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Indoles paraherquamide

Although mechanistically ambiguous, Williams and co-workers, synthesis of (-p)-paraherquamide B (79) could exemplify an alternative strategy for initiating a Heck cyclization (Scheme 6-13) [281. In this case, indole 77 was exposed to a stoichiometric amount of PdCl2, which potentially generated a 2-palladated intermediate [29]. Intramolecular insertion of the disubstituted alkene and reduction of the resulting neopentyl cr-alkylpalladium intermediate with sodium borohydride provided 78 in 63-80% yield. [Pg.133]

This is an indole alkaloid isolated from Penicilliutn paraherquei [31]. A number of naturally occuring and semi-synthetic analogues (17b-d and 18a, b) of paraherquamide possess marked anthelminitic activity [32,33]. [Pg.76]

The structures of asperparalines A (123), B (124), and C (125) were determined to be spiro compounds made up of an A -methyl succinimide and a cyclopent[f]indolizine having an A methyl amide bridge. Another structural characteristic of asperparalines is a bicyclo[2,2,2]diazaoctane core, and various compounds, such as those of the paraherquamide family mentioned in the following section, contain the same core in their structures. However, all these compounds have an indole moiety in their structures so, it is of great interest that asperparalines have no indole part in their structures. [Pg.596]

Prenyl rearrangement. Efficient total syntheses of 3-ferf-prenylated indole alkaloids employ prenyl shifts fi om C2, which can be considered biomimetic, since it was shown by Williams that the biosynthesis of paraherquamide A (199) from Penicillium sp. proceeds via tert-prenyl shift fi om C2 to C3 starting from precursors like 198 (Scheme 39) [2, 165], in agreement with earlier proposals by Barrow [166] and by Gorst-Allman [167] for the biosynthesis of roquefortine. [Pg.102]

Williams and coworkers [42] utilized a similar palladium(II)-mediated oxidative cyclization/w situ reduction protocol in the total synthesis of (+)-paraherquamide B (101, Scheme 9.14). Indole 99 was treated with 1.2 equiv of PdC and 2 equiv of AgBp4 to presumably form an alkylpalladium species, which was reduced with NaBH4 to ultimately provide 100 in good yield. This compound was further transformed to paraherquamide B in six steps. Williams et al. [43] later described the total synthesis of paraherquamide A utilizing the palladium(II)-mediated cyclization on a structurally similar compound. [Pg.364]

Lion and colleagues prepared 5,6,7-trimethoxyindole for a molecular mimic of combretastatin [30], and indole 21 became the indole unit in rapalexin B in a synthesis of this cruciferous phytoalexin by Pedras and colleagues [31], Indole 22 was needed for a biosynthetic study of the paraherquamide natural products [32], and Corey s team employed 6,7-dimethoxyindole (16) (71%) in their synthesis of aspidophytine [33]. [Pg.326]

Keywords Prenyiated indole alkaloids. Biosynthesis, Paraherquamides, Brevianamides, Roquefortine, Echinulin, Verruculogen, Cyclopiazonic acid. Ergot alkaloids... [Pg.97]

Finally, Zeeck et al. isolated the interesting substances aspergamide A and B from Aspergillus ochraceus [36]. These metabolites, including VM55599, are the only natural members of the paraherquamide family that do not have a spiro-ring system but instead a 2,3-disubstituted indole-derived system. [Pg.115]

These experiments clearly indicate that the C5 units in paraherquamide A are introduced in stereofacially distinct manners. Since it has been established that prenylation of the indole moiety in the biosynthesis of the structurally related brevianamides occurs in an analogous fashion to that postulated for paraherquamide A [19], the prenyl transferase that installs this C5 unit must display DMAPP to the 2-position of the indole in a n-facially indiscriminate manner. [Pg.121]

Although a stoichiometric palladium complex was often required, palladium-catalyzed C-H alkylation of indole at the C2 position was used in syntheses of complex natural products decades ago. For example, in 1993, the total synthesis of (-l-)-paraherquamide B was reported by Williams and coworkers using a reductive... [Pg.507]

C-H alkylation strategy (Scheme 16.3a) [9]. Treatment of indole 16 with Pd(II) according to Trost s C-H alkylation procedure for the syntheses of ibogamine and catharanthine (see Scheme 16.3b) [10] afforded the corresponding heptacyclic compound. After several steps from 18, the synthesis of (+)-paraherquamide B was accomplished. Williams and coworkers also achieved a concise, asymmetric, stereocontrolled total synthesis of stephacidins A and B and notoamide B in 2007 [11]. Additionally, in 2002 and 2003, Corey s group employed an intramolecular C-H alkylation as a key step for the total synthesis of okaramine N, austamide, hydratoaustamide, and deoxyisoaustamide (Scheme 16.3b) [12]. [Pg.509]

C H3MgI and reduction of the indol system afforded the anthelmintic drug substance 188 ([ H]PNU-141962, 2-desoxo[l -methyl- H3]paraherquamide), thereby reconstituting the skeleton of 184 in a slightly modified form. The synthesis depicted was designed as a pilot smdy for the preparation of the respective tritium and carbon-14-labeled isotopomers. It illustrates a more general C-dealkylation-realkylation approach that is otherwise difficult to accomplish (Section 10.1.2). ... [Pg.517]


See other pages where Indoles paraherquamide is mentioned: [Pg.57]    [Pg.84]    [Pg.28]    [Pg.316]    [Pg.53]    [Pg.364]    [Pg.129]    [Pg.91]    [Pg.245]    [Pg.490]    [Pg.9]    [Pg.381]    [Pg.261]    [Pg.97]    [Pg.104]    [Pg.507]   
See also in sourсe #XX -- [ Pg.507 , Pg.509 ]




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