Biosynthetic pathway for halogenated methoxybenzaldehydes in the white rot fungus Bjerkandera adusta

Through experiments with fluoro-labelled phenylalanine, tyrosine and benzaldehyde, the biochemical pathway leading to the chlorinated methoxybenzaldehydes in the white rot fungus Bjerkandera adusta has now been verified. Cultures of this organism supplied with fluoro-labelled phenylalanine, tyrosine or benzaldehyde showed a bioconversion of these compounds into fluoro-4-methoxybenzaldehyde, fluoro-3-chloro-4-methoxybenzaldehyde and fluoro-3,5-dichloro-4-methoxybenzaldehyde. In addition fluoro-phenylalanine also yielded fluorobenzaldehyde. Fluorodichlorinated compounds were only detected in cultures supplied with ortho substituted fluoro-phenylalanine demonstrating a meta specific halogenation mechanism. These results are the first to give direct evidence of the involvement of both tyrosine and phenylalanine in the biosynthetic pathway of chloromethoxy substituted benzaldehydes in B. adusta and suggest a pathway for the biosynthesis of 3-chloro-4-methoxybenzaldehyde and 3,5-dichloro-4-methoxybenzaldehyde that proceeds either via phenylalanine through benzaldehyde and 4-methoxybenzaldehyde or via tyrosine through 4-methoxybenzaldehyde.