Cyclic peptide analogs of somatostatin

A peptide of the formula:

• ##STR2## in which A.sub.1 is the D- or L-isomer of Cys;
• A.sub.2 is Asn, Gln, an aliphatic amino acid, an aromatic amino acid, or is deleted;
• A.sub.3 is an aromatic amino acid;
• A.sub.4 is His or an aromatic amino acid;
• A.sub.7 is Thr, Ser, or an aliphatic amino acid;
• A.sub.8 is an aromatic amino acid;
• A.sub.9 is the D- or L-isomer or Cys;
• each of R.sub.1 and R.sub.2 is, independently, H, C.sub.1-12 alkyl, C.sub.7-20 phenylalkyl, C.sub.11-20 naphthylalkyl, C.sub.1-12 hydroxyalkyl, C.sub.7-20 hydroxyphenylalkyl, C.sub.11-20 hydroxynaphthylalkyl, or COE.sub.1 where E.sub.1 is C.sub.1-12 alkyl, C.sub.7-20 phenylalkyl, C.sub.11-20 naphthylalkyl, C.sub.1-12 hydroxyalkyl, C.sub.7-20 hydroxyphenylalkyl, or C.sub.11-20 hydroxynaphthylalkyl;
• and
• R.sub.3 is NH.sub.2 or NH--Y--CH.sub.2 --Z where Y is a C.sub.1-12 hydrocarbon moiety and Z is H, OH, CO.sub.2 H, or CONH.sub.2 ;
• and
• a disulfide bond links the side chains of residues A.sub.1 and A.sub.9 ;
• or a pharmaceutically acceptable salt thereof.