Rapid and scalable synthesis of chiral bromolactones as precursors to α-exo-methylene-γ-butyrolactone-containing sesquiterpene lactones

Design of ROS-Triggered Sesquiterpene Lactone SC Prodrugs as TrxR1 Covalent Inhibitors for the Treatment of Non-Small Cell Lung Cancer

Thioredoxin reductase 1 (TrxR1) is an important therapeutic target for nonsmall cell lung cancer (NSCLC) treatment due to its overexpression in NSCLC cells. In this work, to address the deficiency that sesquiterpene lactone containing α-methylene-γ-lactone moiety was rapidly metabolized by endogenous nucleophiles, series of novel thioether derivatives were designed and synthesized based on a reactive oxygen species (ROS)-triggered prodrug strategy. Among them, prodrug 5u exhibited potent cytotoxicity against NSCLC cells and better release rates in response to ROS. The active compound 6a released from 5u covalently binds to Cys475 and Sec498 sites on TrxR1, resulting in inhibition on TrxR1 activity, which led to redox homeostasis disorder, and caused apoptosis and ferroptosis. Moreover, prodrug 5u exhibited significant antitumor efficiency in nude mice and NSCLC organoids. Our results deliver ROS-triggered prodrug 5u as a novel TrxR1 inhibitor for the treatment of NSCLC and provide a promising strategy of ROS-activated prodrug for covalent compounds in cancer therapy.

Collective Synthesis of Highly Oxygenated (Furano)germacranolides Derived from Elephantopus mollis and Elephantopus tomentosus

Germacranolides, secondary metabolites produced by plants, have garnered academic and industrial interest due to their diverse and complex topology as well as a wide array of pharmacological activities. Molephantin, a highly oxygenated germacranolide isolated from medicinal plants, Elephantopus mollis and Elephantopus tomentosus, has exhibited antitumor, inflammatory, and leishmanicidal activities. Its chemical structure is based on a highly strained ten-membered macrocyclic backbone with an (E,Z)-dienone moiety, which is fused with an α-methylene-γ-butyrolactone and adorned with four successive stereogenic centers. Herein, we report the first synthesis of molephantin in 12 steps starting from readily available building blocks. The synthesis features the highly diastereoselective intermolecular Barbier allylation of the β,γ-unsaturated aldehyde with optically active 3-bromomethyl-5H-furan-2-one intermediate and ensuing Nozaki-Hiyama-Kishi (NHK) macrocyclization for the construction of the highly oxygenated ten-membered macrocyclic framework. This synthetic route enabled access to another germacranolide congener, tomenphantopin F. Furthermore, cycloisomerization of molephantin into 2-deethoxy-2β-hydroxyphantomolin could be facilitated by irradiation with ultraviolet A light (λmax=370 nm), which opened a versatile and concise access to the related furanogermacranolides such as EM-2, phantomolin, 2-O-demethyltomenphantopin C, and tomenphantopin C.

Diastereoselective allylation-based asymmetric total synthesis of 1,10-seco-guaianolides

A Cr(II)-mediated Nozaki-Hiyama allylation of aldehydes with functionalized chiral allylbromolactone paved the way to easily access β-hydroxy-aryl/alkyl-α-methylene-γ-butyrolactones in good yields with high diastereoselectivities. A subsequent undemanding translactonization was orchestrated in the efficient first asymmetric total synthesis of two 1,10-seco-guaianolides as a valuable extension of the strategy developed.

3-Methyl 5-{3-[(4-Methylbenzenesulfonyl)oxy]propyl} 4-(2,3-Dichlorophenyl)-2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate

The 1,4-dihydropyridine is a ubiquitous scaffold employed not only in medicinal chemistry but also in organic synthesis, given its ability to act as a hydrogen transfer reagent, thus emulating NAD(P)H reducing agents. In this work, we describe the synthesis of 3-methyl 5-{3-[(4-methylbenzenesulfonyl)oxy]propyl} 4-(2,3-dichlorophenyl)-2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate as scaffold, which enables downstream derivatization towards new 1,4-dihydropyridine molecules. Inspired by the literature, a new two-step synthesis was planned that involved: (i) synthesis of a silylated 1,4-dihydropyridine derivative and (ii) deprotection and tosylation in one step using tosyl fluoride.

Synthesis of α-exo-Methylene-γ-butyrolactones: Recent Developments and Applications in Natural Product Synthesis

The α-exo-methylene-γ-butyrolactone moiety is present in a vast array of structurally diverse natural products and is often central to their biological activity. In this short review, we summarize new approaches to α-exo-methylene-γ-butyrolactones developed over the past decade as well as their applications in total synthesis.

1 Introduction

2 Approaches to α-exo-Methylene-γ-butyrolactones

2.1 Enantioselective Synthesis via Lactonization Approaches

2.2 Enantioselective Halolactonizations

2.3 Enantioselective Barbier-Type Allylation

2.4 C–H Insertion/Olefination Sequences

2.5 Alkene Cyclization

2.6 Strain-Driven Dyotropic Rearrangement

3 β-(Hydroxymethylalkyl)-α-exo-methylene-γ-butyrolactones

4 Applications in Total Synthesis

4.1 Sesquiterpene Lactones

4.2 Lignans

4.3 Other Monocyclic Natural Products

4.4 Choice of Methodology in Recent Total Syntheses

5 Summary and Outlook

An access to highly enantioenriched cis-3,5-disubstituted γ-lactones from α-bromoacetate and silyl enol ether

A novel synthetic strategy for highly enantioenriched cis-3,5-disubstituted γ-lactones has been developed by the AgOTf-promoted nucleophilic substitution of α-bromoacetates with silyl enol ethers and subsequent reductive lactonization. The utility of this synthetic method was further demonstrated through the concise stereodivergent synthesis of cis- and trans-2,4-disubstituted tetrahydrofurans.

Total Syntheses of Paraconic Acids and 1,10-seco-Guaianolides via a Barbier Allylation/Translactonization Cascade of 3-(Bromomethyl)-2(5H)-furanone

A palladium-catalyzed Barbier allylation/translactonization cascade reaction was established for the rapid construction of β,γ-disubstituted α-exo-methylene-γ-butyrolactone, an important motif in sesquiterpenes. Dimethyl zinc played significant roles in both steps for the umpolung of π-allylpalladium as a nucleophile and promoting a Lewis acid-mediated translactonization. This sequence showed a broad substrate scope and was further harnessed for the synthesis of two paraconic acids as well as the first protecting-group-free total synthesis of two 1,10-seco-guaianolides.

Synthesis and Biological Evaluation of Analogues of Butyrolactone I as PTP1B Inhibitors

In recent years, a large number of pharmacologically active compounds containing a butenolide functional group have been isolated from secondary metabolites of marine microorganisms. Butyrolactone I was found to be produced by Aspergillus terreus isolated from several marine-derived samples. The hypoglycemic activity of butyrolactone I has aroused our great interest. In this study, we synthesized six racemic butenolide derivatives (namely BL-1–BL-6) by modifying the C-4 side chain of butyrolactone I. Among them, BL-3 and BL-5 improved the insulin resistance of HepG2 cells and did not affect the proliferation of RIN-m5f cell line, which indicated the efficacy and safety of BL-3 and BL-5. Furthermore, BL-3, BL-4, BL-5, and BL-6 displayed a significant protein tyrosine phosphatase 1B (PTP1B) inhibitory effect, while the enantiomers of BL-3 displayed different 50% percentage inhibition concentration (IC₅₀) values against PTP1B. The results of molecular docking simulation of the BLs and PTP1B explained the differences of biological consequences observed between the enantiomers of BL-3, which supported BLs as PTP1B inhibitors, and also indicated that the chirality of C-4 might influence the inhibitory effect of the BLs. Our findings provide a novel strategy for the development of butyrolactone derivatives as potential PTP1B inhibitors for the treatment of type 2 diabetes mellitus.

Synthesis and cytotoxic evaluation of halogenated α-exo-methylene-lactones

α-exo-Methylene-γ-butyrolactones and α-exo-methylene-δ-valerolactones constitute an important group of natural and bioactive products. A simple and general protocol of halolactonization of dienoic acids to obtain various α-exo-methylene-lactones in excellent yields is described. The resulting halogenated α-exo-methylene-lactones were found to exhibit potent cytotoxic activities.

Synthesis and Cytotoxic Evaluation of 3-Methylidenechroman-4-ones

In the search for new anticancer agents, a library of variously substituted 3-methylidenechroman-4-ones was synthesized using Horner–Wadsworth–Emmons methodology. Acylation of diethyl methylphosphonate with selected ethyl salicylates furnished 3-diethoxyphosphorylchromen-4-ones which were next used as Michael acceptors in the reaction with various Grignard reagents. The adducts were obtained as the mixtures of trans and cis diastereoisomers along with a small amount of enol forms. Their relative configuration and preferred conformation were established by NMR analysis. The adducts turned up to be effective Horner–Wadsworth–Emmons reagents giving 2-substituted 3-methylidenechroman-4-ones, which were then tested for their possible cytotoxic activity against two leukemia cell lines, HL-60 and NALM-6, and against MCF-7 breast cancer cell line. All new compounds (14a–o) were highly cytotoxic for the leukemic cells and showed a moderate or weak effect on MCF-7 cells. Analog 14d exhibited the highest growth inhibitory activity and was more potent than carboplatin against HL-60 (IC₅₀ = 1.46 ± 0.16 µM) and NALM-6 (IC₅₀ = 0.50 ± 0.05 µM) cells. Further tests showed that 14d induced apoptosis in NALM-6 cells, which was mediated mostly through the extrinsic pathway.