Derivatives of indole useful in treating oesteoporosis

A compound of formula (I) or a salt thereof, or a solvate thereof, wherein: A represents an optionally substituted aryl group or an optionally substituted heterocyclyl group; Ra represents -CO-NRsRt wherein Rs and Rt each independently represents hydrogen, alkyl, substituted alkyl, optionally substituted alkenyl, optionally substituted aryl, optionally substituted arylalkyl, optionally substituted heterocyclyl or an optionally substituted heterocyclylalkyl group, or Rs and Rt together with the nitrogen to which they are attached form a heterocyclyl group; R1 and R2 each independently represents hydrogen, hydroxy, amino, alkoxy, optionally substituted aryloxy, optionally substituted benzyloxy, alkylamino, dialkylamino, halo, trifluoromethyl, trifluoromethoxy, nitro, alkyl, carboxy, carbalkoxy, carbamoyl, alkylcarbamoyl, or R1 and R2 together represent methylenedioxy, carbonyldioxy or carbonyldiamino; and R3 represents hydrogen, alkanoyl, alkyl, aminoalkyl, hydroxyalkyl, carboxyalkyl, carbalkoxyalkyl, carbamoyl or alkylsulphonyl and arylsulphonyl; a process for the preparation of such a compound, a pharmaceutical composition containing such a compound and the use of such a compound or composition in medicine.