4-Hydroxybenzoic acid: a likely precursor of 2,4,6-tribromophenol in Ulva lactuca

The green marine alga Ulva lactuca is known to contain simple bromophenols, especially 2,4,6-tribromophenol, but the precursor of these compounds in the alga is not known. With the aim of identifying potential precursors, the alga was analyzed for the presence of phenolic compounds. The compounds identified by gas chromatography-mass spectrometry were phenol, 4-hydroxybenzoic acid, 4-hydroxyphenylacetic acid, 4-hydroxyphenyllactic acid, 4-hydroxybenzaldehyde, 3,5-dibromo-4-hydroxybenzoic acid and 2,4,6-tribromophenol. Free L-tyrosine and free L-phenylalanine were also present in the alga. Furthermore, a crude enzyme extract from the alga, which contained bromoperoxidases, was used to brominate a range of phenolic compounds and the formation of bromophenols was monitored. The compounds forming 2,4,6-tribromophenol were phenol, 4-hydroxybenzoic acid, 4-hydroxyphenylacetic acid, 4-hydroxybenzyl alcohol and 2-hydroxybenzyl alcohol. 4-Hydroxybenzoic acid is designated as the most likely precursor of 2,4,6-tribromophenol in U. lactuca and a pathway for its formation from L-tyrosine, via 4-hydroxyphenylpyruvic acid, is proposed.