| 摘要 |
Method of providing an analgesic effect by administring compounds having the general formula I <IMAGE> (I) in which each of R1 and R4 is independently hydrogen or a C1-4 alkyl, and each of R2 and R3 is independently hydrogen, fluorine, chlorine, bromine or a C1-4 alkyl or their pharmaceutically acceptable salts. The invention provides also compounds of fromula (I) where each of R1, R2 and R3 is independently hydrogen or C1-4 alkyl.
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