Synthesis and Properties of Cobalamin Derivatives Incorporating Halogenated Alkenyl Ligands
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Synthesis of organocobalamins has been shown to be a complex process due to the conditions required to coordinate the organic molecules to the cobalt metal centre. It has been found that due to the light and air sensitive nature of typical organocobalamins, a strict air-free and dark environment is required to successfully synthesise the desired compounds. There is an abundance of literature reported on alkyl and alkynylcobalamins compared with alkenylcobalamins. The attempted synthesis of halogenated vinylcobalamins was conducted using two different methods to coordinate a halogenated alkenyl ligand to the cobalt metal centre of vitamin B12. The reduction method used sodium borohydride and a reverse addition of the reduced Co(I) species to the ligand resulted in several different complexes being produced. The final attempt of this method resulted in the formation of a new compound, shown by the new aromatic peaks observed in the 1H NMR spectrum. Unfortunately, this new compound was unable to be fully characterised due to decomposition, and the LC-MS results proved inconclusive. The reduction-free method used copper(I) acetate to remove the cyanide ligand from the beta axial site and a base, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), to deprotonate the trichloroethene ligand. In the final attempt of this method, it was found that a room temperature reaction for 4 hours resulted in the observation of several new compounds. The 1H NMR spectrum from this synthesis indicated a new major complex was present in the product mixture, with five new aromatic proton peaks (7.24 ppm, 6.85 ppm, 6.82 ppm, 6.25 ppm, and 6.05 ppm). However, once again LC-MS analysis of the product mixture was inconclusive.