Synthesis and characterization of two potential impurities (des‐ethyl‐Ganirelix) generated in the Ganirelix manufacturing process

Abstract

Controlling certain diseases using peptide drugs has remarkably increased in the past two decades. In this regard, a generic formulation is an upfront solution to fulfill market demands. Ganirelix, a leading peptide active pharmaceutical ingredient (API) primarily used as a gonadotropin‐releasing hormone antagonist (GnRH), has established a potential market value worldwide. But its generic formulation mandates detailed impurity profiles from a synthetic source and contemplates the sameness of a reference‐listed drug (RLD). Post‐chemical synthesis and processing of Ganirelix, some commercial sources have revealed two new potential impurities among many known, which show the deletion of an ethyl group from the hArg(Et)2 residue at the sixth and eighth positions, named des‐ethyl‐Ganirelix. These impurities are unprecedented in traditional peptide chemistry, and such monoethylated‐hArg building blocks are not easily accessible commercially to synthesize these two impurities. Here, we have outlined the synthesis, purification, and enantiomeric purity characterization of the amino acids and their incorporation in the Ganirelix peptide sequence to synthesize these potential peptide impurities. This methodology will enable the convenient synthesis of side‐chain substituted Arg and hArg derivatives in peptide drug discovery platforms.

Synthesis of Novel Arginine Building Blocks with Increased Lipophilicity Compatible with Solid-Phase Peptide Synthesis

“…The conversion of amines into guanidines with thiourea and S-methylthiourea requires initial activation with mercury [10,[15][16][17][18] or copper salts [18], diisopropylcarbodiimide (DIC) [19], N-iodosuccinimide (NIS) [20], 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide (EDC) [21] or 1-methyl-2-chloropyridinium iodide (Mukaiyama's reagent) [10,17,[20][21][22]. Amines can also be converted into guanidines by using S-methylthiourea preactivated by methyl iodide [23]. N-trifluoromethanesulfonyl (triflyl) guanidines (E, Figure 1b) were described for the first time in 1998 [2,8] and represent a novel class of functionalized guanidines efficient for guanidinylation of amines [24], amino acid derivatives and peptides in solution [8], as well as on the solid support [2,8].…”