Vitamin B 12 , chemically known as cobalamin, is a complex organometallic cofactor associated with several cobalamin-dependent enzymes. Its reduced form, cob(I)alamin, is one of the most powerful nucleophiles known. Following reduction of hydroxocobalamin (OH-Cbl) by sodium borohydride, cob(I)alamin was shown to react readily with sucralose (1',6'-dichloro-1',6'-dideoxy-β-Dfructofuranosyl-4-chloro-4-deoxy-α-D-galactopyranoside; a synthetic sweetener) in an aqueous system to form an alkylcobalamin (Suc-Cbl). This occurred by replacement of one of the three chlorides on sucralose with a cobalamin moiety. The efficiency of trapping sucralose in presence of excess Cbl(I) was estimated to be > 90%. Furthermore, in an in vitro study using human liver S9 with NADPH regeneration, in presence of OH-Cbl and sucralose, Suc-Cbl was shown to be formed. The Suc-Cbl was characterized primarily by LC-ESI + -MS/MS. Considering human consumption of sucralose from food and beverages, such reaction between the sweetener and reduced vitamin B 12 could occur in vivo.