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.

在植物中广泛分布的五环三萜类化合物（pentacyclic triterpenes）中，γ-香树脂醇（γ-amyrin）与异乌苏烯醇（isoursenol）鲜有报道，被认为是自然界中较为稀有的成分。本研究推测，这类三萜类化合物实则因光谱表征手段不足，常被研究者常规性忽略。γ-香树脂醇通过α-香树脂醇（α-amyrin）的甲酸（HCOOH）异构化反应制备得到，而异乌苏烯醇则从异源表达的鲨烯环氧环化酶（oxidosqualene cyclase）的催化产物中分离获得。借助精准的核磁共振波谱（NMR）与气相色谱-质谱联用（GC-MS）数据，本研究采用代谢组学策略，在多种植物样本中成功鉴定出异乌苏烯醇与γ-香树脂醇。