(2S)-2-(9H-Fluoren-9-ylmethoxycarbonylamino)-3-(1H-tetrazol-5-yl)propanoic acid and (2S)-2-(9H-fluoren-9-ylmethoxycarbonylamino)-3-(2H-tetrazol-5-yl)propanoic acid (Compound SP410, Fmoc-Ala(5-Tet)-OH) (900 mg, 2.37 mmol) were dissolved in tetrahydrofuran (2.7 ml), N,N-diisopropylethylamine (0.36 mL, 2.61 mmol) was added and the mixture was stirred for 5 minutes. A solution of trityl chloride (628 mg, 2.25 mmol) dissolved in tetrahydrofuran (0.6 ml) was added to the aforementioned reaction solution, and the mixture was stirred for 90 minutes. The reaction solution was filtered, and the collected reaction solution was concentrated under reduced pressure, and the residue was purified by reverse-phase silica gel column chromatography (10 mM aqueous ammonium acetate solution/methanol) to afford (2S)-2-(9H-fluoren-9-ylmethoxycarbonylamino)-3-(1-trityltetrazol-5-yl)propanoic acid and (2S)-2-(9H-fluoren-9-ylmethoxycarbonylamino)-3-(2-trityltetrazol-5-yl)propanoic acid (Compound SP409, Fmoc-Ala(5-Tet(Trt))-C)H) (644 mg, 44%).
