Inhibition of the Bacterial Enoyl Reductase FabI by Triclosan: A Structure-Reactivity Analysis of FabI Inhibition by Triclosan Analogues

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• 作者：Sharada Sivaraman ; Todd J. Sullivan ; Francis Johnson ; Polina Novichenok ; Guanglei Cui ; Carlos Simmerling ; and Peter J. Tonge
• 刊名：Journal of Medicinal Chemistry
• 出版年：2004
• 出版时间：January 29, 2004
• 年：2004
• 卷：47
• 期：3
• 页码：509 - 518
• 全文大小：152K
• 年卷期：v.47,no.3(January 29, 2004)
• ISSN：1520-4804

文摘

To explore the molecular basis for the picomolar affinity of triclosan for FabI, the enoyl reductaseenzyme from the type II fatty acid biosynthesis pathway in Escherichia coli, an SAR studyhas been conducted using a series of triclosan analogues. Triclosan (1) is a slow, tight-bindinginhibitor of FabI, interacting specifically with the E·NAD⁺ form of the enzyme with a K₁ valueof 7 pM. In contrast, 2-phenoxyphenol (2) binds with equal affinity to the E·NAD⁺ (K₁ = 0.5M) and E·NADH (K₂ = 0.4 M) forms of the enzyme and lacks the slow-binding step observedfor triclosan. Thus, removal of the three triclosan chlorine atoms reduces the affinity of theinhibitor for FabI by 70 000-fold and removes the preference for the E·NAD⁺ FabI complex.5-Chloro-2-phenoxyphenol (3) is a slow, tight-binding inhibitor of FabI and binds to the E·NAD⁺ form of the enzyme (K₁ = 1.1 pM) 7-fold more tightly than triclosan. Thus, while thetwo ring B chlorine atoms are not required for FabI inhibition, replacement of the ring A chlorineincreases binding affinity by 450 000-fold. Given this remarkable observation, the SAR studywas extended to the 5-fluoro-2-phenoxyphenol (4) and 5-methyl-2-phenoxyphenol (5) analoguesto further explore the role of the ring A substituent. While both 4 and 5 are slow, tight-bindinginhibitors, they bind substantially less tightly to FabI than triclosan. Compound 4 binds toboth E·NAD⁺ and E·NADH forms of the enzyme with K₁ and K₂ values of 3.2 and 240 nM,respectively, whereas compound 5 binds exclusively to the E·NADH enzyme complex with aK₂ value of 7.2 nM. Thus, the ring A substituent is absolutely required for slow, tight-bindinginhibition. In addition, pK_a measurements coupled with simple electrostatic calculations suggestthat the interaction of the ring A substituent with F203 is a major factor in governing theaffinity of analogues 3-5 for the FabI complex containing the oxidized form of the cofactor.