| abstract |
A compound of the formula : <CHEM> wherein R<1> is aryl which may have suitable substituent(s), X is -O- or <CHEM> (in which R<3> is hydrogen or lower alkyl), A is a bond or lower alkylene which may have lower alkyl group(s), and R<2> is hydrogen or an acyl group, and a pharmaceutically acceptable salt thereof, processes for their preparation and pharmaceutical compositions comprising them as an active ingredient in admixture with pharmaceutically acceptable carriers. |