A practical synthesis of the ¹³C/¹⁵N- labelled tripeptide N-formyl- Met-Leu-Phe, useful as a reference in solid- state NMR spectroscopy

• Sven T. Breitung,
• Jakob J. Lopez,
• Gerd Dürner,
• Clemens Glaubitz,
• Michael W. Göbel and
• Marcel Suhartono

Beilstein J. Org. Chem. 2008, 4, No. 35, doi:10.3762/bjoc.4.35

• [16][17]. (See Supporting Information File 1.) In case of a successful peptide extension, the Fmoc-protecting group was removed with piperidine (25% in DMF). Afterwards, the last coupling step was started by adding a solution of 13C/15N-labelled Fmoc-Met-OH (250 mg, 0.66 mmol), HOBt*H2O (145 mg, 0.945

• mmol) and DIC (145 µL, 0.945 mmol) in NMP (2.5 mL). In case of quantitative coupling (Kaiser test), the Fmoc-protecting group was removed and the resin was washed with DMF (5 ×) and CH2Cl2 (5 ×). The beads were dried in the syringe under reduced pressure. Formylation of the N-terminus: For the