Chemoselective ligation based on a molecular lock mechanism using squarate moiety in aqueous buffer

ORGN 633

Yan-Yeung Luk, yluk@syr.edu and Preeti Sejwal, psejwal@syr.edu. Department of Chemistry; Department of Biomedical and Chemical Engineering, Syracuse University, 1-014 CST, 111 College Place, Syracuse, NY 13244
We report a new highly chemoselective reaction that proceeds in an aqueous buffer tolerating the presence of a wide variety of amino acids including lysine. This reaction is between a cysteine or the N-terminus cysteine of a peptide and a modified squarate moiety. We will present our working hypothesis of a molecular lock mechanism, which guided us to fine-tune of the squarate derivatives to achieve high selectivity with quantitative yield in aqueous buffer. In contrast to the reaction of maleimide-thiol coupling, our reaction can tolerate the presence of an internal cysteine within a peptide, and thus provides a means to expand the scope peptide immobilization methodology. Furthermore, the squarate substrate is not degraded by the key relevant enzymes from cells. We will present our on-going exploration of using this ligation in a living mammalian cell to interrogate difficult cell signaling pathways involving glycosylation.