An Efficient Buchwald–Hartwig/Reductive Cyclization for the Scaffold Diversification of Halogenated Phenazines: Potent Antibacterial Targeting, Biofilm Eradication, and Prodrug Exploration

Bacterial
biofilms are surface-attached communities comprised of
nonreplicating persister cells housed within a protective extracellular
matrix. Biofilms display tolerance toward conventional antibiotics,
occur in ∼80% of infections, and lead to >500000 deaths
annually.
We recently identified halogenated phenazine (HP) analogues which
demonstrate biofilm-eradicating activities against priority pathogens;
however, the synthesis of phenazines presents limitations. Herein,
we report a refined HP synthesis which expedited the identification
of improved biofilm-eradicating agents. 1-Methoxyphenazine scaffolds
were generated through a Buchwald–Hartwig cross-coupling (70%
average yield) and subsequent reductive cyclization (68% average yield),
expediting the discovery of potent biofilm-eradicating HPs (e.g., 61: MRSA BAA-1707 MBEC = 4.69 μM). We also developed
bacterial-selective prodrugs (reductively activated quinone-alkyloxycarbonyloxymethyl
moiety) to afford HP 87, which demonstrated excellent
antibacterial and biofilm eradication activities against MRSA BAA-1707
(MIC = 0.15 μM, MBEC = 12.5 μM). Furthermore, active HPs
herein exhibit negligible cytotoxic or hemolytic effects, highlighting
their potential to target biofilms.

细菌生物被膜（bacterial biofilms）是附着于固体表面的微生物群落，由包裹于保护性细胞外基质中的非复制型持留菌构成。该类群落对常规抗生素具有耐受性，约占临床感染病例的80%，每年导致超过50万例患者死亡。
我们近期发现了卤代吩嗪（halogenated phenazine, HP）类似物，其对重点防控病原体展现出清除生物被膜的活性；但吩嗪类化合物的合成存在诸多局限。本文报道了一种优化后的HP合成方法，显著加速了高效生物被膜清除剂的发现进程。通过布赫瓦尔德-哈特维希交叉偶联反应（Buchwald–Hartwig cross-coupling，平均产率70%）与后续还原环化步骤（平均产率68%），我们快速构建了1-甲氧基吩嗪骨架，并由此筛选得到强效的生物被膜清除型HP（例如化合物61：对耐甲氧西林金黄色葡萄球菌（methicillin-resistant Staphylococcus aureus, MRSA）BAA-1707的最小生物被膜清除浓度（minimum biofilm eradication concentration, MBEC）为4.69 μM）。我们还开发了细菌选择性前药（采用还原激活型醌-烷氧羰氧甲基基团）以制备HP 87，该化合物对MRSA BAA-1707展现出优异的抗菌与生物被膜清除活性（最低抑菌浓度（minimum inhibitory concentration, MIC）= 0.15 μM，MBEC=12.5 μM）。此外，本文所涉及的活性HP几乎无细胞毒性或溶血性效应，凸显了其靶向生物被膜的应用潜力。