[ETA(5)-CYCLOPENTADIENYL]METAL TRICARBONYL PYRYLIUM-SALTS - NOVEL REAGENTS FOR THE SPECIFIC CONJUGATION OF PROTEINS WITH TRANSITION ORGANOMETALLIC LABELS

New specific reagents for the conjugation of organo transition metal s pecies to proteins are described. These reagents are pyrylium salts be aring a (eta(5)-C5H4)M(CO)(3) (M = Mn and Re) at position 4. They coup le with simple amines (n-butylamine and tert-butylamine) and to lysine side chains of proteins (bovine serum albumin and lysozyme) with vary ing yields. In almost all cases, the final conjugated species is a pyr idinium salt, with the exception of lysozyme, for which the reaction e nds at the divinylogous amide form. Differences in reactivity for bovi ne serum albumin and lysozyme can be explained in terms of differences of isoelectric point and steric local environment around the reactive lysine residue.