Pyrano carbazole alkaloids

The molybdenum-mediated arylamine cyclization was also applied to the total synthesis of pyrano[3,2-a]carbazole alkaloids (Scheme 26). Reaction of the 5-aminochromene 71 with the complex salt 62 affords the complex 72, which on oxidative cyclization provides girinimbine 73, a key compound for the transformation into further pyrano[3,2-a] carbazole alkaloids. Oxidation of 73 with DDQ leads to murrayacine 74, while epoxidation of 73 using meta-chloro-perbenzoic acid (MCPBA) followed by hydrolysis provides dihydroxygirinim-bine75 [113]. 

In 1964, Chakraborty et al. isolated girinimbine (115) from the stem bark of M. koenigii (108). Girinimbine represented the first pyrano[3,2-a]carbazole alkaloid isolated from natural sources. Later, Joshi et al. isolated the same alkaloid from the roots of a different source, C. heptaphylla (91). Based on chemical degradation studies. 

In 1996, Ito et al. reported the isolation of clauszoline-A (167) and clauszoline-B (168) from the acetone extract of the stem bark of C. excavata collected in Singapore (74). These alkaloids represented the first, naturally occurring 2,8-dioxygenated-3-formylcarbazole alkaloids with a dimethylpyran ring fused to C-7 and C-8 of the carbazole nucleus. The extracts of the leaves and bark of this tree have been used in traditional medicine for the treatment of snakebites and abdominal pain (74). One year later, the same group isolated another pyrano[2,3-fl]carbazole alkaloid, clauszoline-H (169), from the roots of the same natural source in Japan (47) (Scheme 2.34). 

In 1991, Furukawa et al. reported the isolation of pyrayafoline B (170) from the stem bark of M. euchrestifolia collected in May in Taiwan (87). In the same year, the same group isolated a further pyrano[2,3- ]carbazole alkaloid, pyrayafoline E (171), from the stem bark of M. euchrestifolia. Pyrayafoline E was isolated from Nature in racemic form (70). These alkaloids are the first members of the naturally occurring 2,7-dioxygenated-3-methylcarbazole alkaloids having a dimethyl pyran ring fused to C-6 and C-7 of the carbazole nucleus (70,87) (Scheme 2.35). 

Recently, Tripathi et al. reported a new pyrano[3,2-a]carbazole alkaloid, 7-isovaleryl-oxy-8-methoxygirinimbine (1569) from the leaves of Murraya koenigii (896) (Scheme 6.2). 

The alkaloid, acronycine, a pyrano[2,3-c]acridine (Table 12.1, ref.58), and the carbazole alkaloids (ref.81) contain cyclic systems derived from 2-hydroxy... 

Reviews have been published on Rhazyal and indoline Vinca alkaloids, and a book d has been devoted to the chemistry, botany, folklore, and biological activities associated with Vinca species. A table surveys all the Rutaceae species so far studied and lists the alkaloids obtained therefrom canthinone, euxylo-phorine, and pyrano-carbazoles of the murrayacine-mahanimbine series have been obtained from this family. 

Cycloaddition reactions continue to find application in the synthesis of natural products and related substances containing indole and carbazole rings. Moody has published a summary of syntheses of carbazole alkaloids in which cycloadditions of pyrano[3,4-b]indol-3-ones figure prominently. <94SL681>... 

Moreover, following the same synthetic approach, an efficient iron-mediated synthesis of pyrano[3,2-a]carbazole alkaloids has been reported. The first total syntheses of O-methylmurrayamine A and 7-methoxymurrayacine, as well as the first asymmetric synthesis of (-)-tra j-dihydroxygirinimbine (Scheme 4-130), have been accomplished using this strategy. ... 

Moody, C.J. and Shah, P. (1989h) Diels-Alder reactivity of pyrano[3,4-b]indol-3-ones. Part 4. Synthesis of the carbazole alkaloids carbazomycin A and B and hyellazole. J. Chem. Soc. Perkin Trans. I, 2463-2471. 

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