Improved Two-Step Synthesis of d -Penicillamine: Mechanistic Insights and Structural Identification of Key Process-Related Substances

A two-step synthetic route to d-penicillamine from penicillin G potassium (KpenG) was developed and improved, building upon a previously reported one-pot method. This process improvement increased the overall isolated yield from 39.94% to 69.20%. Guided by high-performance liquid chromatography (HPLC) monitoring, a stepwise feeding strategy was employed to isolate and prepare the process-related substances. Comprehensive structural characterization of these substances was performed using NMR, MS, and IR spectroscopy. This work is the first to elucidate the dominant reaction pathway for d-penicillamine formation, in which hydrazine hydrate acts as the nucleophile to cleave KpenG, while potential degradation pathways are also clarified. Accordingly, the study provides essential mechanistic insights and practical guidance for optimizing the laboratory-scale synthesis of d-penicillamine, establishing a foundation for future scale-up studies.