THE 2ND ISOLABLE B-12-THIOLATE COMPLEX, (PENTAFLUOROPHENYLTHIOLATO)COBALAMIN - SYNTHESIS AND CHARACTERIZATION

The synthesis, isolation, and characterization of (pentafluorophenylth iolato)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 accomplish ed by the dropwise addition of 0.93 equiv of C6F5SH in MeOH under argo n to 1 equiv of HOCbl . HOAc (50.7 mg) in MeOH, all at -15 degrees C a nd under darkened, red-light-only conditions. The desired C6F5SCbl pro duct was precipitated by the addition of cold, degassed acetone, isola ted, and then characterized by FABMS and UV-visible, H-1 NMR, and F-19 NMR spectroscopies. Also reported is a H-1 NMR method for the detecti on of impurities in cobalamins. With the requisite, isolable RSCbl pre cursor to RS. and (.)Cbl radicals now in hand, the needed chemical pre cedent studies of the proposed H-. abstraction step from the substrate in ribonucleoside triphosphate reductase by a RS. analogue of the pro tein-S-. site an now possible.