| abstract |
(57) [Summary] The present invention provides a compound of the formula (I): wherein R 1 and R 2 are independently hydroxy or alkoxy of 1 to 4 carbon atoms. And R 3 and R 4 are independently methyl or ethyl, or R 3 and R 4 together with the nitrogen atom to which they are attached are pyrrolidino, methylpyrrolidino, dimethylpyrrolidino, piperidino, morpholino or hexamethyleneimino ring Which comprises administering a therapeutically effective amount of a compound of formula (I) to the subject. |