Scheme 3.

Substrate scope of Thal (purified enzyme) analysed by LC–MS suggests a broad tolerance of different Trp alkyl amides and peptides. A. General reaction scheme. B. Secondary and tertiary Trp N‐alkyl amides are readily converted by Thal. C. Bromination of dipeptides containing l‐Trp at the N‐terminus. D. Peptides carrying a d‐Trp residue indicate a wide tolerance of residues attached to the carboxy group. Apart from various dipeptides, 22 is also brominated by Thal. General reaction conditions: 0.5 mm substrate, 95 μm Thal, 2.5 U mL⁻¹ PrnF, 1.0 μm FAD, 50 mm NADH, 30 mm NaBr, phosphate buffer pH 7.4. Conversions mentioned in brackets refer to LC–MS data.