Synthesis of desmosine-BSA/KLH conjugates via Sonogashira/Negishi cross-coupling reactions

Desmosine is an elastin crosslinking amino acid that is expected to be a useful biomarker of diseases related to elastin degradation including chronic obstructive pulmonary disease (COPD). In this study, conjugates of desmosine and carrier proteins, such as bovine serum albumin (BSA) and keyhole limpet hemocyanin (KLH), with linkers were designed and prepared for the creation of an effective antibody to be used in the development of an enzyme-linked immunosorbent assay (ELISA) system. Synthesis of desmosine along with the linkers having appropriate lengths was achieved via stepwise and chemo/regioselective palladium-catalyzed Sonogashira and Negishi cross-coupling reactions starting from an alkyne with protecting groups over nine steps. Subsequently, Michael addition with a thiolated carrier protein (BSA/KLH) was carried out using Traut’s reagent to afford seven types of desmosine-BSA/KLH conjugates.