Evaluation of cotton as a carrier for solid-phase peptide synthesis.

Cotton as a new support for the solid-phase synthesis of peptides was evaluated under the conditions of both Boc/Bzl and Fmoc/But strategy. Syntheses of peptides containing only bifunctional amino acids gave comparable results, but peptides containing trifunctional amino acids are clearly advantageously synthesized using the Fmoc approach. The comparison of cotton with other planar carriers (paper or polypropylene membranes) and with classical pellicular ones has shown practical applicability of cotton as the replacement of more sophisticated carriers. N-Methylimidazole was shown to be the optimal acylation catalyst for the modification of the cellulose carrier. Stability of the ester bond to the cotton was studied and shown to be adequate for the syntheses of small to medium size peptides. A relatively low level of substitution of cotton carrier in connection with its ability to soak the solvent was used for the complete elimination of a synthetic vessel. Couplings can be performed by wetting the carrier with the coupling solution, and all solvents can be removed either by squeezing it together with a porous material (paper) or by centrifugation. This leads to a significant decrease of solvent consumption. The efficiency of solvent elimination by centrifugation was demonstrated by the synthesis of model peptide ACP 65-74 in which only one wash between coupling and deprotection and between deprotection and coupling was used and which afforded the product of the same quality as the product synthesized using the standard protocol. Bromophenol blue monitoring has been proven as the optimal way of monitoring the acylation reaction progress. Peptides directly bound to cotton were shown to be useful in enzyme-linked immunosorbent assay tests.