Compounds of formula (I):
or, where appropriate, a solt or amide thereof, wherein R' is hydrogen or C1-6 alkyl; R2 is hydrogen or CO2R3 where R3 is hydrogen or C1-8
alkyl; X and X' are independently a double or triple bond; A and B are hydrogen when X is a double bond or A and B
are both absent when X is a triple bond; A' and B' are hydrogen when X' is a double bond or A' and B' are both absent when X' is a triple bond;
n is 0 or an integer of from 1 to 4; and m is an integer of from 2 to 7; processes for preparing such compounds; pharmaceutical compositions containing such compounds and the use of such compounds and compositions in medicine.