Four unusual cyclopeptides, zelkovamycins B–E (1–4), were isolated from an endophytic Kitasatospora sp. Zelkovamycin B was featured by an unprecedented 3-methyl-5-hydroxypyrrolidine-2,4-dione ring system linked to the cyclopeptide skeleton. Their structures and full configurations were established by spectroscopic analysis, Marfey’s method, and NMR calculations. A plausible biosynthetic pathway for zelkovamycins was proposed based on gene cluster analysis. Zelkovamycin E displayed potent inhibitory activity against H1N1 influenza A virus.

中文翻译：

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Zelkovamycins B-E，含有罕见氨基酸残基的环状八肽，来自内生北孢子菌

四个异常环肽，zelkovamycins B-E（1 - 4），从内生分离Kitasatospora藻。Zelkovamycin B 的特点是前所未有的 3-methyl-5-hydroxypyrrolidine-2,4-dione 环系统与环肽骨架相连。它们的结构和完整构型是通过光谱分析、Marfey 方法和 NMR 计算确定的。基于基因聚类分析提出了一种可能的榉木霉素生物合成途径。Zelkovamycin E 对 H1N1 甲型流感病毒显示出有效的抑制活性。