The GLP-1 analog liraglutide was acquired commercially (Hørsholm Pharmacy). Native GLP-1, native GLP-2, and the GLP-2 analog teduglutide were prepared by automated solid-phase peptide synthesis (SPPS) using the Fmoc/tBu strategy on pre-loaded PHB TentaGel resin (Rapp polymere GmbH, Tuebingen, Germany). The couplings were performed using Fmoc-Nα-protected amino acids, N,N-diisopropylcarbodiimide and ethyl cyanoglyoxylate-2-oxime (oxyma) in N,N-dimethylformamide (Iris Biotech GmbH, Marktredwitz, Germany) for 2 × 2 h. The N-deprotections were performed using 40% piperidine in N-methyl-2-pyrrolidione (Iris Biotech GmbH, Marktredwitz, Germany) for 3 min followed by 20% piperidine in N-methyl-2-pyrrolidione for 17 min. Finally, the peptide was simultaneously side-chain deprotected and released from the solid support by a TFA cocktail containing trifluoro acetic acid (TFA) (Iris Biotech GmbH, Marktredwitz, Germany), triethylsilane (Sigma–Aldrich, Brøndby, Denmark), and H2O (95/2.5/2.5) as scavengers for 2 h. The peptide was precipitated by the addition of diethylether (Sigma–Aldrich, Brøndby, Denmark). The peptide was purified by RP-HPLC and identified by LC-MS. The final products were obtained with >95% purity.
Wismann P., Barkholt P., Secher T., Vrang N., Hansen H.B., Jeppesen P.B., Baggio L.L., Koehler J.A., Drucker D.J., Sandoval D.A, & Jelsing J. (2017). The endogenous preproglucagon system is not essential for gut growth homeostasis in mice. Molecular Metabolism, 6(7), 681-692.
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