Mini-Reviews in Organic Chemistry - Volume 14, Issue 6, 2017

Background: Quaternary α-amino acids with a tetrasubstituted carbon stereocenter have a variety of biological activities. Due to the steric hindrance of the quaternary carbon centers, highly efficient asymmetric catalytic synthesis is greatly challenging. Objective: In this paper, with a focus on the asymmetric formation of chemical bonds in reactions, the asymmetric catalytic synthesis of quaternary α-amino acids in recent years is reviewed. Conclusion: Several representative catalytic asymmetric reactions are introduced, and the effects of different catalysts on the reaction results are discussed.

Background: Nucleoside triphosphates (NTPs) synthesis has recently been an area of searching for new methods and possible applications in biochemistry and medicine. However, we still lack a universal tool to synthesize NTPs easily and efficiently. For years, the most popular method has been the “one-pot, three step” conception by Ludwig with its subsequent improvements which used Yoshikawa's et al. monophosphorylation method. Further investigation of these reactions has proven many disadvantages: low yields, many byproducts and problems with purification. But they were a starting point for a whole branch of NTPs synthetic methods. Method: Analysis of this evolution process demonstrates some correctness: using a pyrophosphate as a nucleophile and mechanism involving a cyclic intermediates at some stage. What is changing is the idea of phosphorus center activation and the resulting improvements and limitations. Conclusion: In this paper we would like to discuss some new achievements in NTPs synthesis considering their role in changing the strategy of phosphorus center activation depending on the needs

Background: Benzodiazepines (BDZs) are the bicyclic heterocyclic compounds in which benzene ring is fused to seven membered ring containing two nitrogen atoms. There are different types of BDZs such as 1, 2-benzodiazepines, 1, 3-benzodiazepines, 1, 4-benzodiazepines, 1, 5-benzodiazepines- 2, 3-benzodiazepines possess anxiolytic, anticonvulsant, antipsychotics, muscle relaxant and antimicrobial activities. Method: Modifications and substitutions have been made in both rings by employing different methods to obtain a large number of BDZs. Due to their biological potentials the benzodiazepine nucleus has continued to attract many investigators to synthesize and screen their analogues for all possible biological activities. Conclusion: This current review article describes the synthetic approaches and biological activities of benzodiazepines.

Background: Microwave technology is of great splendor in organic synthesis where it is applied efficaciously to synthesize a wide range of biologically active as well as industrially important compounds. Carbazole analogues are one of such important pharmacophores that are gaining considerable prominence nowadays. Besides their wide range of biological features, they possess opto-electronic as well as polymeric properties. This review highlights the entire progress of microwave assisted synthetic methodologies for carbazoles. Methods: The key reactions are Fischer indolization, Suzuki-Miyaura cross-coupling, catalytic oxidative cyclization, cycloaddition and polymerization. Conclusion: We have summarized a comprehensive reportage of these approaches to mild and efficient syntheses of carbazole under microwave irradiations.

Background: Cornus mas L. is a small tree of the Cornaceae plant family, widely spread in South Eastern Europe and Asia. The fruits of Cornus mas L. have been reported to possess anti-inflammatory, cardioand hepatoprotective, cytotoxic, antibacterial, antigenotoxic and diuretic effects. A high number of bioactive compounds have been identified in Cornus mas fruits, among which flavonoids exert favorable health effects especially by acting as potent antioxidants. Method: The main step in the isolation of flavonoids from vegetal matrices is extraction. Apart the usually applied methods of organic compounds characterization like mass spectrometry (MS), ultraviolet and visible (UV-Vis) and infrared (IR) spectroscopy, the advanced analytical techniques such as high performance liquid chromatography (HPLC) and nuclear magnetic resonance (NMR) are reliable tools in flavonoids structure determination. Conclusion: This review focuses on the recent published studies regarding the extraction, characterization and biological activities of flavonoids isolated from these fruits in order to understand their high potential as a source of bioactive compounds and their importance in developing new pharmacological products.

Background: A number of atmospheric pollutants, such as polycyclic aromatic hydrocarbons, volatile organic compounds, and heavy metals, are monitored by environmental researchers. Among these atmospheric pollutants, polycyclic aromatic hydrocarbons play an important role owing to their nature, which is carcinogenic and toxic to human beings. A number of researchers have monitored these atmospheric pollutants using active and passive samplers, and a few have monitored their concentrations using biological specimens such as lichens and mosses. Method: We reviewed the biomonitoring of atmospheric polycyclic aromatic hydrocarbons using various biological specimens. For this purpose, we examined nearly 35 research papers published since 2013 in various reputed international journals. From this study, it is clear that biological specimens are useful for monitoring the concentrations of atmospheric polycyclic aromatic hydrocarbons. Results: A number of PAHs exist in the atmosphere, but according to the United States Environmental Protection Agency (US EPA), only the following 16 are considered priority PAHs due to the availability of data and their carcinogenic and toxic nature: Napthalene (Nap), Acenaphthylene (Acy), Acenaphthene (Acp), Fluorene (Flu), Phenanthrene (Phe), Anthracene (Ant), Fluoranthene (Flt), Pyrene(Pyr), Benz[a]anthracene (BaA), Chrysene(Chry), Benzo[b]fluoranthene (BbF), Benzo [k]fluoranthene (BkF), Benzo[a]pyrene(BaP), Indeno [1,2,3-cd]pyrene(IcdP), Dibenz[a,h]anthracene (DahA), and Benzo[ghi] perylene(BghiP). These PAHs are collected by various procedures, such as active sampling of total suspended particulate matter and PM2.5, and passive sampling. Along with these conventional methods, biological species are also used to monitor PAHs. In this study, we reviewed research papers published since 2013 that described the monitoring of atmospheric PAHs with a number of biological materials such as lichens, mosses, and other plant materials. Conclusion: Based on the review, we conclude that several researchers have successfully used biological materials to monitor the levels of atmospheric PAHs in different countries and from different sampling sites. However, the data obtained in these studies can be reliable only when they are compared with conventional instrumental methods. Most of the studies compare their results with those obtained from either active or passive air sampling methods. The major advantage of biomonitoring studies is the low cost of sampling and that provides reasonably reliable data.

Objective: This review describes the discovery during the last five years of novel compounds with significant antimicrobial activity from marine actinomycetes; descriptions include their origins, relevant structures and antimicrobial activities. These antimicrobial compounds belong to several structural classes including alkaloids, peptides, polyketides, macrolides, glycosides, phenols and others. They further express antimicrobial activity against Gram-positive, Gram-negative and fungal pathogens. Method: We additionally summarize the present knowledge of marine actinomycetes, as a potential source for producing antibiotics. Significantly, more than 15 kinds of structures, such as xinghaiamine A (12), and arenimycin (82), showed antimicrobial activity against multidrug resistant (MDR) pathogenic strains. Compounds such as mollemycin A (17, IC50 values of 10 - 50 nM ) and glycosylated macrolactins (83 and 84, MIC values of 0.055 - 0.220 μM) showed potent activity and may be considered as candidates with significant potential for antibiotic drug discovery. Three different types of compounds, lajollamycins (8-11), bahamaolides (95 and 96) and glycosylated benzoxazine (102 and 103) showed inhibitory activity against Candida albicans isocitrate lyase (ICL). Conclusion: As compiled in this review, antimicrobial natural products are frequently found in marine actinomycetes and are an important supply of molecules with great potential for biotechnological applications. Marine actinomycetes, therefore, attracted recent research interest. The opportunities and challenges for exploring marine actinomycetes-derived natural products need to be further elucidated.