Transition metal-diene complexes in organic synthesis - 16.1

Direct oxidation of bromo-derived Fischer-Borsche oxo-ring using molecular iodine with combined experimental and computational study

A direct oxidation of the bromo-derived Fischer-Borsche oxo-ring leading to carbazolequinone has been developed by using molecular iodine. This unprecedented transformation has been used for the modular synthesis of the anti-cardiotonic agent murrayaquinone. Furthermore, the present method has been generalized to a broad range of functional groups, with good to excellent yield.

[Development of New Synthetic Methods for Carbazole Compounds Aimed at Drug Discovery and Exploratory Research on Pharmaceutical Materials]

We are developing the synthesis of biologically interesting carbazole compounds, including natural products by tandem cyclic reactions. In this report, we describe the new synthesis of carbazole-1,4-quinones as follows; 1) the synthesis of carbazole-1,4-quinones using a tandem ring closing metathesis (RCM) -dehydrogenation reaction, 2) a novel one-pot synthesis of carbazole-1,4-quinone by consecutive Pd-catalyzed cyclocarbonylation, desilylation, and oxidation reactions. Two new synthetic strategies were applied to the synthesis of carbazole-1,4-quinone alkaloids and ellipticine quinones, and then the antiproliferative activity against HCT-116 and HL-60 cells of the synthesized compounds were evaluated.

Synthesis of indole derivatives as prevalent moieties present in selected alkaloids

Indoles are a significant heterocyclic system in natural products and drugs. They are important types of molecules and natural products and play a main role in cell biology. The application of indole derivatives as biologically active compounds for the treatment of cancer cells, microbes, and different types of disorders in the human body has attracted increasing attention in recent years. Indoles, both natural and synthetic, show various biologically vital properties. Owing to the importance of this significant ring system, the investigation of novel methods of synthesis have attracted the attention of the chemical community. In this review, we aim to highlight the construction of indoles as a moiety in selected alkaloids.

Nitric Oxide Inhibitory Carbazole Alkaloids from the Folk Medicine Murraya tetramera C.C. Huang

The phytochemical investigation of the leaves and stems of Murraya tetramera C.C. Huang, a traditional folk medicine used as an anti-inflammatory agent, yielded 19 simple carbazole alkaloids, two of which (1-ethoxy-3-methyl-9H-carbazol-2-ol (1) and 7-hydroxy-2,8-dimethoxy-6-methyl-9H-carbazole-1-carbaldehyde (2)) are new ones. The structures of the new compounds were determined by extensive spectroscopic analysis including NMR and HR-EI-MS experiments, as well as comparison with the reported data. Most of the isolates showed potent inhibitory effects on NO production in LPS-stimulated BV-2 microglial cells with IC₅₀ values ranging from 5.1 to 15.1 μM.

Antibacterial Activity of Murrayaquinone A and 6-Methoxy-3,7-dimethyl-2,3-dihydro-1H-carbazole-1,4(9H)-dione

The antibacterial activity of Murrayaquinone A (10), a naturally occurring carbazoloquinone alkaloid, and 6-methoxy-3,7-dimethyl-2,3-dihydro-1H-carbazole-1,4(9H)-dione (11), a synthetic carbazoloquinone, both obtained during the development of the synthesis of Carbazomycin G, having unique quinone moiety, was studied against Gram-positive (Bacillus subtilis and Staphylococcus aureus) and Gram-negative (Escherichia coli and Pseudomonas sp.) bacteria. Compound 10 showed antibacterial activities against both of Escherichia coli and Staphylococcus aureus whereas compound 11 indicated the activity against Staphylococcus aureus only. Both compounds 10 and 11 exhibited minimum inhibitory concentration (MIC) of 50 μg mL⁻¹ against Staphylococcus aureus.

Constituents of the roots of Clausena lansium and their potential anti-inflammatory activity

Eight new carbazole alkaloids, claulamines C (1), D (2), and E (5) and clausenalines B-F (3, 4, 6-8), four new coumarins, clausemarins A-D (9-12), and 43 known compounds were isolated from the roots of Clausena lansium. The structures of the new compounds were established on the basis of 2D-NMR spectroscopic analysis, and their absolute configurations were established from their ECD spectra. The configuration of wampetin was revised as E using a NOESY experiment. Most of the isolated compounds were evaluated for their potential anti-inflammatory activity. The results showed that compounds 9, 13-18, and 20-22 exhibited strong inhibition of superoxide anion generation with IC50 values ranging from 1.9 to 8.4 μM, while compounds 18, 19, and 21 inhibited elastase release with IC50 values in the range from 2.0 to 6.9 μM.

First total syntheses of chrestifoline-B and (±)-chrestifoline-C, and improved synthetic routes to bismurrayafoline-A, bismurrayafolinol and chrestifoline-D

We describe an efficient synthesis of the methylene-bridged biscarbazole alkaloids bismurrayafoline-A, bismurrayafolinol and chrestifoline B–D using an Ullmann-type coupling at the benzylic position.

Iodine-catalyzed aromatization of tetrahydrocarbazoles and its utility in the synthesis of glycozoline and murrayafoline A: a combined experimental and computational investigation

A new protocol for the aromatization of tetrahydrocarbazoles has been achieved using a catalytic amount of iodine. The role of iodine has been explained by DFT, and its scope is extended to the total synthesis of glycozoline and murrayafoline A.

A benzoisofuranone derivative and carbazole alkaloids from Murraya koenigii and their antimicrobial activity

A benzoisofuranone derivative, 3xi-(1xi-hydroxyethyl)-7-hydroxy-1-isobenzofuranone, and a dimeric carbazole alkaloid, 3,3'-[oxybis(methylene)]bis(9-methoxy-9H-carbazole), along with six known carbazole alkaloids and three known steroids were isolated from the stem bark of Murraya koenigii. The structures of these compounds were established unambiguously by UV, IR, MS and a series of 1D and 2D NMR analyses. The minimum inhibitory concentrations (MIC) of these compounds were found to be in the range 3.13-100 microg/ml.

DoubleN-Arylation of Primary Amines: Carbazole Synthesis from 2,2‘-Biphenyldiols

The double N-arylation of primary amines with 2,2'-biphenylylene ditriflates was investigated for the synthesis of multisubstituted carbazoles. Palladium complexes supported by 2-dicyclohexylphosphino-2'-methylbiphenyl or Xantphos [4,5-bis(diphenylphosphino)-9,9-dimethylxanthene] were found to be efficient catalysts for the reaction. The catalysts allow the use of anilines with an electron-donating or electron-withdrawing substituent and multisubstituted 2,2'-biphenylylene ditriflates as substrates. Ammonia equivalents, such as O-tert-butyl carbamate, are also employable as a nitrogen source to give the N-protected carbazoles which can easily give the corresponding N-unsubstituted carbazoles after deprotection. By using this methodology, a carbazole alkaloid, mukonine, is synthesized in 40% yield for five steps, in comparable efficiency to the recent precedents.

A New Dimeric Carbazole Alkaloid from Glycosmis stenocarpa Roots

A new dimeric pyranocarbazole alkaloid, bisisomahanine (1), was isolated from the roots of Glycosmis stenocarpa (DRAKE) TAN., along with two known monomeric carbazole alkaloids, murrayafoline-A (2) and murrayanine (3). The planar structure of bisisomahanine was determined to be 9,9''-dihydroxy-3,3'',8,8''-tetramethyl-3,3''-bis-(4-methyl-3-pentenyl)-3,3'',11,11''-tetrahydro-10,10''-(bipyrano[3,2-a]carbazole) from the combination of spectroscopic and chemical evidence. Bisisomahanine is the first dimeric prenylated pyranocarbazole alkaloid with a 1,1' type of linkage; the NMR and CD spectroscopic data indicated it to be a mixture of diastereomers having a dominant configuration at the axis of chirality. (1)H- and (13)C-NMR assignments of murrayafoline-A were made on the basis of 2D-experiments.

Novel syntheses of murrayaquinone A and furostifoline through 4-oxygenated carbazoles by allene-mediated electrocyclic reactions starting from 2-chloroindole-3-carbaldehyde

The formal total synthesis of murrayaquinone A (1) and the total synthesis of furostifoline (5) were completed by the construction of 4-oxygenated 3-methylcarbazoles 7 based on a new type of electrocyclic reaction through 2-alkenyl-3-allenylindole intermediates 8 derived from the 2-alkenyl-3-propargylindoles 9, starting from 2-chloroindole-3-carbaldehyde (11). The N,O-bisbenzyloxymethyl group of 16c and 22 underwent a Birch reduction followed by treatment with Triton B to produce the known 4-hydroxy-3-methylcarbazole (7a) and 4-hydroxy-3-methylfuro[3,2-a]carbazole (7b) as precursors of murrayaquinone A (1) and furostifoline (5), respectively. The trifluoromethanesulfonyloxy-3-methylfuro[3,2-alcarbazole (24), prepared from 7b, was subjected to reductive cleavage to provide furostifoline (5).

[Synthesis of carbazole derivatives. 1. The reaction of 3-(2-nitroethenyl)-indole-2-malonic acid esters with Michael acceptors]

Michael-type reaction of compounds of type 9 were studied. Addition reactions with acrolein and methyl vinyl ketone, respectively, lead--depending on the conditions--to pyridoindoles of type 16 and 14 and/or to tetrahydrocarbazoles of type 17 and 15. With Triton B compounds 15 undergo retro-Michael-type elimination of the nitromethyl group, followed by hydrolysis/decarboxylation and dehydrogenation, leading to the disubstituted carbazoles 20. In the case of 17a, the primary elimination product 18 could be isolated. The synthetic potential of these reaction types is discussed. Some of the described compounds and derivatives of them show antimycobacterial activity.