MECHANISMS OF REDUCTIVE METHYLATION OF NAD+ ANALOGS BY A TRANS-DIMETHYLCOBALT(III) COMPLEX

Various NAD+ analogues are readily reduced by a trans-dimethylcobalt(III) complex, trans-[CoMe2(L)] (L = 11-hydroxy-2,3,9,10-tetramethyl-1,4,8,11-tetraazaundeca-1,3,8,10-tetraene-1-olate), to yield the corresponding methylated NADH analogues, while cis-dialkyl- or monoalkylcobalt(III) complexes show no reactivity towards NAD+ analogues. The charge distribution of the NAD+ analogues, as well as the thermodynamic stability of the products, is shown to be an important factor in determining the isomer distribution of the methylated products. The observed second-order rate constants for the reduction of NAD+ analogues by trans-[CoMe2(L)] in acetonitrile at 298 K are much larger than those estimated for outer-sphere electron transfer from trans-[CoMe2(L)] to NAD+ analogues.