Removal of the phosphate group in mechanism-based inhibitors of inositol monophosphatase leads to unusual inhibitory activity

Inositol monophosphatase is widely held to be the therapeutic target for inhibition by lithium ion in the treatment of bipolar disorder. In a continued effort to improve the bioavailability of alternative inhibitors, we have designed and tested two new series of compounds; phosphonates and product-like mimics. Phosphonate substrate mimics were competitive inhibitors of reduced potency as compared to phosphate based inhibitors. Product mimics however, showed various inhibitory modes of action. The 6-butylamino derivative 6p was an uncompetitive inhibitor when acting alone (K(i)= 0.3 mM) but displayed non-competitive inhibition in the presence of inorganic phosphate. This compound represents a new lead in the search for a viable replacement for lithium ion therapy.