Furocarbazole alkaloids

Furostifoline, the first furocarbazole alkaloid obtained from natural sources, was isolated from the root bark of Murraya euchrestifolia (Rutaceae) [41 ]. The extracts of the 

The regioselective nudeophUic attack of the arylamine at the 2-methoxy-substituted iron complex salt is controlled by the methoxy group, which directs the arylamine to the para-position. Moreover, electrophilic attack takes place at the sterically less-hindered orfho-amino position. Iron-mediated oxidative cyclization of the resulting iron complex to the carbazole followed by proton-catalyzed aimulation of the furan ring provides 8-methoxyfurostifoline. Oxidation with 2,3-dich]oro-5,6-dicyano-l,4-benzoquinone (DDQ) to O-methylfurodausine-A followed by deavage of the methyl ether provides furoclausine-A (five steps, 9 % overall yidd). 

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In 1990, Ito and Furukawa reported the isolation of furostifoline (224) and the isomeric eustifoline-D (227) from the root bark of M. euchrestifolia. These were the first furocarbazole alkaloids obtained from a natural source (101). Seven years later, Wu et al. reported the isolation of further furocarbazole alkaloids, furoclausine-A (225) and furoclausine-B (226) from the root bark of a different plant source, C. excavata (128). Furoclausine-B (226) was isolated from nature in optically active form [mId -32.73 (c 0.022, MeOH), however, the absolute stereochemistry is not known (128,175,176) (Scheme 2.55). 

In the preparation of the furocarbazole alkaloid, furostifoline, which followed a similar synthetic strategy, o-anilineboronic acid was replaced by... 

The 3-methylcarbazole origin of the carbazole alkaloids of higher plants and the wider participation of 2-hydroxy-3-methylcarbazole in the formation of pyranocarbazoles, as well as furocarbazoles, has been further substantiated by the isolation of several derivatives of 3-methylcarbazoles, such as mukoenine-A (girinimbilol) (55), heptaphylline (76), furostifoline (224), furoclausine A (225), girinimbine (115), and murrayacine (124). Girinimbilol (55) could be considered the... 

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