Abstract
A classical Friedel-Crafts alkylation of different indoles catalyzed by AlCl3·6H2O has been developed for a well-known important natural product, celastrol, resulting in a series of derivatives for further biological evaluation. The catalyst loading was reduced to 5 mol %, the reaction proceeds at ambient temperature and reaction time is only 3 h. The product yields range from 20% to 99%. A reaction mechanism is also proposed, based on our experiment results.
Highlights
Celastrol is a traditional Chinese medicine, first extracted from Tripterygium wilfordii Hook F.( known as Thunder of God Vine or by the Chinese name ‘Lei Gong Teng”), which belongs to the Celastraceae family of plant species [1]
We report our development of one novel, efficient and convenient method for the Michael-type Friedel-Crafts addition of indoles to the para-quinone methide of celastrol
We tested if indole could undergo Friedel-Crafts alkylation by the para-quinone methide of celastrol without metal salt catalysis
Summary
Celastrol is a traditional Chinese medicine, first extracted from Tripterygium wilfordii Hook F. Structural determination revealed that celastrol is a pentacyclic triterpenoid possessing a chemically active para-quinone methide (pQM). Celastrol could suppress the NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells) activation by targeting cysteine 179 in the IKK (IκB kinase) and showed anti-inflammatory and anti-tumor activities in animal models [8]. Several reports have revealed that the nucleophilic Michael addition could be catalyzed by 30 mol % of Fe(acac) (Tris(acetylacetonato)iron(III)) [26], copper-Fe [27], and even a pure organic chiral ligand [28], resulting in excellent yield, high stereoselectivity and enantioselectivity None of these methods have been tried in the chemical modification of celastrol. We report our development of one novel, efficient and convenient method for the Michael-type Friedel-Crafts addition of indoles to the para-quinone methide of celastrol
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