Reactions of fac-[Re(CO)3(H2O)3]+ with nucleoside diphosphates and thiamine diphosphate in aqueous solution investigated by multinuclear NMR spectroscopy

Products formed between monoester diphosphates (MDPs) and fac-[Re(CO)(3)(H2O)(3)]OTf at pH 3.6 were examined. Such adducts of the fac [Re(CO)(3)](+) moiety have an uncommon combination of properties for an inert metal center in that sharp NMR signals can be observed, yet the products are equilibrating at rates allowing NMR EXSY cross-peaks to be observed. Thiamine diphosphate (TDP) and uridine 5'-diphosphate (5'-UDP) form 1:1 bidentate {P alpha,P beta} chelates, in which the MDP binds Re(l) via P alpha and P beta phosphate groups. Asymmetric centers are created at Re(I) (R-Re/S-Re) and P alpha (Delta/Lambda), leading to four diastereomers. The two mirror pairs of diastereomers (R-Re Delta/S-Re Lambda) and (R-Re Lambda/S-Re Delta) for TDP (no ribose) and for all four diastereorners (R-Re Lambda. R-Re Lambda S-Re Lambda, S-Re Lambda) for 5'-UDP (asymmetric ribose) gave two and four sets of NMR signals for the bound MDP, respectively. P-31 alpha-P-31 alpha EXSY cross-peaks indicate that the fac-[Re(CO)(3)(H2O)({P alpha, P beta} MDP)]- isomers interchange slowly on the NMR time scale, with an average k approximate to 0.8 s-1 at 32 degrees C the EXSY cross-peaks could arise from chirality changes at only Re(l) or at only P alpha. Guanosine 5'-diphosphate (5'.-GDP), with a ribose moiety and a Re(l)-binding base, formed both possible diastereomers (R-Re and S-Re) of the fac-[Re(CO)(3)(H2O)({N7,P beta}GDP)]- macrochelate, with one slightly more abundant diastereomer suggested to be R-Re by Mn2+, ion H-1 NMR signal line-broadening combined with distances from molecular models. Interchange of the diastereomers requires that the coordination site of either N7 or P beta move to the H2O site. P-31 alpha-P-31 alpha EXSY cross-peaks indicate a k approximate to 0.5 s(-1) at 32 degrees C for R-Re-tO-S-Re interchange. The similarity of the rate constants for interchange of fac-[Re(CO)(3)(H2O)({P alpha,P beta}MDP)]- and fac-[Re(CO)(3)(H2O)(tN7,P beta}GD,P)]- adducts suggest strongly that interchange of P beta and H2O coordination positions accounts for the EXSY cross-peaks present in the spectra of all adducts.