Pyrylium ions are useful reagents to selectively modify the amino group of
protein lysine residues. This property was exploited here to label proteins
with chromium tricarbonyl complexes in the form of 4-benchrotrenyl pyridin
ium ions. Kinetic studies of the reaction of a series of benchrotrenyl pyry
lium salts with water and n-butylamine were performed and revealed that the
overall reactivity of these compounds was highly dependent on their substi
tution pattern. These compounds could find application in protein X-ray cry
stallography. (C) 1999 Elsevier Science Ltd. All rights reserved.