Fig. 3. Halogenated natural products arising from the halogenation of indolic substrates: all include regioselective halogenation of tryptophan as a first step in their biosynthesis (tryptophan halogenase name and regiochemistry noted below each corresponding natural product). Examples include (C7) pyrrolnitrin 24,¹²⁰ (C6) thienodolin 25,⁷¹ Di-alboflavusin A1 26,⁷⁵ (C5) pyrroindomycin B 27,⁷⁶ (C2) chondramide D 28¹¹⁷ (C6, C7) kutzneride 29,¹²¹ keramamide A 30¹¹⁶ Tryptophan halogenases involved in the biosyntheses of these natural products are depicted, and are colour coded in accordance with the regiochemistry of the halogenation that they mediate. Chlorination is indicated in blue. Different regio-chemistries for chlorination are represented by different shades of blue.