Multinuclear 1 H/ 13 C/ 15 N chemical shift assignment of therapeutic octreotide acetate performed at natural abundance.

Octreotide acetate, the active pharmaceutical ingredient in the long-acting release (LAR) drug product Sandostatin®, is a cyclic octapeptide that mimics the naturally occurring somatostatin peptide hormone. Modern NMR can be a robust analytical method to identify and quantify octreotide molecules. Previous 1 H chemical shift assignments were mostly performed in organic solvents, and no assignments for heteronuclear 13 C, 15 N, and aromatic 1 H nuclei are available. Here, using state-of-the-art 1D and 2D homo- and heteronuclear NMR experiments, octreotide was fully assigned, including water exchangeable amide protons, in aqueous buffer except for 13 CO and 15 NH of F1, 15 NH of C2, and 15 NζHζ of K5 that were not observed because of water exchange or conformational exchange. The solution NMR spectra were then directly compared with 1D 1 H/ 13 C/ 15 N solid-state NMR (SSNMR) spectra showing the potential applicability of 13 C/ 15 N SSNMR for octreotide drug product characterization.