Department of Chemistry, Vanderbilt University, Nashville, Tennessee 37235, United States.
Department of Aquatic Health Sciences, Virginia Institute of Marine Science, William & Mary, Gloucester Point, Virginia 23062, United States.
J Nat Prod. 2020 Apr 24;83(4):1069-1081. doi: 10.1021/acs.jnatprod.9b01094. Epub 2020 Feb 21.
The marine toxin goniodomin A (GDA) is a polycyclic macrolide containing a spiroacetal and three cyclic ethers as part of the macrocycle backbone. GDA is produced by three species of the genus of dinoflagellates, blooms of which are associated with "red tides", which are widely dispersed and can cause significant harm to marine life. The toxicity of GDA has been attributed to stabilization of the filamentous form of the actin group of structural proteins, but the structural basis for its binding is not known. Japanese workers, capitalizing on the assumed rigidity of the heavily substituted macrolide ring, assigned the relative configuration and conformation by relying on NMR coupling constants and NOEs; the absolute configuration was assigned by degradation to a fragment that was compared with synthetic material. We have confirmed the absolute structure and broad features of the conformation by X-ray crystallography but have found GDA to complex with alkali metal ions in spite of two of the heterocyclic rings facing outward. Such an arrangement would have been expected to impair the ability of GDA to form a crown-ether-type multidentate complex. GDA shows preference for K, Rb, and Cs over Li and Na in determinations of relative affinities by TLC on metal-ion-impregnated silica gel plates and by electrospray mass spectrometry. NMR studies employing the K complex of GDA, formed from potassium tetrakis[pentafluorophenyl]borate (KBArF), reveal a major alteration of the conformation of the macrolide ring. These observations argue against the prior assumption of rigidity of the ring. Alterations in chemical shifts, coupling constants, and NOEs indicate the involvement of most of the molecule other than ring F. Molecular mechanics simulations suggest K forms a heptacoordinate complex involving O, O, O, O, O, and the C-26 and C-27 hydroxy groups. We speculate that complexation of K with GDA electrostatically stabilizes the complex of GDA with filamentous actin in marine animals due to the protein being negatively charged at physiological pH. GDA may also cause potassium leakage through cell membranes. This study provides insight into the structural features and chemistry of GDA that may be responsible for significant ecological damage associated with the GDA-producing algal blooms.
海洋毒素冈田酸 A（GDA）是一种多环大环内酯化合物，含有一个螺缩醛和三个环醚作为大环骨架的一部分。GDA 由三种属的甲藻产生，这些藻类的大量繁殖与“赤潮”有关，赤潮广泛分布，会对海洋生物造成严重危害。GDA 的毒性归因于稳定肌动蛋白组结构蛋白的丝状形式，但它的结合结构基础尚不清楚。日本研究人员利用大环内酯环的假定刚性，通过依赖 NMR 偶合常数和 NOE 来分配相对构型和构象；绝对构型通过降解到与合成材料进行比较的片段来分配。我们已经通过 X 射线晶体学证实了绝对结构和构象的广泛特征，但发现 GDA 尽管有两个杂环向外，也会与碱金属离子络合。这种排列方式预计会削弱 GDA 形成冠醚型多齿络合物的能力。尽管 GDA 中的两个杂环向外，但 GDA 在金属离子浸渍硅胶板上的 TLC 和电喷雾质谱测定相对亲和力的实验中，表现出对 K、Rb 和 Cs 的偏好，而对 Li 和 Na 的偏好较低。NMR 研究采用由四（五氟苯基）硼酸钾（KBArF）形成的 GDA 的 K 络合物，揭示了大环内酯环构象的重大变化。这些观察结果反驳了先前对环刚性的假设。化学位移、偶合常数和 NOE 的变化表明除了环 F 之外，分子的大部分都参与其中。分子力学模拟表明，K 形成一个七配位络合物，涉及 O、O、O、O、O 和 C-26 和 C-27 羟基。我们推测，由于生理 pH 下蛋白质带负电荷，K 与 GDA 的络合静电稳定了 GDA 与海洋动物丝状肌动蛋白的络合物。GDA 也可能导致钾通过细胞膜渗漏。这项研究提供了对 GDA 的结构特征和化学性质的深入了解，这可能是与产生 GDA 的藻类大量繁殖相关的重大生态破坏的原因。
