Synthesis,bioactivities And Phloem Mobility Of Phenazine-1-carboxylic Acid-amino Acid Conjugates

Phenazine-1-carboxylic acid(PCA)is a natural product isolated from metabolites extracted from phytopathogens sp.M18.PCA has been proven effective against a number of soil-borne fungal phytopathogens and registered for biofungicide against rice sheath blight in China.As one kind of fungicide from nature,PCA is noted for its high efficiency,low toxicity,environmental friendliness and improvement of the crop growth.But PCA didn’t have phloem mobility and couldn’t control root or vascular system pathogens.In order to improve the phloem mobility and bioactivities of PCA,PCA as the lead compounds,the amino acid(esters)owning phloem mobility meditated by the plant endogenous transports were chosen to conjugate with PCA in this paper and a series of PCA-amino acid(esters)conjugates were designed and synthesized.The conjugates were evaluated for their fungicidal activities against Rhizoctonia solani Kuhn and their phloem mobility in Ricinus communis was determined by HPLC.19 novel compounds that had not been reported were synthesized firstly.They consisted of 17 conjugates of PCA with amino acid esters and 2 conjugates of PCA with amino acid.Bioassay results showed that these novel compounds exhibited obvious inhibitory activity to mycelial growth of Rhizoctonia solani Kuhn.EC50(50% effective concentration)values of them were: PCA-L-glycine ethyl ester 0.057 mmol/L,PCA-L-alanine methyl ester 0.061 mmol/L,PCA-D-alanine methyl ester 0.062 mmol/L,PCA-L-alanine ethyl ester 0.045 mmol/L,PCA-D-alanine ethyl ester 0.046 mmol/L,PCA-L-phenylalanine methyl ester 0.095 mmol/L,PCA-D-phenylalanine methyl ester 0.088 mmol/L,PCA-L-phenylalanine ethyl ester 0.132 mmol/L,PCA-L-leucine methyl ester 0.106 mmol/L,PCA-D-leucine methyl ester 0.089 mmol/L,PCA-L-leucine ethyl ester 0.071 mmol/L,PCA-L-valine methyl ester 0.019 mmol/L,PCA-D-valine methyl ester 0.015 mmol/L,PCA-L-valine ethyl ester 0.097 mmol/L,PCA-L-isoleucine methyl ester 0.073 mmol/L,PCA-L-glutamic acid,1,5-diethyl ester 0.030 mmol/L,PCA-L-tyrosine ethyl ester 0.069 mmol/L,PCA-L-alanine 0.142 mmol/L and PCA-D-alanine 0.151 mmol/L.And the EC50 value of PCA was 0.111 mmol/L.The bioassay results showed that most of conjugates exhibited higher fungicidal activities against Rhizoctonia solani Kuhn than PCA.In particular,conjugates PCA-L-valine methyl ester and PCA-D-valine methyl ester exhibited the best fungicidal activities(4 to 5 times as much as that of PCA).The results also indicted that the fungicidal activity of conjugates was associated with their hydrophobicity.With the hydrophobicity of conjugates increasing,the fungicidal activity of conjugates increased.However,when the hydrophobicity increased to a certain level,the fungicidal activity of conjugates began to decline.Furthermore,the results of fungicidal evaluation indicated that the conformation of conjugates didn’t affect their fungicidal activity.The phloem mobility of conjugates in Ricinus communis was determined by HPLC.The results showed that PCA-L-alanine had good phloem mobility and its concentration in phloem sap increased with the increase of time(the maximum concentration was 12.69μ mol/L in phloem sap within 5 hours).But other conjugates didn’t have phloem mobility.It affected the phloem mobility of these conjugates that the conformation of conjugates and whether their α-carboxy were binding or not.Conjugates with L-amino acid and whose α-carboxy weren’t binding could exhibit phloem mobility.Although PCA-L-alanine exhibited good phloem mobility,its fungicidal activity declined compared with PCA.And the phloem mobile mechanism of PCA-L-alanine and developing compounds with high activities and good phloem mobility remain to be further research.