The crystal structure of S-deoxo[Ile^3]amaninamide, a nontoxic synthetic derivative of the Amanita phalloides mushroom toxins (amatoxins), has been determined by single-crystal X-ray diffraction. The crystals are monoclinic, space group P2_1, with 2 formula units per unit cell. Cell dimensions are a = 12.147 A, b = 11.250 A, c = 19.267 A, and (β = 92.41°. The structure was determined by molecular replacement methods and refined by least-squares techniques to a final R value of 0.065 for 3894 independent observations. Six intramolecular hydrogen bonds hold the bicyclic octapeptide in a compact conformation, which is very similar to the conformation of the naturally occurring (and toxic) amatoxin, (β-amanitin. The study demonstrates that the 30-fold reduction in binding affinity to RNA polymerase B of the title amatoxin, and probably of most of the other amatoxin analogues with altered side chain 3, is not due to alteration of backbone conformation. The three water molecules and two ethanol molecules, crystallized with the amatoxin, form a strong and extensive intermolecular hydrogen-bonding system.

中文翻译：

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S-deoxo[Ile3]amaninamide 的晶体和分子结构：鹅膏菌毒素的合成类似物

S-deoxo[Ile^3]amaninamide 是一种无毒合成的鹅膏菌毒素 (amatoxins) 衍生物，已通过单晶 X 射线衍射确定。晶体为单斜晶系，空间群为 P2_1，每个晶胞有 2 个分子式单位。单元格尺寸为 a = 12.147 A、b = 11.250 A、c = 19.267 A 和 (β = 92.41°。结构是通过分子置换方法确定的，并通过最小二乘法技术细化到 3894观察结果。六个分子内氢键将双环八肽保持在紧凑的构象中，这与天然存在的（和有毒的）鹅膏菌素（β-鹅膏菌素）的构象非常相似。研究表明，与标题为鹅膏菌素的 RNA 聚合酶 B，并且可能大多数其他具有改变的侧链 3 的鹅膏菌毒素类似物不是由于骨架构象的改变。三个水分子和两个乙醇分子，与鹅膏菌素一起结晶，形成一个强大而广泛的分子间氢键系统。