A compound of general formula (I): ##STR00017## in which R is an amino or guanidino group; R.sup.2 is acetyl or trifluoroacetyl; X is CONH, NHCO or O; n is an integerfrom 2 to 6; and Y is C.sub.2 C.sub.8 alkyl, C.sub.3 C.sub.8 cycloalkyl, C.sub.1 C.sub.4 alkoxyalkyl, an amino acid or dipeptide, or a pharmaceutically acceptable salt, ether, ester or salt of such ester thereof, with the proviso that