Lessons and revelations from biomimetic syntheses

Discovery of a Fungal P450 with an Unusual Two-Step Mechanism for Constructing a Bicyclo[3.2.2]nonane Skeleton

The successful biomimetic or chemoenzymatic synthesis of target natural products (NPs) and their derivatives relies on enzyme discovery. Herein, we discover a fungal P450 BTG5 that can catalyze the formation of a bicyclo[3.2.2]nonane structure through an unusual two-step mechanism of dimerization and cyclization in the biosynthesis of beticolin 1, whose bicyclo[3.2.2]nonane skeleton connects an anthraquinone moiety and a xanthone moiety. Further investigation reveals that BTG5-T318 not only determines the substrate selectivity but also alters the catalytic reactions, which allows the separation of the reaction to two individual steps, thereby understanding its catalytic mechanism. It reveals that the first heterodimerization undergoes the common oxidation process for P450s, while the second uncommon formal redox-neutral cyclization step is proved as a redox-mediated reaction, which has never been reported. Therefore, this work advances our understanding of P450-catalyzed reactions and paves the way for expansion of the diversity of this class of NPs through synthetic biology.

Total Synthesis of Ganoderma Meroterpenoids Cochlearol B and Its Congeners Driven by Structural Similarity and Biological Homology

Secondary metabolites that have the same biological origin must share some relationship in their biosynthesis. Exploring this relationship has always been a significant task for synthetic biologists. However, from the perspective of synthetic chemists, it is equally important to propose, prove, or refute potential biosynthetic pathways in order to elucidate and understand the biosynthesis of homologous secondary metabolites. In this study, driven by the high structural similarity between the homologous Ganoderma meroterpenoids cochlearol B and ganocin B, two chemically synthetic strategies were designed and investigated sequentially for the synthesis of cochlearol B from ganocin B. These strategies include intramolecular metal-catalyzed hydrogen atom transfer (MHAT) and intramolecular photochemical [2+2] cycloaddition. The aim was to reveal their potential biosynthetic conversion relationship using chemical synthesis methods. As a result, a highly efficient total synthesis of cochlearol B, cochlearol T, cochlearol F, as well as the formal total synthesis of ganocins A-B, and ganocochlearins C-D, has been achieved. Additionally, a novel synthetic approach for the synthesis of 6,6-disubstituted 6H-dibenzo[b,d]pyran and its analogues has been developed through palladium(II)-catalyzed Wacker-type/cross-coupling cascade reactions.

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.

Biomimetic Synthesis of an Antiviral Cinnamoylphloroglucinol Collection from Cleistocalyx operculatus: A Synthetic Strategy Based on Biogenetic Building Blocks

A synthetic strategy based on biogenetic building blocks for the collective and divergent biomimetic synthesis of cleistoperlones A-F, a cinnamoylphloroglucinol collection discovered from Cleistocalyx operculatus, has been developed. These syntheses proceeded successfully in only six to seven steps starting from commercially available 1,3,5-benzenetriol and involving oxidative activation of stable biogenetic building blocks as a crucial step. Key features of the syntheses include a unique Michael addition/ketalization/1,6-addition/enol-keto tautomerism cascade reaction for the construction of the dihydropyrano[3,2-d]xanthene tetracyclic core of cleistoperlones A and B, and a rare inverse-electron-demand hetero-Diels-Alder cycloaddition for the establishment of benzopyran ring in cleistoperlones D-F. Moreover, cleistoperlone A exhibited significant antiviral activity against acyclovir-resistant strains of herpes simplex virus type 1 (HSV-1/Blue and HSV-1/153).

Natural Product Synthesis: The Endless Quest for Unreachable Perfection

Total synthesis is a field in constant progress. Its practitioners aim to develop ideal synthetic strategies to build complex molecules. As such, they are both a driving force and a showcase of the progress of organic synthesis. In this Perspective, we discuss recent notable total syntheses. The syntheses selected herein are classified according to the key strategic considerations for each approach.

Biogenetic space-guided synthesis of rearranged terpenoids

Natural product chemistry is constantly challenged by newly discovered, complex molecules. Elements of complexity arise from unprecedented frameworks, with a large amount of densely packed stereogenic centres and different functional groups along with a generally high oxidation state. As a prime example, rearranged triterpenoids possess all these elements. For their total synthesis, a limit of what is considered sensible in terms of steps and yield is frequently reached. As an alternative, semisynthetic approaches have gained a great amount of attention in recent years. In this featured article, we present our and others' contributions towards the development of efficient and economic syntheses of complex terpenoid natural products and elaborate on the underlying rationale of biogenetic space-guided synthetic analysis.

Bioinspired Synthesis of Spirochensilide A from Lanosterol

A bioinspired synthesis of spirochensilide A from commercially available lanosterol is reported. The synthesis features a directed C-H oxidation, a Wagner-Meerwein-type double methyl migration, a Meinwald rearrangement, and a double-bond isomerization/spiroketal formation cascade. The proposed biosynthetic speculation was modified by this synthetic sequence, which also served as a platform for the synthesis of other lanostanes with migrating methyl groups.

Nonenzymatic Reactions in Natural Product Formation

Biosynthetic mechanisms of natural products primarily depend on systems of protein catalysts. However, within the field of biosynthesis, there are cases in which the inherent chemical reactivity of metabolic intermediates and substrates evades the involvement of enzymes. These reactions are difficult to characterize based on their reactivity and occlusion within the milieu of the cellular environment. As we continue to build a strong foundation for how microbes and higher organisms produce natural products, therein lies a need for understanding how protein independent or nonenzymatic biosynthetic steps can occur. We have classified such reactions into four categories: intramolecular, multicomponent, tailoring, and light-induced reactions. Intramolecular reactions is one of the most well studied in the context of biomimetic synthesis, consisting of cyclizations and cycloadditions due to the innate reactivity of the intermediates. There are two subclasses that make up multicomponent reactions, one being homologous multicomponent reactions which results in dimeric and pseudodimeric natural products, and the other being heterologous multicomponent reactions, where two or more precursors from independent biosynthetic pathways undergo a variety of reactions to produce the mature natural product. The third type of reaction discussed are tailoring reactions, where postmodifications occur on the natural products after the biosynthetic machinery is completed. The last category consists of light-induced reactions involving ecologically relevant UV light rather than high intensity UV irradiation that is traditionally used in synthetic chemistry. This review will cover recent nonenzymatic biosynthetic mechanisms and include sources for those reviewed previously.

Bioinspired Palladium-Catalyzed Intramolecular C(sp3 )-H Activation for the Collective Synthesis of Proline Natural Products

Bioinspired palladium-catalyzed intramolecular cyclization of amino acid derivatives containing a vinyl iodide moiety by C-H activation enabled rapid access to a wide range of functionalized proline derivatives with an exocyclic olefin. To demonstrate the practicality of this methodology, the functionalized prolines were used as intermediates for the synthesis of several natural products: lucentamycin A, oxotomaymycin, oxoprothracarcin, and barmumycin.

Biogenesis-Inspired, Divergent Synthesis of Spirochensilide A, Spirochensilide B, and Abifarine B Employing a Radical-Polar Crossover Rearrangement Strategy

Triterpenoids and related abeo-steroids are of interest to the scientific community for their potent and varied biological activities as well as their unique structures. Within this large and diverse family of natural products, the fir metabolites (-)-spirochensilide A and B are particularly noteworthy for their controversial biogenesis. We herein report the chemical synthesis of the spirochensilides, which involves a concerted sequence of bioinspired rearrangements contributing to its resolution. Points of divergence after each rearrangement step also allow for an approach to the abifarine family of natural products with abifarine B as a synthetic target. Key to this strategy is a radical-polar crossover event to initiate the first rearrangement without the need for a sacrificial functionality to be introduced beforehand.

Evaluation of the photodecarbonylation of crystalline ketones for the installation of reverse prenyl groups on the pyrrolidinoindoline scaffold

We report synthetic efforts toward the regiocontrolled installation of the prenyl moiety in debromoflustramine A by the regiospecific photodecarbonylation of a prenyl-substituted ketone. Synthetic approaches to access the plausible photodecarbonylation substrates beginning from tryptamine were evaluated. Initial attempts to synthesize a suitable substrate for photodecarbonylation were hampered by a lack of substrate crystallinity (a prerequisite for solid-state photochemistry). Ultimately, a crystalline substrate could be accessed to attempt the key step by judicious selection of N-substituents. Although the photodecarbonylation did not result in the desired reverse prenylation, this study highlights the troubleshooting and optimization required for crystal phase photochemistry and underscores methods that can be used to control substrate crystallinity.

Biomimetic Synthesis of Natural Products: A Journey To Learn, To Mimic, and To Be Better

Total synthesis of natural products has been one of the most exciting and dynamic areas in synthetic organic chemistry. Nowadays, the major challenge in this field is not whether a given target of interest can be synthesized but how to make it with commendable efficiency and practicality. To meet this grand challenge, a wise way is to learn from Mother Nature who is recognized for her superb capability of forging complicated and sometimes beyond-imagination molecules in her own delicate way. Indeed, since Sir Robert Robinson published his groundbreaking synthesis of tropinone in 1917, biomimetic synthesis of natural products, a process of imitating nature's way to make molecules, has evolved into one of the most popular research directions in organic synthesis.Our group has been engaging in biomimetic synthesis of natural products in the past decade. During this time, we have come to realize that the successful implementation of a biomimetic synthesis entails the orchestrated combination of bioinspiration and rational design. On the one hand, we prefer to utilize some elegant bioinspired transformations (e.g., Diels-Alder dimerization, 6π-electrocyclization, and [2 + 2]-photocycloaddition) as the key steps of our synthesis, which enable rapid construction of the core skeletons of the chased targets with high efficiency; on the other hand, various powerful reactions (e.g., dyotropic rearrangement of β-lactone, tandem aldol condensation/Grob fragmentation reaction, and organocatalytic asymmetric Mukaiyama-Michael addition) are rationally designed by us, which allow for facile access to the requisite precursors for attempting biomimetic transformations. In some cases, the proposed biomimetic transformation may fail to give a satisfactory result in practice, and thus we opt to develop creative tactics (e.g., hydrogen atom transfer-triggered vinyl cyclobutane ring opening/oxygen insertion/cyclization cascade) that can meet the challenge. Guided by this synthesis concept, we have achieved the total syntheses of multiple families of natural products of great importance in both chemistry and biology, representatives of which include xanthanolides, cytochalasans, and plakortin-type polyketides. Of note, most of these targets could be accessed in a concise, efficient, and scalable manner, which paves the way for further exploration of their biological functions and medicinal potential. Moreover, owing to their biomimetic nature, our syntheses provide valuable information for deciphering the underlying biosynthetic pathways of the chased targets, which could not be attained by other synthetic modes.

Bioinspired Fibers with Controlled Wettability: From Spinning to Application

Our knowledge on spider silks shows the importance of joining heterogeneous structures and surface chemical compositions in preparing fibers, fibrous surfaces, and 3D materials with a controllable wettability. We start our review with spider silk and proceed to the historical development of nature-inspired spinning processes, their products, and their advantages and disadvantages. Relevant wetting states are then summarized in fiber-based systems. Recent applications are reviewed, including one-dimensional spindle-knotted fibers for highly efficient fog harvesting, long-distance transport, and stimulus-responsive wettability and two-dimensional spindle-knotted fibrous systems for water collection, functional surfaces, and filtration. Finally, we offer some perspective on future research trends regarding biomimetic fibers for wetting-controlled engineering.

Biogenesis-Guided Synthesis and Structural Revision of Sarocladione Enabled by Ruthenium-Catalyzed Endoperoxide Fragmentation

Sarocladione is the first 5,10:8,9-diseco-steroid with a 14-membered macrocyclic diketone framework to have been isolated from a natural source. Herein we report a biomimetic synthesis of sarocladione in only two or seven steps from inexpensive, commercially available ergosterol. The key feature of this synthesis was a novel ruthenium-catalyzed endoperoxide fragmentation, which transformed various saturated endoperoxides into olefinic diketones by cleavage of two C-C bonds. This synthesis allowed us to unambiguously determine the structure of sarocladione and provided experimental support for its revised biosynthetic origin. This work also vividly demonstrates that consideration of the biogenesis is a powerful tool for elucidating the structures of natural products.

Nonbiomimetic total synthesis of indole alkaloids using alkyne-based strategies

Biomimetic natural product synthesis is generally straightforward and efficient because of its established feasibility in nature and utility in comprehensive synthesis, and the cost-effectiveness of naturally derived starting materials. On the other hand, nonbiomimetic strategies can be an important option in natural product synthesis since (1) nonbiomimetic synthesis offers more flexibility and can demonstrate the originality of chemists, and (2) the structures of derivatives accessible by nonbiomimetic synthesis can be considerably different from those that are synthesised in nature. This review summarises nonbiomimetic total syntheses of indole alkaloids using alkyne chemistry for constructing core structures, including ergot alkaloids, monoterpene indole alkaloids (mainly corynanthe, aspidosperma, strychnos, and akuammiline), and pyrroloindole and related alkaloids. To clarify the differences between alkyne-based strategies and biosynthesis, the alkynes in nature and the biosyntheses of indole alkaloids are also outlined.

Biomimetic Approaches to the Synthesis of Natural Disesquiterpenoids: An Update

Natural disesquiterpenoids represent a small group of secondary metabolites characterized by complex molecular scaffolds and interesting pharmacological profiles. In the last decade, more than 400 new disesquiterpenoids have been discovered and fully characterized, pointing out once more the "magic touch" of nature in the design of new compounds. The perfect blend of complex and unique architectures and biological activity has made sesquiterpene dimers an attractive and challenging synthetic target, inspiring organic chemists to find new and biomimetic approaches to replicate the efficiency and the selectivity of natural processes under laboratory conditions. In this work, we present a review covering the literature from 2010 to 2020 reporting all the efforts made in the total synthesis of complex natural disesquiterpenoids.

Late-Stage Diversification of Natural Products

Late-stage diversification of natural products is an efficient way to generate natural product derivatives for drug discovery and chemical biology. Benefiting from the development of site-selective synthetic methodologies, late-stage diversification of natural products has achieved notable success. This outlook will outline selected examples of novel methodologies for site-selective transformations of reactive functional groups and inert C-H bonds that enable late-stage diversification of complex natural products. Accordingly, late-stage diversification provides an opportunity to rapidly access various derivatives for modifying lead compounds, identifying cellular targets, probing protein-protein interactions, and elucidating natural product biosynthetic relationships.

Advances in Biomimetic Systems for Molecular Recognition and Biosensing

Understanding the fundamentals of natural design, structure, and function has pushed the limits of current knowledge and has enabled us to transfer knowledge from the bench to the market as a product. In particular, biomimicry―one of the crucial strategies in this respect―has allowed researchers to tackle major challenges in the disciplines of engineering, biology, physics, materials science, and medicine. It has an enormous impact on these fields with pivotal applications, which are not limited to the applications of biocompatible tooth implants, programmable drug delivery systems, biocompatible tissue scaffolds, organ-on-a-chip systems, wearable platforms, molecularly imprinted polymers (MIPs), and smart biosensors. Among them, MIPs provide a versatile strategy to imitate the procedure of molecular recognition precisely, creating structural fingerprint replicas of molecules for biorecognition studies. Owing to their affordability, easy-to-fabricate/use features, stability, specificity, and multiplexing capabilities, host-guest recognition systems have largely benefitted from the MIP strategy. This review article is structured with four major points: (i) determining the requirement of biomimetic systems and denoting multiple examples in this manner; (ii) introducing the molecular imprinting method and reviewing recent literature to elaborate the power and impact of MIPs on a variety of scientific and industrial fields; (iii) exemplifying the MIP-integrated systems, i.e., chromatographic systems, lab-on-a-chip systems, and sensor systems; and (iv) closing remarks.

Total synthesis of terpenes via palladium-catalysed cyclization strategy

Nature's synthetic plans to construct molecules have been developed over millions of years of evolution and frequently prove to be among the most sophisticated. Mimicking nature's route can be a direct and feasible way for synthetic organic chemists to construct complicated molecules. However, lacking nature's ability to manipulate enzymes often prevents us from reproducing the same route. Modifying nature's approaches can provide a simpler synthetic alternative to access complex structural target molecules. Here we report a strategy that simplifies the synthesis of terpenes by inverting the order of nature's two-phase biosynthesis route. We first unite simple molecules into a polyfunctionalized linear polyenyne, with all the desired carbons and oxygens in the targeted places. This compound then undergoes polyenyne cycloisomerization, in the presence of all the functional groups, to give polyoxidized terpenes. The key reaction is a palladium-catalysed polyenyne cycloisomerization that not only tolerates the presence of all of the oxygen functionalities, but also is facilitated by them.

Diastereoselective construction of the benzannulated spiroketal core of chaetoquadrins enabled by a regiodivergent cascade

A remarkable acid-mediated methodology for the regiodivergent construction of a biologically interesting tricyclic benzannulated-spiroketal skeleton with diastereomeric specificity was uncovered to efficiently access analogs of chaetoquadrins .

Bacterial terpene biosynthesis: challenges and opportunities for pathway engineering

Terpenoids are the largest and structurally most diverse class of natural products. They possess potent and specific biological activity in multiple assays and against diseases, including cancer and malaria as notable examples. Although the number of characterized terpenoid molecules is huge, our knowledge of how they are biosynthesized is limited, particularly when compared to the well-studied thiotemplate assembly lines. Bacteria have only recently been recognized as having the genetic potential to biosynthesize a large number of complex terpenoids, but our current ability to associate genetic potential with molecular structure is severely restricted. The canonical terpene biosynthetic pathway uses a single enzyme to form a cyclized hydrocarbon backbone followed by modifications with a suite of tailoring enzymes that can generate dozens of different products from a single backbone. This functional promiscuity of terpene biosynthetic pathways renders terpene biosynthesis susceptible to rational pathway engineering using the latest developments in the field of synthetic biology. These engineered pathways will not only facilitate the rational creation of both known and novel terpenoids, their development will deepen our understanding of a significant branch of biosynthesis. The biosynthetic insights gained will likely empower a greater degree of engineering proficiency for non-natural terpene biosynthetic pathways and pave the way towards the biotechnological production of high value terpenoids.

Chemistry, bioactivity and biosynthesis of cyanobacterial alkylresorcinols

Covering: up to 2019 Alkylresorcinols are amphiphilic metabolites, well-known for their diverse biological activities, produced by both prokaryotes and eukaryotes. A few classes of alkylresorcinol scaffolds have been reported from the photoautotrophic cyanobacteria, ranging from the relatively simple hierridins to the more intricate cylindrocyclophanes. Recently, it has emerged that cyanobacteria employ two different biosynthetic pathways to produce unique alkylresorcinol scaffolds. However, these convergent pathways intersect by sharing biosynthetic elements which lead to common structural motifs. To obtain a broader view of the biochemical diversity of these compounds in cyanobacteria, we comprehensively cover the isolation, structure, biological activity and biosynthesis of their mono- and dialkylresorcinols. Moreover, we provide an overview of the diversity and distribution of alkylresorcinol-generating biosynthetic gene clusters in this phylum and highlight opportunities for discovery of novel alkylresorcinol scaffolds. Because some of these molecules have inspired notable syntheses, different approaches used to build these molecules in the laboratory are showcased.

Biomimetic Synthesis of Psiguajdianone Guided Discovery of the Meroterpenoids from Psidium guajava

Psiguajdianone (1), a novel caryophyllene-derived meroterpenoid dimer, was isolated from Psidium guajava. The structure of 1 was determined by X-ray analysis and confirmed by total synthesis. Our synthetic strategy involves biomimetic cascade Knoevenagel condensation/hetero-Diels-Alder reaction and dimerization. Notably, the caryophyllene-derived meroterpenoids obtained during our synthesis were first identified as artifacts in the laboratory, and five of them were proven to be natural products present in the plant. Moreover, these compounds show significant anti-inflammatory activity.

Gold(I)-Mediated Cycloisomerization/Cycloaddition Enables Bioinspired Syntheses of Neonectrolides B-E and Analogues

Development of a synthetic route to the oxaphenalenone (OP) natural products neonectrolides B-E is described. The synthesis relies on gold-catalyzed 6-endo-dig hydroarylation of an unusual enynol substrate as well as a one-pot Rieche formylation/cyclization/deprotection sequence to efficiently construct the tricyclic oxaphenalenone framework in the form of a masked ortho-quinone methide (o-QM). A tandem cycloisomerization/[4 + 2] cycloaddition strategy was employed to quickly construct molecules resembling the neonectrolides. The tricyclic OP natural product SF226 could be converted to corymbiferan lactone E and a related masked o-QM. Our study culminates with the application of the tandem reaction sequence to syntheses of neonectrolides B-E as well as previously unreported exo-diastereomers.

Synthesis of 6,12-Disubstituted Methanodibenzo[b,f][1,5]dioxocins: Pyrrolidine Catalyzed Self-Condensation of 2′-Hydroxyacetophenones

The preparation of unprecedented 6,12-disubstituted methanodibenzo[b,f][1,5]dioxocins from pyrrolidine catalyzed self-condensation of 2′-hydroxyacetophenones is herein described. This method provides easy access to this highly bridged complex core, resulting in construction of two C–O and two C–C bonds, a methylene bridge and two quaternary centers in a single step. The intricate methanodibenzo[b,f][1,5]dioxocin compounds were obtained in up to moderate yields after optimization of the reaction conditions concerning solvent, reaction times and the use of additives. Several halide substituted methanodibenzo[b,f][1,5]dioxocins could be prepared from correspondent 2′-hydroxyacetophenones.

Biomimetic Enantioselective Total Synthesis of (-)-Robustanoids A and B and Analogues

We report a step-economical, enantioselective total synthesis of (-)-robustanoid B and (-)-robustanoid A and four novel natural product-like compounds. Our strategy relied on our biosynthetic hypothesis and on a novel complexity generation methodology, namely, the one-pot hydroxylative double cyclization reaction. The latter consists of a modified 3,3-dimethyldioxirane-triggered epoxidation-epoxide-ring-opening cyclization reaction cascade and Trost's regioselectivity umpolung methodology ("anti-Michael addition").

Rapid Generation of Molecular Complexity by Chemical Synthesis: Highly Efficient Total Synthesis of Hexacyclic Alkaloid (-)-Chaetominine and Its Biosynthetic Implications

The efficiency becomes a key issue in today's natural product total synthesis. While biomimetic synthesis is one of the most elegant strategies to achieve synthetic efficiency and thus to approach the ideal synthesis, most biogenetic pathways are unknown or unconfirmed. In this account, we demonstrate, through the shortest and also the most efficient asymmetric total syntheses of the hexacyclic alkaloid (-)-chaetominine to date, that on the basis of biogenetic thinking, one can develop quite efficient bio-inspired total synthesis, which in turn serves to suggest and chemically validate plausible biosynthetic routes for the natural product. The synthetic strategy thus developed is also inspiring for the development of other synthetic methods and efficient total synthesis of other natural products.

Bioinspired Synthesis of (+)-Cinchonidine Using Cascade Reactions

The development of efficient syntheses of complex natural products has long been a major challenge in synthetic chemistry. Designing cascade reactions and employing bioinspired transformations are an important and reliable means of achieving this goal. Presented here is a combination of these two strategies, which allow efficient asymmetric synthesis of the cinchona alkaloid (+)-cinchonidine. The key steps of this synthesis are a controllable, visible-light-induced photoredox radical cascade reaction to efficiently access the tetracyclic monoterpenoid indole alkaloid core, as well as a practical biomimetic cascade rearrangement for the indole to quinoline transformation. The use of stereoselective chemical transformations in this work makes it an efficient synthesis of (+)-cinchonidine.

Dearomative Cascade Photocatalysis: Divergent Synthesis through Catalyst Selective Energy Transfer

The discovery and application of dearomative cascade photocatalysis as a strategy in complex molecule synthesis is described. Visible-light-absorbing photosensitizers were used to (sequentially) activate a 1-naphthol derived arene precursor to divergently form two different polycyclic molecular scaffolds through catalyst selective energy transfer.

Asymmetric Induction via a Helically Chiral Anion: Enantioselective Pentacarboxycyclopentadiene Brønsted Acid-Catalyzed Inverse-Electron-Demand Diels-Alder Cycloaddition of Oxocarbenium Ions

An enantioselective catalytic inverse-electron-demand Diels-Alder reaction of salicylaldehyde acetal-derived oxocarbenium ions and vinyl ethers to generate 2,4-dioxychromanes is described. Chiral pentacarboxycyclopentadiene (PCCP) acids are found to be effective for a variety of substrates. Computational and X-ray crystallographic analyses support the unique hypothesis that an anion with point-chirality-induced helical chirality dictates the absolute sense of stereochemistry in this reaction.

Total synthesis of complex terpenoids employing radical cascade processes

Covering: 2011-2017Radical cyclizations have a rich history in organic chemistry and have been particularly generous to the field of natural product synthesis. Owing to their ability to operate in highly congested molecular quarters, and with significant functional group compatibility, these transformations have enabled the synthesis of numerous polycyclic terpenoid natural products over the past several decades. Moreover, when programmed accordingly into a synthetic plan, radical cascade processes can be used to rapidly assemble molecular complexity, much in the same way nature rapidly constructs terpene frameworks through cationic cyclization pathways. This review highlights recent total syntheses of complex terpenoids (from 2011-2017) employing C-C bond-forming radical cascade sequences.

A biosynthetically inspired synthesis of (-)-berkelic acid and analogs

We describe a complete account of our total synthesis and biological evaluation of (-)-berkelic acid and analogs. We delineate a synthetic strategy inspired by a potentially biomimetic union between the natural products spicifernin and pulvilloric acid. After defining optimal parameters, we executed a one-pot silver-mediated in situ dehydration of an isochroman lactol to methyl pulvillorate, the cycloisomerization of a spicifernin-like alkynol to the corresponding exocyclic enol ether, and a subsequent cycloaddition to deliver the tetracyclic core of berkelic acid. Our studies confirm that the original assigned berkelic acid structure is not stable and equilibrates into a mixture of 4 diastereomers, fully characterized by X-ray crystallography. In addition to berkelic acid, C22-epi-berkelic acid, and nor-berkelic acids, we synthesized C26-oxoberkelic acid analogs that were evaluated against human cancer cell lines. In contrast to data reported for natural berkelic acid, our synthetic material and analogs were found to be devoid of activity.

Natural products as inspiration for the development of new synthetic methods

Natural products have played an important role in shaping modern synthetic organic chemistry. In particular, their complex molecular skeletons have stimulated the development of many new synthetic methods. We highlight in this article some recent examples of synthetic design inspired by the biosynthesis of natural products.