N-Aryl-3,4-Dihydroisoquinoliniums

Quaternary benzo[c]phenanthridine alkaloids(QB As),a small family of isoquinoline alkaloids,have attracted much attention of organic chemists and pharmacologists for their special structure and various bioactivities.Sanguinarine(SA)and chelerythrine(CHE)are two common and representative QBAs.However,developing QBAs-type drugs have been severely limited due to their source and modification challenge.Therefore,with the aim of exploring new promising secondary lead compounds,we have successfully explored biomimetic imitation strategy,namely designing a series of structurally simple,novel and easily modifiable analogues according to the preliminary structure-activity relationship(SAR)and structure characters of natural products SA and CHE.N-Aryl-3,4-dihydroisoquinolin-2-ium salts(ADHIQs)can be considered as structurally simple analogues of quaternary benzo[c]phenanthridine alkaloids such as SA and CHE.Our previous studies proved that ADHIQs generally possess excellent antimicrobial,anticancer and acaricidal activities,similar to or higher than that of SA and CHE.These results indicated that ADHIQs not only can be ideal secondary lead compounds of SA and CHE but also possess greater potential than corresponding natural compounds to develop QBA-like antimicrobial,anti-cancer and acaricidal agents.As our continuous research,herein,we further designed and synthesized a series of new ADHIQs more structurally similar to CHE,aiming for finding more potent molecules.Meanwhile,we also explored the antifungal and anti-proliferation activity in vitro of target compounds,as well as their qualitative SAR analysis.The main results were listed as follows.1.Five series of ADHIQs compounds with OMe or OH on A-ring were designed based on the structural similarity and structure characters of SA and CHE.(?)series A:R1=H;R2=H;R3=OMeseries B:R1=OMe;R2=H;R3=OMeseries C:R1=OMe;R2=Br;R3=OMeseries D:R1=H;R2=H;R3=OHseries E:R1=H;R2=H;R3=OAc,OEt or OBn;R4=2'-Iseries A-D:R4=halogen,CF3,NO2,CN,OMe,CH3 or OH2.2-(3,4-dimethoxyphenyl)acetic acid or 2-(3,4-dimethoxyphenyl)acetic acid were used as starting materials to synthesize 114 target compounds via 6-9 steps,including series A(8-OMe,36 compounds),series B(7,8-diOMe,28 compounds),series C(5-Br-7,8-diOMe,10 compounds)and seires D(8-OH,37 compounds).Series E(3 compounds)were synthesized from Dll via 3 steps.The structure of all synthetic compounds were confirmed by 1H NMR,13C NMR,MS.Due to the structural similarity,only part target compounds were confirmed by HRMS.All the target compounds were new compounds.3.Based on the mycelia growth rate method,all the target compounds were initially screened for antifungal activity in vitro against eleven common plant pathogenic fungi.Thiabendazole(TBZ),a commercial fungicide,were used as a positive control.SA and CHE were used as reference controls.The results were shown as follows:(1)All the compounds presented inhibition activity in varying degrees against each fungus at 150?M,and the activity of some compounds was higher than that of SA and/or CHE,the reference controls.(2)For five series compounds A-E,D possessed higher inhibition against Alternaria alternate and Pyricularia oryza,whereas A-C and E showed higher sensitivity against Fusarium solani and Fusarium graminearum.4.The compounds with higher initial activities were further subjected to median effective concentrations(EC50)assay.The results showed that there was obviously positive correlation between antifungal activity and concentrations of compounds in certain concentration range.Most tested compounds showed more remarkable inhibition effect against Fusarium solani with EC50 values of<10 ?g/mL.Among them,A6(8-OMe,3'-Cl),B11(7,8-diOMe,2'-I)and B15(7,8-diOMe,2',4'-diCl)presented the highest antifungal activity(EC50<1?g/mL),which were much higher than that of positive control and reference controls.5.The target compounds were screened for the cytotoxic activity in vitro against human gastric cell line MKN-45 and human acute promyelocytic leukemia cell line NB4 by MTT assay.The results showed that forty tested compounds presented cytotoxicity in varying degrees against MKN-45 cells and NB4 cells.Most tested compounds showed significant inhibition effect with IC50 values of<10 ?M,of which some compounds showed higher activity than DDP,a positive drug,SA and CHE.All not only displayed the excellent cytotoxicity against both MKN-45 and NB4 cells(IC50=2.03,2.30,uM,respectively),but also possessed higher selectivity to cancer cells in comparison with normal cells primary cultured goat fetal fibroblasts(PCGFF)and primary cultured porcine fetal kidney cells(PCKFKC).6.Cytotoxic mechanism was investigated preliminarily by AO/EB staining and Annexin V/PI double staining.The results showed that the target compounds were able to induce apoptosis in a concentration-dependent manner.Moreover,flow cytometry analysis presented that most apoptosis cells induced by target compounds were early apoptosis cells7.The target compounds possessed the similar structure-activity relationship between antifungal activity and cytotoxic activity.In general,the substituents on A-ring and C-ring not only can affect the antifungal and cytotoxic activities,but also existed combined effect on the activity.Electrondrawing groups on C-ring always increased the activity,whereas electrondonating groups on C-ring always led to a decrease on the activity.For the substituents on A-ring,8-OBn and 8-OEt had no significant effect on the two bioactivities in comparison with 8-OMe;8-OH and 8-OAc always induced decrease on the two bioactivities,relative to 8-OMe;7,8-diOMe remarkably enhanced the antifungal activity in comparison with 8-OMeIn conclusion,we designed and synthesized five new series of N-Aryl-3,4-dihydroisoquinolin-2-ium salts(114 compounds in total)with 8-OR or 7,8-diOMe.Afterwards,all the target compounds were assayed systematically for antifungal activity and cytotoxic activity,and their S AR was discussed.The results in this study indicated that the new ADHIQs possess great potential to develop new antifungal or anticancer drugs.The study provides important theoretical significance and reference value for subsequent optimum structural design of ADHIQs and development of new drugs.It is necessary to further study on bioactivity in vivo and activity mechanism of ADHIQs.