| To fight with microbial resistance and protect public health,it is urgent to develop new drugs that control the spread of microbial resistance.Quinazolone is a kind of antibacterial skeleton that differs from the C-3 position of clinical antiinfective quinolone,and the increase of quinolone-resistant bacteria is mainly relevant to carboxyl group at C-3 position.Therefore,it has aroused widespread attention.Recently,quinazolones have brought to the forefront in the treatment of microbial infections.Such derivatives showed excellent antibacterial effectiveness,broad antibacterial spectrum and favorable pharmacokinetic properties in combating many drug-resistant strains,and their structures were generally characterized with the presence of azoles.The five-membered heteroaromatic thiazole could engage with important biological targets such as key metabolic enzymes,nucleic acids and amino acids in microorganisms through non-covalent interactions like hydrogen bond and electrostatic interaction to enhance molecular bioactivity,thus it is widely applied in many antibacterial drugs and makes great contributions to the development of anti-infective diseases.In view of these,a series of new structurely antibacterial molecules were constructed in this work by utilizing combination principle to incorporate quinazolone with thiazole,which based on the structural characteristics and development trends of quinazolones as well as the research of thiazoles on our group.It was mainly involved in three series of quinazolone thiazoles,and their structures were confirmed by modern spectroscopic techniques.The structure-activity relationships of new compounds were discussed by exploring the antimicrobial effect of all quinazolone thiazoles.In addition,other biological studies and possible antibacterial mechanisms on highly active compounds were preliminarily explored.The main research works were summarized as follows:1.Design and synthesis of new quinazolone thiazoles:(a)Preparation of new imine-derived quinazolinone thiazoles:The quinazolone skeletons Ⅱ-2a-d were constructed by formamidine acetate and O-aminobenzoic acid containing different substituents as starting materials.The important intermediatesⅡ-3a-d were obtained by substitution of brominated 2-acetylthiazoles.The condensation of compound Ⅱ-3a with different primary amines and hydrazines resulted in the formation of methylenimine derivations Ⅱ-4a-e and hydrazones Ⅱ-5a-e.Moreover,the precursor Ⅱ-3a was treated with hydroxylamine hydrochloride to produce oxime Ⅱ-6,which was further modified by halides to afford oxime derivativesⅡ-7a-g.(b)Preparation of new enone-bridged quinazolone thi azoles:Using important intermediate Ⅱ-3a as starting material,a series of corresponding target enone-bridged quinazolone thiazoles Ⅲ-1a-e,Ⅲ-2a-n,Ⅲ-3a-e and Ⅲ-4 were obtained by aldol reactions repectively with various five-member aromatic aldehydes,substituted benzaldehydes,benzoheterocyclic aldehydes and condensed aromatic aldehyde.The aliphatic quinazolone thiazole Ⅲ-5 was prepared by the condensation of Ⅱ-3a and DMF-DMA at 80℃.The prepared intermediates Ⅱ-3b-c with different substituents on quinazolone were reacted with 4-trifluoromethoxybenzaldehyde to access target molecules Ⅲ-6a-b based on antimicrobial data.(c)Preparation of new hydroxy ethyl-bridged quinazolone thiazoles:Taking the important intermediates Ⅱ-3a-d as starting materials,the target products Ⅳ-1a-k were offered by additive reaction with different phosphonates.Reduction of compound Ⅱ-3a by sodium borohydride provided product Ⅳ-2,which was chlorinated by thionyl chloride to preduce the target molecule Ⅳ-3.2.The structures of all newly prepared quinazolone-thiazoles were confirmed by 1H NMR,13C NMR,HRMS and/or X-ray single crystal diffraction,and the purities of the compounds were tested by HPLC.3.Antimicrobial abilities of newly prepared quinazolone thiazoles:(a)In Series Ⅱ novel imine-derived quinazolone thiazole compounds,some of the target compounds could significantly inhibit the growth of bacteria or fungi.Especially,the hexyl oxime derivative Ⅱ-7d showed favorable antibacterial efficacy on Pseudomonas aeruginosa with MIC value of 0.01 mM,which was superior to reference drugs chloramphenicol and norfloxacin.(b)In Series Ⅲ ketone-bridged quinazolone thiazole compounds,phenyl-derived target molecules generally possessed good antibacterial activity and especially compound Ⅲ-2j displayed excellent inhibitory effect against Pseudomonas aeruginosa and Escherichia coli with MIC values of 1 μg/mL,which was better than clinical drug norfloxacin.(c)In Series Ⅳ hydroxyethyl-bridged quinazolone thiazoles,most of target molecules showed poor antibacterial activity while the chlorinated molecule Ⅳ-3 without phosphonate gave better inhibition on the growth of Escherichia coli and Escherichia coli ATCC 25922 than norfloxacin(MIC=0.003 mM).4.The preliminary structure-activity relationship of hybrids of quinazolone and thiazoles:(a)The presence of chlorine at C-7 position of quinazolone played an important role on bioactivity of compounds and the same situations were applied to the introduction of 2-acetylthi azole at N-3 position of quinazolone.(b)In Series Ⅱ,the oxime derivatives showed better antibacterial effect than other imines.In the methylimine derivatives,the water-soluble groups were beneficial to the antibacterial activity while the hydrophobic aliphatic chains were unfavorable.It also found that the substitution of saturated alkyl chain on oxime was more beneficial to the bioactivity than that of unsaturated chain.(c)In Series Ⅲ,the introduction of phenyl groups was more advantageous than that of other aromatic rings in inhibiting bacterial growth and substituents on phenyl group were also crucial for inhibiting the growth of bacteria.(d)In Series Ⅳ,the presence of phosphonates increased the water solubilities but was adverse to the antibacterial activities,and the presence of chlorine atom was more favorable than that of hydroxyl group.5.The potential druggability of new quinazolone thiazoles:(a)In series Ⅱ the active molecule Ⅱ-7d not only have good pharmacokinetics,drug similarity and low cytotoxicity to normal liver cells,but also could quickly exhibit bactericidal effect and slow resistant development against Pseudomonas aeruginosa(b)In series Ⅲ,compound Ⅲ-2j with low hemolysis could hinder formation of bacterial biofilms and induce ROS generation,which could take responsibility for emerging low resistance.In addition,compound Ⅲ-2j gave synergistic effects against some gram-negative bacteria in combination with norfloxacin.(c)In series Ⅳ,the active compound Ⅳ-3 could not only exhibit low resistant development to Escherichia coli,but also meet with Lipinski’s rule and possessed the same oral bioavailability score as Norfloxacin,showing good drug similarity and excellent pharmacokinetic properties.6.Antibacterial mechanism of new quinazolone thiazoles:(a)In Series Ⅱ,compound Ⅱ-7d could not only disturb bacterial cell membrane to induce bacterial death,but also inhibit bacterial growth by interacting with DNA topoisomerase Ⅳ and embedding in DNA.(b)In series Ⅲ compound Ⅲ-2j could not only destroy outer and inner membranes of bacteria,resulting in the leakage of cytoplasmic contents,but also disrupt normal metabolic function by inhibiting lactate dehydrogenase.Meanwhile,Ⅲ-2j could insert into DNA to exert powerful biological activity.(c)In series Ⅳ,compound Ⅳ-3 could not only permeate bacterial membrane and inhibt bacterial metabolism,but also bind to DNA topoisomerase Ⅳ to exert antibacterial effect.This work developed three series of novel antibacterial molecules by incorporating thiazole into quinazolone.The antimicrobial ability,druggability potentiality and mechanism of action were investigated.Sixty-eight molecules were synthesized including 59 target molecules and 9 intermediates.Some of target molecules showed stronger or comparable antibacterial abilities in comparison to clicinal drugs.The highly active compounds not only possessed excellent biological properties with low toxicity,slow resistance and rapid sterilization,but also showed synergistic effects in combination with clinical drug.The preliminary mechanistic exploration showed that the highly active compounds could interfere with the bacterial cell membrane,lead to the leakage of intracellular proteins,inhibit bacterial metabolism and embed into DNA.These results implied that these highly active compounds have potentiality as new antimicrobial agents and are worthy of further study. |
