Isatin-based spiro indolenine alkaloids from Isatis indigotica Fortune with anti-neuroinflammatory and acetylcholinesterase inhibitory effects

Compounds 1a/1b are a pair of enantiomers characterized by an unprecedented 6/5/6/5/6 N ,O-heterocyclic scaffold with a unique spiro[4.5] core. Compound 2 is the first 6/5/6/5/5/6 hexacyclic skeleton fused with an unexpected dispiro[4.4.0.4] system.