. " represents H, CH3 or CH2 OH; and when R7 represents CH2 OH, R8 is then other than H and p equals 1; Otherwise p=0;Group (OC2 H3 R7) represents one or other of the following chains: ##STR9## R1 and R2 having the meanings given in paragraph (i); (iii) R4 represents the group: ##STR10## where n is 0 or 1 and R1, R2 and R3 have the meanings given above, R6 represents hydrogen, hydroxyl, halogen, an a" . . . .