Gem-diphosphonic acids, and pharmaceutical compositions containing them

Compounds of formula (I) ##STR17## wherein:

• R.sub.1 and R.sub.2, which can be the same or different, are hydrogen or C.sub.1 -C.sub.4 alkyl:
• (A) is hydrogen or hydroxy,
• (B) is a straight or branched C.sub.1 -C.sub.8 alkylene or, together with the adjacent nitrogen atom, a group of formula ##STR18## wherein the groups N(R.sub.3) and (CH.sub.2).sub.n may be in the 1,1;
• 1,2;
• 1,3;
• or 1,4 position of the ring;
• m is the integer 5 or 6;
• n is an integer 1 to 5;
• R.sub.3 is hydrogen, straight or branched C.sub.1 -C.sub.9 alkyl;
• (C) is straight or branched C.sub.1 -C.sub.5 alkylene, phenylene, an aralkylene chain of formula ##STR19## in which n is as above defined;
• R.sub.4 is hydrogen or a group of formula ##STR20## in which R.sub.7 and R.sub.8, which are the same or different, are hydrogen, straight or branched C.sub.1 -C.sub.6 alkyl, or one of R.sub.7 and R.sub.8 is as above defined and the other one is a group of formula ##STR21## in which R.sub.9 is hydrogen, straight or branched C.sub.1 -C.sub.4 alkoxy;
• R.sub.5 and R.sub.6 are 2-haloethyl or R.sub.5 and R.sub.6, together with the nitrogen atom to which they are bound, are a 1-aziridinyl residue of formula ##STR22## and isomers, diastereoisomers, and pharmaceutically acceptable salts thereof.