Synthesis Of Amino Acid Acylated Products Of Silybin And Its Hepatoprotective Effect Against CCl₄-induced Acute Hepatic Damage In Mice

As a non-toxic bioactive component in milk thistle,silybin demonstrated a variety of pharmacological acitivities.It has been used to protect against liver conditions such as hepatitis and cirrhosis in clinical for many years.Silybin also exhibited versatile anti-cancer effects,such as prostate cancer,skin cancer,blade cancer,lung cancer,colon cancer,and so on.Its deficiency related to the issues of the poor solubility and bioavailability.To solve the problems,world scientists prepared and studied many of its derivatives,including complex(such as meglumine, phosphatidylcholine complex,cyclodextrin complex),ester salt of polyacids(such as phthalic ester salt,succinic ester salt and phosphoric ester salt),glucosides,etc.The efforts achieved success somewhat,and launched drugs in different forms.On the other hand,the studies on structure reforms made no breakthough.It seemed that sylibin couldn't be significantly changed in its structure to keep its efficacy.To improve the solubility and bioavailability of silybin,a series of amino acid derivatives on its primary hydroxyl at position 23 have been prepared.The biological activity of the products have been evaluated as well.The five amino-acids,glycine,L-alanine,L-phenylalanine,L-leucine and L-serine were protected first with tert-Butoxycarbonyl(Boc) by using Di-tert-butyl dicarbonate and sodium hydroxide in tert-butanol in high yield and good purity.Through Mitsunobu reaction they reacted with silybin in the presence of diethyl azodicarboxylate(DEAD) and triphenylphosphine(TPP), generated the corresponding N-Boc-amino acid ester at the position 23 of silybin.The acidic hydrolysis furnished the target molecules as free amino esters.It was found that the water solubilities of their hydrochlorides were as high as 500 to 1,000 times of silybin.The liver-protective effect of the esters were evaluated on the model of acute liver injury induced induced by carbon tetrachloride(CCl₄) in mice.It was found that 23-O-glycyl-silybin,23-O-phenylalanyl-silybin,23-O-leucyl-silybin and 23-O-seryl-silybin were more effective than silybin at the same dose(200mg·kg^-1).The efficacies were further improved with the higher concentrations.The rest one,23-O-alanyl silybin was effective as well at low concentration,but it did not seem to be more effective than silybin until its dose was increased up to 300 mg·kg^-1.In comparison with the mice of negative control group,the five esters in the dose of 300mg·kg^-1 did not cause any substantial abnormality on serum AST or ALT(P＞0.05).That indicated the safety of these esters.