Endothelin antagonistic cyclic pentapeptides

A cyclic pentapeptide of the formula:

• cyclo (--X.sup.1 --X.sup.2 --X.sup.3 --X.sup.4 --X.sup.5 --) (I)
• wherein X.sup.n (n=1-5) represents amino acid residues, respectively, and X.sup.1 is D-Phe, D-Tyr, D-Tha, D-Tza, D-Nal, D-Bta, D-Trp, D-Trp(O), D-Trp(CHO) or D-Trp((CH.sub.2).sub.m COR.sup.1), wherein m is from 0 to 6, and R.sup.1 is a hydroxyl group, a C.sub.1 -C.sub.6 alkoxy group, an amino group or a C.sub.1 -C.sub.6 monoalkylamino group, provided that when m=0, R.sup.1 is not a hydroxyl group;
• X.sup.2 is D-Asp, D-Glu, or D-Cys(O.sub.3 H);
• X.sup.3 is Pro, Hyp, Pip, Thz, .beta.-Ala, Gly, Ala, .alpha.-Aba, Aib, Val, Nva, Leu, Ile, aIle, Nle, Met, Met(O), Met(O.sub.2), Phe, Tza, Tha, Tyr, Trp, His, Arg, Lys, Lys(CHO), Orn, Orn(CHO), Asn, Gln, Asp, Glu, Cys(O.sub.3 H), Cys, Ser or Thr wherein those .alpha.-amino acids having a hydrogen atom on the .alpha.-amino group are optionally substituted by a C.sub.1 -C.sub.6 alkyl or C.sub.3 -C.sub.7 cycloalkyl group which optionally has a group selected from the group consisting of an imidazolyl group, a carboxyl group, a sulfo group and a hydroxy group;
• X.sup.4 is D-Ala, D-Thr, D-.alpha.-Aba, D-Val, D-Nva, D-Leu, D-Ile, D-aIle, D-Nle, D-tert-Leu, D-Cpg, D-Chg, D-Dpg, D-Pen, Aib, Ac.sub.3 c, Ac.sub.4 c, Ac.sub.5 c, Ac.sub.6 c, Ac.sub.7 c, D-Phg, D-Thg, D-Fug, D-Tzg or D-Itg wherein those .alpha.-amino acids having a hydrogen atom at the .alpha.-position are optionally substituted by a C.sub.1 -C.sub.3 alkyl group;
• X.sup.5 is Pro, Pip, Thz, His, Ala, .alpha.-Aba, Val, Nva, Leu, Ile, aIle, Nle, Met, C.sub.3 al, C.sub.4 al, C.sub.5 al or C.sub.6 al wherein those .alpha.-amino acids having hydrogen atom on the .alpha.-amino group are optionally substituted by a C.sub.1 -C.sub.6 alkyl group;
• or a pharmaceutically acceptable salt thereof.