Pyranocarbazoles

In 1985, Furukawa et al. reported the isolation of pyrayaquinone-A (175) and pyrayaquinone-B (176) from the root bark of M. euchrestifolia (157). Three years later, the same authors reported a further pyranocarbazole-l,4-quinone alkaloid, pyraya-quinone-C (177) from the root bark of the same natural source. The absolute configuration of this isolate is not known (22) (Scheme 2.37). 

In 2004, Cuong ef a. reported the isolation of bisisomahanine (209) from the roots of G. stenocarpa (30). Bisisomahanine was obtained in optically active form (Md 13.1, c 0.25, CHCI3). However, the absolute configuration is not known. This alkaloid represented the first dimeric prenylated pyranocarbazole alkaloid with a 1,1 -linkage (30). 

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... 

Chakraborty, D.P., Barman, B.K. and Bose, P.K. (1 964) Structure of girinimbine, a pyranocarbazole derivative isolated from Murraya koenigii Spreng. Scientific Culture 30, 445. 

The structures of several carbazoles and pyranocarbazoles have been confirmed by synthesis these include lansine [2-hydroxy-3-formyl-6-methoxycarbazole - a... 

Nonstructure elucidation of seven pyranocarbazole alkaloids of Murraya koenigii [mahanimbine, koenimbine, (-)-mahanine, koenine, koenigine, koenidine, and ( + )-isomahanimbine] have now been published.Mur-rayacine, a minor alkaloid of the same plant, has been isolated from the roots of Clausena heptaphylla. The stems of another Clausena species, C. anisata Willd., contain atanisatin (1), and the roots contain a second new alkaloid, clausanitin (2). ... 

Dihydrooxepino[3,2-a]carbazole derivatives are formed in moderate to rather high yields on photochemical rearrangement of pyranocarbazole alkaloids, for example mahanimbine <88TL6625>. 

Xon-tryptamines.—Mukonine (1), from the stem bark of Murraya koenigii Spreng., is simply " the methyl ester of mukoeic acid (l-methoxycarbazole-3-carboxylic acid), isolated earlier from the same source. A pyranocarbazole... 

A soln. of startg. pyranocarbazole in benzene irradiated at room temp, in a quartz immersion well photochemical reactor using a low- or medium-pressure Hg-vapour lamp (400 W 365 nm) under Nj for 4 h - product. Y 60%. F.e.s. A. Chakrabarti, D.P. Chakraborty, Tetrahedron Letters 29, 6625-8 (1988). 

In 2011, a palladium-catalyzed C-O coupling was developed for the synthesis of benzannulated oxazepino- and pyranocarbazoles. In the absence of a ligand, the desired product can be produced in excellent yields (Scheme 4.14). 

Pyranocarbazoles like girinimbine (3) can be detected readily by the formation of an immediate blue colour with BF3-etherate (16). Pyrano-coumarins like seselin (4) (32) do not respond to this test. 

The characteristic carbazolopyrilium ion at m/z 248 observed 18) in the mass spectra of pyranocarbazoles like girinimbine (3) and mahanim-bine (10) is paralleled in the mass spectra of carbazoloquinones like... 

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