dimethyl rotundioate 、 alkaline earth salt of/the/ methylsulfuric acid 生成 (3S,4S,4aR,6aR,6bS,8aS,11R,12R,12aS,14aR,14bR)-3,12-Diacetoxy-4,6a,6b,11,12,14b-hexamethyl-2,3,4,4a,5,6,6a,6b,7,8,9,10,11,12,12a,14,14a,14b-octadecahydro-1H-picene-4,8a-dicarboxylic acid dimethyl ester