Are Isoursenol and γ‑Amyrin Rare Triterpenes in Nature or Simply Overlooked by Usual Analytical Methods?

Among
pentacyclic triterpenes commonly found in plants, γ-amyrin
and isoursenol are seldom reported and considered rare in nature.
It was hypothesized that these triterpenes are instead routinely overlooked
due to inadequate spectral characterization. γ-Amyrin was prepared
by HCOOH isomerization of α-amyrin, and isoursenol was isolated
from products of a heterologously expressed oxidosqualene cyclase.
With precise NMR and GC-MS data, a metabolomics strategy was used
to identify isoursenol and γ-amyrin in a wide range of plants.