Current Organic Chemistry - Volume 25, Issue 9, 2021

In recent years, supramolecular systems for nano-medicine, and in particular for photodynamic therapy, have gained great attention for their uses as smart and engineered therapeutic agents. We proposed a collection of very recent articles on supramolecular complexes for photodynamic therapy based on different photosensitizers assembled with cyclodextrins, cucurbiturils, calixarenes, pillararenes, or involved in nanobox and tweezer structures, nanoparticles, aggregates and micelles, that are dynamic assemblies inspired to biological systems. Despite the advantages of traditional Photodynamic therapy (PDT), which is a non-invasive, reliable and highly selective clinical treatment for several pathological conditions, different drawbacks are still smothering the applicability of this clinical treatment. In this contest, a new supramolecular approach is emerging, in fact, the reversible formation of these supramolecular assemblies, combined with the possibility to modify their dimensions and shapes in the presence of a guest make them similar to biological macromolecules, such as proteins and enzymes. Furthermore, due to the relatively weak and dynamic nature of supramolecular assemblies, they can undergo assembly and disassembly very fast as well as responses to external stimuli, such as biological (e.g. enzyme activation), chemical (e.g. redox potential or pH), and physical (e.g. temperature, light or magnetic fields). Therefore, the responsiveness of these supramolecular assemblies represents a highly promising approach to obtain potentially personalized PDT.

The increasing importance of visible light photoredox catalysis as a powerful strategy for the activation of small molecules require the development of new effective radical sources and photocatalysts. The unique properties of organoboron compounds have contributed significantly to the rapid progress of photocatalysis. Since the first work on the topic in 2005, many researchers have appreciated the role of boron-containing compounds in photocatalysis, and this is reflected in several publications. In this review, we highlight the utility of organoboron compounds in various photocatalytic reactions enabling the construction of carbon- carbon and carbon-heteroatom bonds. The dual role of organoboron compounds in photocatalysis is highlighted by their applications as reactants and as well as organic photocatalysts.

The present review describes 108 new examples of naturally occurring flavans and flavanones having cytotoxic potential, which have been reported during the period of 2005 to mid-2020. These compounds are found either as aglycones or as glycosides, comprising flavans, flavanones, isoflavanones and miscellaneous flavanones (homo- and bi-flavanones). The main topics addressed in this review are source, structure, and cytotoxic activity in detail and the structure-activity relationship.

Natural products are the most effective source of potential drug leads. The total synthesis of bioactive natural products plays a crucial role in confirming the hypothetical complex structure of natural products in the laboratory. The total synthesis of rare bioactive natural products is one of the great challenges for the organic synthetic community due to their complex structures, biochemical specificity, and difficult stereochemistry. Subsequently, the total synthesis is a long process in several cases, and it requires a substantial amount of time. Microwave irradiation has emerged as a greener tool in organic methodologies to reduce reaction time from days and hours to minutes and seconds. Moreover, this non-classical methodology increases product yields and purities, improves reproducibility, modifications of selectivity, simplification of work-up methods, and reduces unwanted side reactions. Such beneficial qualities have stimulated this review to cover the application of microwave irradiation in the field of the total synthesis of bioactive natural products for the first time during the last decade. An overview of the use of microwave irradiation, natural sources, structures, and biological activities of secondary metabolites is presented elegantly, focusing on the involvement of at least one or more steps by microwave irradiation as a green technique.

The analogs of 6-Amino uracil are essential components due to their biological activities. The uracil is used as an important component for the synthesis of heterocyclic compounds like pyrrolo-, pyrido-, pyrimidine-pyrimido scaffolds. Herein, the application of this compound is reviewed as a precursor in the synthesis of many heterocyclic cores from 2016 to 2020.