Copyright © 1996, 2001 by Galen Daryl Knight and VitaleTherapeutics, Inc.

Riboflavin Analogues

Drugs based upon phenothiazine, such as chlorpromazine and trifluoperazine, are known to be substrates for the flavin-containing monooxygenase. Although this activity alone is cause for concern, this base also resembles the tricyclic ring system of riboflavin, a vitamin used in the synthesis of a cofactor for this enzyme, FAD. Substituting the ribityl moiety of riboflavin with arabityl or galactityl moieties, substituting chlorine for the methyl groups at positions 7 and 8, or moving the methyl group at position 8 to position 6 produces substances that interfere with flavin metabolism (flavin antagonists). Although these are normally not encountered in our environment, galactoflavin is known to produce congenital malformations in animals, illustrating the gravity of exposures to these riboflavin analogues.

Of greater concern to our health are flavin analogues that we all might encounter. L-Lyxoflavine, another flavin analogue containing the lyxityl stereoisomer instead of the ribityl chain, is a growth promoter when used in feedstuffs. Irradiation products of riboflavin, lumichrome and lumiflavin, also have the same tricyclic ring in common with riboflavin, and, like riboflavin, produce reactive and potentially carcinogenic oxygen species when exposed to light and air. Finally, phenarsazine is a toxic substance that may concern us all. The extent of its use and our exposure risks are being investigated.


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