Tripartilactam (1) is a natural macrocyclic lactam originally reported to have a unique [18,8,4]-tricyclic framework. However, the validity of this structure has been contested since niizalactam C (2), bearing a [18,6,6]-tricyclic skeleton, was proposed as an alternative structure in 2015. In the present study, a comprehensive reinvestigation of NMR spectroscopic data and a 13C-13C COSY NMR experiment identified direct 13C-13C coupling, thus leading to the unequivocal revision of the structure of tripartilactam as niizalactam C (2). In addition, whole-genome sequencing analysis of the tripartilactam-producing bacterial strain and subsequent bioinformatics and mutagenesis analyses identified its biosynthetic pathway, which probably utilizes one of the type I polyketide synthase (PKS) modules iteratively during its biosynthesis and exhibits spontaneous [4+2] cycloaddition from the precursor compound, sceliphrolactam, in the post-PKS process.

中文翻译：

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三部分内酰胺的结构修正和生物合成途径。

三部分内酰胺 (1) 是一种天然大环内酰胺，最初据报道具有独特的 [18,8,4]-三环骨架。然而，自从 2015 年提出具有 [18,6,6]-三环骨架的硝唑内酰胺 C (2) 作为替代结构以来，这种结构的有效性一直受到质疑。数据和 13C-13C COZY NMR 实验确定了直接的 13C-13C 偶联，从而导致三部分内酰胺的结构明确修订为硝基内酰胺 C (2)。此外，对产三内酰胺菌株的全基因组测序分析以及随后的生物信息学和诱变分析确定了其生物合成途径，