Total Synthesis of (&plusmn;)-Carquinostatin A, and Asymmetric Total Synthesis of (<i>R</i>)-(−)-Carquinostatin A and (<i>S</i>)-(+)-Carquinostatin A

Abstract

Total syntheses of ( )-carquinostatin A (1), and (R)-( )-carquinostatin A (1a) together with its enantiomer, (S)-( )-carquinostatin A (1b), possessing radical scavenging activity, were newly achieved. ( )-Carquinostatin A (1) was synthesized from 1-acetonyl-6-bromo-3-ethoxy-2-methylcarbazole (6), which was derived from the known 1-acetonyl-3-ethoxy-2-methylcarbazole (5). Introduction of a prenyl group at the 6-position of carbazole was successful in two steps. For the synthesis of (R)-( )-carquinostatin A (1a) and (S)-( )-carquinostatin A (1b), (R)-( )-1-(2-acetoxypropyl)-3-hydroxy-2-methylcarbazole (15a) and (S)-( )-3-hydroxy-1-(2-hydroxypropyl)-2-methylcarbazole (15b), prepared by lipase-QLM catalyzed enantioselective transesterification of 3-hydroxy-1-(2-hydroxypropyl)-2-methylcarbazole (14), were used as the chiral starting material.

Simple indole alkaloids and those with a nonrearranged monoterpenoid unit

“…53 The total syntheses of ve amaryllidaceae alkaloids, lycoranines A (92) and B (93), 2-methoxypratosine (94), oxoassoanine (95), and anhydrolycorinone (96) Oxoassoanine (95) and anhydrolycorinone (96) were synthesized by intramolecular biaryl coupling involving t-BuOK-initiated single electron transfer to the C-Br bond (Scheme 24). 55 The halodecarboxylation of arenedicarxylic acid leading to a dihalogenated product was applied for the synthesis of kalbretorine (97). Treatment of dicarboxylic acid 98 with PhI(OAc) 2 and KI produced diiodide 99, which was transformed into 97 in 3 steps (Scheme 25).…”

“…Diacetates (R)-(À)-233 and (S)-(+)-233, obtained by transesterication of racemic diol 232 with lipase-QLM followed by acetylation, were converted to (R)-(À)-231 (natural) and (S)-(+)-231, respectively (Scheme 56). 97 Furoclausine-A (234) was synthesized based on a one-pot construction of a carbazole framework through the reaction of substituted anilines 236 with cyclohexadienyliumiron complexes 235 as the key step (Scheme 57). 98 Carbazole 242 The iron-mediated formation of carbazole was efficiently employed in the total synthesis of rac-lavanduquinocin (243) (Scheme 59).…”

Effects of Carbazole Derivatives on Neurite Outgrowth and Hydrogen Peroxide-Induced Cytotoxicity in Neuro2a Cells

“…Compound 7 was synthesized by the method previously reported [38]. Compounds 8 , 9 , 10 , 11 , and 12 ((±)carquinostatin A) were synthesized by the method previously reported [3]. Compounds 13 , 14 , 15 , 16 , 17 , 18 (carbazomadurin A), and 19 (( S )-(+)-carbazomadurin B) were synthesized as reported earlier [4].…”

“…Carbazole alkaloids, which are produced by plants such as those of the genus Murraya or Clausena [1], have recently attracted much attention because 1) they have various abilities such as anti-microbial, anti-tumor, anti-pileptic, anti-histaminic, anti-oxidant and anti-inflammatory actions [2]; and 2) they are being used as lead compounds for drug development [3,4,5]. Recently, we synthesized some carbazole derivatives having anti-oxidant ability, which was evaluated in terms of their radical-scavenging activity against 2,2-diphenyl-1-picrylhydrazyl (DPPH) and/or 2,2′-azinobis-(3-ethylbenzhiazolic-6-sulfonate) cations (ABTS) [5,6].…”

Total Synthesis of Carbazole Alkaloids – Ekeberginine, Harmandianamine A, and Furanoclausamine B

“…It may be mentioned that the incorporation of prenyl groups to carbazoles is notably challenging, and there are only a limited number of means to this end. They are (a) reaction of a prenyl–nickel complex with halocarbazoles,7 (b) ozonolysis of an allyl side chain followed by a Wittig reaction8 and (c) cross olefin metathesis of an allyl derivative 9…”