Zinc Substitution of Cobalt in Vitamin B12: Zincobyric acid and Zincobalamin as Luminescent Structural B12‐Mimics

摘要

Replacing the central cobalt ion of vitamin B12 by other metals has been a long‐held aspiration within the B12‐field. Herein, we describe the synthesis from hydrogenobyric acid of zincobyric acid (>Znby) and zincobalamin (>Znbl), the Zn‐analogues of the natural cobalt‐corrins cobyric acid and vitamin B12, respectively. The solution structures of >Znby and >Znbl were studied by NMR‐spectroscopy. Single crystals of >Znby were produced, providing the first X‐ray crystallographic structure of a zinc corrin. The structures of >Znby and of computationally generated >Znbl were found to resemble the corresponding Co^II‐corrins, making such Zn‐corrins potentially useful for investigations of B12‐dependent processes. The singlet excited state of >Znby had a short life‐time, limited by rapid intersystem crossing to the triplet state. >Znby allowed the unprecedented observation of a corrin triplet (E ^T=190 kJ mol⁻¹) and was found to be an excellent photo‐sensitizer for ¹O2 (ΦΔ=0.70).