Cholecystokinin Heptapeptide Analogues Containing Amino Acids with Branched Side-Chains in Positions 2, 5, and 7

Using solid phase synthesis we prepared the cholecystokinin (CCK) fragment Boc-CCK-7 (Boc-Tyr(SO−3Na+)-Met-Gly-Trp-Met-Asp-PheNH2), designated Ia, and six analogues, Ib-Ig. In the analogues Ib and Ic the methionine (Met) residue in the carboxyterminal part of the molecule was substituted for L- or D-2,4,6-trimethylphenylalanine (PheMe3). In the analogues Id and Ie phenylalanine (Phe) was substituted by L- or D-PheMe3 and neopentylglycine (Neo) was inserted in place of this Met residue, and in the analogues If and Ig, in addition to PheMe3 substitution in the carboxy terminus, both Met residues were replaced by Neo. Gall bladder and anorectic bioassays of these analogues revealed that most of them behaved as CCK-8 agonists. Insertion of a substituted aromatic side-chain in the place of the Met5 residue led to suppression and dissociation (analogue Ib) or extinction (Ic) of the investigated biological activities while a combination of the branched amino acid residues of the L-configuration in analogue Id preserved dissociation of gall bladder and anorectic activity observed in Boc/Neo5/CCK-7 with a prolongation of anorectic effect. A combination of the same residues in the L- and D-configurations in analogue Ie, decreased by 10 the biological activities measured. The biological potency of analogues If and Ig with both Met residues substituted for Neo was, without significant dissociation, 3 to 10 times lower and differed in both analogues depending on the configuration of the PheMe3 residue. The analogue If with L-PheMe3 was more potent than its D-PheMe3 isomer, confirming a necessity for the L-amino acid residue in the carboxy terminus for biological activity