Preparation of Glycyrrhetic Acid .BETA.-Glycosides Having .BETA.(1.RAR.2)-Linked Disaccharides by the Use of 2-O-Trichloroacetyl-.BETA.-D-pyranosyl Chlorides and Their Cytoprotective Effects on Hepatic Injury in Vivo.

Stepwise glycosidation was adopted for the construction of glycyrrhetic acid beta-glycosides (27-30) having beta (1-->2)-linked disaccharides such as 2-O-beta-D-glucuronopyranosyl-beta-D-glucopyranose, 2-O-beta-D-glucuronopyranosyl-beta-D-galactopyranose, 2-O-beta-D-glucopyranosyl-beta-D-glucuronopyranose and 2-O-beta-D-galactopyranosyl-beta-D-glucuronopyranose. In the first glycosidation, 2-O-trichloroacetyl-beta-D-payranosyl chlorides (9-11) were utilized as starting sugar derivatives to react with methyl glycyrrhetinate (5): Glycosidation of 5 with 9 and 10 gave beta- and alpha-monoglycosides (12) and (13), and (15) and (16), respectively. Treatment of the beta-glycosides 12 and 15 with ammonia-saturated ether gave products (14) and (17), respectively. The glycosidation of 5 with 11 followed by treatment with ammonia-saturated ether gave compounds (18) and (19), respectively. The second step glycosidations of 14 and 17 with methyl 2,3,4-tri-O-acetyl-alpha-D-glucuronatopyranosyl bromide (20) gave diglycoside derivatives (23) and (24), respectively, and that of 18 with 2,3,4,6-tetra-O-acetyl-alpha-D-glucopyranosyl bromide (21) and -alpha-D-galactopyranosyl bromide (22) gave diglycoside derivatives (25) and (26), respectively. The removal of the protecting groups of 23-26 gave diglycosides 27-30, respectively, having a beta-D-glucuronopyranose (beta-D-glcUA) as one of two sugar components in the molecules. The cytoprotective effects of the synthesized glycosides 27-30 on carbon tetrachloride (CCl4)-induced hepatotoxicity in vivo were compared with diglycosides 31-33 having only neutral sugar components and naturally occurring glycyrrhizin (34) having two acidic sugar components (beta-D-glcUA).(ABSTRACT TRUNCATED AT 250 WORDS)