Synthesizing 9-Benzyl-3-(Di(1H-Indol-3-Yl)Methyl)-9H-Carbazole

Introduction

Cancer is one of the leading cause of death globally. The World Health Organization (WHO) stated, over the next 20 years, the numbers of new cancer cases are likely to continue increase by around 70%. Chemotherapy is one of the most popular method used in cancer treatment. Despite there are many anticancer drugs in the market, the clinical application of the anticancer drugs is still limited because of their unwanted side effects, high cost and drug resistance of the cancerous cells. Hence, the pharmaceutical researchers have focused on the research and development to discover a more potent drug to fight the cancer.

Carbazoles are the key structural motif of many biologically activities and are regarded as one of the important heterocyclic class of anticancer agents. So, those carbazole derivatives that exerts the anticancer activities have undergone clinical trials and research. Some carbazoles with potent anticancer activity have undergone clinical trials. This research proposes to synthesize Bis(indolymethyl)carbazoles, which is 9-benzyl-3-(di(1H-indol-3-yl)methyl)-9H-carbazole. This is because both indole and carbazole derivatives could exerts anticancer properties. So, by combining both together, it will enhance their anticancer effect.

Research Question of the Project

Can 9-benzyl-3-(di(1H-indol-3-yl)methyl)-9H-carbazole be synthesized by employing iodine as a catalyst?

Research Objective of Project

To synthesize 9-benzyl-3-(di(1H-indol-3-yl)methyl)-9H-carbazole using iodine as a catalyst and characterize 9-benzyl-3-(di(1H-indol-3-yl)methyl)-9H-carbazole via infrared spectrum (IR) and proton nuclear magnetic resonance (H-NMR) spectroscopies.

Research Hypotheses of Project

H0: 9-benzyl-3-(di(1H-indol-3-yl)methyl)-9H-carbazole cannot be synthesized by employing iodine as catalyst.

H1: 9-benzyl-3-(di(1H-indol-3-yl)methyl)-9H-carbazole can be synthesized by employing iodine as catalyst.

Literature Review

Indoles

Indole is a group that consist of a benzene ring and a pyrrole group. Bisindolylmethanes (BIMs) can be isolated from sources such as from marine natural sources or terrestrial source. Indoles that were found in some human food could be a potential source of new classes of chemotherapeutic agents and some of it were found to inhibit the carcinogenic process in animal model. Besides that, the ability to inhibit the tumor growth in breast, uterus and liver can also be found in indole metabolites of cruciferous vegetables which are indole-3-carbinol and 3,3’-diindolylmethane. Numerous activities were reported regarding cancer chemotherapy with the use of BIMs. In the review, BIMs derivatives had shown to be able to inhibit cancer cells growth, have antitumorigenic activities, exhibit antimicrobial and antifungal activities, anti-inflammatory and so on. This showed that BIMs is important for its anticancer properties and have the potential to be used as anticancer agents. Besides all these, BIMs has other function such as transquilizers and as dietary supplement.

The 3-carbon atom position at the indole ring is the more reactive compare to the other position. For this reason, 3,3’-BIMs are preferred and are the majority BIMs that were found in literature. In 1886, 3,3’-BIMs were first prepared by Fischer through Friedel-Crafts reaction using indoles and carbonyl compounds as reactant in the condition of acid or base.

Previous Studies on Compounds containing Bis-Indole Group

In one of the studies, the researchers used DNA-based electrochemical biosensors to rapidly detect chemical compound that may have the ability and properties of antitumor agents that interfere the nucleic acids. Currently, this DNA biosensor technologies are under focused due to their ability in low-cost detecting specific DNA sequences not only in human, but in viral and in bacterial nucleic acids. Based on the study, the growth of cancer cell lines at lung, renal and breast was found to be reduced by 5,5’-dimethoxy-3,3’-methanediyl-bis-indole in a dose dependent method. Their result indicate that BIMs has the potential to be used as antitumor chemotherapeutic agent.

Carbazole

Carbazole was isolated first isolated by Graebe and Glaser from coal tar in 1872. Carbazoles is a tricyclic heteroaromatic alkaloids, made up by two benzene rings and a pyrrole group. Carbazoles represent a vital compound of indole containing heterocycles which is studied for their antitumor properties. A number of carbazoles have been approved and accepted to be used in cancer therapy after undergone clinical trials for their potent anticancer properties. Anticancer activity can be shown by the carbazole compound through the DNA intercalation. Besides that, telomerase and topoisomerase I/II which are the DNA-dependent enzymes can be inhibited by carbazoles as well. These activities were benefits by its structural integrity which are planar, polycyclic and aromatic. Carbazole alkaloids which can be found from the natural sources such as Clausena plants has shown its potential to inhibit tumor growth through direct cytotoxicity, induction of tumor cell apoptosis, and/or immune potentiation.

Over the years, a lot of attempts had been made to synthesize carbazole derivatives for the purpose of cancer research. The process and mechanism on how they act have been summarized. The promising compound with high potency had shown to be effectively reduce the cancer cell growth and entered the clinical trials.

It has been reported that a new catalyst PPh3.CF3SO3H (20 mol%). was used in the synthesis of di(diindolylmethyl)carbazole derivatives. The reaction between of 9-alkylcarbazol-3,6- dicarboxaldehydes and indole derivatives gives a good yield of Di(diindolylmethyl)carbazoles, given that they are in the condition required such as presence of catalyst PPh3.CF3SO3H in CHCl3 at room temperature.

Iodine as catalyst

Bis(indolyl)alkane can be produced through the electrophilic substitution reaction between carbonyl compound and indoles in the presence of Lewis acid, Brønsted acids or montmorillonite clay K-10 in promoting the reaction. However, in the presence reactant that carry nitrogen, Lewis acid such as InCl3, PPh3·HClO4 and so on are susceptible to undergo decomposition or deactivated and this foster the use of Lewis acid in excess amount. These problems can be circumvented by using the expensive triphenylphosphonium perchlorate, lithium perchlorate, and cyanuric chloride. However, these catalysts are not beneficial that they need longer reaction time and are not environmental friendly. Thus, iodine which is cheap and easy to handle is chosen to be the catalyst for this research project. More importantly, iodine is a nontoxic Lewis acid catalyst and can catalyses various reaction with high efficiency and selectivity.

Research Methodology

The proposed Bis(indolylmethyl)carbazoles will be synthesised and then extracted using rotavapor. The crude product will be purified by column chromatography. Lastly, the compound will be chracterised and identified using IR and H-NMR spectroscopies. Before the synthesis of 9-benzyl-3-(di(1H-indol-3-yl)methyl)-9H-carbazole, the starting materials of it have to be prepared, which are and 9-benzyl-9H-carbazole-3-carbaldehyde and indole.

Synthesis of starting materials, benzyl-9H-carbazole-3-carbaldehyde

First, 9H-carbazole will undergo alkylation by using benzyl bromide in dimethylformamide (DMF) in the presence of sodium hydride (NaH) at room temperature, forming 9-benzyl-9H-carbazole. Next, 9-benzyl-9H-carbazole will undergo aldol condensation phosphorus oxychloride (POCl3) in DMF. Initially the reaction will perform at 0°C in ice bath for 1 hour then heat at 90°C for another 2 hours to yield 9-benzyl-9H-carbazole-3-carbaldehyde.

Synthesis of 9-benzyl-3-(di(1H-indol-3-yl)methyl)-9H-carbazole

In order to synthesis the product which is 9-benzyl-3-(di(1H-indol-3-yl)methyl)-9H-carbazole, 1 mmol of 9-benzyl-9H-carbazole-3-carbaldehyde and 2 mmol of indole will be mixed at room temperature in the presence of iodine as the catalyst and acetonitrile as solvent for both of the reactant. The mixture will be stirred by the magnetic stirrer until the reaction is complete.

Extraction, Purification and Characterisation of the compound

When the reaction is completed, the mixture will be moved to a separating funnel where water and ethylacetate will be poured and mixed. The mixture will be shake and two layers will form where ethylacetate will be at the top layer while water at the bottom layer. Only the organic layer will be obtained from the mixture by using separating funnel. Then, the organic layer will be evaporated by rotavapor where the temperature is set at 78°C, the boiling point of ethylacetate, leaving only the crude product. The remaining water contained in it will be removed by drying over with anhydrous sodium sulphate. Next, to ensure a pure product, impurities will be removed by column chromatography and lastly, the pure product will be characterized via Infrared (IR) and Proton Nuclear Magnetic Resonance (1H-NMR) spectroscopies.