A Unified Total Synthesis of the Actinoallolides, a Family of Potent Anti‐Trypanosomal Macrolides

E- and Z-trisubstituted macrocyclic alkenes for natural product synthesis and skeletal editing

Many therapeutic agents are macrocyclic trisubstituted alkenes but preparation of these structures is typically inefficient and non-selective. A possible solution would entail catalytic macrocyclic ring-closing metathesis, but these transformations require high catalyst loading, conformationally rigid precursors and are often low yielding and/or non-stereoselective. Here we introduce a ring-closing metathesis strategy for synthesis of trisubstituted macrocyclic olefins in either stereoisomeric form, regardless of the level of entropic assistance. The goal was achieved by addressing several unexpected difficulties, including complications arising from pre-ring-closing metathesis alkene isomerization. The power of the method is highlighted by two examples. The first is the near-complete reversal of substrate-controlled selectivity in the formation of a macrolactam related to an antifungal natural product. The other is a late-stage stereoselective generation of an E-trisubstituted alkene in a 24-membered ring, en route to the cytotoxic natural product dolabelide C.

Synthesis of bioactive natural products and their analogs at room temperature – an update

Sustainability is a concept that is employed to distinguish methods and procedures that can ensure the long-term productivity of the environment as it includes environmental, social, and economic dimensions. New generations can live on this planet with less hazardous substances and minimum requirement of energy for chemical transformations as green chemistry is related to creativity and the development of innovative research. Among the 12 principles of this clean chemistry, the sixth principle is devoted to the “design of energy efficiency” which discloses that less or the minimum amount of energy is required to conduct a specific reaction with optimum productivity. The most successful way to save energy is to construct strategies/methodologies that are capable enough to carry out the chemical transformations at ambient temperature and standard pressure. Hence, the present review wishes to cover the synthesis of bioactive natural products and their derivatives at room temperature. Bioactive secondary metabolites play a crucial role in the drug discovery together with drug development process; chiefly anticancer along with antibiotic molecules is noticeably enriched with molecules of natural origin. Natural sources, structures, and biological activities of natural products are highlighted in this review and it is also aimed to offer an overview of the design and synthesis of bioactive natural products and their analogs at room temperature for the first time efficiently.

Macrolides from rare actinomycetes: Structures and bioactivities

Rare actinomycetes are the sources of numerous biologically active secondary metabolites with diverse structures. Among them are macrolides, which have been shown to display several antibiotic activities. In this review, twenty-six groups of macrolides from rare actinomycetes are presented, with their bioactivities and structures of representatives from each group. It has been divided according to the classes of macrolides. The most interesting groups with a wide range of biological activities are ammocidins, bafilomycins, neomaclafungins, rosaramicins, spinosyns, and tiacumicins. Most macrolides are obtained from the genus, Micromonospora, with smaller contributions from genera such as Saccharothrix, Amycolatopsis, Nocardiopsis and Catenulispora. These macrolides display unique cytotoxic, antibacterial, antifungal, antimicrobial, insecticidal, anti-trypanosomal, antimalarial, antiprotozoal, antimycobacterial and anti-herpetic activity. Based on their noticeable bioactivities and diverse structures, macrolides from rare actinomycetes deserve to be investigated further for future applications in medicine. This work highlights the bioactivities and structures of important classes of macrolides from rare actinomycetes, which could be used in medicine in the future or which are already in the market.

A synthesis-enabled relative configurational assignment of the C31-C46 region of hemicalide

With 21 unknown stereocentres embedded in spatially separated stereoclusters, the cytotoxic polyketide hemicalide represents a seemingly intractible structural assignment problem. Herein, through the targeted synthesis of configurationally defined fragments, as...

Total Synthesis of Mycinamicin IV as Integral Part of a Collective Approach to Macrolide Antibiotics

The total synthesis of the 16‐membered macrolide mycinamicin IV is outlined, which complements our previously disclosed, largely catalysis‐based route to the aglycone. This work must also be seen in the context of our recent conquest of aldgamycin N, a related antibiotic featuring a similar core but a distinctly different functionalization pattern. Taken together, these projects prove that the underlying blueprint is integrative and hence qualifies for a collective approach to this prominent class of natural products. In both cases, the final glycosylation phase mandated close attention and was accomplished only after robust de novo syntheses of the (di)deoxy sugars of the desosamine, chalcose, mycinose and aldgarose types had been established. Systematic screening of the glycosidation promoter was also critically important for success.

Late-Stage Diversification: A Motivating Force in Organic Synthesis

Interest in therapeutic discovery typically drives the preparation of natural product analogs, but these undertakings contribute significant advances for synthetic chemistry as well. The need for a highly efficient and scalable synthetic route to a complex molecular scaffold for diversification frequently inspires new methodological development or unique application of existing methods on structurally intricate systems. Additionally, synthetic planning with an aim toward late-stage diversification can provide access to otherwise unavailable compounds or facilitate preparation of complex molecules with diverse patterns of substitution around a shared carbon framework. For these reasons among others, programs dedicated to the diversification of natural product frameworks and other complex molecular scaffolds have been increasing in popularity, a trend likely to continue given their fruitfulness and breadth of impact. In this Perspective, we discuss our experience using late-stage diversification as a guiding principle for the synthesis of natural product analogs and reflect on the impact such efforts have on the future of complex molecule synthesis.

Conquering peaks and illuminating depths: developing stereocontrolled organic reactions to unlock nature's macrolide treasure trove

The structural complexity and biological importance of macrolide natural products has inspired the development of innovative strategies for their chemical synthesis. With their dense stereochemical content, high level of oxygenation and macrocyclic cores, we viewed the efficient total synthesis of these valuable compounds as an aspirational driver towards developing robust methods and strategies for their construction. Starting out from the initial development of our versatile asymmetric aldol methodology, this personal perspective reflects on an adventurous journey, with all its trials, tribulations and serendipitous discoveries, across the total synthesis, in our group, of a representative selection of six macrolide natural products of marine and terrestrial origin - swinholide A, spongistatin 1, spirastrellolide A, leiodermatolide, chivosazole F and actinoallolide A.

Total synthesis of the actinoallolides and a designed photoaffinity probe for target identification

The actinoallolides are a family of polyketide natural products isolated from the bacterium Actinoallomurus fulvus. They show potent biological activity against trypanosomes, the causative agents of the neglected tropical diseases human African trypanosomiasis (sleeping sickness) and Chagas disease, while exhibiting no cytotoxicity against human cell lines. Herein, we give a full account of our strategy evolution towards the synthesis of this structurally unique class of 12-membered macrolides, which culminated in the first total synthesis of (+)-actinoallolide A in 20 steps and 8% overall yield. Subsequent late-stage diversification then provided ready access to the congeneric (+)-actinoallolides B-E. Enabled by this flexible and efficient endgame sequence, we also describe the design and synthesis of a photoaffinity probe based on actinoallolide A to investigate its biological mode of action. This will allow ongoing labelling studies to identify their protein binding target(s).