Synthesis And Anticancer Activity Study Of α,β-unsaturated Carbonyl-modified 18β-glycyrrhetinic Acid Derivatives

Cancer is one of the complex diseases.Its multidrug resistance and poor prognosis make the development of antitumor drugs still a difficult task though many treatments and drugs are available in clinic recently.Natural products,especially triterpenoids,have excellent skeletons and various bioactivities.The numerous triterpene derivatives have shown good tumor prevention and therapeutic potential.18β-glycyrrhetinic acid(18β-GA)consists of oleanane-type pentacyclic triterpenoids,which is the main active ingredient of glycyrrhetinic acid in traditional Chinese medicine Glycyrrhiza uralensis Fisch..18β-GA possesses anti-inflammatory,antiviral,hepatoprotective and other activities including antitumor activities.However,its defects such as poor water solubility and low bioavailability limit its use and are still far from the clinical drugs.Therefore,we can introduce the active groups into the structure of 18β-GA,which is expected to yield lead compounds with better water solubility,high efficiency for cancer cells and low toxicity for normal cells.In this study,the two series of α,β-unsaturated carbonyl-modified 18β-GA derivatives were designed and synthesized.Their cytotoxic activities were tested by MTT assay and the potential protein targets of the active derivatives were predicted.This study is broadly divided into the following three parts:In the first part,the two series of 18β-GA derivatives were synthesized.In series I,the cinnamic acid oxime ester 18β-GA derivatives were synthesized by introducing the benzyl ester group to the C-30 position,and then the cinnamic acid oxime ester groups containing various substituents were introduced to the C-3 position.In series II,phenylmethyl groups containing various electron-withdrawing substituents were added to the C-2 position to form an extra-cyclic α,β-unsaturated carbonyl structure with the carbonyl group at the C-3 position of the A ring.In addition,alkyl triphenylphosphonium cation with different carbon chains was attached at the C-30 position,which is able to target the drug to mitochondria in tumors.Both of the two series were synthesized as 4-step reactions with 57 intermediates and products.The melting points,NMR spectrogram(H1 and C13)of those 29 new products were tested for structure characterization.In the second part,the cytotoxicity of all 18β-GA derivatives was tested by MTT assay against four human cancer cell lines including human breast cancer MCF-7,human colon cancer HCT-116,human glioma SH-SY5Y and human liver cancer HepG2 and one human normal liver cell QSG-7701.The results shown that the second series derivatives 67a,67h and 67j displayed the best anti-proliferative activity against HCT-116,SH-SY5Y and HepG2 with IC50 values of 1.52 to 3.46 μM.However,the activity still differed from the positive control drug doxorubicin.In the third part,the potential protein targets of three active 18β-GA derivatives 67a,67h and 67j were predicted through Super-PRED which is an open source database followed by KEGG pathway enrichment and protein interaction network analysis.The results demonstrated that the human STAT3 might be the key protein target for these three active derivatives.Finally,the results of molecular docking were analyzed and presented using software such as AutoDockTools.The results displayed that compound 67a,67h and 67j are able to bind strongly to STAT3 protein generating intermolecular forces such as hydrogen bonding and hydrophobic interactions.