Nav: Home

Microwave-assisted iodine-catalyzed rapid synthesis of 6H-indolo[2,3-b]quinolines

October 12, 2017

Indoloquinoline alkaloids have received significant popularity because of their antimalarial and DNA intercalating properties as well as their use as folk medicines for the control of fever, amoebiasis and malaria. Related metabolites include cryptotackieine and norcryptotackieine which are linear indolo[2,3-b]quinoline alkaloids. These molecules have demonstrated numerous medicinal activities including antimicrobial, and cytotoxicity. They act through DNA intercalation and inhibition of topoisomerase II inhibition. Consequently, organic and medicinal chemists and biologists have become interested in their concise preparation and studies of their biological activities. A few synthetic routes have been developed for the preparation of these structurally unique and complex indole heterocycles. Interestingly, most of these available methods are one-pot methods. For example, high temperature reaction of molecular iodine-catalyzed reaction in diphenyl ether, pivalic acid and ruthenium-exchanged FAU-Y zeolite in 1,4-dioxane is performed. N-Bromosuccinimide at room temperature is found to be good for this purpose. The principal limitation is that almost all of these methods require a very long time. Moreover, the yields of the target molecules are low.

The current research is aimed to develop an efficient synthetic method for the synthesis of indoloquinoline alkaloids mentioned above. Considering the known procedures and analyzing the conditions of the experiments, the iodine-catalyzed tandem method is proved to be excellent. Despite the superiority of iodine, this method produces products with low to moderate yields, requires long reaction time and high temperature. Therefore, an improvement of molecular iodine-catalyzed reaction for this purpose is necessary.

Our research group has been exploring microwave-induced reactions for more than 25 years. Reactions conducted under microwave oven are known to be rapid and successful at much less drastic conditions. Moreover, they also produce the target molecules in better yields without giving side reactions in most of the examples. In conventional methods, unwanted side reactions in many instances lower the yields of the products or produce mixture of products and therefore, isolation of the desired compounds become tedious. On the basis of several successes on microwave-induced chemistry and our interests in the preparation of medicinally useful compounds, we have investigated the preparation of cryptotackieine and norcryptotackieine and their derivatives in automated microwave oven in tightly sealed reaction container.

Indole-3-carboxyaldehyde and two equivalents of aniline in presence of 10 mol% of molecular iodine at 600C and 300 watt power in a sealed vessel are irradiated in an automated microwave. It is interesting to note that the reaction proceeds rapidly with an increase in the yield of the product compared to the conventional heating (oil bath or heating mantle) at much higher temperature. The structure of the starting reactants and products suggests a most probable mechanism. Dehydration to imine from aldehyde and amine, nucleophilic reaction of the imine, annulation and subsequent aromatization occurs in a tandem process in a one-pot method.

This method is extended for the preparation of 6H-indolo[2,3-b]quinolines. As expected, the previously known compounds are synthesized very rapidly and with simple work-up, and without extensive purification. No solvent is used when one of the reactants is liquid or oil. These reactions are also performed in the presence of solvents (THF, MeOH, CHCl3, and CH2Cl2). THF and MeOH are proved to be the best solvent whereas CHCl3 and CH2Cl2 are moderately good for this method.

An expeditious simple and rapid microwave-assisted procedure for the synthesis of significant types of indoloquinolines using molecular iodine as catalyst in a one-pot is developed. The procedure described herein is the first rapid method for the synthesis of novel indoloquinolines. The rate acceleration by microwave-induced method is probably due to the alteration of the transition state of the series of reactions that occur in this tandem process. The benefit of this process is the lowered energy consumption compared to traditional method under reflux or high temperature that requires input of latent heat of vaporization. In this method, vaporization is not possible and so little expenditure of latent heat occurs. The non-ionizing radiation of the microwave is absorbed very efficiently by the reactants and polar solvents and thereby accelerates the process in an unbelievable way.
Prakash T. Parvatkara,b, P. S. Parameswaranc, Debasish Bandyopadhyayd, Sanghamitra Mukherjeed, Bimal K. Banikd,e*

aDepartment of Chemistry, Goa University, Taleigao Plateau, Goa 403 206, India;

bCurrent Address: Department of Chemistry and Chemical Biology, Northeastern University, Boston, MA 02115, United States

cCSIR-National Institute of Oceanography, Regional Centre, Kochi 682 018, India

dDepartment of Chemistry, The University of Texas-Pan American, Edinburg, TX 78539, United States; eCurrent Address: Community Health System of South Texas, 3135 South Sugar Road, Edinburg, TX 78539, United States; Phone: 281-813-2104, Fax: 956-259-8085; Email:;

Bentham Science Publishers

Related Molecules Articles:

The inner lives of molecules
Researchers from Canada, the UK and Germany have developed a new experimental technique to take 3-D images of molecules in action.
Novel technique helps ID elusive molecules
Stuart Lindsay, a researcher at Arizona State University's Biodesign Institute, has devised a clever means of identifying carbohydrate molecules quickly and accurately.
How solvent molecules cooperate in reactions
Molecules from the solvent environment that at first glance seem to be uninvolved can be essential for chemical reactions.
A new way to display the 3-D structure of molecules
Berkeley Lab and UC Berkeley Researchers have developed nanoscale display cases that enables new atomic-scale views of hard-to-study chemical and biological samples.
Bending hot molecules
Hot molecules are found in extreme environments such as the edges of fusion reactors.
At attention, molecules!
University of Iowa chemists have learned about a molecular assembly that may help create quicker, more responsive touch screens, among other applications.
Folding molecules into screw-shaped structures
An international research team describes the methods of winding up molecules into screw-shaped structures.
Artificial molecules
A new method allows scientists at ETH Zurich and IBM to fabricate artificial molecules out of different types of microspheres.
Molecules that may keep you young and alive
A new study may have uncovered the fountain of youth: plant extracts containing the six best groups of anti-aging molecules ever seen.
Fun with Lego (molecules)
A great childhood pleasure is playing with Legos® and marveling at the variety of structures you can create from a small number of basic elements.

Related Molecules Reading:

Molecules: The Elements and the Architecture of Everything
by Theodore Gray (Author), Nick Mann (Photographer)

Reactions: An Illustrated Exploration of Elements, Molecules, and Change in the Universe
by Theodore Gray (Author)

We Are All Made of Molecules
by Susin Nielsen (Author)

Molecules Of Emotion: The Science Behind Mind-Body Medicine
by Candace B. Pert (Author)

Elements: A Visual Exploration of Every Known Atom in the Universe
by Theodore Gray (Author), Nick Mann (Photographer)

DMT: The Spirit Molecule: A Doctor's Revolutionary Research into the Biology of Near-Death and Mystical Experiences
by Rick Strassman (Author)

Napoleon's Buttons: How 17 Molecules Changed History
by Penny Le Couteur (Author), Jay Burreson (Author)

Explore Atoms and Molecules!: With 25 Great Projects (Explore Your World)
by Janet Slingerland (Author), Matt Aucoin (Illustrator)

The Billion Dollar Molecule: One Company's Quest for the Perfect Drug
by Barry Werth (Author)

Atoms and Molecules (My Science Library)
by Tracy Maurer (Author)

Best Science Podcasts 2018

We have hand picked the best science podcasts for 2018. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Why We Hate
From bullying to hate crimes, cruelty is all around us. So what makes us hate? And is it learned or innate? This hour, TED speakers explore the causes and consequences of hate — and how we can fight it. Guests include reformed white nationalist Christian Picciolini, CNN commentator Sally Kohn, podcast host Dylan Marron, and writer Anand Giridharadas.
Now Playing: Science for the People

#482 Body Builders
This week we explore how science and technology can help us walk when we've lost our legs, see when we've gone blind, explore unfriendly environments, and maybe even make our bodies better, stronger, and faster than ever before. We speak to Adam Piore, author of the book "The Body Builders: Inside the Science of the Engineered Human", about the increasingly amazing ways bioengineering is being used to reverse engineer, rebuild, and augment human beings. And we speak with Ken Thomas, spacesuit engineer and author of the book "The Journey to Moonwalking: The People That Enabled Footprints on the Moon" about...