Gateway synthesis of daphnane congeners and their protein kinase C affinities and cell-growth activities

Total Syntheses of Phorbol and 11 Tigliane Diterpenoids and Their Evaluation as HIV Latency-Reversing Agents

Tigliane diterpenoids possess exceptionally complex structures comprising common 5/7/6/3-membered ABCD-rings and disparate oxygen functionalities. While tiglianes display a wide range of biological activities, compounds with HIV latency-reversing activity can eliminate viral reservoirs, thereby serving as promising leads for new anti-HIV agents. Herein, we report collective total syntheses of phorbol (13) and 11 tiglianes 14-24 with various acylation patterns and oxidation states, and their evaluation as HIV latency-reversing agents. The syntheses were strategically divided into five stages to increase the structural complexity. First, our previously established sequence enabled the expeditious preparation of ABC-tricycle 9 in 15 steps. Second, hydroxylation of 9 and ring-contractive D-ring formation furnished phorbol (13). Third, site-selective attachment of two acyl groups to 13 produced four phorbol diesters 14-17. Fourth, the oxygen functionalities were regio- and stereoselectively installed to yield five tiglianes 18-22. Fifth, further oxidation to the most densely oxygenated acerifolin A (23) and tigilanol tiglate (24) was realized through organizing a 3D shape of the B-ring. Assessment of the HIV latency-reversing activities of the 12 tiglianes revealed seven tiglianes (14-17 and 22-24) with 20- to 300-fold improved efficacy compared with prostratin (12), a representative latency-reversing agent. Therefore, the robust synthetic routes to a variety of tiglianes with promising activities devised in this study provide opportunities for advancing HIV eradication strategies.

Tigliane Diterpenoids

The distribution, chemistry, and molecular bioactivity of tiglianes are reviewed from the very beginning of the studies on these diterpenoids, summarizing their clinical and toxicological literature mostly in its more recent and controversial aspects, and critically analyzing various proposals for their biosynthesis.

Novel Skeletal Rearrangements of the Tigliane Diterpenoid Core

To investigate the role of the secondary 5-hydroxy group in the activity of the anticancer drug tigilanol tiglate (2b) (Stelfonta), oxidation of this epoxytigliane diterpenoid from the Australian rainforest plant Fontainea picrosperma was attempted. Eventually, 5-dehydrotigilanol tiglate (3a) proved too unstable to be characterized in terms of biological activity and, therefore, was not a suitable tool compound for bioactivity studies. On the other hand, a series of remarkable skeletal rearrangements associated with the presence of a 5-keto group were discovered during its synthesis, including a dismutative ring expansion of ring A and a mechanistically unprecedented dyotropic substituent swap around the C-4/C-10 bond. Taken together, these observations highlight the propensity of the α-hydroxy-β-diketone system to trigger complex skeletal rearrangements and pave the way to new areas of the natural products chemical space.

Asymmetric Construction of the Core of C6, C7-Epoxy Daphnane Diterpenoid Orthoesters

Asymmetric construction of the core of C6, C7-epoxy daphnane diterpenoid orthoesters is developed through a convergent synthetic strategy. The salient features include a diastereoselective nucleophilic assembly of two bulky cyclic fragments, an oxidative cleavage/transesterification/aldol cascade to fashion the seven-membered ring, and a base-mediated transesterification/retro-aldol/aldol/epoxidation cascade to install the epoxy moiety with proper stereochemistry.

Tigliane and daphnane diterpenoids from Thymelaeaceae family: chemistry, biological activity, and potential in drug discovery

Tigliane and daphnane diterpenoids are characteristically distributed in plants of the Thymelaeaceae family as well as the Euphorbiaceae family and are structurally diverse due to the presence of polyoxygenated functionalities in the polycyclic skeleton. These diterpenoids are known as toxic components, while they have been shown to exhibit a wide variety of biological activities, such as anti-cancer, anti-HIV, and analgesic activity, and are attracting attention in the field of natural product drug discovery. This review focuses on naturally occurring tigliane and daphnane diterpenoids from plants of the Thymelaeaceae family and provides an overview of their chemical structure, distribution, isolation, structure determination, chemical synthesis, and biological activities, with a prime focus on the recent findings.

Practical synthesis of the therapeutic leads tigilanol tiglate and its analogues

Tigilanol tiglate is a natural product diterpenoid in clinical trials for the treatment of a broad range of cancers. Its unprecedented protein kinase C isoform selectivity make it and its analogues exceptional leads for PKC-related clinical indications, which include human immunodeficiency virus and AIDS eradication, antigen-enhanced cancer immunotherapy, Alzheimer's disease and multiple sclerosis. Currently, the only source of tigilanol tiglate is a rain forest tree, Fontainea picrosperma, whose limited number and restricted distribution (northeastern Australia) has prompted consideration of designed tree plantations to address supply needs. Here we report a practical laboratory synthesis of tigilanol tiglate that proceeds in 12 steps (12% overall yield, >80% average yield per step) and can be used to sustainably supply tigilanol tiglate and its analogues, the latter otherwise inaccessible from the natural source. The success of this synthesis is based on a unique strategy for the installation of an oxidation pattern common to many biologically active tiglianes, daphnanes and their analogues.

Hydroxy-directed iridium-catalyzed enantioselective formal β-C(sp2)-H allylic alkylation of α,β-unsaturated carbonyls

Hydroxy-directed iridium-catalyzed enantioselective formal β-C(sp2)-H allylic alkylation of kojic acid and structurally related α,β-unsaturated carbonyl compounds is developed. This reaction, catalyzed by an Ir(i)/(P,olefin) complex, utilizes the nucleophilic character of α-hydroxy α,β-unsaturated carbonyls, to introduce an allyl group at its β-position in a branched-selective manner in good to excellent yield with uniformly high enantioselectivity (up to >99.9 : 0.1 er). To the best of our knowledge, this report represents the first example of the use of kojic acid in a transition metal catalyzed highly enantioselective transformation.

Potential HIV latency-reversing agents with STAT1-activating activity from the leaves of Wikstroemia chamaedaphne

Developing highly effective HIV latency-reversing agent is an inportmant approach for the treatment of AIDS via the "shock and kill" of latent HIV. In this study, two unreported modified daphnane-type diterpenes (chamaedaphnelide A and epi-chamaedaphnelide A) and one unreported tigliane-type diterpene (chamaedaphnelide B), along with four known daphnane-type diterpenes and one known tigliane-type diterpene were obtained from the leaves of Wikstroemia chamaedaphne. Chamaedaphnelide A and epi-chamaedaphnelide A represents the first A ring cleavage daphnane-type backbone. Chamaedaphnelide A, epi-chamaedaphnelide A, chamaedaphnelide B, and 6α,7α-epoxy-5β-hydroxy-12-deoxyphorbol-13-decanoate showed HIV latency-reversing activity, especially chamaedaphnelide B and 6α,7α-epoxy-5β-hydroxy-12-deoxyphorbol-13-decanoate displayed equally potential to positive drugs prostratin with reversing latent HIV on more than 100-fold compared to unstimulated cells. Furthermore, the activation of STAT1 was involved in the HIV latency-reversing activity of these diterpenes, firstly demonstrating that daphnane- and tigliane-type diterpenes can rapidly activate STAT1 activity. Indeed, these results also supported that activating STAT1 activity is a pathway for reversing latent HIV.

On drug discovery against infectious diseases and academic medicinal chemistry contributions

This perspective is an attempt to document the problems that medicinal chemists are facing in drug discovery. It is also trying to identify relevant/possible, research areas in which academics can have an impact and should thus be the subject of grant calls. Accordingly, it describes how hit discovery happens, how compounds to be screened are selected from available chemicals and the possible reasons for the recurrent paucity of useful/exploitable results reported. This is followed by the successful hit to lead stories leading to recent and original antibacterials which are, or about to be, used in human medicine. Then, illustrated considerations and suggestions are made on the possible inputs of academic medicinal chemists. This starts with the observation that discovering a "good" hit in the course of a screening campaign still rely on a lot of luck - which is within the reach of academics -, that the hit to lead process requires a lot of chemistry and that if public-private partnerships can be important throughout these stages, they are absolute requirements for clinical trials. Concerning suggestions to improve the current hit success rate, one academic input in organic chemistry would be to identify new and pertinent chemical space, design synthetic accesses to reach these and prepare the corresponding chemical libraries. Concerning hit to lead programs on a given target, if no new hits are available, previously reported leads along with new structural data can be pertinent starting points to design, prepare and assay original analogues. In conclusion, this text is an actual plea illustrating that, in many countries, academic research in medicinal chemistry should be more funded, especially in the therapeutic area neglected by the industry. At the least, such funds would provide the intensive to secure series of hopefully relevant chemical entities which appears to often lack when considering the results of academic as well as industrial screening campaigns.

Total Synthesis of Resiniferatoxin

From both structural and functional perspectives, the large family of daphnane diterpene orthoesters (DDOs) represent a truly remarkable class of natural products. As potent lead compounds for the treatment of pain, neurodegeneration, HIV/AIDS, and cancer, their medicinal potential continues to be heavily investigated, yet synthetic routes to DDO natural products remain rare. Herein we report a distinct approach to this class of complex diterpenes, highlighted by a 15-step total synthesis of the flagship DDO, resiniferatoxin.

Highly efficient construction of an oxa-[3.2.1]octane-embedded 5-7-6 tricyclic carbon skeleton and ring-opening of the bridged ring via C-O bond cleavage

We report herein a highly efficient strategy for construction of a bridged oxa-[3.2.1]octane-embedded 5–7–6 tricyclic carbon skeleton through [3 + 2] IMCC (intramolecular [3 + 2] cross-cycloaddition), and the substituents and/or stereochemistries on C-4, C-6, C-7 and C-10 fully match those in the rhamnofolane, tigliane and daphnane diterpenoids. Furthermore, ring-opening of the bridged oxa-[3.2.1]octane via C–O bond cleavage was also successfully achieved.

We reported a highly efficient construction of an oxa-[3.2.1]octane-embedded 5–7–6 tricyclic carbon skeleton with a full match of the substituents and stereochemistries on C-4/-6/-7/-10 with those in the rhamnofolane/tigliane/daphnane diterpenoids.

Yuanhuacin and Related Anti-Inflammatory and Anticancer Daphnane Diterpenes from Genkwa Flos-An Overview

The dried flower buds of the plant Daphne genkwa Sieb. et Zucc. have been largely used in traditional Chinese medicine for the treatment of inflammatory diseases. Numerous diterpenoids have been isolated from the Genkwa Flos (yuanhua in Chinese), including a series of daphnane-type diterpene designated as yuanhuacin (YC, often improperly designated as yuanhuacine) and analogues with a patronymic name. The series includes ten daphnane-type diterpenes: yuanhuacin, yuanhuadin (YD), yuanhuafin (YF), yuanhuagin (YG), yuanhuahin (YH), yuanhuajin (YJ), yuanhualin (YL), yuanhuamin (YM), yuanhuapin (YP), and yuanhuatin (YT). They are distinct from the rare flavonoid yuanhuanin. The series comprises several anticancer agents, such as the lead compound YC, which has revealed potent activity in vitro and in vivo against models of lung and breast cancers. The main signaling pathways implicated in the antitumor effects have been delineated. Protein kinase C is a key factor of activity for YC, but in general the molecular targets at the origin of the activity of these compounds remain little defined. Promising anticancer effects have been reported with analogues YD and YT, whereas compounds YF and YP are considered more toxic. The pharmacological activity of each compound is presented, as well as the properties of Genkwa Flos extracts. The potential toxic effects associated with the use of these compounds are also underlined.

Unified Total Syntheses of Rhamnofolane, Tigliane, and Daphnane Diterpenoids

Rhamnofolane, tigliane, and daphnane diterpenoids are structurally complex natural products with multiple oxygen functionalities, making them synthetically challenging. While these diterpenoids share a 5/7/6-trans-fused ring system (ABC-ring), the three-carbon substitutions at the C13- and C14-positions on the C-ring and appending oxygen functional groups differ among them, accounting for the disparate biological activities of these natural products. Here, we developed a new, unified strategy for expeditious total syntheses of five representative members of these three families, crotophorbolone (1), langduin A (2), prostratin (3), resiniferatoxin (4), and tinyatoxin (5). Retrosynthetically, 1-5 were simplified into their common ABC-ring 6 by detaching the three-carbon units and the oxygen-appended groups. Intermediate 6 with six stereocenters was assembled from four achiral fragments in 12 steps by integrating three powerful transformations, as follows: (i) asymmetric Diels-Alder reaction to induce formation of the C-ring; (ii) π-allyl Stille coupling reaction to set the trisubstituted E-olefin of the B-ring; and (iii) Eu(fod)₃-promoted 7-endo cyclization of the B-ring via the generation of a bridgehead radical. Then 6 was diversified into 1-5 by selective installation of the different functional groups. Attachment of the C14-β-isopropenyl and isopropyl groups led to 1 and 2, respectively, while oxidative acetoxylation and C13,14-β-dimethylcyclopropane formation gave rise to 3. Finally, formation of an α-oriented caged orthoester by C13-stereochemical inversion and esterification with two different homovanillic acids delivered 4 and 5 with a C13-β-isopropenyl group. This unified synthetic route to 1-5 required only 16-20 total steps, demonstrating the exceptional efficiency of the present strategy.

Yuanhuacine Is a Potent and Selective Inhibitor of the Basal-Like 2 Subtype of Triple Negative Breast Cancer with Immunogenic Potential

The heterogeneity of triple negative breast cancer (TNBC) has led to efforts to further subtype this disease with the hope of identifying new molecular liabilities and drug targets. Furthermore, the finding that TNBC is the most inherently immunogenic type of breast cancer provides the potential for effective treatment with immune checkpoint inhibitors and immune adjuvants. Thus, we devised a dual screen to identify compounds from natural product extracts with TNBC subtype selectivity that also promote the expression of cytokines associated with antitumor immunity. These efforts led to the identification of yuanhuacine (1) as a potent and highly selective inhibitor of the basal-like 2 (BL2) subtype of TNBC that also promoted an antitumor associated cytokine signature in immune cells. The mechanism of action of yuanhuacine for both phenotypes depends on activation of protein kinase C (PKC), defining a novel target for the treatment of this clinical TNBC subtype. Yuanhuacine showed potent antitumor efficacy in animals bearing BL2 tumors further demonstrating that PKC could function as a potential pharmacological target for the treatment of the BL2 subtype of TNBC.

Balancing skeleton and functional groups in total syntheses of complex natural products: a case study of tigliane, daphnane and ingenane diterpenoids

Total synthesis of natural products has greatly contributed to natural product research, organic synthesis and drug discovery and development. However, in most cases, the efficiency of total synthesis is far from sufficient for direct practical industrial application. Thus, designing a concise and efficient synthetic route with balanced efforts between building the complex skeleton and introducing functional groups is highly desirable. In this critical review, we first present an introduction of this issue and a philosophical framework that cover possible synthetic approaches. Next, we have chosen the biogenetically closely related, biologically important and synthetically extremely challenging natural products, tiglianes, daphnanes and ingenanes as the particular case for the discussion, since in the past 40 years many synthetic approaches have been reported. The successes and pitfalls included therefore serve as the basis to draw some conclusions that may inspire future development in this area.

Fragment Coupling Reactions in Total Synthesis That Form Carbon-Carbon Bonds via Carbanionic or Free Radical Intermediates

Fragment coupling reactions that form carbon-carbon bonds are valuable transformations in synthetic design. Advances in metal-catalyzed cross-coupling reactions in the early 2000s brought a high level of predictability and reliability to carbon-carbon bond constructions involving the union of unsaturated fragments. By comparison, recent years have witnessed an increase in fragment couplings proceeding via carbanionic and open-shell (free radical) intermediates. The latter has been driven by advances in methods to generate and utilize carbon-centered radicals under mild conditions. In this Review, we survey a selection of recent syntheses that have implemented carbanion- or radical-based fragment couplings to form carbon-carbon bonds. We aim to highlight the strategic value of these disconnections in their respective settings and to identify extensible lessons from each example that might be instructive to students.

Structural insights into C1-ligand interactions: Filling the gaps by in silico methods

Protein Kinase C isoenzymes (PKCs) are the key mediators of the phosphoinositide signaling pathway, which involves regulated hydrolysis of phosphatidylinositol (4,5)-bisphosphate to diacylglycerol (DAG) and inositol-1,4,5-trisphosphate. Dysregulation of PKCs is implicated in many human diseases making this class of enzymes an important therapeutic target. Specifically, the DAG-sensing cysteine-rich conserved homology-1 (C1) domains of PKCs have emerged as promising targets for pharmaceutical modulation. Despite significant progress, the rational design of the C1 modulators remains challenging due to difficulties associated with structure determination of the C1-ligand complexes. Given the dearth of experimental structural data, computationally derived models have been instrumental in providing atomistic insight into the interactions of the C1 domains with PKC agonists. In this review, we provide an overview of the in silico approaches for seven classes of C1 modulators and outline promising future directions.

Stereoselective Construction of the Methylcyclopentane Core of Peditithins B-H with Five Continuous Stereocenters

A stereoselective construction of the methylcyclopentane core (3) of jatrophane diterpenoids peditithins B-H was achieved in 14 steps from commercially available d-(+)-ribono-1,4-lactone (9). The linear 5-ene-heptanal derived from 9 was cyclized to the five-membered ring by an intramolecular carbonyl ene reaction, and five continuous stereocenters on 3 were stereoselectively introduced via a successive substrate-controlled manner, involving diastereoselective 1,4-addition, MoOPH-induced hydroxylation, and stereospecific epoxidation.

Synthetic applications of type II intramolecular cycloadditions

Type II intramolecular cycloadditions ([4+2], [4+3], [4+4] and [5+2]) have emerged recently as an efficient and powerful strategy for the construction of bridged ring systems. In general, type II cycloadditions provide access to a wide range of bridged bicyclo[m.n.1] ring systems with high regio- and diastereoselectivity in an easy and straightforward manner. In each section of this review, an overview of the corresponding type II cycloadditions is presented, which is followed by highlights of method development and synthetic applications in natural product synthesis. The goal of this review is to provide a survey of recent advances in the field covering literature up to 2020. The review will serve as a useful reference for organic chemists engaged in the total synthesis of natural products containing bridged bicyclo[m.n.1] ring systems and provide strong stimulus for invention and further advances in this exciting research field.

Daphnanes diterpenes from the latex of Hura crepitans L. And activity against human colorectal cancer cells Caco-2

Hura crepitans (Euphorbiaceae) is a tree from South America that produces an irritant latex used as a fish poison. A bio-guided fractionation of an ethanolic extract of the latex led to the isolation and structural identification of three known daphnane-type diterpenes (1-3) including huratoxin (1), together with two new analogs (4, 5). Compound 1 was found to exhibit significant and selective cell growth inhibition against the colorectal cancer cell line Caco-2, with morphological modifications suggesting formations mimicking the intestinal crypt architecture. The underlying mechanism of 1 was further investigated, in comparison with 12-O-tetradecanoylphorbol-13-acetate (TPA), revealing two different mechanisms.

Total synthesis of crotophorbolone

As a natural diterpenoid, crotophorbolone possesses a challenging trans,trans-5/7/6 framework decorated with six contiguous stereogenic centers and is structurally and biogenetically related to tigliane-type diterpenoids with intriguing bioactivities such as phorbol and prostratin. Based on the convergent strategy, we completed an eighteen-step total synthesis of crotophorbolone starting from (−)-carvone and (+)-dimethyl-2,3-O-isopropylidene-l-tartrate. The key elements of the synthesis involve expedient installation of the six-membered ring and the five-membered ring with multiple functional groups at an early stage, cyclization of the seven-membered ring through alkenylation of the ketone between the five-membered ring and the six-membered ring, functional group-sensitive ring-closing metathesis and final selective introduction of hydroxyls at C₂₀ and C₄.

Convergent total synthesis of crotophorbolone was accomplished in 18 longest linear steps. Observation of unexpected thermodynamic stability of a cis,trans-5/7/6 tricycle would benefit synthetic design of tigliane- and daphnane-related diterpenoids.

Deconstructive Reorganization: De Novo Synthesis of Hydroxylated Benzofuran

An unprecedented deconstructive reorganization strategy for the de novo synthesis of hydroxylated benzofurans from kojic acid- or maltol-derived alkynes is reported. In this reaction, both the benzene and furan rings were simultaneously constructed, whereas the pyrone moiety of the kojic acid or maltol was deconstructed and then reorganized into the benzene ring as a six-carbon component. Through this strategy, at least one free hydroxyl group was introduced into the benzene ring in a substitution-pattern tunable fashion without protection-deprotection and redox adjustment. With this method, a large number of hydroxylated benzofuran derivatives with different substitution-patterns have been prepared efficiently. This methodology has also been shown as the key step in a collective total synthesis of hydroxylated benzofuran-containing natural products (11 examples).

Daphneodorins A-C, Anti-HIV Gnidimacrin Related Macrocyclic Daphnane Orthoesters from Daphne odora

Three novel gnidimacrin related macrocyclic daphnanes (GMDs), daphneodorins A-C (2-4), were isolated from Daphne odora Thunb., together with gnidimacrin (1). Their structures were established by extensive physicochemical and spectroscopic analyses. Compounds 2 and 3 potently inhibited HIV-1 replication at subnanomolar concentrations (EC50 0.16 and 0.25 nM, respectively). Compounds 2-4 represent a novel type of GMDs that are highly oxygenated on the macrocyclic ring, suggesting good potential for anti-HIV drug development by further chemical modification.

Brønsted-acid-catalyzed one-pot tandem annulation/[5 + 2]-cycloaddition of o-propargyl alcohol benzaldehydes with alkynes: regioselective and stereoselective synthesis of dibenzo[a,f]azulen-12-ones

The one-pot synthesis of dibenzo[a,f]azulen-12-ones has been established starting from o-propargyl alcohol benzaldehydes and alkynes.

Facile synthesis of the daphnane and tigliane framework by semi-flow tube-based-bubbling photooxidation and diastereoselective conjugate addition

The common [5-7-6] tricyclic framework in tigliane and daphnane natural diterpenes containing five contiguous stereocenters has been synthesized in 9 steps from readily available starting materials in a completely stereocontrolled manner.

Stereoselective synthesis and application of isopulegol-based bi- and trifunctional chiral compounds

A new family of isopulegol-based bi- and trifunctional chiral ligands such as triols, tetrols, aminodiols and aminotriols was developed from commercially available (−)-isopulegol with antibacterial, antifungal and antioxidant activities.

Catalytic regio- and stereoselective intermolecular [5+2] cycloaddition via conjugative activation of oxidopyrylium

A catalytic stereodivergent intermolecular [5+2] cycloaddition of maltol-type oxidopyrylium through conjugative activation was reported.

Stereoselective Synthesis and Investigation of Isopulegol-Based Chiral Ligands

A library of isopulegol-based bi-, tri- and tetrafunctional chiral ligands has been developed from commercially available (−)-isopulegol and applied as chiral catalysts in the addition of diethylzinc to benzaldehyde. Michael addition of primary amines towards α-methylene-γ-butyrolactone, followed by reduction, was accomplished to provide aminodiols in highly stereoselective transformations. Stereoselective epoxidation of (+)-neoisopulegol, derived from natural (−)-isopulegol, and subsequent oxirane ring opening with primary amines afforded aminodiols. The regioselective ring closure of N-substituted aminodiols with formaldehyde was also investigated. Hydroxylation of (+)-neoisopulegol resulted in diol, which was then transformed into aminotriols by aminolysis of its epoxides. Dihydroxylation of (+)-neoisopulegol or derivatives with OsO₄/NMO gave neoisopulegol-based di-, tri- and tetraols in highly stereoselective reactions. The antimicrobial activity of aminodiol and aminotriol derivatives as well as di-, tri- and tetraols was also explored. In addition, structure–activity relationships were examined by assessing substituent effects on the aminodiol and aminotriol systems.

Systematic synthetic study of four diastereomerically distinct limonene-1,2-diols and their corresponding cyclic carbonates

In order to produce versatile and potentially functional terpene-based compounds, a (R)-limonene-derived diol and its corresponding five-membered cyclic carbonate were prepared. The diol (cyclic carbonate) comprises four diastereomers based on the stereochemical configuration of the diol (and cyclic carbonate) moiety. By choosing the appropriate starting compounds (trans- and cis-limonene oxide) and conditions, the desired diastereomers were synthesised in moderate to high yields with, in most cases, high stereoselectivity. Comparison of the NMR data of the obtained diols and carbonates revealed that the four different diastereomers of each compound could be distinguished by reference to their characteristic signals.

Screening for selective anticancer activity of plants from Grazalema Natural Park, Spain

Since plants are an important source of anticancer drugs, we have carried out a random screening for selective anticancer activity of 57 extracts from 45 plants collected in Grazalema Natural Park, an area in the South of Spain of high plant diversity and endemism. Using lung cancer cells (A549) and lung non-malignant cells (MRC-5), we found that several extracts were more cytotoxic and selective against the cancer cells than the standard anticancer agent cisplatin. Five active extracts were further tested in cancer and normal cell lines from other tissues, including three skin cell lines with increasing degree of malignancy. An extract from the leaves of Daphne laureola L. (Thymelaeaceae) showed a striking potency and selectivity on lung cancer cells and leukemia cells; the IC₅₀ values against these cancer cells were approximately 10,000-fold lower than against the normal cells. Daphnane-type diterpene orthoesters may be responsible for this highly selective anticancer activity.

Improved synthesis of 8-oxabicyclo[3.2.1]octanes via tandem C-H oxidation/oxa-[3,3] Cope rearrangement/aldol cyclization

A tandem C-H oxidation/oxa-[3,3] Cope rearrangement/aldol reaction of allylic silylethers promoted by T⁺BF₄^-(tempo oxoammonium tetrafluoroborate)/ZnBr₂ has been successfully developed allowing the efficient construction of 8-oxabicyclo[3.2.1]octanes and their analogs with a wide substrate scope.

Asymmetric synthesis of the fully functionalized six-membered ring of trigoxyphin A

An asymmetric synthesis strategy of the fully functionalized six-membered ring of trigoxyphin A, a daphnane-type diterpenoid, has been accomplished concisely from a d-tartrate derivative on a multi-gram scale.

Ynol Ethers as Ketene Equivalents in Rhodium-Catalyzed Intermolecular [5 + 2] Cycloaddition Reactions

The previously unexplored metal-catalyzed [5 + 2] cycloadditions of vinylcyclopropanes (VCPs) and electron-rich alkynes (ynol ethers) have been found to provide a highly efficient, direct route to dioxygenated seven-membered rings, a common feature of numerous natural and non-natural targets and building blocks for synthesis. The reactions proceed in high yield at room temperature and tolerate a broad range of functionalities. Substituted VCPs were found to react with high regioselectivity.

Novel LCK/FMS inhibitors based on phenoxypyrimidine scaffold as potential treatment for inflammatory disorders

Tyrosine kinases including LCK and FMS are involved in inflammatory disorders as well as many types of cancer. Our team has designed and synthesized thirty novel pyrimidine based inhibitors targeting LCK, classified into four different series (amides, ureas, imines (Schiff base) and benzylamines). Twelve of them showed nanomolar IC₅₀ values. Compound 7g showed excellent selectivity profile and was selectively potent over FMS kinase (IC₅₀ value of 4.6 nM). Molecular docking study was performed to help us rationalize the obtained results and predict the possible binding mode for our compounds in both LCK and FMS. Based on the obtained biological assay data and modelling results, a detailed SAR study was discussed. As a further testing regarding the anti-inflammatory effect of the new compounds, in vitro cellular assay over RAW 264.7 macrophages was performed. Compound 7g exhibited excellent anti-inflammatory effect. Therefore, we report the design of novel phenoxypyrimidine derivatives as potent and selective LCK inhibitors and the discovery of 7g as potent and selective FMS/LCK dual inhibitor for the potential application in inflammatory disorders including rheumatoid arthritis (RA).

Total Syntheses of the Reported Structures of Curcusones I and J through Tandem Gold Catalysis

Total syntheses of the reported structures of the rhamnofolane diterpene natural products curcusones I and J in racemic form were achieved. The synthetic strategy features a novel tandem gold-catalyzed furan formation and furan-allene [4+3] cycloaddition to build the 5,7-fused ring system with an oxa-bridge in one step, and a stereoselective exo-Diels-Alder reaction to form the 6-membered ring. The newly developed tandem gold catalysis is quite general and can be scaled up. Our syntheses suggest that structural revisions of curcusones I and J are needed.