Phosphorylation of serine, threonine, and tyrosine controls fundamental mammalian cell events and is achieved by kinases which, in turn, are in dynamic relationship with phosphatases. Few selective inhibitors of protein tyrosine and dual specificity phosphatases are readily available. Based on SAR studies of naturally occurring phosphatase inhibitors and following up on previously published research, we have designed a new pharmacophore model V and synthesized a new library of functional analogues of V. All synthetic steps were carried out and optimized employing combinatorial chemistry methods on Wang resin. All compounds were tested in vitro for their ability to inhibit recombinant human protein tyrosine (PTP1B) and dual-specificity (Cdc25B(2) and VHR) phosphatases. Th ree of the approximately 70 compounds in our library inhibited Cdc25B(2) by 50% at 375-490 mu M. No compounds inhibited PTP1B, and only one blocked VHR. Cell-culture studies revealed no toxicity to human breast cancer cells with two of the phosphatase inhibitors. (C) 2000 John Wiley & Sons, Inc.