Further investigation of the structural requirements of a series of benzylphosphonic acid inhibitors of human prostatic acid phosphatase has led to the highly potent series of α- aminobenzylphosphonic acids. The α-benzylaminobenzylphosphonic acid, with an IC50= 4 nM, exhibited a 3500-fold improvement in potency over the carbon analogue, α-phenylethyl. The enhanced potency may be due to a combination of four favorable interactions ...