Stereoselective Total Synthesis of Carolacton

Stereoselective synthesis of the northern hemisphere of the proposed structure of neaumycin B

The stereoselective synthesis of the northern hemisphere (C20-C41) of the purported structure of the extremely potent anticancer natural product neaumycin B has been accomplished. Twelve out of nineteen asymmetry centers have been installed chemically. The key highlights of this synthesis include the Krische iridium catalyzed anti-diastereoselective carbonyl crotylation, the Crimmins aldol reaction, HWE olefination, CBS reduction, vanadium promoted stereoselective epoxidation, Evans methylation and spiroketalization.

Stereoselective synthesis of thailandamide A methyl ester

A convergent strategy for the stereoselective synthesis of the methyl ester of the structurally challenging and highly labile antibacterial polyene polyketide natural product thailandamide A has been developed. The key steps include the Zincke aldehyde reaction, Stille cross coupling, Negishi reaction, Julia-Kocienski olefination, cross metathesis, and the less explored Pd(I)-based Heck coupling to access different unsaturation bonds. Additionally, Urpi acetal aldol, Evans methylation, and Crimmins acetate aldol reactions were employed to construct four out of six asymmetric centers of the molecule.

Total Synthesis of Carolacton and Demethylcarolactons with Potent Antiviral Activity

Carolacton, a naturally occurring MTHFD1 inhibitor, exhibits potent inhibitory activity against various RNA viruses including SARS-CoV-2. Herein, we present a concise total synthesis of carolacton, featuring the Krische allylation, Marshall coupling, NHK coupling, and RCM reaction as key elements. Additionally, we have synthesized three simplified carolacton analogues, one of which, namely, 14-demethyl-carolacton, exhibited notable antiviral activity. The present work paves the way for further exploration of the therapeutic potential of carolacton and its analogues.

Total Synthesis of Antibacterial Macrolide Sorangiolide A

A convergent route for the asymmetric total synthesis of antibacterial macrolide sorangiolide A has been developed for the first time. The key feature of this synthesis includes Krische iridium-catalyzed anti-diastereoselective carbonyl crotylation, Crimmins acetate aldol, Yamaguchi esterification, Julia-Kocienski olefination, Horner-Wadsworth-Emmons olefination, and ring-closing metathesis. The origin of the low intensity of the 13C{1H} NMR signals of the C1 and C2 centers of the natural product has been investigated, disclosing possible forms of existence for the natural product in the solution phase.

Stereoselective Synthesis of α-Fluoro Carboxylic Acids by Ireland-Claisen Rearrangement

Stereoselective synthesis of α-fluoro carboxylic acids by the Ireland-Claisen rearrangement can provide a straightforward approach to this class of compounds. We report a systematic investigation of base-dependent stereocontrol in the Ireland-Claisen rearrangement of α-fluoro esters. For substrates with various substitution patterns, the use of KN(SiMe3)2 in toluene afforded rearrangement products corresponding to the (Z)-enolate intermediate with a practically useful diastereoselectivity and yield. In contrast, lower yields and diastereoselectivity were consistently observed with the use of lithium diisopropylamide (LDA) in tetrahydrofuran (THF).

Total synthesis of the antibacterial polyketide natural product thailandamide lactone

Stereoselective total synthesis of the structurally intriguing polyketide natural product thailandamide lactone was accomplished, and done so using a convergent approach for the first time to the best of our knowledge. The key features of this synthesis included use of a Crimmins acetate aldol reaction, Evans methylation, Urpi acetal aldol reaction, Sharpless asymmetric epoxidation and subsequent γ-lactonization for the installation of six asymmetric centers and the use of the Negishi reaction, Julia-Kocienski olefination, cross metathesis, HWE olefination and intermolecular Heck coupling for construction of a variety of unsaturated linkages. Pd(i)-based Heck coupling was introduced, for the first time to the best of our knowledge, quite efficiently to couple the major eastern and sensitive western segments of the molecule. The antibacterial activity of thailandamide lactone was also evaluated.

An Update on Pharmacological Relevance and Chemical Synthesis of Natural Products and Derivatives with Anti SARS-CoV-2 Activity

Natural products recognized traditionally as a vital source of active constituents in pharmacotherapy. The COVID-19 infection caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is highly transmissible, pathogenic, and considered an ongoing global health emergency. The emergence of COVID-19 globally and the lack of adequate treatment brought attention towards herbal medicines, and scientists across the globe instigated the search for novel drugs from medicinal plants and natural products to tackle this deadly virus. The natural products rich in scaffold diversity and structural complexity are an excellent source for antiviral drug discovery. Recently the investigation of several natural products and their synthetic derivatives resulted in the identification of promising anti SARS-CoV-2 agents. This review article will highlight the pharmacological relevance and chemical synthesis of the recently discovered natural product and their synthetic analogs as SARS-CoV-2 inhibitors. The summarized information will pave the path for the natural product-based drug discovery of safe and potent antiviral agents, particularly against SARS-CoV-2.

Orthogonal genome-wide screens of bat cells identify MTHFD1 as a target of broad antiviral therapy

Bats are responsible for the zoonotic transmission of several major viral diseases, including those leading to the 2003 SARS outbreak and likely the ongoing COVID-19 pandemic. While comparative genomics studies have revealed characteristic adaptations of the bat innate immune system, functional genomic studies are urgently needed to provide a foundation for the molecular dissection of the viral tolerance in bats. Here we report the establishment of genome-wide RNA interference (RNAi) and CRISPR libraries for the screening of the model megabat, Pteropus alecto. We used the complementary RNAi and CRISPR libraries to interrogate P. alecto cells for infection with two different viruses: mumps virus and influenza A virus, respectively. Independent screening results converged on the endocytosis pathway and the protein secretory pathway as required for both viral infections. Additionally, we revealed a general dependence of the C1-tetrahydrofolate synthase gene, MTHFD1, for viral replication in bat cells and human cells. The MTHFD1 inhibitor, carolacton, potently blocked replication of several RNA viruses, including SARS-CoV-2. We also discovered that bats have lower expression levels of MTHFD1 than humans. Our studies provide a resource for systematic inquiry into the genetic underpinnings of bat biology and a potential target for developing broad-spectrum antiviral therapy.

Total synthesis: the structural confirmation of natural products

This feature article highlights total synthesis as one of the reliable tools for the structural confirmation of natural products.

Biselyngbyolides A & C: their total synthesis and anticancer activities

Convergent strategies for the first total synthesis of biselyngbyolide C and an alternative route for the total synthesis of biselyngbyolide A have been developed. The key strategic feature in this study is Heck macrocyclization. The use of intramolecular Heck coupling for biselyngbyolide B was demonstrated by us earlier; however such a strategy has not been explored further for the other members of this family of natural products, in particular, where sensitive skipped olefins are involved. The other highlights of this synthetic study include iterative Crimmins acetate aldol and Wittig olefination processes, followed by the less explored cobalt-hydride-based reduction of an activated olefin and Shiina esterification. Our synthetic study enabled us to amend the reported NMR data of biselyngbyolides A and C. An evaluation of the anticancer activities of both biselyngbyolides A and C revealed that the apoptosis generated in cancer cells followed an intrinsic pathway.

Collaboration in Natural Product Total Synthesis: Carolacton – A Decade of Discovery

Carolacton, a macrocyclic natural product with impressive anti-biofilm biological activity, has been a focus in multiple research groups for the past decade. Chemists and biologists, alike, have been interested in uncovering the mechanism of action and have made great strides towards this goal. Carolacton causes cellular defects in Streptococcus mutans biofilm, which leads to decreases in cellular viability. As biological targets have been uncovered, synthetic chemists have devised synthetic routes that have helped uncover the important chemical functionalities that lead to biological activity. Herein, we discuss our synthetic collaboration that galvanized an entire research program around the natural product carolacton.

Turning the Tide: Natural Products and Natural-Product-Inspired Chemicals as Potential Counters to SARS-CoV-2 Infection

The novel and highly pathogenic severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which causes coronavirus disease 2019 (COVID-19), has become a continued focus of global attention due to the serious threat it poses to public health. There are no specific drugs available to combat SARS-CoV-2 infection. Natural products (carolacton, homoharringtonine, emetine, and cepharanthine) and natural product-inspired small molecules (ivermectin, GS-5734, EIDD-2801, and ebselen) are potential anti-SARS-CoV-2 agents that have attracted significant attention due to their broad-spectrum antiviral activities. Here, we review the research on potential landmark anti-SARS-CoV-2 agents, systematically discussing the importance of natural products and natural-product-inspired small molecules in the research and development of safe and effective antiviral agents.

Instructive Advances in Chemical Microbiology Inspired by Nature's Diverse Inventory of Molecules

Natural product antibiotics have played an essential role in the treatment of bacterial infection in addition to serving as useful tools to explore the intricate biology of bacteria. Our current arsenal of antibiotics operate through the inhibition of well-defined bacterial targets critical for replication and growth. Pathogenic bacteria effectively utilize a diversity of mechanisms that lead to acquired resistance and/or innate tolerance toward antibiotic therapies, which can result in devastating consequences to human life. Several research groups have established innovative programs that work at the chemistry-biology interface to develop new molecules that aim to define and address concerns related to antibiotic resistance and tolerance. In this Review, we present recent progress by select research groups that highlight a diversity of integrated chemical biology and medicinal chemistry approaches aimed at the development and utilization of chemical tools that have led to promising new microbiological insights that may lead to significant clinical advances regarding the treatment of pathogenic bacteria.

Total synthesis of nafuredin B

Total synthesis of marine secondary metabolite nafuredin B has been achieved for the first time using a convergent strategy. Sharpless epoxidation followed by acid catalyzed epoxide opening were adopted to install the tetrasubstituted hydroxy center, whereas the iterative Julia-Kocienski olefination, Wittig olefination and HWE olefination afforded the olefin bonds. Ring closing metathesis in the presence of a free tetrasubstituted hydroxy group provided the unsaturated δ-lactone moiety. This synthetic study provided unambiguous structural confirmation of the isolated nafuredin B.

Synthetic Simplification of Carolacton Enables Chemical Genetic Studies in Streptococcus mutans

Understanding the broader biological impact of carolacton, a macrolactone natural product, has been ongoing for the past decade. Multiple studies have shown connections to regulatory systems, acid tolerance mechanisms, biofilm formation, and recently folate dehydrogenase (FolD). Progress elucidating the cause of biofilm-specific activity in Streptococcus mutans has been limited due to low-throughput analyses of carolacton-treated cells. We disclose the discovery of a simplified carolacton-inspired analog that demonstrates inhibitory activity against S. mutans biofilm cells. This discovery permitted a proof of concept chemical genetic screen of S. mutans mutants identifying the carbon catabolite protein A signaling pathway as a putative target.

Studies toward the synthesis of macrotermycin C: stereoselective construction of the acyclic skeleton of the aglycon

The first asymmetric synthesis of the acyclic skeleton of the aglycon of macrotermycin C has been achieved in 17 linear steps with 5.7% overall yield following a convergent approach.

Total Synthesis of Cytospolide Q

A flexible and convergent strategy for the stereoselective total synthesis of bioactive marine natural product cytospolide Q has been developed. The key features of this synthesis include Evans anti-aldol reaction for the installation of C-2 and C-3 stereocenters and cycloetherification via epoxide opening followed by concomitant lactonization for the construction of tetrahydrofuran and γ-butyrolactone scaffolds. This synthetic study also revealed that protected oxygenated functionality (methyl ester or benzyl ether) at C-1 position participated readily in epoxide opening.

Studies Directed toward the Stereoselective Synthesis of Cytospolide E

Our exhaustive effort toward the total synthesis of cytotoxic marine nonanolide cytospolide E has been detailed. To achieve this synthesis, we have explored both the ring-closing metathesis and lactonization-based macrocyclization strategies using a variety of precursors. Unfortunately, none of them provided the desired product. The ring-closing metathesis approach provided mainly the macrocycle with Z-olefin, whereas the macrolactonization strategy culminated in 8-epi-9-epi-cytospolide E following the regioselective formation of a 10-membered macrocycle over a 9-membered macrocycle.

Studies toward the synthesis of strevertenes A and G: stereoselective construction of C1–C19segments of the molecules

Efficient route for the stereoselective synthesis of common C₁–C₁₉segment of strevertenes A and G has been developed.

Natural Products as Platforms To Overcome Antibiotic Resistance

Natural products have served as powerful therapeutics against pathogenic bacteria since the golden age of antibiotics of the mid-20th century. However, the increasing frequency of antibiotic-resistant infections clearly demonstrates that new antibiotics are critical for modern medicine. Because combinatorial approaches have not yielded effective drugs, we propose that the development of new antibiotics around proven natural scaffolds is the best short-term solution to the rising crisis of antibiotic resistance. We analyze herein synthetic approaches aiming to reengineer natural products into potent antibiotics. Furthermore, we discuss approaches in modulating quorum sensing and biofilm formation as a nonlethal method, as well as narrow-spectrum pathogen-specific antibiotics, which are of interest given new insights into the implications of disrupting the microbiome.

Diverted Total Synthesis of Carolacton-Inspired Analogs Yields Three Distinct Phenotypes in Streptococcus mutans Biofilms

The oral microbiome is a dynamic environment inhabited by both commensals and pathogens. Among these is Streptococcus mutans, the causative agent of dental caries, the most prevalent childhood disease. Carolacton has remarkably specific activity against S. mutans, causing acid-mediated cell death during biofilm formation; however, its complex structure limits its utility. Herein, we report the diverted total synthesis and biological evaluation of a rationally designed library of simplified analogs that unveiled three unique biofilm phenotypes further validating the role of natural product synthesis in the discovery of new biological phenomena.

The carolactam strategy is ineffective: synthesis and biological evaluation of carolactam

The lactam analogue of carolacton was prepared which has lost biofilm inhibitory activity towards Streptococcus mutans.