Total synthesis achieves indigotinoline A and revises the stereochemistry of isatindigotindoline B, suggesting new insights into alkaloid pathways.
The first total synthesis of scarce alkaloid indigotinoline A from Isatis indigotica was achieved in six steps from a known carboxylic acid (13% overall yield). The distinctive 6/5/6/5/6 N,O-heterocycle was efficiently assembled via a one-pot triple cascade, Povarov-type cyclization, intramolecular substitution, and visible-light-mediated oxidative rearrangement, followed by bioinspired N-oxidation/1,2-migration. This synthesis also prompted re-examination of proposed biosynthetic precursor isatindigotindoline B, leading to revision of its stereochemistry based on spectroscopic analysis.
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Li et al. (2026) studied this question.
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