Browsing by Author "Kumar, Sunil"

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Diversity-Oriented Synthesis of Coumarin-Linked Benzimidazoles via a One-Pot, Three-Step, Intramolecular Knoevenagel Cyclization
(2017-04-01)
Yao, Po-Hsin Eric
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Kumar, Sunil
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Liu, Yu-Li
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Fang, Chiu-Ping
;
Liu, Chia-Chen
Diversity-oriented synthesis of coumarin-linked benzimidazoles from N-(2-aminophenyl)-2-cyanoacetamide was achieved via a one-pot, three-step sequential reaction in excellent. yields. In situ intramolecular cyclization of the cyanoacetamide afforded benzimidazoles which subsequently underwent a Knoevenagel condensation of the 2-cyanome-thylbenzimidazoles with salicylaldehydes promoted by triethylamine to reach the target compounds. An important intermediate, 2-(2-imino-2H-chromen-3-yl)-1H-benzimidazole was characterized by X-ray analysis and further hydrolyzed to 2-(coumarin-3-yl)benzimidazole in acidic condition. Among the synthesized compounds, some were found to be promising inhibitors of porcine kidney D-amino acid oxidase (pkDAO).
Enantiospecific Synthesis of Imidazoquinazolin-2-ones via Base-Catalyzed Tandem Cyclization
(2017-09-29)
Kumar, Sunil
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Ho, Pei-Heng
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Barve, Indrajeet J.
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Sun, Chung-Ming
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應用化學系
A facile protocol for the enantiospecific synthesis of novel (S)-3-substituted imidazo[2,l-b]quinazoline-2-ones via tandem reaction of substituted (S)-3-amino-4-aminomethylbenzoates and cyanogen bromide under basic conditions is explored. This tandem process involves addition reaction of substituted (S)-3-amino-4-aminomethylbenzoates to CNBr to yield 2-imino tetrahydroquinazoline carboxylate intermediates followed by insitu intramolecular aminolysis to afford the triheterocyclic imidazo[2,l-b]quinazoline-2-ones in good yields and high enantiomeric purity.
Post-Pictet-Spengler Cyclization (PPSC): A Strategy to Synthesize Polycyclic beta-Carboline-Derived Natural Products and Biologically Active N-Heterocycles
(1970-01-01)
Singh, Rahul
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Kumar, Sunil
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Patil, Madhuri T.
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Sun, Chung-Ming
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Salunke, Deepak B.
Pictet-Spengler reaction is a typical condensation reaction of beta-arylethylamine or Tryptamine with an aldehyde or ketone followed by ring closure to generate tetrahydroisoquinoline (THIQ) and Tetrahydro-beta-carboline (TH beta C), respectively. Both these key skeletons represent huge range of structurally diverse naturally occurring isoquinoline and indole alkaloids. Nature has synthesized structurally complex Reserpine, Ajmalicine as well as other related alkaloids using various biosynthetic pathwaysviaPictet-Spengler reaction followed by post-Pictet-Spengler cyclization (PPSC) stratergy. This biosynthetic process is the short and reliable method to access diverse range of polycyclic heterocycles. Over the period of last sixty years, several researchers have synthesized complex alkaloids without highlighting the synthetic utility of the post-Pictet-Spengler cyclization strategy. We summarized the synthesis of numerous natural products and related natural product inspired heterocyclic scaffolds which follow the PPSC strategy to demonstrate its usefulness for the construction of diverse compound collection. 1. Introduction 2. beta-Carboline Fused Heterocycles Synthesized via post-Pictet-Spengler C1-N2 Cyclization 3. beta-Carboline Fused Heterocycles Synthesized via post Pictet-Spengler C1-N9 Cyclization 4. beta-Carboline Fused Heterocycles Synthesized via post-Pictet-Spengler C3-N2 Cyclization 5. beta-Carboline Fused Heterocycles Synthesized via post-Pictet-Spengler C1-C3 Cyclization 6. Conclusion
Regioselective Synthesis of Angular Isocoumarinselenazoles: A Benzoselenazole-directed, Site-specific, Ruthenium-catalyzed C(sp(2))-H Activation
(2018-03-01)
Dhole, Sandip
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Liao, Jen-Yu
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Kumar, Sunil
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Salunke, Deepak B.
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Sun, Chung-Ming
The synthesis of new, angular isocoumarinselenazoles is described, which involves the construction of 2-amino benzoselenazoles and their regioselective C2N-alkylation and alkyne insertion. An expeditious and metal-free synthesis of 2-aminobenzoselenazoles by the reaction of methyl 3-amino-4-fluorobenzoate and isoselenocyanates was achieved. Further N-alkylation of the 2-aminobenzoselenazoles resulted the formation of two regioisomers with different reactivities towards the alkyne insertion. The regioselective construction of the a-pyrone ring on the benzo[1,3-d] selenazole skeleton was achieved via a ruthenium (II)-catalyzed oxidative annulation. It is clear that the selenazole nitrogen plays an important role in the observed selectivity.
Thiazole: A Privileged Motif in Marine Natural Products
(2019-01-01)
Kumar, Sunil
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Aggarwal, Ranjana
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應用化學系
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Department of Applied Chemistry
Marine natural products have proven to be a rich source of drugs and drug leads. These natural products are secondary metabolites and show biological activity against bacteria, fungi and viruses. Natural products containing thiazole ring occur often in marine sources. They exhibit diverse and remarkable biological activities, including antitumor, antibacterial, anti-inflammatory and cytotoxic activities, to name a few. This review surveys the natural thiazole derivatives that have been isolated from marine microorganisms, with emphasis on biological implications in last three decades.