Chemistry of Fmoc Peptide Synthesis on Membranes

Abstract

Peptide synthesis is a repetitive procedure schematically shown in Fig. 1. Each cycle of deprotection, wash, coupling and wash introduces one amino acid building block (residue) to the growing chains anchored covalently to an insoluble solid support via the carboxy terminus. Temporary protection for the α-amino group of the incoming residue, which is removed in each cycle (deprotection), ensures that the residue is coupled to the growing chain only once. Coupling requires prior activation of the carboxy group of the incoming residue, as explained in more detail below. To prevent undesired reactions, the side-chain functional groups are also protected during the synthesis and are deprotected together at the end of the synthesis. Between individual operations, the support has to be thoroughly washed in order to remove excess reagents from the growing chains. This is actually the most important feature of solid-phase peptide synthesis (SPPS) for which Bruce Merrifield was awarded the Nobel Prize in 1984. Typically, the peptides are cleaved from the support together with the side-chain protecting groups, but there are several experimental procedures, which require solid-phase-bound peptides. The SPOT technique uses membranes as the solid support and enables the parallel synthesis and testing of hundreds to thousands of peptides at different locations on one membrane (Frank 1992).