title: Fast and selective labeling of N-terminal cysteines at neutral pH via thiazolidino boronate formation.
abstract: Facile labeling of proteins of interest is highly desirable in proteomic research as well as in the development of protein therapeutics. Herein we report a novel method that allows for fast and selective labeling of proteins with an N-terminal cysteine. Although N-terminal cysteines are well known to conjugate with aldehydes to give thiazolidines, the reaction requires acidic conditions and suffers from slow kinetics. We show that benzaldehyde with anortho-boronic acid substituent readily reacts with N-terminal cysteines at neutral pH, giving rate constants on the order of 103M-1s-1. The product features a thiazolidono boronate (TzB) structure and exhibits improved stability due to formation of the B-N dative bond. While stable at neutral pH, the TzB complex dissociates upon mild acidification. These characteristics make the TzB conjugation chemistry potentially useful for the development of drug-protein conjugates that release the small molecule drug in acidic endosomes.
authors.affiliation: A Department of Chemistry, Merkert Chemistry Center, Boston College, 2609 Beacon Street, Chestnut Hill, MA 02467.
authors.forename: Anupam
authors.initials: A
authors.lastname: Bandyopadhyay
authors.affiliation: A Department of Chemistry, Merkert Chemistry Center, Boston College, 2609 Beacon Street, Chestnut Hill, MA 02467.
authors.forename: Samantha
authors.initials: S
authors.lastname: Cambray
authors.affiliation: A Department of Chemistry, Merkert Chemistry Center, Boston College, 2609 Beacon Street, Chestnut Hill, MA 02467.
authors.forename: Jianmin
authors.initials: J
authors.lastname: Gao