In 5 ml of anhydrous N,N-dimethylformamide was dissolved 0.334 g of the compound obtained in Example 16, to which was added 0.132 g of sodium N-methyldithiocarbamate, folowed by stirring at room temperature for 1.5 hour. To the reaction mixture was added 30 ml of ethyl acetate, which was washed with water and then dried (MgSO4). The solvent was distilled off under reduced pressure, and the residue was subjected to a silica gel column chromatography, followed by elution with ethyl acetate-chloroform-methanol (15:15:1). Fractions containing the end product were combined and concentrated under reduced pressure to give 0.206 g of the subject compound as powders.
