Deltorphin analogues were substituted by a series of achiral CR,R-dialkyl cyclic R-amino acids (1-aminocycloalkane-1-carboxylic acids, Acxc, where x ) a hexane, pentane, or propane cycloalkane ring) in position 2, 3, 4, or 2 and 3 in deltorphin C, and in position 2 in [Ac6c2,- des-Phe3]deltorphin C hexapeptide. Receptor assays indicated that even though Ac6c2 and Ac6c3 exhibited a diminished Kiä by ca. 20-fold (2.5-3.3 nM) relative to deltorphin C (Kiä ) 0.15 nM), selectivity was marginally elevated (Kií/Kiä ) 1250) or enhanced by about 70%, and both peptides fitted stringent iterative calculations for a two-site binding model (è ) 0.625 and 0.766, respectively, P < 0.0001). The disubstituted [Ac6c2,3]- or [Ac6c2,des-Phe3]deltorphin analogues yielded peptides with decreased Kiä, such that the latter peptide was essentially inactive. The presence of Ac5c or Ac3c in place of Phe3 further diminished Kiä (15.4 to 19.0 nM), yet ä selectivity only fell about one-half (Kií/Kiä ) 440 and 535, respectively), and only the former peptide fitted a two-site binding model (è ) 0.799). The replacement of Asp4 by Ac6c, Ac5c, or Ac3c produced essentially nonselective analogues through the acquisition of high í affinities (2.5, 0.58, and 0.27 nM, respectively) while maintaining high ä affinities (Kiä ) 0.045-0.054 nM) which were about 3-fold greater than that of deltorphin C. Using pharmacological assays in vitro (mouse vas deferens and guinea pig ileum), position 3-substituted analogues all indicated substantial losses in bioactivity, whereas substitution by 1-aminocycloalkanes at the fourth position retained high ä activity. In fact, the bioactivity of [Ac3c4]deltorphin C indicated a peptide with relatively weak ä selectivity, which was comparable to the observations with the receptor binding data. In summary, the data confirmed that (i) ä selectivity occurs in the absence of D-chirality at position 2, (ii) the aromaticity of Phe3 is replaceable by an achiral residue with a hydrophobic ring-saturated side chain, and (iii) the acquisition of dual high-affinity analogues occurs through the elimination of the anionic function at position 4 and replacement by an amino acid with a hydrophobic side chain.
Design and synthesis of 1-aminocycloalkane-1-carboxylic acid-substituted deltorphin analogues: Unique delta and mu opioid activity in modified peptides
GUERRINI, Remo;SALVADORI, Severo;
1996
Abstract
Deltorphin analogues were substituted by a series of achiral CR,R-dialkyl cyclic R-amino acids (1-aminocycloalkane-1-carboxylic acids, Acxc, where x ) a hexane, pentane, or propane cycloalkane ring) in position 2, 3, 4, or 2 and 3 in deltorphin C, and in position 2 in [Ac6c2,- des-Phe3]deltorphin C hexapeptide. Receptor assays indicated that even though Ac6c2 and Ac6c3 exhibited a diminished Kiä by ca. 20-fold (2.5-3.3 nM) relative to deltorphin C (Kiä ) 0.15 nM), selectivity was marginally elevated (Kií/Kiä ) 1250) or enhanced by about 70%, and both peptides fitted stringent iterative calculations for a two-site binding model (è ) 0.625 and 0.766, respectively, P < 0.0001). The disubstituted [Ac6c2,3]- or [Ac6c2,des-Phe3]deltorphin analogues yielded peptides with decreased Kiä, such that the latter peptide was essentially inactive. The presence of Ac5c or Ac3c in place of Phe3 further diminished Kiä (15.4 to 19.0 nM), yet ä selectivity only fell about one-half (Kií/Kiä ) 440 and 535, respectively), and only the former peptide fitted a two-site binding model (è ) 0.799). The replacement of Asp4 by Ac6c, Ac5c, or Ac3c produced essentially nonselective analogues through the acquisition of high í affinities (2.5, 0.58, and 0.27 nM, respectively) while maintaining high ä affinities (Kiä ) 0.045-0.054 nM) which were about 3-fold greater than that of deltorphin C. Using pharmacological assays in vitro (mouse vas deferens and guinea pig ileum), position 3-substituted analogues all indicated substantial losses in bioactivity, whereas substitution by 1-aminocycloalkanes at the fourth position retained high ä activity. In fact, the bioactivity of [Ac3c4]deltorphin C indicated a peptide with relatively weak ä selectivity, which was comparable to the observations with the receptor binding data. In summary, the data confirmed that (i) ä selectivity occurs in the absence of D-chirality at position 2, (ii) the aromaticity of Phe3 is replaceable by an achiral residue with a hydrophobic ring-saturated side chain, and (iii) the acquisition of dual high-affinity analogues occurs through the elimination of the anionic function at position 4 and replacement by an amino acid with a hydrophobic side chain.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
