Synthesis and characterization of iodopropyl derivatives of adenosine 3′,5′-cyclic-monophosphate: Potential affinity labels of cAMP binding sites in enzymes

Abstract

The syntheses of two potential cAMP affinity lables, 1,N ⁶-(3-iodopropyleno)adenosine 3′,5′-cyclic-monophosphate and 2′-O-(2-iodo-3-hydroxypropyl) adenosine 3′,5′-cyclic-monophosphate, by a two-step chemical procedure are described. TheN ⁶- and 2′-O-allyl intermediates were prepared selectively by alkylation of cAMP in organic and alkaline aqueous solutions, respectively. Treatment of theN ⁶-allyl derivative withN-iodosuccinimide resulted in iodine addition to the double bond and cyclization to theN ¹ position of the purine ring. The iodohydrin analog was synthesized by reaction of 2′-O-allyl-cAMP with potassium iodide and thallium trichloride in acetate buffered solution. The products were isolated by column chromatography and characterized by thin-layer chromatography, elemental analysis, and ultraviolet,¹³C, and¹H NMR spectroscopy. The cAMP analogs were found to react with lysine and cysteine. Both cAMP derivatives were tested for their reaction with the low-K _m cAMP phosphodiesterase of human platelets. The ribose-substituted analog functioned as a competitive inhibitor (K _I=0.72 μM) and caused a time-dependent irreversible inactivation of the phosphodiesterase. In contrast, the purine-substituted derivative acted neither as a reversible competitive inhibitor nor as an irreversible inactivator of the enzyme. These results indicate the specificity of these potential cAMP analogs in their interaction with the phosphodiesterase.