A compound represented by formula (I): ** Formula ** or a pharmaceutically acceptable salt, wherein: R1 and R2 are independently selected from the group consisting of hydrogen, methyl and ethyl； R1 and R2 together can be>； = O； also, R1 and R2 together with the connecting carbon atom can form a 3-membered carbon ring； A is selected from the group consisting of phenyl, phenyl substituted with R3, pyridinyl, pyridinyl substituted with R4, pyrimidinyl, pyrimidinyl substituted with R5, pyrrolyl, pyrrolyl substituted with R6, pyridazinyl, pyridazinyl substituted with R7, pyrazolyl and pyrazolyl substituted with R8； R3 is 1 to 5 substituents independently selected from the group consisting of halogen, (C1-C3) alkyl, (C2-C3) alkenyl, (C3-C4) cycloalkyl, (C1-C3) alkoxy, trifluoromethyl and cyano； R4 is 1 to 4 substituents independently selected from the group consisting of halogen, (C1-C3) alkyl, (C2-C3) alkenyl, (C3-C4) cycloalkyl, (C1-C3) alkoxy, trifluoromethyl and cyano； R5 is 1 to 3 substituents independently selected from the group consisting of halogen, (C1-C3) alkyl, (C2-C3) alkenyl, (C3-C4) cycloalkyl, (C1-C3) alkoxy, trifluoromethyl and cyano； R6 is 1 to 4 substituents independently selected from the group consisting of (C1-C3) alkyl, (C2-C3) alkenyl, and (C3-C4) cycloalkyl； R7 is 1 to 3 substituents independently selected from the group consisting of halogen, (C1-C3) alkyl, (C2-C3) alkenyl, (C3-C4) cycloalkyl, (C1-C3) alkoxy, trifluoromethyl and cyano； R8 is 1 to 3 substituents independently selected from the group consisting of (C1-C3) alkyl, (C2-C3) alkenyl, and (C3-C4) cycloalkyl.Un compuesto representado por la fórmula (I):**Fórmula** o una sal farmacéuticamente aceptable, en donde: R1 y R2 se seleccionan independientemente del grupo que consiste en hidrógeno, metilo y etilo； R1 y R2 juntos pueden ser >；= O； también, R1 y R2 junto con el átomo de carbono que los conecta pueden formar un anillo de carbono de 3 miembros； A se selecciona del grupo que consis
