Current Organic Synthesis - Volume 14, Issue 2, 2017

With its introduction as a moulding material in 1940s, the polyamides (PAs) have been transformed into true engineering thermoplastics over a period of time. Owing to high thermal and chemical resistances in combination with exceptional mechanical durability, these classes of polymers have come a long way in establishing themselves as materials of choice for diverse application types. The recent technical advancements through the incorporation of novel functionalities to the basic amide structure of PAs has further enhanced their performance which contributed for an exponential growth in high-demand uses, especially in automotive and electrical industries. By keeping in view of the typical role played by PAs in various industrial sectors, this review article is designed to start with a brief historical background, which indulges into a comprehensive discussion to explore the recent developments in the research and design of next generation PA compounds and their engineered composites. Apart from the currently operating, more dominant and conventional class of polyamide- 6 and polyamide-66, this work further focusses towards the development of new class of amides through selective compounding of different diamine and dicroboxlyic acid monomers, especially intended for niche markets. In addition, we also discussed about some reactive and long fibre-reinforced PA products developed by global commercial entities to substitute certain metal-based appliances in house-hold and precision machine products. Finally, the very recent research activities involved in the synthesis of bio-based PAs and their composites are also presented here.

Poly lactic acids (PLA) received greater attention among other biodegradable plastics as they exhibit higher strength, stiffness, molecular weight and biocompatibility. PLA are polymers in which the stereo chemical structures are modified by polymerizing according to different versatile and flexible applications. The increased demands for PLA resins create a promising and attractive positive impact on the global agricultural economy by being nontoxic for both human body and the environment. However, the inherent brittleness of PLA essentially hampers its wide applications frame. PLA surface modification through blending, polymerization, filler and fiber reinforcement for fabricating high end composite products perfectly overcomes its shortcomings for various purposes. Present review article is designed to be a comprehensive source of recent literature on PLA structure, synthesis, modification and its different applications. This review article also aims to cover the reported research work of PLA biocomposites and nanocomposites, including manufacturing techniques and there diverge industrial applications.

The amounts of plastics consumed annually all over the world have been growing substantially. Although low density, strength, user-friendly designs, processing capabilities, long life, as well as light weight coupled with high cost-effectiveness make plastics very promising candidates for several applications, they however have ecological issues in terms of waste disposal which has become a major worldwide problem. In fact, there are both technological and economic issues preventing progresses in this field. Here, an overview of the recycling and recovery of polymer waste is provided, followed by a brief discussion on the current recycling methods and technologies covering primary (re-extrusion), secondary (mechanical), tertiary (chemical), and quaternary (energy recovery) processes. Global polymer recycling markets are then reviewed.

In previous years natural fibers are frequently used to reinforce materials. The biodegradability is the main advantage of natural fibers. The disadvantage of using natural fibers in polymer composite material is their poor adhesion ability with a polymeric matrix which affects the various physical and mechanical properties of the composite material. To overcome this disadvantage, the surface of the natural fibers needs to be modified so that a good fiber-matrix adhesion can be established. The various treatment methods such as physical treatment and chemical treatment methods for the improvement of fiber-matrix adhesion have been discussed in this paper. So the overall objective of this review paper is to highlight the previous and recent studies related to the surface treatment of natural fibers and their reinforcement in thermoplastic polymer matrix composites. The improvement in various properties specifically mechanical properties by reinforcing these fibers into thermoplastic polymer matrix composites has also been reported in this paper.

Development of a new polymer from renewable resources is getting serious attention from researchers due to the environmental issue caused by petroleum based polymer. The aim of this paper is to study the behavior of sugar palm starch (SPS) based thermoplastic containing agar in the range from 10 to 40 wt%. The thermoplastics were melt-mixed and then hot pressed at 140 oC for 10 minutes followed by flexural, impact and thermogravimetric analysis. Thermogravimetric analysis (TGA) showed that incorporation of agar increased the char residue content from 9.17 to 10.87 wt%. For mechanical properties, the addition of agar improved the flexural strength and modulus of SPS/agar blends. The impact strength of thermoplastic SPS was increased respectively with the addition of agar. However, at higher agar content (30 wt% to 40 wt%), the impact strength was decreased which attributed to high rigidity of the material at this ratio. In conclusion, incorporation of agar has improved the flexural, impact and thermal properties of thermoplastic SPS which widened the potential application of this biopolymer in future.

In the current scenario, the availability of safe and clean drinking water is decreasing day by day. To overcome this difficulty, Nanotechnology has been undertaken to explore various efficient ways for treatment of waste water in a more precise and accurate way with the support of various nanomaterials. Nanoparticles (NPs) have huge potential that enables them to participate in waste water treatment and/or water purification technologies. Their exclusive features such as high surface area, high mechanical properties, greater chemical reactivity, lower cost and energy, allow them to eliminate precisely toxic metal ions, viruses, bacteria, organic and inorganic solutes from the waste water. Different types of nanomaterials such as metal nanoparticles, nanosorbents, bioactive nanoparticles, nanofiltration (NF) membranes; carbon nano tubes (CNTs), zeolites and clay are proved to be efficient materials for waste water treatment. This review discusses recent developments in various nanomaterials used for waste water treatment and/or water purification technologies such as adsorption, catalysis and disinfection. Special attention has been given to three major classes such as organic, inorganic and biological water pollutants. In addition, promises, facts and challenges of these new technologies have been seriously examined.

Biofibres have gained a considerable attention due to benefits such as environmentally friendly, renewability, biodegradability, low weight and cost. Although many researches have been done on sugar palm fibres (SPF), there are few studies on characterizing their micromechanical properties by using nanoindentation. The hardness and elastic modulus of isolated SPF is 11.3±0.545 MPa and 149±4.96 MPa respectively. The hardness properties were found to be comparable with the other established fibres i.e. bamboo (12.9±0.378 MPa), jute (11.2±0.47 MPa) and hemp (7.2±0.303 MPa). Then, biopolymer derived from sugar palm starch (SPS) and sugar palm fibre reinforced sugar palm starch (SPF/SPS) biocomposite were successfully developed by using hot press with the presence of glycerol as plasticizer. These environmentally friendly materials were tested for their low velocity impact response. The result shows that SPF/SPS exhibited the best impact properties compared to SPS. The impact load of composites increases with increasing impact energy for both SPS and SPF/SPS specimens.

In the recent years, the research about polyurethane (PU) composites (thermoplastic, thermoset, biobased polyurethane with synthetic fibers (glass, aramid and carbon) and natural fibers used as reinforcement of polymers has been increased due to their biodegradability, lightness, reduced cost and favorable mechanical properties. Unique mechanical, thermal, and chemical properties of Polyurethanes (thermoset/thermoplastic) can be designed by the reaction of various polyhydric compounds (polyols) and polyisocyanates which is derived from the formation of cross-linked polyurethanes. One of the challenges that researchers face today is to achieve satisfactory interfacial bonding which will result in products with better mechanical and thermal properties. Composites having better mechanical and thermal properties could find more industrial applications and consequently would have greater commercial acceptance. However, this is difficult due to the hydrophilicity of the fibers and the hydrophobicity of polymers such as polyurethane. In this review paper, comprehensive review about PU and its polymer composites were presented with concentrating on the effect of the different kinds of natural and synthetic fibers on the PU based polymer composites products. We also discussed the effect of chemical treatments of natural fibers on improvement of interfacial bonding between natural fiber and polyurethane matrix for development of advanced materials with better mechanical and thermal properties.

Carbon nanotube (CNT) is a promising allotrope of carbon having exceptional mechanical, electrical, thermal and multifunctional properties. Applications of CNTs are increased when it is chosen as an effective filler in polymer composites. The chemical functionalized CNTs are more compatible as reinforcing agent in polymer composites due to its polar nature. This review involves the preparation, characterization and various applications of CNT/polymer composites. Different methods of functionalization of CNTs are discussed and compared with respect to their advantages. The properties of polymers, copolymers and biopolymers based CNT embedded nanocomposites are elaborated. The applications of CNT/polymer nanocomposites are discussed in comparison to reported results.

Development of new bio- based composites from renewable resources is getting wide attention from researchers due to environmental issue caused by traditional composites. Rice husk is a new potential renewable source of fillers for bio-composites to produce green products. Rice husk is the outer sheath surrounding rice grains during their growth. The aim of this work is to systematically review the parameters that affect the rice husk -polymeric composites in order to enhance their usage in various sustainable designs and applications. it is dedicated that rice husk composites are not used effectively due to the lack of understanding over its potential for such green composites. Moreover, systematic review of the published works demonstrated that the lack of awareness to environmental problems and technology as well as socio-economy problems prevent proper utilization of rice in bio-composites for sustainable products. Moreover, systematic discussions of the parameters that affect the performance of rice husk - composites are illustrated in this work to enhance its implementations for future sustainable products.

Background:α-Aminophosphonates are an important class of compounds in medicinal chemistry with a wide range of biological effects. Despite the numerous synthetic methods for α-aminophosphonates reported in literature, there is still a need for the development of a simpler and greener protocol, for high throughput library synthesis. Objective: The primary objective of this work was to develop a simple, mild, eco-benign and low cost protocol, to obtain a wider variety of α-Aminophosphonates for biological screening. Method: We report herein a simple and green methodology for the synthesis of α-Aminophosphonates, in good yields, through the zinc triflate-catalyzed one-pot multi-component reaction of aldehydes, amines and dialkyl phosphites, at room temperature, under solvent-free conditions. Results: The one-pot three-component condensation of aldehydes, amines and dialkyl phosphites, performed at room temperature, under solvent-free conditions, in the presence of a catalytic amount of zinc triflate (10 mol%), gave the corresponding α-Aminophosphonates in 72-93% yield. The present method was found to be tolerant toward various aldehydes, amines and dialkyl phosphites. A mechanistic rationalization for this reaction is also provided. Conclusion: We have successfully developed an efficient, green and straightforward methodology for the synthesis of α-Aminophosphonates, through the zinc triflate-catalyzed one-pot multi-component reaction of aldehydes, amines and dialkyl phosphites, at room temperature, under solvent-free conditions. This synthetic strategy offers significant advantages such as good yields, versatile substituents, mild reaction conditions, easy workup and environmental safety, what make this protocol more amenable for high throughput library synthesis.

Background: (-)-Tatarinoids A, B, and C are 3 of 19 compounds that have been isolated from the rhizome of the plant Acorus tatarinowii. Used in Chinese medicine, Acorus tatarinowii possesses pharmacological effects on the central nervous system by regulating cyclic adenosine monophosphate (cAMP) activity. Previously published computational studies suggested R configurations for all three natural products. No synthesis of (-)- Tatarinoids A and B had been reported, while (-)- Tatarinoid C had been previously investigated and we have reported on the first total synthesis of its enantiomer. Objective: Herein, we describe the syntheses of (-)-Tatarinoids A, B, and C in 1 to 5 steps. Herein we also report on how our synthetic studies of (-)-Tatarinoids A, B, and C allowed for structure elucidation and we revised the stereochemical configurations of all three natural products. Method: (-)-Tatarinoid A and (-)-Tatarinoid C are both constructed in 3 steps from 1-bromo-2,4,5- trimethoxybenzene. Results: We have completed the syntheses of these natural products in overall yields of 63% and 74%, respectively and in greater than 99% ee. (-)-Tatarinoid B is also synthesized from 1-bromo-2,4,5-trimethoxybenzene in five steps with an overall yield of 11% and in greater than 99% ee. Conclusion: We have concluded the correct stereochemical assignment for all three Tatarinoids is an S configuration rather than the originally proposed R stereochemistry.

New 5-oxazolones have been synthesized via N-protected amino acids which were prepared from various aryl acyl halides and L-amino acids, with DCC. Then, we studied the ring opening reactions of 5-oxazolones with nucleophilic attack by primary aryl amines to obtain new racemic benzamide derivatives. All new synthesized compounds have been characterized by FTIR, 1H, 13C NMR, GC/MS, LC/MS and Qtof analyses. X-Ray results of N-(1-((4-chlorophenyl)amino)-3-methyl-1-oxopentan-2-yl)-3-(trifluoromethyl)benzamide clearly showed absolute stereostructure.

Background: Pyrimidines are an important component of nucleic acids and they have been used as building blocks in pharmaceuticals for the synthesis of antiviral, antineoplastic, antibacterial, and antifungal agents. Similarly, the related thiouracil derivatives are potential therapeutics as antiviral, anticancer, and antimicrobial agents. For example, S-alkylation and N-alkylation products have been recently reported as novel antibacterial, cytotoxic agents and unique HIV reverse transcriptase inhibitors. Methods: The antiviral activity of HAV was determined through treatment of Vero cells with test materials 24 hr pre-infection with an HAV model. HAV was 10-fold serially diluted in medium 199-E supplemented with 2% FCS (GIBCO-USA). The end point dilution that induced 5% infectivity was determined. The antiviral activity of the tested compounds was calculated by subtracting the infectivity titer of the cells treated with the virus test material from that of the non-treated cells. Results: Anticancer activity of the new compounds against MCF-7 and HEPG-2 showed compound 2 the most potent active, followed by compound 6; their half maximal inhibitory concentrations(IC50) were 20.72, 25.46, 29.02 and 37.15, whereas compound 1 showed the lowest activity, with IC50 values of38.5 and 62.02. The antiviral activity of the synthesized compounds revealed that all the tested compounds showed variable degrees of antiviral activity with IC50 values ranging from 26.3 to 349.70. Results showed that compounds 1 and 3 had the highest antiviral activity, with a high percentage of viral reduction. Conclusion: The findings in results demonstrate the potential for thiouracils to serve as lead compounds for further development as medicinal agents.

Objective: The objective of this study was to provide experimental chemists with useful guidance for proper choice of a reasonable cyclization precursor in macrolactonization in which there are several options in disconnection analysis. Method: A combination of DFT calculations and MD simulations was used to achieve the aim. In the former method, (1) structures having a local minimum energy near the macrocyclic structure are located by DFT calculations starting from coordinates generated by breaking the corresponding ester C–O bonds (2) among the structures obtained, the one with the shortest distance between the carbon and oxygen atoms and the carboxylic carbon atom is selected as the most likely candidate for macrolactonization. The latter approach involves that (1) global minimum structures for the possible macrocyclization precursors are located by molecular mechanics calculations (2) each of the structures is subjected to MD simulations and a structure maintaining the shortest distances between the two reacting centers during the simulations is selected as a reasonable cyclization precursor. Results: The utility of the computation-assisted disconnection approach was verified by the synthesis of prunustatin A, whose synthesis has already been reported by us, and demonstrated by the application to the synthesis of neoantimycin, a 15-membered macrocyclic depsipeptide. Conclusion: It was demonstrated that the approach provides useful guidance for designing synthetic strategies for synthetic chemists because of the relatively high speed and simplicity of the calculations involved.

Background: N-Heterocycles are of special interest because, many natural and synthetic bioactive compounds are found to be N-containing heterocycles and they constitute an important class of pharmacophores in medicinal chemistry. Recently, 1,2,3-triazoles have been found to possess a vast range of vital applications in the agrochemical, pharmaceutical, and materials field. In addition, various compounds of the 1,2,3-triazole family have shown a broad spectrum of biological properties such as antibacterial, and anti-HIV activity. 1,3,4- Oxadiazoles are important oxygen and nitrogen containing heterocyclic compounds, they possess desirable electronic and charge-transport properties. Methods: Two mammalian cell lines were grown in RPMI-1640 medium, supplemented with 10% heat inactivated FBS, 50 units/mL of penicillin and 50 g/mL of streptomycin and maintained at 37 °C in a humidified atmosphere containing 5% CO2. The cells were maintained as “monolayer culture” by serial sub-culturing. Preliminary cytotoxicity was performed using SRB method. Results: Sebacoyl chloride and decanedihydrazide dihydrochloride are utilized as versatile building blocks to annulate a series of novel azole and/ or azine systems. The in vitro anti-tumor activities of the synthesized compounds were evaluated against human breast cancer cell line (MCF-7) and human cervical cancer cell line (HeLa). The obtained data indicated that the majority of the tested compounds possess significant anti-tumor activities against the tested tumor cell lines. Conclusion: Sebacoyl chloride, decanedihydrazide dihydrochloride and N-nucleophiles are useful precursors for the synthesis of different functionalized N- heterocycles. The cytotoxic study revealed that the majority of the tested compounds possess significant anti-tumor activity towards the tested tumor cell lines.