An Im proved Ox i da tive Cleav age Method for Large Scale Prep a ra tion of Some Acid-labile Aglycones from Glycosides Perng-Haur Wang ( ), Sheng-Jye Jou ( ), Wen-Chuan Chen ( ) and Shoei-Sheng Lee* ( ) School of Phar macy, Col lege of Med i cine, Na tional Tai wan Uni ver sity, Tai pei 100, Tai wan, R.O.C. A prac ti cal method for large-scale prep a ra tion of acid-labile aglycones in clud ing protopanaxadiol, protopanaxatriol, cycloastragenol, and jujubogenin from the cor re spond ing glycoside con tain ing frac tion was de vel oped. The key point of this im proved method is to gen er ate and main tain the crit i cal re ac tion con di tions, an hy drous and strongly ba sic, in situ. This ef fort over comes the weak ness of the re ported method for ox i da - tive cleav age of glycones and scales up the prep a ra tion of these acid-labile aglycones for fur ther stud ies. INTRODUCTION Bioactive triterpenoid glycosides bear ing a ste roid nu- cleus, such as ginsenosides, are very abun dant in quite a few Chi nese herbal med i cines. These glycosides, how ever, seem to be poorly ab sorbed via the gas tro in tes ti nal tract. For in - stance, a re port in di cated that only 0.1% of ginsenoside Rb 1, a ma jor saponin in Panax gin seng, was ab sorbed af ter oral ad - min is tra tion in rats. 1 Glycosides could be con verted into the cor re spond ing aglycones or par tially hy dro lyzed prod ucts by hydrolytic en zymes pres ent in the G-I tract or by microflora. 2 Whether these par tial or com plete hy dro ly sis prod ucts play a ma jor role on the phar ma co log i cal ac tiv i ties needs to be clar i - fied. Thus, the pro vi sion of these com pounds be came the first task to over come. The aglycones are gen er ally ob tained via acid hy dro ly sis or methanolysis. These meth ods, how ever, have their lim i ta tion, es pe cially for acid la bile aglycones such as protopanaxadiol (1) and protopanaxatriol (2), the aglycones of the abun dant ginsenosides Rb 1 (3) and Rg 1 (4), re spec tively, pres ent in Panax notoginseng (Burk.) F. H. Chen (Araliaceae). 3 These two compounds, possessing a 20-OH and a D 24 func tion group, will be con verted into the pyran-bearing panaxadiol ( 1a) and panaxatriol (2a), re spec- tively, upon acid hy dro ly sis of the cor re spond ing glycoside. 4 Un der acidic con di tions, cycloastragenol (5), the gen u ine agly - cone of astragalosides from Astragalus sp. (Leguminosae), will be con verted to astragenol 5 ( 5a); jujubogenin (6), the aglycone of jujubosides from Zizyphus sp. (Rhamnaceae), will yield degradative prod uct ebelin lactone 6 (6a). To clar ify the bi o log i cal func tions of these acid-labile aglycones, their avail abil ity needs to be solved first. The gen u ine aglycones 5 can be ob tained via en zy matic hy dro ly sis and het er o ge neous acidic hy dro ly sis of the cor re - sponding saponins but only on a small scale. The latter method also yielded 5a as by prod uct. 5 Com pound 6 has been ob tained upon Smith-de Mayo deg ra da tion of jujuboside B, how ever, in very low yield. 6 Re cent stud ies in di cated that ox - i da tive deg ra da tion of the sugar moi ety gave very good yields of 1 and 2 from ginsenosides. 7 The strict re ac tion con di tions, an hy drous and a large ex cess strong al ka line (NaO t Bu), and the re ac tion scale (only a few mil li grams), how ever, ham per the fur ther ap pli ca tion of this method. We thought that this method could be ap plied in large-scale prep a ra tions of the acid-labile aglycones if strict re ac tion con di tions can be eas - ily pro duced and main tained. The fol low ing work de scribes the out come of our ap proach to solve this prob lem. RESULTS AND DISCUSSION The crude glycosides from each plant were ob tained by liq uid-liquid par ti tion ing of the methanolic ex tract. With out further purification, the n-BuOH-soluble fraction of P. notoginseng and Astragalus membranaceus Bunge were used for this study. The CHCl3 -sol u ble frac tion from Colubrina asiatica, which con tains jujubogenin glycosides and fla vo - noids, 8,9 was also used for this study af ter re moval of flavo - noids by pass ing through a Sephadex LH-20 col umn. The re ac tion con di tions for ox i da tive deg ra da tion, an - hy drous and strongly ba sic, were de signed to be pro duced and main tained in situ to avoid any weak ness of this re ac tion. Based on this idea, the wa ter pres ent in the sol vent and the re - Jour nal of the Chi nese Chem i cal So ci ety, 2002, 49, 103-106 103 * Cor re sponding au thor. Tel: +886-2-391-6127; Fax: +886-2-391-6127; E-mail: shoeilee@ha.mc.ntu.edu.tw