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D Timms

Publications and source records attributed to D Timms.

25 records · Page 2Linked to original sources
PubMed1986

New delta-receptor antagonists.

A new delta-selective opiate antagonist has been synthesised in which the two glycine residues of diallyl leucine enkephalin have been replaced by 4-aminobenzoic acid. The compound has a different conformation to that of ICI 174,864 (N,N-diallyl-Tyr-Aib-Aib-Phe-Leu).

Animals↗
PubMed1983

Divergent structure activity relationships in series of enkephalin agonists and cognate antagonists.

Diallylation of the amino group of [Leu]enkephalin methyl ester yields a moderately potent, delta-selective opiate receptor antagonist. The diallyl congeners of a larger range of potent mu-and delta-selective enkephalin agonists have been prepared and were found to be weak, non-selective antagonists as assessed by their ability to antagonise the effects of normorphine and [Leu]enkephalin on the field-stimulated mouse vas deferens. Conversely, whereas [Gly3 psi (CH2S)Phe4,Leu5]enkephalin and [Gly3 psi(CH2S)-D-Phe4,Leu5]enkephalin are virtually inactive as opiate agonists the corresponding diallyl analogues are moderately potent, highly selective delta-antagonists. Analogues of diallyl[Leu]enkephalin in which the Gly2 and Gly3 residues have been replaced by D- and L- Ala have also been prepared and tested as delta-receptor antagonists. In addition, the empiric energy program ECEPP has been used to derive eighteen low energy conformations of diallyl[Leu]enkephalin and to estimate the effect of the D- and L-Ala substitutions on the conformer energies. Two conformers were identified for which there was a partial correlation between the variations in conformational energy and delta-antagonist potency.

Animals↗
PubMedDate not supplied

Construction of protein analogues by site-specific condensation of unprotected fragments.

The extreme sensitivity to periodate of 1-amino, 2-hydroxy compounds permits the selective conversion of N-terminal serine and threonine to an aldehydic group. We have used this reaction to construct analogues of human granulocyte colony stimulating factor (G-CSF) by allowing such oxidized peptides to react with others that have had a hydrazide derivative attached to the C-terminus by reversed proteolysis. Two recombinant analogues of G-CSF were used as starting materials. Both had only a single lysine residue (at position 62 and 75, respectively) followed immediately by a serine. Digestion of each analogue by the lysine-specific protease from Achromobacter lyticus gave two fragments, one of which could be N-terminally oxidized and the other converted to the C-terminal hydrazide derivative by reversed proteolysis using the same enzyme. After preliminary studies with model peptides, we first reacted the corresponding peptide pairs together and then, in order to eliminate the 64-74 disulfide loop, fragment 1-62 from the first analogue with fragment 76-174 from the second. Reactions are efficient (up to 80% product based on the oxidized fragment) and take place under very mild conditions. The hydrazone bond can easily be stabilized by reduction with NaBH3CN. This method represents a new, reasonably general route for the construction of large protein chimeras of precisely controlled structure.

Amino Acid Sequence↗
PubMedDate not supplied

Site-specific religation of G-CSF fragments through a thioether bond.

A new approach is described for linking, through a thioether bond, the C-terminus of one unprotected polypeptide with the N-terminus of another. Homocysteine thiolactone is attached to the C-terminus of one polypeptide by reverse proteolysis and provides through hydroxylamine treatment a free sulfhydryl group. The alpha-amino group of a second polypeptide is selectively iodoacetylated by reaction with iodoacetic anhydride at pH 6.0 or the N-hydroxysuccinimide ester derivative at pH 7.0. Coupling of the two modified fragments occurs in a spontaneous alkylation reaction under mild conditions. After preliminary experiments with small peptides, this approach was extended to large protein fragments derived from recombinant analogs of G-CSF by enzymatic digestion. This approach provides a means of making head-to-tail protein chimeras or introducing noncoded structural elements into a protein.

Acetylation↗