TETA polystyrene

Cleavage of proteins at methionine with cyanogen bromide yields peptides that have homoserine at the COOH-terminus. Treatment of the peptide with anhydrous trifluoroacetic acid results in a lactone that is sufficiently activated to undergo aminolysis by aliphatic amines (Horn, 1975) or sequencing resins (Wachter et ai, 1975 Horn and Laursen, 1973 Bridgen, 1975) (Fig. 5). In this way, peptides are selectively attached at the COOH-terminus without the need for amino or carboxyl protection. Resins incorporating a )5-diamine structure, such as triethylenetetramine (TETA) polystyrene (Horn and Laursen, 1973) and j8-aminoethylaminopropylglass... 

The first resins used for sequencing were derived from cross-linked polystyrene beads, primarily because of their availability and chemical stability and ease of introducing reactive functional groups [synthetic methods are discussed in more detail by Laursen (1975b)]. Two polystyrene-based supports have been used, aminopolystyrene (1) (Laursen et a/., 1975) and TETA polystyrene (2) (Horn and Laursen, 1973), both of which are derived from... 

The TETA resin (2) is most useful for coupling peptides activated by the homoserine lactone or carbonyldiimidazole methods, which are carried out at essentially alkaline pH. Under these conditions the 1,2-diamine structure increases the nucleophilicity of the amino groups by general base catalysis (Page and Jencks, 1972) (Fig. 6). Because the amino groups are at a distance from the polystyrene backbone, it is often possible to attach peptides containing as many as 50-60 residues. 

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