A new polymer-supported TBTU (P-TBTU) has been prepared from polystyrene-bound 1-hydroxybenzotriazole (P-HOBT) and used efficiently as a solid-supported reagent for custom peptide synthesis reactions, and is even effective with wet solvents. The P-HOBT can be recovered by simple filtration and reused for the preparation of new P-TBTU.
Insoluble 1-hydroxybenzotriazole-bound polystyrene was prepared through a series of chemical modifications of commercially available polystyrene. Reaction of 3-nitro-4-chlorobenzyl alcohol or of 3-nitro-4-chlorobenzyl bromide with polystyrene in the presence of aluminium trichloride yielded (3-nitro-4-chloro)benzylated polystyrene. Upon reaction with hydrazine it was converted to (3-nitro-4-hydrazine)benzylated polystyrene which was cyclized, by acidolysis, to yield 1-hydroxybenzotriazole-bound polystyrene.
This was coupled, using N,N' -dicyclohexylcarbodiimide as the coupling agent, to many N-blocked amino acid derivatives, yielding polymeric polystyrene-bound active esters. Such derivatives are highly reactive and their efficacy in the synthesis of several custom peptide synthesis, including that of the tetrapeptide Boc- l -Leu- l -Leu- l -Val- O Bzl- l -Tyr- O Bzl and of thyrotropin-releasing hormone was demonstrated.