SPPS is quick and easy approach to synthesizing peptides and small proteins. The C-terminal amino acid is attached to a cross-linked polystyrene resin via an acid labile bond with a linker molecule. This resin is insoluble in the solvents used for synthesis, making it relatively simple and fast to wash away excess reagents and by-products. The N-terminus is protected with the Fmoc group, which is stable in acid, but removable by base. Any side chain functional groups are protected with base stable, acid labile groups.

Chemical Description

To begin each coupling, the Fmoc group on the resin bound amino acid/peptide is removed with 20% piperidine in N,N-dimethyl formamide (DMF). It is then rinsed and a protected amino acid is added which has been activated at its 'alpha' carboxyl group. The activation is achieved by creating the N-hydroxybenzotriazole (HOBt) ester in situ. The activated A.A. and the resin bound A.A. are allowed to react in the presence of base to form a new peptide bond. This process is repeated until the desired peptide is assembled at the resin.

Once the peptide is complete, it is ready to be cleaved from the resin. This is accomplished using a mixture of trifluoroacetic acid (TFA) and scavangers. Scavangers serve to neutralize cations which are formed during the removal of the side chain protecting groups. The solution is at least 82% TFA, and the rest a mixture of phenol, thioanisol, water, ethanedithiol (EDT), and triisopropylsilane (TIS). The peptide on the resin is allowed to react with the cleavage mixture for several hours, which then affords the peptide in solution. It can then be precipitated and washed in tert-butyl methyl ether, and analyzed or purified as desired.