Name: synthesis of antiviral tetrahydrocarbazole derivatives by photochemical and acid-catalyzed c-h functionalization via intermediate peroxides (chips)
Uploaded: 2014-06-20T14:00:00
Description: Watch this Scientific Journal Video about Synthesis of Antiviral Tetrahydrocarbazole Derivatives by Photochemical and Acid-catalyzed C-H Functionalization via Intermediate Peroxides CHIPS at JoVE.com

Financial support from the DFG (Heisenberg scholarship to M.K., KL 2221/4-1; KL 2221/3-1) and the Max-Planck-Institut fuer Kohlenforschung is gratefully acknowledged.

1. Synthesis of Tetrahydrocarbazole Hydroperoxides
<ol>
	<li>The formation of the hydroperoxide is slowed down if the tetrahydrocarbazole is very colored. In this case, purify it by recrystallization using toluene/pentane or by column chromatography to get a colorless starting material. For purification by column chromatography, pack a column with a lower layer of silica gel and an upper layer of alumina. Put the tetrahydrocarbazole on top of the column and elute with toluene. All the unwanted yellow and black colored ...

<ol>
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Chem. 9, 109-139 (2005).</li><li>Mateo, C. A., Urrutia, A., Rodr&#237;guez, J. G., Fonseca, I., Cano, F. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Photooxygenation+of+1,2,3,4-Tetrahydrocarbazole:+Synthesis+of+Spiro[cyclopentane-1,2'-indolin-3'-one].">Photooxygenation of 1,2,3,4-Tetrahydrocarbazole: Synthesis of Spiro[cyclopentane-1,2'-indolin-3'-one].</a> J. Org. Chem. 61, 810-812 (1996).</li><li>Wasserman, H. H., Ives, J. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Singlet+oxygen+in+organic+synthesis.">Singlet oxygen in organic synthesis.</a> Tetrahedron. 37, 1825-1852 (1981).</li><li>Liguori, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrophilic+Aromatic+Alkylation+by+Hydroperoxides.+Competition+between+Ionic+and+Radical+Mechanisms+with+Phenols.">Electrophilic Aromatic Alkylation by Hydroperoxides. Competition between Ionic and Radical Mechanisms with Phenols.</a> J. Org. Chem. 64, 8812-8815 (1999).</li><li>Dussault, P. H., Lee, H. -. J., Liu, X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Selectivity+in+Lewis+acid-mediated+fragmentations+of+peroxides+and+ozonides:+application+to+the+synthesis+of+alkenes,+homoallyl+ethers,+and+1,2-dioxolanes.">Selectivity in Lewis acid-mediated fragmentations of peroxides and ozonides: application to the synthesis of alkenes, homoallyl ethers, and 1,2-dioxolanes.</a> J. Chem. Soc., Perkin Trans. , 3006-3013 (2000).</li><li>Hock, H., Lang, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Autoxydation+von+Kohlenwasserstoffen+IX.+Mitteil.:+&#220;ber+Peroxyde+von+Benzol-Derivaten.">Autoxydation von Kohlenwasserstoffen IX. Mitteil.: &#220;ber Peroxyde von Benzol-Derivaten.</a> Ber. 77, 257-264 (1944).</li><li>Boggs, S. D., Gudmundsson, K. S., Richardson, L. D. A., Sebahar, P. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tetrahydrocarbazole+derivatives+and+their+pharmaceutical+use.">Tetrahydrocarbazole derivatives and their pharmaceutical use.</a> USA patent WO. 2004/110999 A1. , (2004).</li><li>Gudmundsson, K. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=HCV+Inhibitors.">HCV Inhibitors.</a> USA patent WO 2006/ 121467 A2. , (2006).</li><li>Lennox, W. J., Qi, H., Lee, D. -. H., Choi, S., Moon, Y. -. 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In summary, we could demonstrate that a C-H bond in tetrahydrocarbazoles can be conveniently functionalized to generate C-N-coupling products in a two-step procedure.
The first step is a well-known photocatalyzed oxidation of tetrahydrocarbazole (1) or its derivatives with elemental oxygen17,19, giving a hydroperoxide 2. If performed in toluene, the hydroperoxide products precipitate and can be conveniently isolated by filtration. Further purificati...

The direct functionalization of C-H bonds is an important and long standing goal in organic chemistry1. Such transformations can be very powerful in order to streamline synthesis by saving steps, time and material compared to conventional methods that require the introduction and removal of activating or directing groups. Therefore, the functionalization of C-H bonds is also attractive for green chemistry2. Under oxidative conditions, two C-H bonds or one C-H and one heteroatom-H bond can be transformed to C-C and C-heteroatom bonds, respectively (Figure 1)3-9. Often these oxidative coupling reactions require synthetic oxidants, expensive catalysts or high temperatures. Therefore, many attempts are made to develop methods that use cheap catalysts, benign conditions and oxygen or air as terminal oxidant10.
<img alt="Figure 1" fo:content-width="5in" src="/files/ftp_upload/51504/51504fig1highres.jpg" width="500" /> 
Figure 1. Oxidative coupling reactions. <a href="https://www.jove.com/files/ftp_upload/51504/51504fig1highres.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Many organic compounds react slowly with oxygen from air in autoxidation reactions which can functionalize C-H bonds by effectively inserting O2, forming a hydroperoxide moiety11,12. Autoxidation processes are used on industrial scale to generated oxygenated compounds from hydrocarbon feedstocks, but autoxidation is also an unwanted process if it leads to decomposition of valuable compounds or materials. In some cases, for example diethyl ether, hydroperoxides formed in air can also be explosive. Recently, we discovered a reaction that utilizes an autoxidation to form a new C-C bond from C-H bonds without need of a redox-active catalyst13,14. Simply stirring the substrates under oxygen in the presence of an acid catalyst leads to the formation of the new products. Key to the reaction is the facile formation of intermediate hydroperoxides, which are substituted with the second substrate by acid catalysis15. The reaction, however, is restricted to xanthene and a few related compounds that are easily oxidized under an atmosphere of oxygen and the products have so far not found applications. Nevertheless inspired by this discovery, we developed a related oxidative coupling method that utilizes the principle of C-H functionalization via Intermediate PeroxideS (CHIPS) to synthesize pharmaceutically active indole derivatives16.
Indoles, especially tetrahydrocarbazoles 1, can be easily oxidized to hydroperoxides 2 in the presence of singlet oxygen17-19, which can be generated using a sensitizer and visible light20. A hydroperoxide moiety can in principle act as a leaving group if activated by acid catalysis and allow for the introduction of a nucleophile21,22. Hydroperoxides are also known to undergo acid catalyzed rearrangement reactions as utilized in the industrial synthesis of phenol from cumene, the Hock process23. By careful optimization studies, we could find conditions to favor the desired substitution reaction with N-nucleophiles like anilines 3 over the unwanted decomposition pathways by rearrangement16. Here, we describe this two-step CHIPS procedure in detail, using only visible light, a sensitizer, oxygen and acid. Amongst the selected products are indole derivatives 4, which show high antiviral activity or inhibit the vascular endothelial growth factor (VGF), which can be important for tumor therapy24-26.

<table border="0" cellpadding="0" cellspacing="0" width="797">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">1,2,3,4-Tetrahydrocarbazole</td>
			<td style="width:139px;">Sigma Aldrich</td>
			<td style="width:151px;">T12408</td>
			<td style="width:291px;">If coloured, purification may be necessary. See Protocol 1.1</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Methanol</td>
			<td style="width:139px;">Sigma Aldrich</td>
			<td>322415</td>
			<td>99.8% purity</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">4-Nitroaniline</td>
			<td style="width:139px;">Acros Organics</td>
			<td>128371000</td>
			<td>99% purity</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Trifluoroacetic acid</td>
			<td style="width:139px;">Sigma Aldrich</td>
			<td>T6508</td>
			<td>99% purity</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Acetic acid</td>
			<td style="width:139px;">J. T. Baker</td>
			<td style="width:151px;">JTB RS 426960101</td>
			<td>99-100% purity</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Aniline</td>
			<td style="width:139px;">Merck</td>
			<td>8222560100</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">4-Aminobenzonitrile</td>
			<td style="width:139px;">Sigma Aldrich</td>
			<td>147753</td>
			<td>98% purity</td>
		</tr>
	</tbody>
</table>

synthesis of antiviral tetrahydrocarbazole derivatives by photochemical and acid-catalyzed c-h functionalization via intermediate peroxides (chips)

The direct functionalization of C-H bonds is an important and long standing goal in organic chemistry. Such transformations can be very powerful in order to streamline synthesis by saving steps, time and material compared to conventional methods that require the introduction and removal of activating or directing groups. Therefore, the functionalization of C-H bonds is also attractive for green chemistry. Under oxidative conditions, two C-H bonds or one C-H and one heteroatom-H bond can be transformed to C-C and C-heteroatom bonds, respectively. Often these oxidative coupling reactions require synthetic oxidants, expensive catalysts or high temperatures. Here, we describe a two-step procedure to functionalize indole derivatives, more specifically tetrahydrocarbazoles, by C-H amination using only elemental oxygen as oxidant. The reaction uses the principle of C-H functionalization via Intermediate PeroxideS (CHIPS). In the first step, a hydroperoxide is generated oxidatively using visible light, a photosensitizer and elemental oxygen. In the second step, the N-nucleophile, an aniline, is introduced by Br&#248;nsted-acid catalyzed activation of the hydroperoxide leaving group. The products of the first and second step often precipitate and can be conveniently filtered off. The synthesis of a biologically active compound is shown.

Synthesis of 1-(5-nitroindolin-1-yl)-2,3,4,9-tetrahydro-1H-carbazole (4a):
Synthesized according to Method A, Rf = 0.63 (hexane/ethyl acetate 70:30).
Purification: Purify the product by using Method A, workup variant A1 (steps 2.4, 2.5, 2.6). Orange solid, Yield: 95%.
1H NMR (500 MHz, DMSO-d6): &#948; 10.90 (s, 1H), 7.97 (dd...

Watch this Scientific Journal Video about Synthesis of Antiviral Tetrahydrocarbazole Derivatives by Photochemical and Acid-catalyzed C-H Functionalization via Intermediate Peroxides CHIPS at JoVE.com

Synthesis of Antiviral Tetrahydrocarbazole Derivatives by Photochemical and Acid-catalyzed C-H Functionalization via Intermediate Peroxides CHIPS

A two-step procedure for the synthesis of pharmaceutically active indole-derivatives by C-H functionalization with anilines is described, using photo- and Br&#248;nsted acid catalysis.

Synthesis of Antiviral Tetrahydrocarbazole Derivatives by Photochemical and Acid-catalyzed C-H Functionalization via Intermediate Peroxides (CHIPS)

The direct functionalization of C-H bonds is an important and long standing goal in organic chemistry. Such transformations can be very powerful in order ...

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