Simultaneous Multiple Synthesis of Peptide Amides by the Multipin Method. Application of Vapor-Phase Ammonolysis

Abstract

A method for simultaneously preparing large numbers of peptide amides is described. Side-chain deprotected, support-bound peptide esters (1) and (2) are incubated with ammonia/tetrahydrofuran vapor. The cleaved peptide amides (3) are then eluted from the support with a solvent of choice. The approach is demonstrated in conjunction with the multipin method of multiple peptide synthesis. In this study, chromophoric model systems of support-bound 4-(oxymethyl)benzamido esters of the geneti- cally coded amino acids (except Cys) (4) and glycolamido esters of Ile, Val and Pro (5) were cleaved using the vapor from solutions of 30% ammo- nia in tetrahydrofuran, methanol, and 2-propanol. The best yields were obtained with 30% ammonia in tetrahydrofuran. Although the hindered amino acid esters (4) (Ile, Val, Pro) cleaved with poor efficiency, the corresponding glycolamido esters (5) (Ile, Val, Pro) cleaved with >90% efficiency upon treatment with ammonia/tetrahydrofuran vapor. Racemiza- tion studies on a selection of dipeptides cleaved by the method demons- trated that only low levels of racemate were generated. The approach gives ready access to hundreds to thousands of discrete peptide amides in quantities (10-100 nmol) sufficient for most biological, immunologi- cal, and pharmacological studies