To a suspension of the the commercially available aminomethylated polystyrene resin (Novabiochem) (20 g, 16 mmol) in dimethylformamide (70 ml) was added a solution of the commercially available BAL-Linker (PerSeptive Biosystems GMBH) (12.88 g, 48.0 mmol) and 1-hydroxybenzotriazole (7.26 g, 48.0 mmol) in 70 ml of dimethylformamide. To this was added N,N′-diisopropylcarbodiimide (6.06 g, 48.0 mmol) followed by N,N-diisopropylethylamine (6.19 g, 48.0 mmol). The reaction was allowed to stir 20 h at room temperature. The resin was filtered and washed as follows: 3×dimethylformamide (50 ml), 3×tetrahydrofuran (50 ml), 3×dichloromethane (50 ml), 3×ether (50 ml). The resin was dried in vacuo and isolated: 23.92 g. IR spectroscopy showed an aldehyde stretching band at 1674 cm−1. To a part of this resin (0.200 g, 0.160 mmol) in 1,2-dichloroethane (8 ml) at room temperature, was added benzyl amine (0.171 g, 1.60 mmol) followed by sodium triacetoxyborohydride (0.339 g, 1.60 mmol). The reaction was allowed to shake 20 h at room temperature, filtered and washed as follows: 3×dimethylformamide/water (90/10) (8 ml); 3×dimethylformamide (8 ml); 3×dichloromethane (8 ml). The resin was suspended in dimethylformamide, treated with (8-naphthalen-1-ylmethyl-4-oxo-1-phenyl-1,3,8-triaza-spiro[4.5]dec-3-yl)-acetic acid (0.274 g, 0.640 mmol), 1-hydroxybenzotrazole (0.099 9, 0.640 mmol) and N,N′-diisopropylcarbodiimide (0.081 g, 0.640 mmol). The reaction was allowed to shake for 20 h at room temperature. The resin was filtered, suspended in dimethylsulfoxide and heated to 40° C. for 1 h. The resin was again filtered, suspended in dimethylsulfoxide (8 ml) and heated to 40° C. for 1 h. The resin was filtered and washed as follows: 3×dimethylformamide/water (90/10) (8 ml); 3×dimethylformamide (8 ml); 3×dichloromethane (8 ml) and air-dried. The resin was treated with trifluoroacetic acid/water (95/5) (8 ml) for 1 h at room temperature. The filtrate was collected and concentrated in vacuo to give the desired product.
