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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