Biosynthesis halogenated tyrosines

In this review, we discuss the isolation, structure, physicochemical and spectral data of all bromotyrosine derivatives isolated from marine organisms. The biosynthesis, total synthesis, and bioactivity of the bromotyrosine derivatives are also reviewed. Neither tyrosine derivatives without halogenation, nor indole alkaloids (with or without halogenation), are included in this review. Proteins or peptides containing bromotyrosine units are not included in this review since they are considered as primary metabolites. Cyclopeptides containing halogenated tyrosine units are, however, discussed in this review. 

Of the more than 4500 known naturally occurring organohalogen compounds, a large fraction are alkaloids [1,3]. Most of these halogenated pyrroles, indoles, carbazoles, carbolines, tyrosines, and others have a marine origin. The present chapter surveys the occurrence, structure, and biosynthesis of these fascinating natural products. However, given their sheer number, this review focuses mainly on recent examples. 

Figure 14 Biosynthesis of PKS-NRPS hybrid compounds in myxobacteria (b). Biosynthesis of chondramide D (34) in Chondromyces crocatus Cm c5. The DH domain from module 1 (marked with an asterisk) is most likely inactive. During the assembly of the chondramide backbone, an unusual extender unit - a /3-amino acid - is incorporated by NRPS module 6. The precursor is generated by the tyrosine amino mutase (TAM) CmdF, which converts L-tyrosine into R-/3-tyrosine (see box). The function of the terminal phosphoenolpyruvate synthase (PEP) domain is still unknown. Macrocyclization catalyzed by the TE domain yields chondramide C (40), which can be further transformed to the chlorinated derivative chondramide D (34). The halogenation process catalyzed by CmdE may also take place on the assembly line intermediate.

Electrophilic aromatic halogenations occur in the biosynthesis of numerous naturally occurring molecules, particularly those produced by marine organisms. In humans, the best-known example occurs in the thyroid gland during the biosynthesis of thyroxine, a thyroid hormone involved in regulating growth and metabolism. The amino acid tyrosine is first iodinated by thyroid peroxidase, and two of the iodinated tyrosine molecules then couple. The... 

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