Compounds of the general formula (I) and the salts thereof, preferably the pharmaceutically acceptable salts thereof; in which R
1
is straight-chain C
1-8
-alkanoyloxy, straight-chain C
1-8
-alkoxy, straight-chain C
1-8
-alkoxy-straight-chain-C
1-8
-alkoxy, straight-chain C
1-8
-alkoxycarbonylamino, straight-chain C
0-8
-alkylcarbonylamino, optionally N-mono- or N,N-di-C
1-8
-alkylated amino or hydroxy or straight-chain omega-hydroxy-C
1-8
-alkyl.
通式(I)及其盐的化合物,优选其药用可接受的盐;其中R1为直链C1-8-烷酰氧基,直链C1-8-烷氧基,直链C1-8-烷氧基-直链C1-8-烷氧基,直链C1-8-烷氧羰基
氨基,直链C0-8-烷基羰基
氨基,可选N-单或N,N-二C1-8-烷基化的
氨基或羟基或直链ω-羟基-C1-8-烷基。