -amyrin respectively [21]. α-Amyrin contains the ursane (C19, C20 dimethyl) and -
amyrin the oleanane (C20 dimethyl) substitution patterns respectively.