The present invention is directed to compounds of the general formula I and pharmaceutically acceptable salts thereof: ##STR1## wherein: R=ethyl, propyl or isopropyl; and A=(CH.sub.2).sub.n wherein n is 2, 4 or 5, and C(CH.sub.2).sub.3.
本发明涉及一般式I的化合物及其药学上可接受的盐:##STR1## 其中:R = 乙基,丙基或异丙基; A = (CH.sub.2).sub.n,其中n为2、4或5,以及C(CH.sub.2).sub.3。