Identification of 5-(Aryl/Heteroaryl)amino-4-quinolones as Potent Membrane-Disrupting Agents to Combat Antibiotic-Resistant Gram-Positive Bacteria

Abstract

Nosocomial infections caused by resistant Gram-positive organisms are on the rise, presumably due to a combination of factors including prolonged hospital exposure, increased use of invasive procedures, and pervasive antibiotic therapy. Although antibiotic stewardship and infection control measures are helpful, newer agents against multidrug-resistant (MDR) Gram-positive bacteria are urgently needed. Here, we describe our efforts that led to the identification of 5-amino-4-quinolone 111 with exceptionally potent Gram-positive activity with minimum inhibitory concentrations (MICs) ≤0.06 μg/mL against numerous clinical isolates. Preliminary mechanism of action and resistance studies demonstrate that the 5-amino-4-quinolones are bacteriostatic, do not select for resistance, and selectively disrupt bacterial membranes. While the precise molecular mechanism has not been elucidated, the lead compound is nontoxic displaying a therapeutic index greater than 500, is devoid of hemolytic activity, and has attractive physicochemical properties (clog P = 3.8, molecular weight (MW) = 441) that warrant further investigation of this promising antibacterial scaffold for the treatment of Gram-positive infections.

Gram Scale Synthesis of Membrane-Active Antibacterial 4-Quinolone Lead Compound

“…Dismayingly, the antibiotic pipeline is sparsely populated, with approximately 30-fold less candidates than the oncology pipeline and less candidates today than in the 1970s. , The relatively short duration and low costs of antibiotic courses, the inflexible nature of regulatory hurdles during antibiotic clinical trials, and a tendency to reserve novel antibiotics serve as economic disincentives for large pharmaceutical companies, and 15 of 18 of the largest of these have abandoned the therapeutic area . The major thrust of the preclinical stages of current antimicrobial development is now carried out by nonprofit agencies and through governmental initiatives and public–private partnerships, while hit identification and hit-to-lead optimization are predominantly the remit of academic centers and are commonly prosecuted by screening of natural and synthetic compound libraries or pursuing modifications of existing antibiotics. ,,, In one such campaign, Nair and co-workers screened the NERCE library against methicillin-resistant Staphylococcus aureus (MRSA) USA300 and identified DNAC-2. , …”

“…Quinolines and related heterocycles, chemical classes under which DNAC-2 can be classified, are privileged motifs in medicinal chemistry and provide scaffolds amenable to multiparametric hit-to-lead optimization of potency, drug disposition properties, and therapeutic index. , Indeed, extensive explorations of structure–activity relationship (SAR) studies of DNAC-2 in collaboration with our group recently led to the identification of a novel class of 5-arylamino-4-quinolones including a promising lead compound 1 . Quinolone 1 showed mechanistic congruence with the hit quinolinol, leading to partial membrane depolarization and also affecting the morphology of the S.…”

“…13,14 Indeed, extensive explorations of structure−activity relationship (SAR) studies of DNAC-2 in collaboration with our group recently led to the identification of a novel class of 5arylamino-4-quinolones including a promising lead compound 1. 12 Quinolone 1 showed mechanistic congruence with the hit quinolinol, leading to partial membrane depolarization and also affecting the morphology of the S. aureus membrane while displaying a >128-fold improvement in antibacterial activity as measured by the minimum inhibitory concentration (MIC) compared to DNAC-2. Although 1 possesses a desirable antibiotic target profile given its potency against numerous clinically relevant strains of gram-positive bacteria, attractive physicochemical properties, good oral bioavailability, and greater than 500-fold selectivity for bacterial over eukaryotic membranes, further studies are hindered by limited access to the lead compound.…”

“…aureus membrane while displaying a >128-fold improvement in antibacterial activity as measured by the minimum inhibitory concentration (MIC) compared to DNAC-2. Although 1 possesses a desirable antibiotic target profile given its potency against numerous clinically relevant strains of gram-positive bacteria, attractive physicochemical properties, good oral bioavailability, and greater than 500-fold selectivity for bacterial over eukaryotic membranes, further studies are hindered by limited access to the lead compound. , …”

“…Previously, Schultz and co-workers utilized a Buchwald–Hartwig amination reaction to install the 5-(trifluoromethyl)­pyridine-2-yl-amino moiety on a precursor 5-bromo-4-quinolinol at the C5 position and furnish the lead compound 1 . However, the observed conversion was low (∼5%) and required purification by high performance liquid chromatography (HPLC).…”