Preparation of [3α-^3H]3β-Hydroxy-18β-and 3α-Hydroxy-18(β and α)-glycyrrhetic Acid and Radioimmunoassay of Glycyrrhetic Acid

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[3α-^3H]3β-Hydroxy-18β-glycyrrhetic acid (5) for radioimmunoassay (RIA) of glycyrrhetic acid (GA) was prepared along with a small amount of the 3α-hydroxy compound (6) by the reduction of 3-oxo-18β-GA (1) with [^3H]sodium borohydride.The ratios of 3β-hydroxy to 3α-hydroxy-GA (7 : 8 and 9 : 10) in the reduciton products of 3-oxo-GA (1 and 2) with sodium borohydride, with hindered borohydride and with aluminum isopropoxide were determined by high-performance liquid chromatography. Sodium borohydride and potassium tri-sec-butyl borohydride allowed stereoselective reduction of the 3-oxo group to the 3β-hydroxy and 3α-hydroxy group, respectively, leaving the 11-oxo group untouched. Potassium-tri-sec-butyl borohydride was the most useful reducing agent for preparation of 3α-hydroxy-GA(8 and 10) from 3-oxo-GA.Separation of the bound and free fraction for RIA of GA, in which anti-glycyrrhetyl-30-glycine-bovine serum albumin antiserum was used as the antibody, was carried out by a double antibody method using a goat antiserum to rabbit immunoglobulin G. A satisfactory standard curve for RIA of GA was obtained in the range of 2-200 ng/ml. The accuracy of this RIA of serum samples without extraction of GA from them is high, and should be satisfactory for application to pharmacodynamic studies of GA.
公益社団法人日本薬学会の論文
1988-09-25