Rare .alpha.-alkyl isomers of cobalamins: synthesis, characterization, and properties of two diastereomers of the .alpha.-alkylcobalamin, .alpha.-(2-oxo-1,3-dioxolan-4-yl)cobalamin

The synthesis, characterization, 2-D NMR (HOHAHA, NOESY, HMQC, and HMBC spectroscopies), and reactivities of a new α-alkylcobalamin are described (an α-alkylcobalamin has the axial alkyl group attached to the cobalt from the «bottom» or α face of the corrin ring). The α-alkylcobalamin, α-(2-oxo-1,3-dioxolan-4-yl) cobalamin (1), is the first example of an α-alkylcobalamin with a secondary alkyl group and the first case with a chiral alkyl group (i.e., where α-alkylcobalamin diastereomers are produced). It is also the first α-alkylcobalamin completely characterized (HPLC, UV-visible, IR, FAB-MS, and 1- and 2-D NMR methods). Anaerobic photolysis converts 1 to its β isomer, β-(2-oxo-1,3-dioxolan-4-yl) cobalamin (2), where the alkyl group is now attached to the cobalt from the usual, β or «top» side of the corrin