Two new [named xylapyrrosides A (1) and B (2)] along with two known [pollenopyrrosides A (3) and B (=acortatarin A, 4)] naturally occurring spirocyclic pyrrole alkaloids were isolated and identified as minor components from the EtOH extract of the dried mycelia of the edible medicinal fungus Xylaria nigripes. Their structures were established by a combination of interpretation of spectroscopic data and single-crystal X-ray diffraction analyses. The isolates possess a unique tricyclic skeleton comprising a common bicyclic 2-formyl-pyrrole-fused morpholine, with a variable ketohexoside ring. This class of alkaloids is quite rare from natural sources. In this study, the total syntheses of compounds 1, 2 and 4 were successfully achieved by two alternative strategies, and three new analogs [named xylapyrrosides A₁ (1a), A₂ (1b) and B₁ (2a)] were also produced. Notably, the total synthesis of such spiroketal alkaloids with a pyranose ring (e.g.,1) was accomplished for the first time. The absolute configurations of the new isolates can be thereafter unequivocally secured by the total syntheses. The above isolated and synthesized spiro-alkaloids were found to show moderate antioxidant effects by preventing the oxidative stress-induced cytotoxicity of A7r5 rat vascular smooth muscle cells (VSMCs).

中文翻译：

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Xylapyrrosides A和B，来自Xylaria nigripes的两种稀有的糖吗啉螺环草吡咯来源的生物碱：分离，完整的结构阐明和总合成

从EtOH中分离出两种新的[命名为xylapyrrosides A（1）和B（2）]以及两种已知的[pollenopyrrosides A（3）和B（= acortatarin A，4）]天然存在的螺环吡咯生物碱。食用菌Xylaria nigripes干菌丝体的提取物。它们的结构是通过对光谱数据的解释和单晶X射线衍射分析的结合而建立的。分离物具有独特的三环骨架，其包含具有可变的酮己糖苷环的常见双环2-甲酰基-吡咯稠合的吗啉。这类生物碱在天然来源中非常罕见。在这项研究中，化合物1、2和4的总合成通过两种替代策略和三种新的类似物[名为xylapyrrosides A ₁（1a），A ₂（1b）和B ₁（2a）]也被产生。值得注意的是，这种具有吡喃糖环（例如1）的螺环生物碱的总合成是第一次完成。此后，新分离株的绝对构型可以通过总合成方法明确地得到保障。发现上述分离和合成的螺生物碱通过防止氧化应激诱导的A7r5大鼠血管平滑肌细胞（VSMC）的细胞毒性而显示出适度的抗氧化作用。