Mini-Reviews in Organic Chemistry - Volume 15, Issue 6, 2018

Ginsenosides present various application in many areas, however, considering that the preparation of natural ginsenosides is comparatively in straitened circumstances, and not conducive to industrial production; the chemosynthesis and structural modification on natural ginsenosides with high yield and ready availability are significant in the discovery of new active ingredients and industrialization. Therefore, restriction on the achievement of ginsenosides from plants can be possibly solved by the method; moreover, derivatives of ginsenosides are be applied to the study of structure-activity relationship, thereby being beneficial to the development of new drugs. This paper reviews recent progress of the synthesis and structural modification for different types of ginsenosides, especially showing solicitude for damaran-type ginsenosides, which contain diverse ways of synthesis and modification (such as esterification, alkylation, sulfation, oxidation and catalytic hydrogenation). The prospect of ginsenosides in chemistry is evaluated synchronously.

Heterocyclic scaffolds like imidazole and pyrazole are attractive options to medicinal and synthetic chemists for the development of drugs. Nature utilizes the unique type of imidazole ring in numerous biological molecules such as histamine, vitamin B12, deoxyribonucleic acid (DNA) and haemoglobin for exerting various biological functions. This shows that the imidazole ring is vital to many physiological processes and hence important for modulating altered physiology. Imidazole and pyrazole analogues have been reported to show a varied spectrum of activities like antibacterial, antifungal, antiviral, antimalarial, antitubercular, antileishmanial, anticancer, anti-inflammatory, antineuropathic, antiparasitic, antihistaminic, antihypertensive, antiobesity, etc. and hence are valuable scaffolds for the development of new therapeutic agents. Many azole-based antibacterial and antifungal agents have been extensively studied as drug candidates and some of them are used clinically for instance ketoconazole, itraconazole, fluconazole, posaconazole and voriconazole, which suggests their great development value. Myriad of structural modifications on these scaffolds have provided a wide spectrum of activity and scope for the enhancement of activity. Reviews on the biological importance of these scaffolds have been published over the past decade or two. However, we did not come across reviews that combined the synthetic strategies of some bioactive substituted imidazole and pyrazole compounds along with the impact of substitutions on their anti-infective activity. The pursuit of structurally novel anti-infective imidazoles and pyrazoles with increased potency, broader spectrum and lower toxicity is a highly challenging task and is of great interest in medicinal chemistry. This review will be useful for synthesizing imidazole and pyrazole analogues for the development of new potent anti-infective agents that will also help overcome the issue of emerging multidrug resistance observed with the existing anti-infective drugs.

Allylation reaction has been considered to be the most intriguing means for building collections of functionalized allylic compounds. The application of allylic alcohols for coupling reaction is complicated and typically summarized as four types such as they act as: allylation reagents, aldehyde/ ketone sources, allylic ether reagents, and as allylic alcohol sources. The molecular insights enunciated herein allude to abundant opportunities for acting as allylation reagents as well as serving as aldehyde/ ketone sources. It is our intent to propose that the domain of allylation reaction and the formation of aldehydes and ketones could enjoy additional benefits by having knowledge of the application of allylic alcohols in the organic synthesis.

The oxidation of thiophene (TH) and its derivatives is vital in the oxidative desulfurization (ODS). As a safer and greener oxidant with lower cost, molecular oxygen has been employed in the ODS process as a substitution of H2O2 or other organic hydroperoxide in many research works in recent years. However, the activation of dioxygen under mild conditions is still not an easy problem to solve. In this contribution, we reviewed reports on novel catalysts or systems for aerobic oxidation of TH and related sulfur compounds developed in recent years. The catalysts and systems are classified to five types and the component, catalytic activity and reaction mechanism are illustrated briefly in each part.

The control of Tuberculosis (TB) is becoming more challenging due to drug resistance. Therefore, there is a dire need for newer drugs to tackle the nuances of resistant strains. Many molecular scaffolds are in the pipeline against TB. Among them, carbazole has a distinct advantage over other scaffolds because of its various sources i.e. medicinal plants, coal tar, and synthesis, besides the excellent antitubercular efficacy. This review provides an overview of carbazole alkaloids and their synthetic derivatives reported against Mycobacterium tuberculosis H37Rv (Mtb). The structure-activity relationship is also established to understand the molecular requirements for design and development of more potent antitubercular drugs.

Background: Hexachlorocyclohexane (HCH) isomers have been largely employed as pesticides during the 1960's-1970's, and included into the Stockholm Convention persistent organic pollutant list in 2009 with the aim to reach their global elimination. β -HCH isomer is characterized by a strong lipophilicity, bio-persistence and potential harmful properties for human health. Dispersion of industrial processes and uncontrolled waste storage caused a global environmental β-HCH contamination. This still represents a public and occupational health concern, not only for past-exposed subjects, but also for the populations that may still be exposed to highly polluted environmental matrices and food. Objective: To provide a critical overview of the existing evidence exploring β-HCH biomonitoring data and possible health effects in workers involved in the production and use of such compound. Methods: A systematic search and revision of available literature was performed in Pubmed, Scopus, and ISI Web of Science databases. Results: Conclusive evidence concerning the possible dose-response relationship in β-HCH occupational settings cannot be extrapolated due to the heterogeneity in explored contexts, and the lack of information on environmental conditions and levels of exposure. Nevertheless, biomonitoring data support the need for a deeper understanding of the toxico-kinetic and dynamic profile of the substance, once absorbed into the organism, and possible early alterations in endocrine signaling. Conclusion: The potential toxicity, bioaccumulation and bio-magnification properties of β-HCH make necessary to plan preventive actions aimed to manage the β-HCH risk, through the reduction of exposure levels and the definition of health surveillance programs, including biological monitoring investigations, for the general and occupational exposed populations.

This review gives an overview of utilization of ultrasound for the synthesis of various heterocyclic compounds. Ultrasonic irradiation has been considered as an efficient methodology in many organic syntheses. With ultrasonic assistance short reaction times, good selectivity and high yields are reported. The use of ultrasound irradiation in organic reactions has been increasing rapidly in recent years.