Ritonavir Impurity S is a structurally related synthetic byproduct arising from the amidation step in Ritonavir production. It retains the core dipeptide scaffold (pyrrolidin-2-one and 3-methylbutyric acid moieties) but features an additional N-terminal cyclohexylmethyl group and a truncated C-terminal sulfonamide linkage compared to the parent compound. The molecule exhibits two chiral centers, a disulfide bridge, and a hydrophobic alkyl chain that disrupts the pharmacophoric interactions of Ritonavir. This impurity is generated via premature termination of the peptide coupling reaction, resulting in a non-pharmacologically active analog. It functions as a critical HPLC reference standard for quantifying process-related impurities in Ritonavir drug substance.
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