tert-Butoxycarbonylaminoacyl-4-(oxymethyl)phenylacetamidomethyl-resin, a more acid-resistant support for solid-phase peptide synthesis

Abstract

Some of the peptide chains esterified to the hydroxymethyl-poly(styrene-co-divinylbenzene) resin are lost by acidolysis during solid-phase peptide synthesis. This loss has been minimized by using 4-(hydroxymethyl)phenylacetamidomethylpoly(styrene-co-divinylbenzene) as the solid support. The phenylacetamidomethyl (Pam) bridge between the peptide and the resin is sufficiently electron withdrawing that the peptidyl-OCH2-Pam-resin is 100 times more stable than the conventional peptidyl-OCH2-resin to cleavage of the ester bond by 50% trifluoroacetic acid in dichloromethane. Boc-Val-OCH2-Pam-resin, which was prepared by two routes, compared favorably with Boc-Val-OCH2-resin for synthesis of the model peptides leucylalanylglycylvaline and decalysylvaline. The greater acid stability of the Pam-resin is expected to result in much higher yields of large peptides prepared by solid-phase peptide synthesis.The solid support commonly used for solid-phase peptide synthesis,3 ie/T-butoxycarbonylaminoacyloxymethylpoly(styrene-co-divinylbenzene), is not completely stable under the acidic conditions required to remove the iert-butoxycarbonyl (Boc) group.4"7 Acidolysis of the benzyl ester link be-

HF‐Free Boc Synthesis of Peptide Thioesters for Ligation and Cyclization

“…Chain loss was considerably slower with the MPAL linker presumably because of the comparably more hindered terminal leucine residue. In both cases the loss of amino acid was in general agreement with previous measurements 22. Although there was chain loss with the MPAL linker, at 1 % over 500 min, it was suitable for in situ neutralization cycles (Figure 1 B).…”

“…The use of Merrifield resin for Boc SPPS was largely abandoned when 4‐(Hydroxymethyl)phenylacetamidomethyl (PAM) and 4‐methylbenzylhydrylamine (MBHA) resins were introduced, primarily because of reported peptide cleavage by TFA over the prolonged (20 min) TFA cleavage cycles 22. However, contemporary Boc SPPS in situ neutralization protocols with their shorter, typically, 2×1 min treatment with TFA per cycle14 are more suitable.…”

“…For this, we used hydroxymethyl resin derivatized with Fmoc‐Gly because Gly is one of the more acid labile residues22 and Fmoc provides a good reporter to monitor loss. The rate of Fmoc‐Gly cleavage by neat TFA was monitored directly by following the release of Fmoc by UV (Figure 1 B).…”

Bruce Merrifield and solid‐phase peptide synthesis: A historical assessment

“…6 What about the SPPS of peptides larger than glucagon, say 90 to 100 residues? Mitchell et al developed a more acid stable PAM resin support [48][49][50] and Kent and coworkers improved the synthetic protocols used with PAM resins and introduced in situ neutralization into SPPS using Boc/Benzyl chemistry for the rapid, efficient synthesis of difficult sequences. 51 In addition, several side reactions were examined and eliminated.…”

Phosphorylation of high‐ and low‐molecular‐mass atrial natriuretic peptide analogs by cyclic AMP‐dependent protein kinase

“…Atrial peptide analogs were synthesized by the Merrifield method using PAM resin [10] for peptide acids, and mBHA resin [11] for peptide amides. Peptides were cleaved from the resins with liquid HF/anisole (9: 1, v/v) for 60 min at 0°C.…”