Enzymatic synthesis of riboflavin and FMN specifically labeled with 13C in the xylene ring.
The condensation of 3-hydroximino-2-butanone (1) with 5-amino-6-ribitylamino-2,4(1H,3H)-pyrimidinedione (2) yields 6,7-dimethyl-8-ribityllumazine (3). At slightly alkaline pH, the carbonyl group of 1 reacts preferentially with the 5-amino group of 2 (regioselectivity, 4:1). Under acidic conditions, the reaction occurs with higher yield and marginal regioselectivity of opposite direction (1:1.4). Appropriately 13C-labeled samples of 1 afford 3 labeled at C-6 alpha, C-6, C-7 or C-7 alpha. [6 alpha, 7 alpha-13C2]-3 was prepared by condensation of 2 with [1,4-13C2]diacetyl. The lumazines 3 were converted to riboflavin by the enzyme, riboflavin synthase, with almost quantitative yield. By this procedure, any C-atom of the carbocyclic moiety of riboflavin can be selectively labeled with 13C at high abundance. Phosphorylation yields the respectively 13C-labeled FMN samples.
D001412:Bacillus subtilis / Q000201:enzymology; D002247:Carbon Isotopes; D005486:Flavin Mononucleotide / Q000138:chemical synthesis*; D007202:Indicators and Reagents; D007553:Isotope Labeling / Q000379:methods; D012256:Riboflavin / Q000138:chemical synthesis*; D012258:Riboflavin Synthase / Q000378:metabolism
D002247:Carbon Isotopes; D007202:Indicators and Reagents; D005486:Flavin Mononucleotide; D012258:Riboflavin Synthase; D012256:Riboflavin