Anti-MRSA activity of isoplagiochin-type macrocyclic bis(bibenzyl)s is mediated through cell membrane damage

作者：Onoda Kenji; Sawada Hiromi; Morita Daichi; Fujii Kana; Tokiwa Hiroaki; Kuroda Teruo; Miyachi Hiroyuki^*

来源：Bioorganic & Medicinal Chemistry, 2015, 23(13): 3309-3316.

DOI：10.1016/j.bmc.2015.04.047

• Isoplagiochin
• Methicillin resistance
• Membrane
• Cell membrane damage
• Structure-activity relationship

We synthesized three geometrical isomers of a macrocyclic bis(bibenzyl) based on isoplagiochin, a natural product isolated from bryophytes, and evaluated their antibacterial activity towards methicillin-resistant Staphylococcus aureus (anti-MRSA activity). The isomer containing a 1,4-linked ring (5) showed only weak activity, whereas the isomers containing a 1,3-linked (6) or 1,2-linked (7) C ring showed potent anti-MRSA activity. Molecular dynamics calculations indicated that these differences are probably due to differences in the conformational flexibility of the macrocyclic ring; the active compounds 6 and 7 were more rigid than 5.
In order to understand the action mechanism of anti-MRSA activity, we investigated the cellular flux of a fluorescent DNA-binder, ethidium bromide (EtBr), in the presence and absence of these macrocycles. The active compound 6 increased the levels of EtBr inflow and outflow in S. aureus cells, as did our potent anti-MRSA riccardin derivative (4), indicating that these compounds increased the permeability of the cytoplasmic membrane. Inactive 5 had no effect on EtBr inflow or outflow. Furthermore, compound 6 abrogated the normal intracellular concentration gradients of Na+ and K+ in S. aureus cells, increasing the intracellular Na+ concentration and decreasing the K+ concentration, while 5 had no such effect. These results indicate that anti-MRSA-active macrocyclic bis(bibenzyl) derivatives directly damage the gram-positive bacterial membrane, resulting in increased permeability.

• 出版日期2015-7-1