Synthesis Of Natural Products Research Articles

Synthesis and Antibacterial Studies of Phenethylamine Alkaloid Natural Products Along with Their Analogues: Discolin A, B, E and Bacillimidazole B

AbstractThe first total synthesis of phenethylamine alkaloid based natural products discolin A, B, E and bacillimidazole B is reported, which were isolated from marine sea bacteria Tenacibaculum discolor sv11 and marine sponge. Total syntheses of discolin A, B, E and bacillimidazole B are achieved in two linear steps including condensation reaction and N-alkylation reaction with an overall yield of 68%, 35%, 65%, and 32%, respectively. A total of 24 analogues are prepared with moderate to excellent yield. All the natural products and their analogues were screened for antibacterial activity. The most active compound showed an IC50 of 122.1 nM against P. aeruginosa.

Chiral Aldehyde Catalysis-Enabled Asymmetric α-Functionalization of Activated Primary Amines.

ConspectusThe development of catalytic activation modes provides a reliable and effective platform for designing new enantioselective reactions and preparing chiral molecules with diverse structures. Chiral aldehyde catalysis is an attractive concept in asymmetric catalysis, which utilizes a chiral aldehyde catalyst to promote the asymmetric hydroamination of allylic amines, the asymmetric α-functionalization of primary amines, or the asymmetric transamination of α-keto esters. Typically, the chiral aldehyde-catalyzed asymmetric α-functionalization of primary amines provides an efficient and straightforward method for the synthesis of α-functionalized chiral amines, which does not require any additional protection or deprotection manipulations of the amine group. However, achieving catalytic stereoselective transformations with high efficiency and enantioselectivity by this strategy has remained an intractable challenge.This Account summarizes our endeavors in the development and application of chiral aldehyde catalysis. Using a chiral aldehyde as a catalyst, we reported the catalytic asymmetric α-C alkylation of 2-aminomalonate with 3-indolylmethanol in 2014, which represents the first chiral aldehyde-catalyzed asymmetric α-functionalization of an activated primary amine. Subsequently, several axially chiral aldehyde catalysts were continuously prepared by using chiral BINOL as the starting material, and their applications in asymmetric synthesis were explored. On the one hand, they were used as organocatalysts to realize the various transformations of α-amino acid esters, such as asymmetric 1,4-addition toward conjugated enones/α,β-unsaturated diesters and cyclic 1-azadienes as well as asymmetric α-arylation/allylation and benzylation with corresponding halohydrocarbons. Notably, taking advantage of the difference in the distribution of catalytic sites between two chiral aldehyde catalysts, we disclosed chiral aldehyde-catalyzed diastereodivergent 1,6-conjugated addition and Mannich reactions. On the other hand, the potential for the cooperative catalysis of a chiral aldehyde with a transition metal has also been demonstrated. Enabled by the combination of a chiral aldehyde, a palladium complex, and a Lewis acid, the enantioselective α-allylation of amino acid esters with allyl alcohol esters was established. Moreover, the ternary catalytic system has been successfully used for the α-functionalization of amino acid esters with 1,3-dienes, allenes, allenylic alcohol esters, 1,3-disubstituted allyl alcohol esters, and arylmethanol esters as well as the asymmetric cascade Heck-alkylation reaction. The combination of a chiral aldehyde and nickel complex allows for the asymmetric α-propargylation of amino acid esters with propargylic alcohol esters and provides excellent enantioselectivities. These transformations provide a large library of optically active amines and amino acids. With those chiral amino acid esters as key building blocks, the synthesis or formal synthesis of multiple natural products and biologically significant unnatural molecules was accomplished. This includes the stereodivergent synthesis of natural pyrrolizidine alkaloid NP25302 and the formal synthesis of natural product (S)-hypoestestatin 1 and manzacidin C, clinical candidate compound (+)-AG-041R, and somatostatin mimetics. It is fully anticipated that chiral aldehyde catalysis will soon witness rapid expansion both in the development of novel asymmetric transformations and in innovative applications for constructing optically active nitrogen-containing molecules with significant values.

An emerging strategy towards the iodine catalyzed synthesis of Streptindole and its derivatives in water medium.

In this study, we propose an alternative metal‐free methodology for the synthesis of Streptindole and its derivatives. This approach employs economically viable and easily handled molecular iodine (I2) as the catalyst in an aqueous medium. The method demonstrates remarkable tolerance towards a diverse array of functional groups. The versatility of the developed protocol is highlighted by its application in the efficient total syntheses of the alkaloid natural products, Streptindole and Arsindoline B accomplished in a single step from indole. Furthermore, the methodology is also useful for the synthesis of pharmaceutically significant compounds, specifically anti‐TMV agents (5c, 5d, and 5e) and an anticancer agent (5f). Control experiments have been carried out to study the plausible catalytic cycle by finding the key intermediates. The experimental findings support the mechanistic pathway involving halogen bond activation in molecular iodine catalysis

Natural Product Synthesis in the 21st Century: Beyond the Mountain Top.

Research into natural products emerged from humanity's curiosity about the nature of matter and its role in the materia medica of diverse civilizations. Plants and fungi, in particular, supplied materials that altered behavior, perception, and well-being profoundly. Many active principles remain well-known today: strychnine, morphine, psilocybin, ephedrine. The potential to circumvent the constraints of natural supply and explore the properties of these materials led to the field of natural product synthesis. This research delivered new molecules with new properties, but also led to fundamental insights into the chemistry of the nonmetal elements H, C, N, O, P, S, Se, and their combinations, i.e., organic chemistry. It also led to a potent culture focused on bigger molecules and races to the finish line, perhaps at the expense of actionable next steps. About 20 years ago, the field began to contract in the United States. Research that focused solely on chemical reaction development, especially catalysis, filled the void. After all, new reactions and mechanistic insight could be immediately implemented by the chemistry community, so it became hard to justify the lengthy procurement of a complex molecule that sat in the freezer unused. This shift coincided with a divestment of natural product portfolios by pharmaceutical companies and an emphasis in academic organic chemistry on applications-driven research, perhaps at the expense of more fundamental science. However, as bioassays and the tools of chemical biology become widespread, synthesis finds a new and powerful ally that allows us to better deliver on the premise of the field. And the hard-won insights of complex synthesis can be better encoded digitally, mined by data science, and applied to new challenges, as chemists perturb and even surpass the properties of complex natural products. The 21st century promises powerful developments, both in fundamental organic chemistry and at the interface of synthesis and biology, if the community of scientists fosters its growth. This essay tries to contextualize natural product synthesis for a broad audience, looks ahead to its transformation in the coming years, and expects the future to be bright.

“Mix and match” auto-assembly of glycosyltransferase domains delivers biocatalysts with improved substrate promiscuity

Glycosyltransferases (GT) catalyse the glycosylation of bioactive natural products, including peptides and proteins, flavonoids, sterols, and have been extensively used as biocatalysts to generate glycosides. However, the often narrow substrate specificity of wild-type GTs requires engineering strategies to expand it. The GT-B structural family is constituted by GTs that share a highly conserved tertiary structure, in which the sugar donor and acceptor substrates bind in dedicated domains. Here, we have used this selective binding feature to design an engineering process to generate chimeric glycosyltransferases that combine auto-assembled domains from two different GT-B enzymes. Our approach enabled the generation of a stable dimer with broader substrate promiscuity than the parent enzymes that was related to relaxed interactions between domains in the dimeric GT-B. Our findings provide a basis for the development of a novel class of heterodimeric GTs with improved substrate promiscuity for applications in biotechnology and natural product synthesis.

Rapid sp3-Enriched Scaffold Generation via a Selective Aziridine Amide Ring-Opening Reaction.

Sp3-enriched small molecules play a critical role in developing drug candidates. While designing analogues with greater sp3 character, a methodology utilizing a less explored cyclic-aziridine amide ring-opening reaction to generate sp3-enriched scaffolds has been developed and reported. This methodology enables rapid access to substructures with higher fsp3 values, attracting greater attention within the past few decades. The reaction exhibits a wide reaction scope, featuring a highly sterically hindered phenolic ether, thiophenolic ethers, protected aniline formations, and aliphatic/heteroaromatic ring-containing aziridine amides as substrates. Additionally, this reaction provides access to congested tertiary ether formations through regioselective transformation, applicable to an extensive range of drug discovery targets, construction of complex small molecules, and natural product syntheses. The scaffolds developed show improved physicochemical properties.

Regiodivergent Synthesis and Biological Activities of Indoloquinoline Based Compounds.

Cryptolepine, neocryptolepine, and isocryptolepine have remained popular synthetic targets ever since their isolation from the aqueous extracts of the West African climbing shrub Cryptolepis sanguinolenta. These natural alkaloids were found to contain significant antimalarial, antiproliferative and antimicrobial activities, making them ideal starting points for the development of novel drug candidates. As natural product synthesis is often plagued with step-heavy procedures and poor atom economy, the discovery of synthetic protocols addressing these concerns are sorely needed. In our laboratories, we have devoted our efforts into the development of regiodivergent synthesis whereby two of the indoloquinoline natural products, namely neocryptolepine and 11H-indolo[3,2-c]quinolines, could be assembled in only a few steps from a common and readily available starting material. Our synthetic endeavors to meet these goals include a cascade palladium-catalyzed Suzuki-Miyuara cross-coupling and intramolecular C-N bond formation and a photochemical nitrene insertion strategy. Furthermore, our methods also allowed for the construction of several diversely functionalized natural product derivatives which were subjected to biological evaluations.

SOLVENTS: From Past to Present.

Technological advancements in organic chemistry cannot be imagined without solvents, an essential evil due to well-recognized safety, health, and environmental risks and yet an integral part of the value chain for almost all industrially manufactured products intended for human use. A solvent serves as an essential liquid medium for different molecules to interact and react, generating products totally different from the original reactants. Reminiscences reveal water to be the first solvent used in the art of organic chemistry. This Viewpoint attempts to capture anecdotal theories and evidence on the use of this "magic liquid" and the progressive adoption of alternative liquid solvents, which have played a pivotal role in the evolution of synthetic organic chemistry. Synthetic organic chemistry, in turn, has sought to compete with nature in mimicking complex natural product syntheses in the laboratory on miniscule time scales compared with millions of years of evolutionary processes.

Bioinspired Skeletal Reorganization Approach for the Synthesis of Steroid Natural Products.

ConspectusSteroids, termed "keys to life" by Rupert Witzmann, have a wide variety of biological activities, including anti-inflammatory, antishock, immunosuppressive, stress-response-enhancing, and antifertility activities, and steroid research has made great contributions to drug discovery and development. According to a chart compiled by the Njardarson group at the University of Arizona, 15 of the top 200 small-molecule drugs (by retail sales in 2022) are steroid-related compounds. Therefore, synthetic and medicinal chemists have long pursued the chemical synthesis of steroid natural products (SNPs) with diverse architectures, and vital progress has been achieved, especially in the twentieth century. In fact, several chemists have been rewarded with a Nobel Prize for original contributions to the isolation of steroids, the elucidation of their structures and biosynthetic pathways, and their chemical synthesis. However, in contrast to classical steroids, which have a 6/6/6/5-tetracyclic framework, rearranged steroids (i.e., abeo-steroids and secosteroids), which are derived from classical steroids by reorganization of one or more C-C bonds of the tetracyclic skeleton, have started to gain attention from the synthetic community only in the last two decades. These unique rearranged steroids have complex frameworks with high oxidation states, are rich in stereogenic centers, and have attractive biological activities, rendering them popular yet formidable synthetic targets.Our group has a strong interest in the efficient synthesis of SNPs and, drawing inspiration from nature, we have found that bioinspired skeletal reorganization (BSR) is an efficient strategy for synthesizing challenging rearranged steroids. Using this strategy, we recently achieved concise syntheses of five different kinds of SNPs (cyclocitrinols, propindilactone G, bufospirostenin A, pinnigorgiol B, and sarocladione) with considerably rearranged skeletons; our work also enabled us to reassign the originally proposed structure of sarocladione. In this Account, we summarize the proposed biosyntheses of these SNPs and describe our BSR approach for the rapid construction of their core frameworks. In the work described herein, information gleaned from the proposed biosyntheses allowed us to develop routes for chemical synthesis. However, in several cases, the synthetic precursors that we used for our BSR approach differed substantially from the intermediates in the proposed biosyntheses, indicating the considerable challenges we encountered during this synthetic campaign. It is worth mentioning that during our pursuit of concise and scalable syntheses of these natural products, we developed two methods for accessing synthetically challenging targets: a method for rapid construction of bridged-ring molecules by means of point-to-planar chirality transfer and a method for efficient construction of macrocyclic molecules via a novel ruthenium-catalyzed endoperoxide fragmentation. Our syntheses vividly demonstrate that consideration of natural product biosynthesis can greatly facilitate chemical synthesis, and we expect that the BSR approach will find additional applications in the efficient syntheses of other structurally complex steroid and terpenoid natural products.

Indolyl‐Ynones: Building Blocks for Molecular Diversity

AbstractThis review centers on the synthetic strategies employed with indolyl‐ynones. Indolyl‐ynone, owing to its highly reactive ynone moiety, frequently partakes in dearomatizing spirocyclization reactions and subsequent rearrangement reactions when subjected to various reaction conditions. Hence, various heterocycles such as densely functionalized spiroindolenines, carbazoles, quinolines and carbo‐and hetero‐cycle substituted indoles are synthesized from indolyl‐ynones. In addition to this, the versatile spirocyclic indole scaffold exhibits the capability to produce tetracyclic and polyclic structures through intricate skeletal rearrangement processes. Moreover, the total synthesis of natural products using the indolyl‐ynone moiety was also compiled in this review.

Palladium N-Heterocyclic Carbene-Catalyzed Aminations: An Outline.

Amination reactions play a pivotal role in synthetic organic chemistry, facilitating the generation of nitrogen-containing scaffolds with broad applications in drug synthesis, material production, polymer formation, and the generation of amino acids and peptides. Amination offers the potential to fine tune the properties of natural products and produce functional materials for various applications. Palladium N-heterocyclic carbene (Pd-NHC) emerges as an innovative and highly effective catalyst in this context. Under favorable reaction conditions, this robust and simple catalyst efficiently facilitates the synthesis of a diverse range of compounds with varying complexity and utility. Pd-NHC complexes exhibit significant σ-electron donating potential, enhancing the ease of the oxidative addition process in their mechanistic pathway. Their steric topography further contributes to a rapid reductive elimination. These complexes demonstrate remarkable stability, a result of the strong Pd-ligand bond. The wide variety of Pd-NHC complexes has proven highly efficient in catalyzing reactions across a spectrum of complexities, from simple to intricate. The domain of aminations catalyzed by Pd-NHC has undergone significant diversification, presenting new opportunities, particularly in the realms of material chemistry and natural product synthesis. This review outlines the advancements in Pd-NHC-catalyzed amination reactions, covering literature up to date.

Recent Advances on the Synthesis of C-Glycosides from 1,2-Glycals

AbstractThe development of stereoselective synthetic routes for C-glycosides has attracted immense attention from carbohydrate chemists over the last two decades. In this short review, progress made over the last decade towards the synthesis of C-glycosides using glycals as precursors is discussed. Glycals have been extensively manipulated to generate oxocarbenium cations or glycosyl anions for the formation of C–C bonds at the anomeric position through attack of C-nucleophiles or via transition-metal-catalyzed coupling reactions. Recent reports on carbon-Ferrier, intramolecular Cope, and Claisen rearrangements, along with various coupling reactions in the presence or absence of directing groups are evaluated herein. Contemporary applications of these reactions in the syntheses of natural products, drugs and scaffolds with bioactive potential are briefly discussed.1 Introduction2 Rearrangement Reactions2.1 Carbon-Ferrier Rearrangement2.2 Other Rearrangement Reactions3 C1 Coupling4 Annulations5 Addition Reactions6 Natural Product Synthesis7 Conclusion

Antimicrobial activity and mechanism of anti-MRSA of phloroglucinol derivatives.

In previous studies, authors have completed the total synthesis of several phloroglucinol natural products and synthesized a series of their derivatives, which were tested with good biological activities. To discover anti-MRSA lead compound and study their mechanism of action. Phloroglucinol derivatives were tested to investigate their activities against several gram-positive strains including Methicillin-resistant Staphylococcus aureus (MRSA). The mechanism study was conducted by determining extracellular potassium ion concentration, intracellular NADPH oxidase content, SOD activity, ROS amount in MRSA and MRSA survival rate under A5 treatment. The in vitro cytotoxicity test of A5 was conducted. The activity of monocyclic compounds was stronger than that of bicyclic compounds, and compound A5 showed the best MIC value of 0.98μg/mL and MBC value of 1.95μg/mL, which were 4-8 times lower than that of vancomycin. The mechanism study of A5 showed that it achieved anti-MRSA effect through membrane damage, which is proved by increased concentration of extracellular potassium ion after A5 treatment. Another possible mechanism is the over ROS production induced cell death, which is suggested by observed alternation of several reactive oxygen species (ROS) related indicators including NADPH concentration, superoxide dismutase (SOD) activity, ROS content and bacterial survival rate after A5 treatment. The cytotoxicity results in vitro showed that A5 was basically non-toxic to cells. Acylphloroglucinol derivative A5 showed good anti-MRSA activity, possibly via membrane damage and ROS-mediated oxidative stress mechanism. It deserves further exploration to be a potential lead for the development of new anti-MRSA agent.

4-Hydroxyphenylacetate 3-Hydroxylase (4HPA3H): A Vigorous Monooxygenase for Versatile O-Hydroxylation Applications in the Biosynthesis of Phenolic Derivatives.

4-Hydroxyphenylacetate 3-hydroxylase (4HPA3H) is a long-known class of two-component flavin-dependent monooxygenases from bacteria, including an oxygenase component (EC 1.14.14.9) and a reductase component (EC 1.5.1.36), with the latter being accountable for delivering the cofactor (reduced flavin) essential for o-hydroxylation. 4HPA3H has a broad substrate spectrum involved in key biological processes, including cellular catabolism, detoxification, and the biosynthesis of bioactive molecules. Additionally, it specifically hydroxylates the o-position of the C4 position of the benzene ring in phenolic compounds, generating high-value polyhydroxyphenols. As a non-P450 o-hydroxylase, 4HPA3H offers a viable alternative for the de novo synthesis of valuable natural products. The enzyme holds the potential to replace plant-derived P450s in the o-hydroxylation of plant polyphenols, addressing the current significant challenge in engineering specific microbial strains with P450s. This review summarizes the source distribution, structural properties, and mechanism of 4HPA3Hs and their application in the biosynthesis of natural products in recent years. The potential industrial applications and prospects of 4HPA3H biocatalysts are also presented.

Cu-Catalyzed Tandem C-N and C-C Bond Formation Leading to 4(1H)-Quinolones: A Scaffold with Diverse Biological Properties from Totally New Raw Materials in a Single Step.

A novel Cu-catalyzed tandem C-N and C-C bond-formation reaction has been developed to furnish 2-substituted-4-(1H)-quinolones. 4-(1H)-quinolones play an important role in medicinal chemistry. Many 2-aryl(alkyl)-4(1H)-quinolones are found to exhibit diverse biological properties. While traditional methods have inherent issues [like starting materials with incompatible functional groups (NH2 and keto groups)], many modern methods either require activated starting materials (like Ynones) or employ expensive metals (Pd, Rh, Au, etc.) involving carbonylation using CO or metal complexes. Our protocol presents an environmentally friendly one-step method for the construction of these useful 2-substituted-4-(1H)-quinolones from easily available aryl boronic acid (or pinacolate ester) and nitriles as new raw materials, using a cheap Cu-catalyst and O2 (air) as a green oxidant. We further extended its application to the synthesis of various natural products, including the first formal total synthesis of punarnavine. A plausible mechanism involving an aryl nitrilium ion (formed due to the intermolecular C-N bond-forming coupling between aryl boron species and the nitrile group) followed by tandem intramolecular C-C bond formation has been proposed.

Total Synthesis of Tetracyclic Spirooxindole Alkaloids via a Double Oxidative Rearrangement/Cyclization Cascade.

Skeleton rearrangement could rapidly transfer simple molecules to complex structures and has significant potential in the total synthesis of natural products. We developed a one-pot reaction cascade of double oxidative rearrangement of furan and indole followed by a nucleophilic cyclization that was successfully applied for the formal synthesis of rhynchophylline/isorhynchophylline and the first total synthesis of (±)-7(R)-geissoschizol oxindole/(±)-7(S)-geissoschizol oxindole. In addition, the geissoschizol oxindoles were revised to their C3 epimers, and the mechanism for the reversed stereochemistry through the retro-Mannich/Mannich cascade was proposed and supported by density functional theory calculations.

Microwave-Promoted Total Synthesis of Puniceloid D for Modulating the Liver X Receptor.

A growing global health concern is metabolic syndrome, which is defined by low HDL, diabetes, hypertension, and abdominal obesity. Nuclear receptors are attractive targets for treatment of diseases associated with metabolic syndrome. Liver X receptors (LXRs) have become one of the most significant pharmacological targets among nuclear receptors. Multiple research studies emphasize the essential function of the liver X receptor (LXR) in the pathophysiology of metabolic syndrome. Puniceloid D, among natural products, demonstrated promising effects on LXRα. However, attempts at the total synthesis of natural products were faced with challenges, including long synthetic steps and low yields, requiring a more efficient approach. In this study, for the first time, we successfully synthesized puniceloid D through a seven-step process and conducted docking studies to gain a comprehensive understanding of the interactions involved in the binding of puniceloid D to LXR within different heterodimeric contexts. Our understanding of the pathophysiology of metabolic syndrome could be improved by these findings, which might assist with the development of novel treatment strategies.

Substrate Directed Regio‐ and Enantioselective Ring‐Opening of Epoxides and Aziridines

AbstractThe oxirane and aziridine rings are valuable building blocks in modern synthetic chemistry and catalytic asymmetric ring opening reactions of these three membered ring systems have emerged as a powerful chemical tool for the synthesis of natural products and biologically active compounds. In this context, the regioselective ring‐opening of structurally or electronically unbiased epoxides and aziridines is challenging. Recently, metal‐catalyzed substrate directed strategies have successfully applied in the regio‐ and enantioselective ring opening of functionalized epoxy alcohols by the Yamamoto group. Subsequently, our group realized the ring opening reactions of functionalized 2,3‐aziridinyl alcohols with the dinuclear zinc complex. These enantioselective nucleophilic ring opening reactions of functionalized epoxy alcohols and aziridinyl alcohols allow for the facile synthesis of amino alcohol derivatives and the introduction of new concepts in catalysis.

Improving and Streamlining Gene Editing in Yarrowia lipolytica via Integration of Engineered Cas9 Protein.

The oleaginous yeast Yarrowia lipolytica is a prominent subject of biorefinery research due to its exceptional performance in oil production, exogenous protein secretion, and utilization of various inexpensive carbon sources. Many CRISPR/Cas9 genome-editing systems have been developed for Y. lipolytica to meet the high demand for metabolic engineering studies. However, these systems often necessitate an additional outgrowth step to achieve high gene editing efficiency. In this study, we introduced the eSpCas9 protein, derived from the Streptococcus pyogenes Cas9(SpCas9) protein, into the Y. lipolytica genome to enhance gene editing efficiency and fidelity, and subsequently explored the optimal expression level of eSpCas9 gene by utilizing different promoters and selecting various growth periods for yeast transformation. The results demonstrated that the integrated eSpCas9 gene editing system significantly enhanced gene editing efficiency, increasing from 16.61% to 86.09% on TRP1 and from 33.61% to 95.19% on LIP2, all without the need for a time-consuming outgrowth step. Furthermore, growth curves and dilution assays indicated that the consistent expression of eSpCas9 protein slightly suppressed the growth of Y. lipolytica, revealing that strong inducible promoters may be a potential avenue for future research. This work simplifies the gene editing process in Y. lipolytica, thus advancing its potential as a natural product synthesis chassis and providing valuable insights for other comparable microorganisms.

Chemoenzymatic Synthesis of Steroidal Products: Recent Advances

AbstractThe synthesis of steroidal products has garnered sustained interest due to their versatile bioactivities and physicochemical properties in pharmaceutics. However, the complicated structure of steroids, especially their highly oxygenated skeleton, has presented significant challenges. Benefitted from recent advancements in bioinformatics, genetics, and enzyme engineering, chemoenzymatic strategy combines the flexibility of chemical synthesis with the high regio‐ and stereo‐selectivity of biocatalysis, being an effective approach for the concise synthesis of natural products. In this concept, we review and discuss the recent advances in chemoenzymatic approaches for efficient synthesis of steroids and their analogs, as well as future research opportunities and challenges.