Structure–reactivity relationship for the cobalt(III) complex-catalysed hydrolysis of adenosine 3′,5′-cyclic monophosphate1

Abstract

Hydrolysis of adenosine 3′,5′-cyclic monophosphate (cAMP) by cobalt(III) complexes [Co(N₄)(H₂O)₂]³⁺ (N₄: two diamines or one tetraamine) has been systematically studied at pH 7 and 50 ^oC. Both the catalytic activity and the product distribution are highly dependent on the nature of the amine ligand. The relative catalytic activities are cyclen (4000) > trien (500) > (tme)₂ (57) > tren (37) > (tn)₂ (22) > 2,3,2-tet (7) > (en)₂ (1) ≫ cyclam, cth, dien. The pseudo-first-order rate constant for the cyclen complex (0.05 M) is 1.2 h^-1 (half-life 35 min), corresponding to a 10¹⁰-fold acceleration with respect to the uncatalysed reaction. Of the two P–O linkages in cAMP, the cyclen, the trien and the 2,3,2-tet complexes preferentially cleave the P–O(5′) linkage, whereas the (tme)₂ and the (tn)₂ complexes promote P–O(3′) scission. Adenosine is the main product for hydrolysis by the (tme)₂ complex, whereas adenosine monophosphates as the hydrolysis intermediates are accumulated in the catalysis by the trien complex.