Fig. 1. (A) Pyrroloindoline synthesis and biosynthesis typically proceed via bimolecular electrophilic substitution of indole at C3 and capture of the resulting indolenium ion by a proximal nitrogen nucleophile. The reaction of tryptophan is often exo-selective. aTautomerization of tryptophan by acid equilibrates to the C2-endo pyrroloindoline.4e,10 (B) Intramolecular C–C bond formation at C3 leads to ansa-bridged macrocyclic pyrroloindolines.
