Design, Synthesis And Antifungal Evaluation Of Novel Compounds As Synergists Of Fluconazole Against Drug-resistant Candida Albicans

Invasive fungal infection?IFIs?belongs to deep mycosis,which is a pathological change and pathophysiological process in which pathogenic fungi invade human tissues and blood,and grow and multiply to cause tissue damage,organ dysfunction and inflammatory reaction.Candida species accounts for more than 80%of the main pathogens,mainly Candida albicans.Other common pathogens include cryptococcus,aspergillus,mucor and so on.Invasive fungal infections are an important cause of human mortality and morbidity,particularly for immunocompromised populations.However,there remains a paucity of antifungal drug treatments available to combat these fungal pathogens.Further,antifungal compounds are plagued with problems such as host toxicity,fungistatic activity,and the emergence of drug resistance in pathogen populations.A promising therapeutic strategy to increase drug effectiveness and mitigate the emergence of drug resistance is through the use of combination drug therapy.In particularly,the combination of antifungal agents with non-antifungal bioactive compounds has received extensive attention.Natural products that have been reported to cooperate with fluconazole against drug-resistant fungi,such as berberine,baicalein,forsythiaside,shikonin,curcumin,licorice,etc.,which can reduce antifungal drugs dosage in combination with fluconazole.The structural modification of the above natural product is aimed at overcoming the disadvantages inherent in itself,such as poor solubility,and searching for molecules having more excellent synergistic activity.The task group simplified the structure of berberine in the early stage.A simple molecule was obtained with its synergistic activity against drug-resistant Candida albicans equal to or slightly superior to berberine.Based on this study,two molecules with higher activity,compound 7d and 3e were selected for structural modification.New compounds were designed and synthesized and screened for anti-resistant fungal activity in vitro.The 1,3-benzodioxole moiety in 7d was retained,and the amide bond in the middle of7d,the aromatic ring of the right part,and the soft chain linking the 1,3-benzodioxole to the phenyl ring were structurally optimized.A total of 63 novel compounds were obtained.The amide bond was replaced by a bisamide bond or an ester bond to give compounds hym-a-1⁷and hym-c-1³ respectively,which showed no synergistic activity.Thus suggested us that the amide bond is necessary to their acticity.Changing the length,the substituents,and the position of the substituents afforded compounds hym-b-1⁵ and hym-e-1¹8.Cycloalkyl groups of 3 to 6 carbon atoms were introduced to the?-carbon atom to the right side of the amide bond in compounds hym-b-1⁵ introduces,and a methyl group was introduced to the?-carbon to the right side of theaamide bond in compounds hym-e-1¹8.The synergistic activity against resistant Candida albicans?100/103?is 1.0-2.0?g/ml and 0.125-16.0?g/ml,respectively,combined with fluconazole at a concentration of 8.0?g/ml.Among the 63molecules,hym-e-14 exhibits execellent synergistic activity with the lowest MIC₈₀ value which is 0.125?g/ml with fluconazole at 8.0?g/ml,better than the control drug 3e?0.5/0.125?g/ml?.Compounds hym-e-12 and hym-e-8 exhibited the same synergistic activity with a MIC₈₀ value of 0.5/0.125?g/ml with fluconazole at 8.0?g/ml which is equivalent to that of the control drug 3e.The optimization of the aromatic rings in the right part contains:changing the subustituents on the phenyl ring in hym-a/b/c,replacing the biphenyl group with biaryl group and changing their substituents in hym-d-1⁹,introducing alkoxy moiety between the aromatic rings in hym-f-1²1.In general,compounds with biphenyl moiety showed higher activity than the compounds with other changed moieties,thus indicated that biphenyl moiety plays an important role in their activity.Compounds bearing three aromatic rings in the right part showed less activity,thus suggested the extension of the biphenyl group with aromatic ring is useless to activity.Among the substituents on the phenyl group in the right part,fluorine atom and methyl group promoted their activity,and the trifluoromethyl group lowered the activity,and the methoxy group caused no synergistic activity.The structures of the 63 compounds have been confirmed by ¹H NMR and LC-MS,and the active compounds and clear structure-activity relationship have been obtained.The results provide a novel method to combat drug-resistant fungi,and the active compounds deserve further research.