Antibacterial activity evaluation of pleuromutilin derivatives with 4(3H)-quinazolinone scaffold against methicillin-resistant Staphylococcusaureus

Growing antibiotic resistance is causing a health care crisis, leading to an urgent need for new antibiotics to tackle serious hospital and community infections. Pleuromutilin, a naturally occurring product with moderate antibacterial activity, has a unique structure that has attracted great efforts to modify its scaffold to obtain lead compounds. Herein, we report the synthesis of a series of novel pleuromutilin derivatives with a scaffold of 4(3H)-quinazolinone or its analogues at the C-14 side chain and investigated their in vitro activity against Staphylococcus aureus and Staphylococcus epidermidis as well as Gram-negative bacteria (Escherichia coli and Salmonella enterica subsp. enterica serovar pullorum). Structure-activity relationship (SAR) studies showed that the substituents on the benzene ring of 4(3H)-quinazolinone was not as important as the substituted position to improve antibacterial activity while the substituted groups on the N-3 position of 4(3H)-quinazolinone had strong impact on the efficacy. The replacement of the benzene moiety of 4(3H)-quinazolinone with other rings (pyridine, pyrrole, thiophene, or cyclopentyl) also showed high antibacterial efficacy, meaning the benzene ring was dispensable for exerting powerful antibacterial properties. In vitro pharmacokinetics investigations and cytotoxicity assays indicated that 2-mercapto-4(3H)-quinazolinone scaffold was superior to 2-(piperazin-1-yl)quinazolin-4(3H)-one. Among this series of pleuromutilin analogues, compound 23 with a structure of 2-mercapto-3H-pyrrolo[2,3-d]pyrimidin-4(7H)-one displayed the best in vitro antibacterial activity against MRSA (MIC = 0.063 μg/mL) and low cytotoxicity to RAW 264.7 cells (IC50＞100 μM) and was demonstrated to inhibit MRSA effectively in a mouse thigh infection model, outperforming the comparator, tiamulin.

Synthesis, Anti-Tomato Spotted Wilt Virus Activities, and Interaction Mechanisms of Novel Dithioacetal Derivatives Containing a 4(3H)-Quinazolinone Pyrimidine Ring

A series of unreported novel dithioacetal derivatives containing a 4(3H)-quinazolinone pyrimidine ring were synthesized, and their antiviral activities were evaluated against tomato spotted wilt virus (TSWV). A three-dimensional quantitative structure-activity relationship (3D-QSAR) analysis was established, and compound D32 was designed and synthesized according to the analysis results of the CoMFA and CoMSIA models. The bioassay results showed that compound D32 exhibited excellent inactivation activity against TSWV, with EC₅₀ values of 144 μg/mL, which was better than those of ningnanmycin (149 μg/mL) and the lead compound xiangcaoliusuobingmi (525 μg/mL). The binding ability of compound D32 to TSWV CP was tested by microscale thermophoresis (MST), and the binding constant value was 4.4 μM, which was better than those of ningnanmycin (6.2 μM) and xiangcaoliusuobingmi (59.1 μM). Therefore, this study indicates that novel dithioacetal derivatives containing a 4(3H)-quinazolinone pyrimidine ring may be applied as new antiviral agents.

Design, Synthesis, and Anti-ToCV Activity of Novel 4(3H)-Quinazolinone Derivatives Bearing Dithioacetal Moiety

Tomato chlorosis virus (ToCV) has caused great harm to the production of tomato worldwide. To develop efficient anti-ToCV agents, some novel 4(3H)-quinazolinone derivatives containing dithioacetal were designed and synthesized, and their anti-ToCV activities were evaluated by microscale thermophoresis (MST) using ToCV coat protein (ToCV-CP) as a new target. The results showed that some compounds had a strong binding capacity to ToCV-CP. In particular, compounds C5 and C22 have an excellent binding capacity to ToCV-CP, with binding constant values of 0.24 and 0.25 μM, respectively. Additionally, reduced ToCV-CP gene expression levels of 81.05 and 87.59% could be achieved when tomato was treated with compounds C5 and C22, respectively, which were obviously higher than the levels after ningnanmycin (NNM) treatment (43.88%) and lead compound Xiangcaoliusuobingmi (XCLSBM) treatment (63.56%). Therefore, this work indicates that 4(3H)-quinazolinone derivatives containing dithioacetal moiety can be used as novel anti-ToCV agents.

A Novel Synthesis of the Efficient Anti-Coccidial Drug Halofuginone Hydrobromide

Background: Halofuginone hydrobromide (1) is recognized as an effective drug against several species of Eimeria (E.) in poultry. In this paper, we describe a convenient and low cost preparation method for the compound, as well as primary validation of its activity. Methods: First, 7-bromo-6-chloroquinazolin-4(3H)-one (2) was prepared from m-chlorotoluene by a conventional process, and then chloroacetone was creatively introduced in two steps. Finally, halofuginone hydrobromide (1) was obtained from 7-bromo-6-chloro-3-(3-cholroacetonyl) quinazolin-4(3H)-one (4) by a four-step reaction sequence including condensation, cyclization, deprotection and isomerization. The structures of the relative intermediates and target compound were characterized by melting point, IR, MS and ¹H-NMR. Besides, the protective effect of compound 1-supplemented chicken diet at doses of 6, 3 and 1.5 mg per 1 kg were evaluated on chickens infected with E. tenella, by reduction in mortality, weight loss, fecal oocyst excretion and gut pathology, respectively. Results: Halofuginone hydrobromide (1) was prepared successfully by and improved and innovative method based on traditional research. Moreover, the synthesized halofuginone hydrobromide significantly exhibited an anti-coccidial property. Conclusions: The fruitful work described in this Communication has resulted in halofuginone hydrobromide, which has a good pharmaceutical development prospects, becoming more available for large-scale production.