Fused aromatic phosphonates of structural formula I are precursors to inhibitors of protein tyrosine phosphatase-1B (PTP-1B). The compounds of the present invention are therefore useful for the treatment in a mammal of a disorder, condition, or disease responsive to inhibition of protein tyrosine phosphatase-1B, including Type 2 diabetes, insulin resistance, a lipid disorder, obesity, Metabolic Syndrome, and cancer.