Bisindoles arcyriarubin

Dihydroarcyriarubin C (104), a new bisindole alkaloid, has been isolated from fruit bodies of a myxomycete Arcyria ferruginea, which was collected at Hao, Yasu-cho, Kochi Prefecture, together with two known bisindoles, arcyriarubin C (2) and arcyriaflavin C (4), and the structure of 104 was elucidated by spectral data. Arcyriaflavin C (4) was also obtained, together with arcyriaflavin B (3), from fruit bodies of Tub if era casparyi, which ( 16839) was collected at Mt. Miune, Monobe-mura, Kochi Prefecture, in November 1997. Arcyriaflavin C (4) was revealed to exhibit cell cycle inhibition activity on HeLa cells on the basis of flow cytometry studies. Fruit bodies of Fuligo Candida, which ( 23446) was collected at Motoyama-cho, Kochi Prefecture, in August 2002, were revealed to contain a relatively high quantity of cycloanthranilylproline (105). 

Fruit bodies of wild myxomycetes often have bright colors. In 1980 Steglich et al. isolated red and yellow pigments from methanol extracts of 2 g of the red fruit bodies of Arcyria denudata [7], Structure of these pigments were elucidated by spectral data as a series of bisindole maleimides, and they were named arcyriarubin B (1), C (2), arcyriaflavin B (3), C (4), and arcyrioxepin A (5). 1, 2, and 5 were red... 

The structures of these bisindole maleimides were confirmed by synthesis. The reaction of indolyl magnesium bromide (10) with 2,3-dibromo-A -methylmaleimide (11) in toluene led to bisindolylmaleimide (12), which was converted into arcyriarubin A (6) through alkaline hydrolysis followed by heating with ammonium acetate (Scheme 1). The reaction of 10 and 11 in THF yielded monosubstitution product (13) which after protection of the indole NH group with the Boc residue was used to prepare unsymmetrically substituted bisindolylmaleimide, arcyriarubin B (1) [8]. 

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