SIMULTANEOUS MULTIPLE SYNTHESIS OF PEPTIDE AMIDES BY THE MULTIPIN METHOD - APPLICATION OF VAPOR-PHASE AMMONOLYSIS

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 genetically coded amino acids (except Cys) 4 and glycolamido esters of Ile, Val and Pro 5 were cleaved using the vapor from solutions of 30% ammonia in tetrahydrofuran) methanol, and 2-propanol. The best yields were obtained with 30% ammonia in tetrahydrofuran. When methanol was used as cosolvent, the amide products were contaminated with methyl ester. When ammonia gas alone was used, very poor yields were recorded. Although the hindered amino acid esters 4(Ile, Val, Pro) cleaved with poor efficiency, the corresponding glycolamido esters S(Ile, Val, Pro) cleaved with >90% efficiency upon treatment with ammonia/tetrahydofuran vapor. Racemization studies on a : selection of dipeptides cleaved by the method demonstrated that only low levels of racemate were generated. Four test peptides 16-19 were prepared and characterized to demonstrate the general utility of the method. The approach gives ready access to hundreds to thousands of discrete peptide amides in quantities (10-100 nmol) sufficient for most biological, immunological, and pharmacological studies.