Controlling the rates of reductively-activated elimination from the (indol-3-yl)methyl position of indolequinones
作者:Steven A. Everett、Matthew A. Naylor、Paola Barraja、Elizabeth Swann、Kantilal B. Patel、Michael R. L. Stratford、Anna R. Hudnott、Borivoj Vojnovic、Rosalind J. Locke、Peter Wardman、Christopher J. Moody
DOI:10.1039/b009652k
日期:——
A series of substituted 3-(4-nitrophenyloxy)methylindole-4,7-diones (Q) were synthesised. The effects of substitution patterns on the indole core on rates of elimination of 4-nitrophenol as a model for drug release following fragmentation of a phenolic ether linker were studied. After reduction to either the radical anion (Q˙−) or hydroquinone (QH2) elimination of 4-nitrophenol occurred from the (indol-3-yl)methyl position. The half-lives of Q˙− radicals at [O2] ≈ 5 µmol dm−3, typical of tumour hypoxia, were t½ ≈ 0.3–1.8 ms, the higher values associated with higher reduction potentials. Half-lives for the autoxidation of the QH2 were markedly longer at the same oxygen concentration (t½ ≈ 8–102 min) and longer still in the presence of 4 µmol dm−3
superoxide dismutase (t½ ≈ 8–19 h). Although the indolequinones were able to eliminate 4-nitrophenol with high efficiency only Q˙− radicals of the 3-carbinyl substituted derivatives did so with sufficiently short half-lives (t½ ≈ 41–2 ms) to compete with electron transfer to oxygen and therefore have the potential to target the leaving group to hypoxic tissue. The hydroquinones are not sufficiently oxygen sensitive to prevent the elimination of 4-nitrophenol (t½ ≈ 1.5–3.5 s) even at oxygen concentrations expected in normal tissue. By incorporating electron rich substituents at the indolyl carbinyl position it is possible to control the rate of reductive fragmentation. This may prove an important factor in the design of an indolequinone-based bioreductive drug delivery system.
合成了一系列取代的3-(4-硝基苯氧基)甲基吲哚-4,7-二酮(Q)。研究了取代模式对吲哚核心在4-硝基苯酚释放速率上的影响,作为药物释放的模型,药物释放是通过酚醚连接链的断裂发生的。在还原为自由基阴离子(Q˙−)或氢醌(QH2)后,4-硝基苯酚从(吲哚-3-基)甲基位置释放。Q˙−自由基在[O2] ≈ 5 µmol dm−3(典型的肿瘤缺氧环境)下的半衰期为t½ ≈ 0.3–1.8毫秒,较高的半衰期值与较高的还原电位相关。在相同的氧浓度下,QH2的自氧化半衰期明显更长(t½ ≈ 8–102分钟),在存在4 µmol dm−3超氧化物歧化酶的情况下更长(t½ ≈ 8–19小时)。尽管吲哚醌能够以高效率释放4-硝基苯酚,但仅有3-羧基取代的Q˙−自由基具有足够短的半衰期(t½ ≈ 41–2毫秒)以与氧的电子转移竞争,因此具有将离去基团靶向缺氧组织的潜力。即使在正常组织中预期的氧浓度下,氢醌的氧敏感性不足以阻止4-硝基苯酚的释放(t½ ≈ 1.5–3.5秒)。通过在吲哚基甲基位置引入富电子取代基,可以控制还原性碎裂的速率。这可能成为设计基于吲哚醌的生物还原药物递送系统的重要因素。