Analogs of Cholecystokinin-heptapeptide (CCK-7), i.e., two epimers of 3-(-sulfooxyphenyl)-2-methylpropanoyl-Met-Gly-Trp-Met-Asp-Phe-NH2, two epimers of 3-(4-sulfooxyphenyl)-2-methylpropanoyl-Nle-Gly-Trp-Met-Asp-Phe-NH2 and [D-Try(SO3H)1]-CCK-7, were prepared by the solution method. The analgesic effects of these analogs were measured by means of the writhing test. These analogs produced analgesic effects after subcutaneous injection in mice. The replacement of the tyrosine(O-sulfate) residue at position 1 by a 3(4-sulfooxyphenyl)-2-methyl-propanoyl group enhanced the analgesic effect, and the configuration of these residues hardly influenced the effect. On the other hand, the replacement of the L-methionine residue at position 2 by an L-norleucine residue in addition to the exchange of the tyrosine(O-sulfate) residue at position 1 for a 3-(4-sulfooxyphenyl)-2-methylpropanoyl group reduced the activity.
Enantiomeric piperazin-2-one derivatives, N, N'-ethylene-bridged alanylphenylalanines (1a or 1b), were synthesized using (S)- or (R)-alanine and phenylalanine as starting materials, and were inserted into the second and third positions of enantiomeric pseudo-tetrapeptides (P1a- or P1b-OEt). The corresponding piperazine derivatives (1a-or 1b-sRed) obtained by selective BH3 reduction of the amide carbonyl groups of 1a or 1b were similarly inserted into the same positions of tetrapeptides (P1a- and P1b-sRed). Enantiomeric N, N'-ethylene-bridged tyrosyltyrosine derivatives (2a or 2b) obtained from (S)- or (R)-tyrosine were also inserted into the first and second positions of two pairs of enantiomeric tetrapeptides (P2a- and P2b-OEt or P'2a- and P'2b-OEt). The opiate activities of the eight peptides thus obtained were studied by use of the mouse vas deferens and the guinea pig ileum assays in order to elucidate the structure-activity relationships of these peptides, especially with respect to stereochemistry.
between llll/dddd enantiomers of Tyr-Arg-Phe-Lys-NH2 and crown ether selectors. Enantioselective proton shifts were observed in studied tetrapeptide tyrosine and phenylalanine residues exclusively for llll enantiomer upon binding with S-(3,3′-diphenyl-1,1′-binaphthyl)-20-crown-6 selector (and dddd enantiomer with R-(3,3′-diphenyl-1,1′-binaphthyl)-20-crown-6 selector), indicating that these two amino acid