Exploring the potential of the vitamin B12 derivative azidocobalamin to undergo Huisgen 1,3-dipolar azide-alkyne cycloaddition reactions

• Published in: Journal of inorganic biochemistry 2024-05, Vol.254, p.112504-112504, Article 112504
• Main Authors: Stackpole, Ben J., Fredericksen, Jessica M., Brasch, Nicola E.
• Format: Article
• Language: English
• Subjects: Azide-alkyne cycloaddition; Bioconjugate; Click reaction; Cobalamin; Huisgen cycloaddition; Vitamin B12
• ISSN: 0162-0134; 1873-3344
• DOI: 10.1016/j.jinorgbio.2024.112504

There is considerable interest in using the metalloprotein cofactor vitamin B12 as a vehicle to deliver drugs and diagnostic agents into mammalian or bacterial cells by exploiting the B12-specific active uptake pathways. Conjugation of the cargo via the β-axial site or the 5’-OH of the ribose of the nucleotide are the most desirable sites, to maximise intracellular uptake. Herein we show the potential of conjugation at the beta-azido ligand of the vitamin B12 derivative azidocobalamin via a click-type azide-alkyne 1,3-dipolar cycloaddition (Huisgen cycloaddition) reaction. Reacting azidocobalamin with dimethyl acetylenedicarboxylate at 40 °C results in essentially stoichiometric conversion of azidocobalamin to the corresponding triazolato complex. The stability of the complex as a function of pH and in the presence of cyanide were investigated. The complex is stable in pD 7.0 phosphate buffer for 24 h. The rate of beta-axial ligand substitution was found to be one order of magnitude slower for the triazolatocobalamin complex compared with azidocobalamin. The beta-axial azido ligand of the vitamin B12 derivative azidocobalamin reacts with an electron deficient alkyne to form the corresponding triazolato complex. [Display omitted] •A new strategy for vitamin B12 conjugates is presented with derivatization via the beta-azido ligand of azidocobalamin.•Azidocobalamin reacts with dimethyl acetylenedicarboxylate via a 1,3-dipolar cycloaddition to form a triazolato complex•The complex is stable in aqueous solution at neutral pH but partially hydrolyses in acidic or basic solution.•The rate constant for substitution of the triazolato ligand by cyanide is one order of magnitude slower than azidocobalamin.