Facile isolation of α-ribazole from vitamin B₁₂ hydrolysates using boronate affinity chromatography

Alpha-ribazole (α-R) is a unique riboside found in the nucleotide loop of coenzyme B₁₂ (CoB₁₂). α-R is not an intermediate of the de novo biosynthetic pathway of coenzyme B₁₂, but some bacteria of the phylum Firmicutes have evolved a two-protein system (transporter, kinase) that scavenges α-R from the environment and converts it to the pathway intermediate α-RP. Since α-R is not commercially available, one must either synthesize α-R, or isolate it from hydrolysates of vitamin B₁₂ (cyano-B₁₂, CNB₁₂), so the function of the above-mentioned proteins can be studied. Here we report a facile protocol for the isolation of α-R from CNB₁₂ hydrolysates. CNB₁₂ dissolved in NaOH (5 M) was heated to 85 °C for 75 min, then cooled to 4 °C for 30 min. The solution was neutralized with HCl (5 M), and the hydrolysate was diluted with an equal volume of ammonium acetate (0.3 M, pH 8.8). Alkaline phosphatase was added and the mixture was incubated at 37 °C for 16 h. After incubation, the sample was loaded onto a boronate affinity resin column, washed with ammonium sulfate (0.3 M, pH 8.8), water (to remove residual corrinoids) and finally with formic acid (0.1 M) to release (α-R). Formic acid was removed by lyophilization, and the final yield of α-R was 85% from the theoretically recoverable amount. Methods for quantifying the concentration of α-R are reported.