| Popis: |
The influence of both the peptide-chain lengths of Boc-oligopeptides and the degree of crosslinking of polymer supports on the coupling efficiencies of the C-terminal amino acids of Bocoligopeptides in the coupling reactions with terminal free amino groups of amino acids linked to polymer supports was investigated. The coupling efficiencies of Boc-oligopeptides (consisting of 3 to 10 amino acid residues) relative to those of Boc-Val-OH or Boc-Met-OH were determined by competitive coupling reactions with amino acids anchored to soluble and crosslinked polystyrene supports, using four systems of coupling reagents dicyclohexylcarbodiimide (DCC) + 1-hydroxy-1 H-benzotriazole, DCC + N-hydroxysuccinimide, DCC + N-hydroxy-5-norbornene-2,3-dicarboximide, and N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline. In the coupling reactions on soluble polystyrene supports, containing 1 mol-% of an amino acid (per styrene monomeric unit), and on poly(styrene-co-divinylbenzene (1%)), containing 1 or 10 mol-% of an amino acid, little influence of peptide-chain lengths was observed. In reactions with amino acids anchored to poly(styrene-co-divinylbenzene (2%)) (containing 2 or 20 mol-% of terminal amino groups), an increase in peptide-chain length of Boc-oligopeptides was found to reduce remarkably the coupling efficiencies of their C-terminal amino acids. With poly(styrene-co-divinylbenzene (2%))s as supports, it was detected that amino groups are present which are sterically inaccessible for peptide fragments such as Boc-Ala-Ala-Leu-Leu-Leu-OH and Boc-Ala-Ala-Leu-Leu-Leu-Pro-Pro-Leu-Leu-Leu-OH. |
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