Redox‐Neutral Syntheses and Electrochemical Studies of 10‐Bromo‐Substituted Light‐Stable Antivitamin B ₁₂ Candidates

This publication describes the straightforward and redox-neutral synthesis of 10-bromophenylethynylcobalamin its facile conversion to 10-bromoaquacobalamin. In this approach, phenylethynyl ligand acts as convenient light-stable protecting group that is removed in quantitative yield under acidic conditions. The proteolytic cleavage at pH 2.0 was studied pseudo-first-order conditions 1.5 times slower than phenylethynylcobalamin with a hydrogen instead bromine C(10). Preliminary electrochemical studies organometallic ethynyl-Cbls (Cbl=cobalamin) are reported for first time. A reduction potential −0.94 V vs. Ag/AgCl determined CoIII/CoI 10-bromophenylethynylcobalamin. positive shift 180 mV compared agreement earlier related cyanocobalamins.