The Second Isolable B12-Thiolate Complex, (Pentafluorophenylthiolato)cobalamin: Synthesis and Characterization

The synthesis, isolation, and characterization of (pentafluorophenylthiolato)cobalamin, C 6 F 5 SCbl, are reported, only the second isolable RSCbl known. The synthesis of C 6 F 5 SCbl in 81% yield is accomplished by the dropwise addition of 0.93 equiv of C 6 F 5 SH in MeOH under argon to 1 equiv of HOCbl·HOAc (50.7 mg) in MeOH, all at −15 °C and under darkened, red-light-only conditions. The desired C 6 F 5 SCbl product was precipitated by the addition of cold, degassed acetone, isolated, and then characterized by FABMS and UV−visible, 1 H NMR, and 19 F NMR spectroscopies. Also reported is a 1 H NMR method for the detection of impurities in cobalamins. With the requisite, isolable RSCbl precursor to RS • and • Cbl radicals now in hand, the needed chemical precedent studies of the proposed H • abstraction step from the substrate in ribonucleoside triphosphate reductase by a RS • analogue of the protein−S • site are now possible.