9-[(PHOSPHONOALKYL)BENZYL]GUANINES - MULTISUBSTRATE ANALOG INHIBITORSOF HUMAN ERYTHROCYTE PURINE NUCLEOSIDE PHOSPHORYLASE

A series of 9-[(phosphonoalkyl)benzyl]guanines was synthesized and tes ted for inhibition of human erythrocyte purine nucleoside phosphorylas e (PNPase). Inhibitors of PNPase should be T-cell selective, immunosup pressive agents with potential clinical utility in the treatment of a wide variety of disorders in which T-lymphocytes are pathogenic. An in itial set of six analogues of the weak PNPase inhibitor 9-benzylguanin e (2) contained a phosphonic acid group linked to the ortho, meta, or para position of the aryl moiety via two-or three-atoms pacers. These compounds allowed us to probe for a favorable interaction with the pho sphate-binding domain. Several additional meta phosphonoalkyl substitu ents were examined in an effort to optimize the spacer. The two most p otent compounds, -9H-purin-9-yl)methyl]benzyl]oxy]-methylphosphonic ac id (3f) and 9H-purin-9-yl)methyl]benzyl]-thio]methylphosphonic acid (3 j), were inhibitors of PNPase with K(i)'s of 5.8 and 1.1 n M, respecti vely. These inhibitors displayed competitive kinetics with respect to inosine and inorganic phosphate, which showed that these compounds pos sess binding determinants for both the purine- and phosphate-binding d omains of the enzyme, characteristics that are consistent with 3f and 3j being multisubstrate analogue inhibitors of PNPase. The potency of 9-benzylguanine (2) was enhanced more than 6000-fold by linking a phos phonic acid residue with a (methylthio)methyl spacer to the meta posit ion of 2 to give 3j, which illustrates the potent enzyme inhibitory pr operties available to multisubstrate analogue inhibitors.