Transition metal (‘Fischer-type’) carbene complexes as protein labelling reagents

The electrophilic property of metallocarbenes of Fischer-type was used to label amino acid derivatives and a model protein in a regio-specific manner with a transition heavy metal complex. Hence, the reaction of (CO)5WC(OMe)Me (1) was shown to involve exclusively the amino group of a series of α-amino esters whether this function was carried by the α-carbon or by the side chain, leading to stable aminocarbenes. With a model protein, namely bovine serum albumin, labelling also occurred involving solely the amine function of some of its lysine residues. Coupling yield was shown to depend both on the pH where the reaction was carried out, and on the quantity of carbene. This work could find an application in the field of protein X-ray crystallography.