The Mechanism of Action of (-)-Lomaiviticin A.
The Mechanism of Action of (-)-Lomaiviticin A.
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DOI：
10.1021/acs.accounts.7b00347
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发表时间：
2017-10-17
影响因子：
18.3
通讯作者：
Herzon SB
中科院分区：
文献类型：
--
作者：
Herzon SB
（-）- lomaiviticin A(4)是一种复杂的c2对称细菌代谢物，含有两个重氮芴官能团。重氮芴由萘醌、环戊二烯和重氮取代基通过σ-键和π键网络融合而成。此外，(-)-lomaiviticin A(4)是一种有效的细胞毒素，在低纳摩尔范围内对许多癌细胞具有半最大抑制效力（IC50）值。由于供应有限，其作用机制自本世纪初被孤立以来一直是一个“黑盒子”。在这篇文章中，我描述了针对(-)-lomaiviticin A(4)的全合成的研究如何为阐明这种代谢物的涌现特性提供了一个平台，从而将化学反应性与细胞表型联系起来。我们首先制定了聚合策略来制备重氮芴（9 + 10→13）。然后，我们利用这种化学方法合成了洛麦维菌素glycon（21/22）和天然单体重氮芴(-)-kinamycin F(3)。洛麦维菌素苷元（21/22）合成的关键步骤是两个单体重氮芴（2 × 18→20）的立体选择性氧化偶联，以建立目标物的碳-碳共合键。由于(-)-lomaiviticin A(4)的糖醛基和碳水化合物残基的绝对立体化学尚不清楚，我们开发了一种半合成途径，通过重氮转移到更丰富的分离物(-)-lomaiviticin C(6)，一步完成，产率为42%。这使我们能够完成(-)-lomaiviticin A(4)的立体化学配位，并提供了可再生的材料来源。利用这种材料，我们确定了(-)-lomaiviticin A(4)的显著细胞毒性作用源于在DNA中诱导高毒性双链断裂（DSBs）。在分子水平上，每一个亲电性重氮芴的1,7-亲核加成触发均溶分解途径，在每一个重氮基团的碳原子上产生sp2自由基。这些自由基从DNA的脱氧核糖中提取氢原子，这是一个已知的启动链切割的过程。利用核磁共振波谱和分子力学模拟来阐明DNA的结合模式。这些研究表明(-)- lomaivitticin A(4)的两个重氮芴都能渗透到双相中。这种非共价结合模式使每个重氮碳原子靠近每条DNA链。在这些研究中，使用含有一种重氮芴的分离物，如(-)-洛马维菌素C(6)和(-)-基那霉素C(2)作为对照。与我们的机制模型一致，这些化合物不会在DNA中诱导dsb，并且效力低几个数量级。反应性研究表明(-)- lomaivitticin A(4)比简单的单体重氮芴具有更强的亲电性。我们将此归因于1,7-加法在过渡态中发展中的负电荷的空间离域。与这种作用机制一致，(-)-lomaiviticin A(4)对DNA DSB修复缺陷的细胞类型表现出选择性的低皮摩尔电位。（-）-lomaiviticin A(4)的涌现性质源于重氮、萘醌、环戊二烯和酮类官能团的特殊排列。这些官能团一起工作，本质上是一种可以暴露在生物条件下的隐蔽的乙烯基。此外，源于二聚化的代谢物的旋转对称性允许它与DNA的反平行对称性相互作用并影响双链的切割。
(–)-Lomaiviticin A (4) is a complex C2-symmetric bacterial metabolite that contains two diazofluorene functional groups. The diazofluorene consists of naphthoquinone, cyclo-pentadiene, and diazo substituents fused through a σ- and π-bonding network. Additionally, (–)-lomaiviticin A (4) is a potent cytotoxin, with half-maximal inhibitory potency (IC50) values in the low nanomolar range against many cancer cell lines. Because of limitations in supply, its mechanism of action had remained a “black box” since its isolation in the early 2000s. In this Account, I describe how studies directed toward the total synthesis of (–)-lomaiviticin A (4) provided a platform to elucidate the emergent properties of this metabolite and thereby connect chemical reactivity with cellular phenotype. We first developed a convergent strategy to prepare the diazofluorene (9 + 10 → 13). We then adapted this chemistry to the synthesis of lomaiviticin aglycon (21/22) and the natural monomeric diazofluorene (–)-kinamycin F (3). The key step in the lomaiviticin aglycon (21/22) synthesis involved the stereoselective oxidative coupling of two monomeric diazofluorenes (2 × 18→ 20) to establish the cojoining carbon–carbon bond of the target. As the absolute stereochemistry of the aglycon and carbohydrate residues of (–)-lomaiviticin A (4) were unknown, we developed a semisynthetic route to the metabolite that proceeds in one step and 42% yield by diazo transfer to the more abundant isolate (–)-lomaiviticin C (6). This allowed us to complete the stereochemical assignment of (–)-lomaiviticin A (4) and provided a renewable source of material. Using this material, we established that the remarkable cytotoxic effects of (–)-lomaiviticin A (4) derive from the induction of highly toxic double-strand breaks (DSBs) in DNA. At the molecular level, 1,7-nucleophilic additions to each electrophilic diazofluorene trigger homolytic decomposition pathways that produce sp2 radicals at the carbon atoms of each diazo group. These radicals abstract hydrogen atoms from the deoxyribose of DNA, a process known to initiate strand cleavage. NMR spectroscopy and molecular mechanics simulations were used to elucidate the mode of DNA binding. These studies showed that both diazofluorenes of (–)-lomaiviticin A (4) penetrate into the duplex. This mode of non-covalent binding places each diazo carbon atom in close proximity to each DNA strand. Throughout these studies, isolates containing one diazofluorene, such as (–)-lomaiviticin C (6) and (–)-kinamycin C (2), were used as controls. Consistent with our mechanistic model, these compounds do not induce DSBs in DNA and are several orders of magnitude less potent. Reactivity studies suggest that (–)-lomaiviticin A (4) is more electrophilic than simple monomeric diazofluorenes. We attribute this to through-space delocalization of the developing negative charge in the transition state for 1,7-addition. Consistent with this mechanism of action, (–)-lomaiviticin A (4) displays selective low-picomolar potencies toward DNA DSB repair-deficient cell types. The emergent properties of (–)-lomaiviticin A (4) derive from the specific arrangement of diazo, naphthoquinone, cyclopentadiene, and ketone functional groups. These functional groups work together to yield, essentially, a masked vinyl radical that can be exposed under biological conditions. Furthermore, the rotational symmetry of the metabolite, deriving from dimerization, allows it to interact with the antiparallel symmetry of DNA and affect cleavage of the duplex.
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影响因子：
15
作者：
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通讯作者：
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影响因子：
2.7
作者：
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通讯作者：
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影响因子：
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作者：
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影响因子：
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作者：
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Hedrick, MP
DOI：
10.1073/pnas.102580399
发表时间：
2002-05-14
影响因子：
11.1
作者：
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通讯作者：
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