Potent and selective irreversible inhibitor of Cdc25 dual specificity phosphatases (Ki values are 32, 96 and 40 nM for inhibition of Cdc25A, -B and -C respectively). Displays 125 - 180-fold selectivity over VH1-related dual-specificity phosphatase and protein tyrosine phosphatase 1b. Inhibits carcinoma cell growth and blocks G2/M phase transition in vitro.