The Brassica rapa oxidosqualene cyclase Bra032185 makes 60% astertarone A (1) and 20 minor triterpenes (0.1-11%). Mechanistic analysis indicates the absence of an enol intermediate to generate the 4 S epimer of 1， unless workup involves saponification. Bra032185 and its closest Arabidopsis thaliana homologue diverged markedly in product profiles over a short evolutionary distance， while developing opposite C18 configurations. Active-site residue comparison of Bra032185 with friedelin and shionone synthases suggests convergent evolution to 3-ketotriterpenes.
The Brassica rapa oxidosqualene cyclase Bra032185 makes 60% astertarone A (1) and 20 minor triterpenes (0.1-11%). Mechanistic analysis indicates the absence of an enol intermediate to generate the 4 S epimer of 1， unless workup involves saponification. Bra032185 and its closest Arabidopsis thaliana homologue diverged markedly in product profiles over a short evolutionary distance， while developing opposite C18 configurations. Active-site residue comparison of Bra032185 with friedelin and shionone synthases suggests convergent evolution to 3-ketotriterpenes.
