Current Organic Synthesis - Volume 15, Issue 2, 2018

Background: Hydroxamic acids are a major class of organic compounds. They have a wide variety of pharmacological actions in targeting cancers, cardiovascular diseases, HIV, Alzheimer's disease, Malaria, Allergic diseases. Objective: The present review focuses on the chemistry of conventional and non-conventional routes for the synthesis of hydroxamic acids reported till date. Conclusion: The hydroxamic acids are conventionally synthesized via carboxylic acid and their acid chloride derivatives. However, some other functional groups i.e. aldehyde, amine, amide and alcohol can also be converted to hydroxamate with ease. The solid phase synthesis techniques are also gaining importance for the synthesis of hydroxamic acids and these pathways have opened a wide arena for the synthesis of diverse and complex hydroxamic acids.

Background: Pyrrolidinone is a five membered heterocyclic ring that is a versatile lead compound for designing powerful bioactive agents. Pyrrolidinone nucleus is one of the most important heterocyclic compound indicating notable pharmaceutical effects. Many procedures for the preparation of pyrrolidinone and also their various reactions offer great scope in the field of medicinal chemistry. This fascinating group of compounds has diverse pharmacological activities such as antibacterial, antifungal, anticancer and anticonvulsant. Objective: The review article proposes to classify comprehensive information on chemistry and pharmaceutical effects of pyrrolidinone in order to open new viewpoint for future studies. Conclusion: It is clear from the review of the topic that a wide spectrum of pyrrolidinone analogues have been synthesized and the majority of these derivatives have indicated different significant biological activities. Thus, these analogues can be used for future progression of novel drugs against many more poor agents.

Background: Currently ruthenium complexes are immerging as effective anticancer agents due to their less toxicity, better antiproliferative and antimetastatic activity, better stability in cellular environment and most importantly variable oxidation and co-ordination states of ruthenium allows binding this molecule with a variety of ligands. So in past few years researchers have shifted their interest towards organoruthenium complexes having good fluorescent profile that may be applicable for cancer theranostics. Nowadays, photodynamic therapy has become more acceptable because of its easy and effective approach towards killing cancer cells. Objective: Objective of this review article is to shed light on synthesis, characterization, stability and fluorescence studies of various ruthenium [Ru(II) and Ru(III)] complexes and different bioactivity studies conducted with the synthesized compounds to test their candidacy as potent chemotherapeutic agents. Methods: Various heterocyclic ligands containing N,O and S as heteroatom mainly were prepared and subjected to complexation with ruthenium-p-cymene moiety. In most cases [Ru(η6-p-cymene)(μ-Cl)Cl]2 was used as ruthenium precursor and the reactions were conducted in various alcohol medium such as methanol, ethanol or propanol. The synthesized complexes were characterized by 1H NMR and 13C NMR spectroscopy, GC-MS, ESI-MS, elemental analysis and single crystal X-ray crystallography methods. Fluorescence study and stability study were conducted accordingly using water, PBS buffer or DMSO. Stable compounds were considered for cell viability studies. To study the efficacy of the compounds in ROS generation as photosensitizers, in few cases, singlet oxygen quantum yields in presence of light were calculated. Suitable compounds were selected for in vitro & in vivo antiproliferative, anti-invasive activity studies. Result: Many newly synthesized compounds were found to have less IC50 compared to a standard drug cysplatin. Those compounds were also stable preferably in physiological conditions. Good fluorescence profile and ROS generation ability were observed for few compounds. Conclusion: Numerous ruthenium complexes were developed which can be used as cancer theranostic agents. Few molecules were synthesized as photosensitizers which were supposed to generate reactive singlet oxygen species in targeted cellular environment in presence of a particular type of light and thereby ceasing cancer cell growth.

Background: Substituted piperazine heterocycles are among the most significant structural components of pharmaceuticals. N1/N4 substituted piperazine containing drugs and biological targets are ranked 3rd in the top most frequent nitrogen heterocycles in U.S. FDA approved drugs. The high demand of N1/N4 substituted piperazine containing biologically active compounds and U.S. FDA approved drugs, has prompted the development of Pd catalyzed C-N bond formation reactions for their synthesis. Buchwald-Hartwig reaction is the key tool for the synthesis of these compounds. Objective: This review provides strategies for Pd catalyzed C-N bond formation at N1/N4 of piperazine in the synthesis of drugs and biological targets with diverse use of catalyst-ligand system and reaction parameters. Conclusion: It is clear from the review that a vast amount of work has been done in the synthesis of N1/N4 substituted piperazine containing targets under the Pd catalyzed Buchwald-Hartwig amination of aryl halides by using different catalyst-ligand systems. These methods have become increasingly versatile as a result of innovation in catalyst design and improvements in reaction conditions. This review gives an overview of recent utilization of Buchwald-Hartwig amination reaction in drug/target synthesis.

Background: The Diels-Alder reaction has been widely utilised in the syntheses of biologically important natural products over the years and continues to greatly impact modern synthetic methodology. Recent discovery of chiral organocatalysts, auxiliaries and ligands in organic synthesis has paved the way for their application in Diels-Alder chemistry with the goal to improve efficiency as well as stereochemistry. Objective: The review focuses on asymmetric syntheses of flavonoid Diels-Alder natural products that utilize chiral ligand-Lewis acid complexes through various illustrative examples. Conclusion: It is clear from the review that a significant amount of research has been done investigating various types of catalysts and chiral ligand-Lewis acid complexes for the enantioselective synthesis of flavonoid Diels-Alder natural products. The results have demonstrated improved yield and enantioselectivity. Much emphasis has been placed on the synthesis but important mechanistic work aimed at understanding the enantioselectivity has also been discussed.

Backiground: Alzheimer's disease is a fatal, complex, neurodegenerative disease over 46 million people live with dementia in the world characterized by the presence of plaques containing β-amyloid and neuronal loss. The GPE acts as a survival factor against β-amyloid insult in brain and suggests a possible new therapeutic strategy for the treatment of Central Nervous System injuries and neurodegenerative disorders. The structural simplicity of GPE makes it a suitable lead molecule for the development of new drugs that to cross the blood-brain barrier. Objective: With these aims in mind, we embarked on a synthetic program focused on the modification of the Lproline residue of GPE in order to investigate its importance on the neuroprotective activities. Method: The general synthetic strategy involved the preparation of several modified proline residues, which were subsequently coupled to N-Boc-glycine-OH and glutamic dimethyl ester hydrochloride. Results: the mixture of compounds 11 was obtained in good yields (72%) under these conditions, and this was readily separated by column chromatography and the components were identified by 1H and 13C NMR spectral, as well as by its EI HRMS. Conclusion: Compound (±)-8 was coupled with L-glutamic dimethyl ester hydrochloride gave a mixture of dipeptides 9a and 9b in a satisfactory yield. The use of T3P as coupling agent of the mixture 10a and 10b with Boc-glycine provided a new analogue of GPE, tripeptide 11, obtained with an overall yield of 65% from (±)-1.

Aims and Objectives: Cantharidin is a terpenoid with a high vesicant potency isolated from Mylabris caraganae and various other insects, which originates from the Chinese traditional medicine and has a long history of use as antiproliferative agent. Modified cantharidin derivatives are researched for retainable antitumor activities and lower toxicity. And imidazolium salt is an important building block in drug discovery with pharmacological activities. This study was undertaken to identify that N-substituted norcantharidin imidazolium derivatives possess potential bioactivity. Material and Method: Using readily available furan, maleic anhydride and imidazoles as starting materials, a series of novel N-substituted norcantharidin imidazolium derivatives have been designed and synthesized. The cytotoxic potential of all newly synthesized N-substituted norcantharidin imidazolium derivatives was assessed in vitro against a panel of human tumor cell lines, Human epidermal carcinoma, human lung carcinoma, liver hepatocellular carcinoma, pheochromocytoma of the rat adrenal medulla. Results: The imidazolium derivatives 6a-6f and 6m-6o, bearing a 5,6-dibromohexahydro-4,7-epoxyisobenzofuran- 1,3-dione or 5-bromo-7-oxabicyclo[2.2.1]hepta- 2,5-diene-2,3-dicarboxylate and electron-donating group, carbonyl and propenyl substituent at position-1 of the imidazole ring, were found to be the most potent compounds as antitumor agents. Notably, compounds 6m and 6n exhibited cytotoxic activity selectively against Hela and A549 cell lines with IC50 values 1.38-fold, 5.04-fold, lower than DDP, while compound 6f showed powerful inhibitory activities selectively against Hela and PC12 cell lines. Conclusion: Steric and electronic effects have an important role in determining the cytotoxic activity of imidazolium salts. The norcantharidin-imidazole 6f, 6m, 6n and 6o can be considered to be promising leads for further structural modifications guided by the valuable information derivable.

Aim and Objective: [(9H-Fluoren-9-yl)methoxy]carbonyl (Fmoc)-protected 2-aminoethanesulfonyl chlorides with various functionalized 1-substituents may be of use as building blocks for the Fmoc strategic synthesis of sulfonopeptides. Material and Method: Fmoc-protected 2-aminoethanesulfonyl chlorides with different functionalized 1- substituents were synthesized via radical addition of N-Fmoc allylamine and xanthates with functionalized Ssubstituents, and subsequent oxidative chlorination with N-chlorosuccimide/HCl. Results: Fmoc-protected 2-aminoethanesulfonyl chlorides with different functionalized 1-substituents were synthesized via radical addition and subsequent oxidative chlorination. The mechanism on the oxidative chlorination is proposed. Conclusion: The current method is an expeditious, convenient, and practical method for the synthesis of Fmocprotected 2-aminoethanesulfonyl chlorides with different functionalized 1-substituents in good to excellent yields.

Aim and Objective: α-Arylglycines belong to an important class of non-proteinogenic amino acids. Petasis 3-component, one-pot reaction lends itself to be suitable for the synthesis of α-Arylglycines. Because of the low reactivity, Petasis reaction requires long reaction time. Our objective is to use ultrasound irradiation to accelerate this versatile Petasis' synthesis of α-Arylglycines. Materials and Methods: Ultrasound irradiation as a physical tool to accelerate the Petasis 3-component reaction without any auxiliary catalyst can significantly shorten the reaction time. The operation is simple. It can be applied to a wide range of substrates. In order to highlight the remarkable utility of the ultrasound in Petasis reaction, we have compared side-by-side the reactivity between the reaction with ultrasound and the one without ultrasound. Results: Using ultrasound, the reaction times of Petasis reactions with various amine substrates including primary and secondary amines, heterocyclic amines, with a wide variety of boronic acids having different substituents (activating and deactivating groups) in the phenyl rings, and with glyoxylic acid and salicylic aldehyde were shortened from 5 to more than 20-fold. Conclusion: We have discovered the first examples of an efficient ultrasound-promoted approach for Petasis reaction to prepare a series of α-arylglycines in high yields and in excellent purities. The low reactivity of the reactions in this study were significantly enhanced by the ultrasound irradiation. By virtue of the acceleration and the operational simplicity, the present ultrasound assisted Petasis reaction can find applications in the synthetic areas of the already widely used Petasis three-component reaction.

Aim and Objective: In the work, we have successfully presented a synthetic route for the synthesis of novel 2',4'-dihydrospiro[chroman-2,3'-pyrazol]-4-one derivatives via one pot multicomponent approach. Material and Method: Substituted 2',4'-dihydrospiro[chroman-2,3'-pyrazol]-4-one were prepared through cascade three-component condensation of ortho-hydroxyacetophenone, β-ketoester, hydrazine in the presence of pyrrolidine as a catalyst under ethanol reflux conditions. Results: A series of novel 2',4'-dihydrospiro[chroman-2,3'-pyrazol]-4-one have been synthesized through a facile strategy. These structures of newly synthesized derivatives were determined by 1H, 13C NMR, HRMS and CHNS analysis. Conclusion: We have achieved the one-pot, three-component synthesis of highly substituted pyrazole spirochromanones in presence of pyrrolidine as a catalyst under ethanol reflux conditions. Using different types of aliphatic and aromatic β-ketoesters, o-hydroxyacetophenone derivatives and different kinds of hydrazine derivatives as building blocks, we could construct novel libraries of substituted pyrazole spirochromanones that make this method suitable for combinatorial and parallel synthesis in drug discovery.

Aim and Objective: Pyrazolo pyridine skeleton is an interesting class of heterocycles due to its diverse biological properties including antitumor, antioxidant and antibacterial activities. The objective of this work was established in vitro antiproliferative activities against MCF-7 (breast cancer) human cell lines for of the synthesized compounds IIIa-e. The effect of the molecular and electronic structures on the biological activity was performed to compare the theoretical data with the experimental observations. Material and Method: The synthesized compounds were prepared by conventional heating and microwave irradiation technique. The structure of the prepared compounds was confirmed by different spectroscopic tools. The compounds IIIa-e was tested for antitumor activity against breast cancer cell line. The quantum chemical, molecular docking and SAR studies were performed for the prepared compounds. Results: The microwave irradiation as a source of energy was used to improve the yield and to reduce the time of the reaction. Under this technique, the reaction time was reduced from 4-8 hours to 15-25 min. The yield of the reactions was increased from 81% to 92%. Also, the obtained products were cleaner. Conclusion: The quantum chemical descriptors confirmed that inhibitor1-(4-methoxyphenyl)-3-(1-methyl-1Himidazol- 4-yl)-6-phenyl-1H-pyrazolo[3,4-b]- pyridine-4-ol (IIIb) is the most potent and reactive among the investigated compounds. This conclusion is congruent with the results obtained experimentally.

Aim and Objective: Synthesis of new α-aminophosphonates containing quinazoline moiety through Kabachnik-Fields reaction in the presence of copper triflate catalyst [32], followed by studying their antimicrobial activities and in vitro anticancer activities against liver carcinoma cell line (HepG2) with the hope that new anticancer agents could be developed. Also, the quantum chemical calculations are performed using density functional theory (DFT) to study the effect of the changes of molecular and electronic structures on the biological activity of the investigated compounds. Material and Method: The structures of the synthesized compounds are confirmed by FT-IR, 1H NMR, 13C NMR, 31P NMR and MS spectral data. The synthesized compounds show significant antimicrobial and also remarkable cytotoxicity anticancer activities against liver carcinoma cell line (HepG2). Density functional theory (DFT) was performed to study the effect of the molecular and electronic structure changes on the biological activity. Results: It was found that the electronic structure of the substituents affects on the reaction yield. The electron withdrawing substituent, NO2 group 3b, on the aromatic aldehydes gave a good yield more than the electron donating substituent, OH group 3c. The electron deficient on the carbon atom of the aldehydic group may increase the interaction of the Lewis acid (Cu(OTf)2) and the Lewis base (imine nitrogen), and accordingly, facilitate the formation of imine easily, which is attacked by the nucleophilic phosphite species to give the α- aminophosphonates. Conclusion: The newly synthesized compounds exhibit a remarkable inhibition of the growth of Grampositive, Gram-negative bacteria and fungi at low concentrations. The cytotoxicity of the synthesized compounds showed a significant cytotoxicity against the liver cancer cell line (HepG 2). Also, it was shown from the quantum chemical calculations that the electron-withdrawing substituent increases the biological activity of the α-aminophosphonates more than the electron donating group which was in a good agreement with the experimental results. Also, a good agreement between the experimental FT-IR and the calculated one was found.