Synthesis Of Piperazine-Amino Acid Conjugate Coupled With Pentacyclic Triterpenic Acid Derivatives And Research On Anti-Sugar And Antibacterial Activity

With maslinic acid,corosolic acid and asiatic acid as the lead compounds,18 novel pentacyclic triterpenic acid derivatives were obtained by introducing piperazine-amino acid conjugates into the C-28 carboxylic sites.The structures of the new derivatives were verified by ¹H/¹³C NMR and HRMS techniques.Next,the inhibitory activity ofα-glucosidase was evaluated in vitro,and the results indicated that most of the derivatives showed different degree of inhibitory activity in ethanol-water and DMSO systems.Theα-glucosidase inhibitory activity of most of the derivatives in DMSO solvent system was higher than that of ethanol-water system in vitro.The in vitroα-glucosidase inhibitory activity of compound 16e(IC₅₀=423μM)was close to that of acarbose(IC₅₀=347μM)in the alcohol-water system,but superior to that of acarbose(IC₅₀=380μM)in the DMSO system.From the perspective of molecular structure,compound 15e(IC₅₀=591μM)and compound 16e(IC₅₀=423μM)had better inhibitory activity because of a free carboxyl group located on the side chain.However,derivatives of serine(15g IC₅₀=2754μM and16g IC₅₀=1316μM)and threonine(15h IC₅₀=2579μM and 16h IC₅₀=1925μM)were introduced into the triterpenoid skeleton.Although these four derivatives have one more freeer hydroxyl group on the side chain than the other derivatives,they have the same inhibitory activity as the other compounds.In conclusion,the hydroxyl groups on the amino acids did not improve the inhibitory activity ofα-glucosidase.Meanwhile,the results of activity test showed that theα-glucosidase activity of the derivatives of CA series was slightly higher than that of MA series,and the two derivatives of AA had better inhibitory activity than that of the structural analogs of CA.From the aspect of structure analysis,it was found that AA series had one more hydroxyl group and one more amino protection group（-Cbz）than CA series,and the amino group in CA series was directly free.We speculated that the free amino group on amino acids might improve the hypoglycemic activity of the derivative weaker than the hydroxyl group on the A ring of the parent compound.In addition,the three series of derivatives showed weaker inhibitory activity than the lead compounds,indicating that the carboxyl group of the lead compounds C-28site was the main active group with inhibitory activity.The results of enzymatic kinetics experiments showed that the inhibition type of the structure modified derivatives was non-competitive,and the inhibition constant K_m was 615±52μM.In vitro antibacterial experiments on the derivatives showed that the corosolic acid series had better improvement effect than its parent compound CA,while the derivatives of hathoic acid series and chiroxoxalic acid series had no obvious improvement.Among all derivatives,compound 16b with phenylalanine had the best antibacterial activity,with MIC=3.125μg/m L,followed by compound 16c with valine derivatives,with MIC=12.5μg/m L.The antibacterial activities of both compounds were superior to CA.In addition,there was no positive correlation between the antibacterial activity of the derivatives and theα-glucosidase inhibitory activity in vitro.