biologically active , backbone - cyclized peptides of the formula : ## str1 ## wherein aa ! or a 1 a 1 ! is a naturally occurring or synthetic amino acid residue , n or e is an integer of 1 - 10 , m or d is 0 or an integer of 1 - 10 , r is a naturally occurring or synthetic amino acid side - chain , e is a hydroxyl moiety or a carboxyl protecting group of a blocking group , optionally covalently attached to an insoluble polymeric support , and the circled line designates a spacer group of ## str2 ## for formula i wherein m is -- s -- s --, -- co -- nh -- or -- s -- and p and q each is an integer of 2 - 10 , or --. sub . p --. sub . x -- y for formula ii wherein m is an amino or carboxyl group or a sulfur atom , p is an integer of 2 - 10 , x is 0 or 1 and y is a side - chain of a backbone amino acid . also , processes for the preparation of these peptides and pharmaceutical compositions containing them .