Enzymatic Synthesis of Noncanonical α-Amino Acids Containing γ-Tertiary Alcohols.

Noncanonical amino acids (ncAAs) containing tertiary alcohols are valuable as precursors of natural products and active pharmaceutical ingredients. However, the assembly of such ncAA scaffolds from simple material by C-C bond formation remains a challenging task due to the presence of multiple stereocenters and large steric hindrance. In this study, we present a novel solution to this problem through highly selective enzymatic decarboxylative aldol addition. This method allows for the streamlined assembly of multifunctionalized ncAAs with γ-tertiary alcohols from readily available materials, such as L -aspartatic acid and isatins, vicinal diones and keto esters. The modularity of electrophiles furnished four classes of ncAAs with decent efficiency as well as excellent site and stereocontrol. Computational modeling was employed to gain detailed insight into the catalytic mechanism and to provide a rationale for the observed selectivities. The method offers a single-step approach to producing multifunctionalized ncAAs, which can be directly utilized in peptide synthesis and bioactivity assessment.

Building Block Extractor: An MS/MS Data Mining Tool for Targeted Discovery of Natural Products with Specified Features.

The utilization of a building-block-based molecular network is an efficient approach to investigate the unknown chemical space of natural products. However, structure-based automated MS/MS data mining remains challenging. This study introduces building block extractor, a user-friendly MS/MS data mining program that automatically extracts user-defined specified features. In addition to the characteristic product ions and neutral losses, this program integrates the abundance of the product ions and sequential neutral loss features as building blocks for the first time. The discovery of nine undescribed sesquiterpenoid dimers from Artemisia heptapotamica highlights the power of this tool. One of these dimers, artemiheptolide I (9), exhibited in vitro inhibition of influenza A/Hongkong/8/68 (H3N2) with an IC50 of 8.01 ± 6.19 µM. Furthermore, two known guaianolide derivatives (16 and 17) possessed remarkable antiviral activity against influenza A/Puerto Rico/8/1934 H1N1, H3N2, and influenza B/Lee/40 with IC50 values ranging from 3.46 to 11.77 µM. In addition to the efficient discovery of novel natural products, this strategy can be generally applied to grab derivatives with specific fragments and enhance the annotation power of LC-MS/MS analysis.

Bisabolane-Type Sesquiterpenoids with a Tetrahydrofuran or Tetrahydropyran Ring from Vernonia solanifolia.

Phytochemical investigation of the aerial parts of Vernonia solanifolia resulted in the isolation of 23 new highly oxidized bisabolane-type sesquiterpenoids (1-23). Structures were determined by interpretation of spectroscopic data, single-crystal X-ray diffraction analysis, and time-dependent density functional theory electronic circular dichroism calculations. Most compounds possess a rare tetrahydrofuran (1-17) or tetrahydropyran ring (18-21). Compounds 1/2 and 11/12 are pairs of epimers isomerized at C-10, while compounds 9/10 and 15/16 are isomerized at C-11 and C-2, respectively. The anti-inflammatory effect in lipopolysaccharide (LPS)-stimulated RAW264.7 macrophages was evaluated for pure compounds. Compound 9 inhibited LPS-stimulated NO production at the concentration of 80 µM. It showed an anti-inflammatory effect by suppressing the activation of the NF-κB signaling pathway.

Naphthylisoquinoline alkaloids, a new structural template inhibitor of Nav1.7 sodium channel.

Voltage-gated sodium channel 1.7 (Nav1.7) remains one of the most promising drug targets for pain relief. In the current study, we conducted a high-throughput screening of natural products in our in-house compound library to discover novel Nav1.7 inhibitors, then characterized their pharmacological properties. We identified 25 naphthylisoquinoline alkaloids (NIQs) from Ancistrocladus tectorius to be a novel type of Nav1.7 channel inhibitors. Their stereostructures including the linkage modes of the naphthalene group at the isoquinoline core were revealed by a comprehensive analysis of HRESIMS, 1D, and 2D NMR spectra as well as ECD spectra and single-crystal X-ray diffraction analysis with Cu Kα radiation. All the NIQs showed inhibitory activities against the Nav1.7 channel stably expressed in HEK293 cells, and the naphthalene ring in the C-7 position displayed a more important role in the inhibitory activity than that in the C-5 site. Among the NIQs tested, compound 2 was the most potent with an IC50 of 0.73 ± 0.03 µM. We demonstrated that compound 2 (3 µM) caused dramatical shift of steady-state slow inactivation toward the hyperpolarizing direction (V1/2 values were changed from -39.54 ± 2.77 mV to -65.53 ± 4.39 mV, which might contribute to the inhibition of compound 2 against the Nav1.7 channel. In acutely isolated dorsal root ganglion (DRG) neurons, compound 2 (10 µM) dramatically suppressed native sodium currents and action potential firing. In the formalin-induced mouse inflammatory pain model, local intraplantar administration of compound 2 (2, 20, 200 nmol) dose-dependently attenuated the nociceptive behaviors. In summary, NIQs represent a new type of Nav1.7 channel inhibitors and may act as structural templates for the following analgesic drug development.

The First Phytochemical Investigation of Artemisia divaricate: Sesquiterpenes and Their Anti-Inflammatory Activity.

Artemisia divaricate belongs to the Artemisia genus of the family of Compositae, a sort of perennial herb endemic in most regions of China. For the first time, a phytochemical investigation was carried out on the whole plant of Artemisia divaricate, resulting in the identification of 39 sesquiterpenes, with 9 of them being new (1-9). The structures of the new compounds were fully established using extensive analysis of MS and 1D and 2D NMR spectroscopic data and density functional theory (DFT) NMR calculations. Their structures involve germacrane, eudesmane, and bisabolane types. All the new isolates were evaluated for their anti-inflammatory activities in lipopolysaccharide (LPS)-stimulated murine macrophages of RAW 264.7 cells. Compounds 2 and 8 showed a significant inhibition effect on NO production, with IC50 values of 5.35 ± 0.75 and 7.68 ± 0.54 µM, respectively.

MNK2-eIF4E axis promotes cardiac repair in the infarcted mouse heart by activating cyclin D1.

Adult mammals have limited potential for cardiac regeneration after injury. In contrast, neonatal mouse heart, up to 7 days post birth, can completely regenerate after injury. Therefore, identifying the key factors promoting the proliferation of endogenous cardiomyocytes (CMs) is a critical step in the development of cardiac regeneration therapies. In our previous study, we predicted that mitogen-activated protein kinase (MAPK) interacting serine/threonine-protein kinase 2 (MNK2) has the potential of promoting regeneration by using phosphoproteomics and iGPS algorithm. Here, we aimed to clarify the role of MNK2 in cardiac regeneration and explore the underlying mechanism. In vitro, MNK2 overexpression promoted, and MNK2 knockdown suppressed cardiomyocyte proliferation. In vivo, inhibition of MNK2 in CMs impaired myocardial regeneration in neonatal mice. In adult myocardial infarcted mice, MNK2 overexpression in CMs in the infarct border zone activated cardiomyocyte proliferation and improved cardiac repair. In CMs, MNK2 binded to eIF4E and regulated its phosphorylation level. Knockdown of eukaryotic translation initiation factor (eIF4E) impaired the proliferation-promoting effect of MNK2 in CMs. MNK2-eIF4E axis stimulated CMs proliferation by activating cyclin D1. Our study demonstrated that MNK2 kinase played a critical role in cardiac regeneration. Over-expression of MNK2 promoted cardiomyocyte proliferation in vitro and in vivo, at least partly, by activating the eIF4E-cyclin D1 axis. This investigation identified a novel target for heart regenerative therapy.

Quaternized Acridine Maleimide MALDI Probe Enables Mass Spectrometry Imaging of Thiols.

Thiols are essential metabolites associated with redox imbalances and metabolic disorders in diseases. Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI MSI) facilitates imaging of metabolites in tissue, but imaging of thiols remains challenging. Here we developed a method to visualize thiols using a stable isotope-labeled (SIL) MALDI probe, a mixture of unlabeled and deuterium-labeled reagents that provided adduct signals at [M]+ and [M + 3]+, to identify endogenous thiols in tissue. A series of MALDI probe candidates were rationally designed, and the structure-effect relationships were determined. First, the reactivity of different warheads toward the thiol group was evaluated, and maleimide was the best for in situ derivatization. Second, an acridine fragment showed the best improvement in MS responses. Third, a permanent charge was introduced for detection improvement in the positive mode. Finally, the hydrogens of methyl group were replaced by deuterium atoms, obtaining the novel SIL MALDI probe and thus facilitating significantly the annotation of thiols. The finally obtained D0/D3-9-((2-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)ethyl)carbamoyl)-10-methylacridin-10-ium iodide (D0/D3-MaI-MADA) enabled direct MSI of thiols in the fine structures of human liver tumors without a reduction procedure. Our work built a SIL MALDI probe for the first time and provided a strategy for the rational design of MALDI probes.

Flavaspidic acid BB combined with mupirocin improves its anti-bacterial and anti-biofilm activities against Staphylococcus epidermidis.

BACKGROUND: The increase in drug-resistant opportunistic pathogenic bacteria, especially of antibiotic-resistant Staphylococcus epidermidis (S. epidermidis), has led to difficulties in the treatment of skin and soft tissue infections (SSTI). The major reason for bacterial resistance is the formation of bacterial biofilm. Here, we report a promising combination therapy of flavaspidic acid BB (BB) and mupirocin, which can effectively eradicate the biofilm of S. epidermidis and eliminate its drug resistance. RESULT: The susceptibility test showed that the combination of BB and mupirocin has good antibacterial and antibiofilm activities, and the fractional inhibitory concentration index (FICI) of BB combined with mupirocin was 0.51 ± 0.00 ~ 0.75 ± 0.05, showing synergistic effect. Moreover, the time-kill curve assay results indicated that the combination of drugs can effectively inhibit the planktonic S. epidermidis. After drugs treatment, the drug-combination showed significantly inhibitory effects on the metabolic activity and total biomass in each stage of biofilm formation. The synergistic effect is likely related to the adhesion between bacteria, which is confirmed by field emission scanning electron microscope. And the expression level of aap, sarA and agrA genes were detected by real-time quantitative PCR (qRT-PCR). CONCLUSION: Our study provides the experimental data for the use of BB for the clinical treatment of skin infections and further demonstrate the potential of BB as a novel biofilm inhibitor.

Chantriolides F-P, Highly Oxidized Withanolides with Hepatoprotective Activity from Tacca chantrieri.

Eleven highly oxidized withanolides, chantriolides F-P (1-11), together with six known analogues (12-17), were isolated from the rhizomes of Tacca chantrieri. Their structures were established on the basis of comprehensive spectroscopic data analysis and comparison with published NMR data, and their absolute configurations were further confirmed by experimental ECD data and single crystal X-ray diffraction analysis. The structures of compounds 5-8 contained a chlorine atom substituted at C-3. Compounds 1 and 12 are a pair of epimers isomerized at C-24 and C-25, while compounds 9 and 16 are isomerized at C-1, C-7, C-24, and C-25. Next, the hepatoprotective effect of all the isolates was evaluated on tert-butyl hydroperoxide (t-BHP)-injured AML12 hepatocytes. Compounds 5-11 and 16 significantly enhanced cell viability. Compound 8 decreased reactive oxygen species accumulation and increased glutathione level in t-BHP injured AML12 hepatocytes through promoting nuclear translocation of nuclear factor erythroid 2-related factor 2 (Nrf2).

Secondary Metabolites and Their Cytotoxic Activity of Artemisia nitrosa Weber. and Artemisia marschalliana Spreng.

As a promising source of biologically active substances, the Artemisia species from Kazakhstan have not been investigated efficiently. Considering the rich history, medicinal values, and availability of the Artemisia plants, systematic investigations of two Artemisia species growing in the East Kazakhstan region were conducted. In this study, one new germacrane-type sesquiterpene lactone (11), together with 10 known sesquiterpenes and its dimer, were characterized from A. nitrosa Weber. Additionally, one new chromene derivative (1') with another 12 known compounds, including coumarins, sesquiterpene diketones, phenyl propanoids, polyacetylenics, dihydroxycinnamic acid derivatives, fatty acids, naphthalene derivatives, flavones, and caffeic acid derivatives were isolated from A. marschalliana Spreng. All compounds were isolated and identified for the first time from these two Artemisia species. The structures of new compounds (11, 1') were established by using UV, TOFMS, LC-MS, 1D and 2D NMR spectroscopic analyses. The cytotoxicity of all isolated compounds was evaluated. As a result, all compounds did not show significant inhibition against HL-60 and A-549 cell lines. The sesquiterpenoids isolated from A. nitrosa were tested for their inhibitory activity against the LPS-induced NO release from the RAW624.7 cells, and neither of them exhibited significant activity.

Macrocephatriolides A and B: Two Guaianolide Trimers from Ainsliaea macrocephala as PTP1B Inhibitors and Insulin Sensitizers.

Macrocephatriolides A and B (1 and 2), two novel guaiane-type sesquiterpene lactone trimers possessing unique linkage patterns, were identified from the whole plant of Ainsliaea macrocephala. The trimeric architecture of 1 features a cyclohexene linkage and a methylene bridge, which were presumably constructed from three constitutive monomers via a Diels-Alder cycloaddition and a Michael addition, respectively. The three monomers of 2 were tethered by a 1,2-ethanediyl and a methylene linkage at the same time. Their complex structures were established by extensive analysis of spectroscopic data inclusive of band-selective CT-HSQC and CT-HMBC and time-dependent density functional theory (TDDFT) ECD calculations. Compound 2 showed potent inhibition against protein tyrosine phosphatase 1B (PTP1B) with an IC50 value of 26.26 ± 0.88 µM but not compound 1. In the kinetic study, compound 2 was disclosed as a competitive inhibitor of PTP1B with a Ki value of 16.34 ± 4.72 µM. In insulin-stimulated C2C12 myotubes, compound 2 dose-dependently enhanced glucose uptake by activating the insulin signaling pathway. Compound 2 might represent a new scaffold of insulin sensitizers.

Anti-inflammatory Eudesmane Sesquiterpenoids from Artemisia hedinii.

Fourteen new eudesmane sesquiterpenoids (1, 3-5, 7-16) and seven known analogues were isolated from the whole plant of Artemisia hedinii. Their structures were elucidated by spectroscopic data analysis and comparison with published NMR data, and their absolute configurations were confirmed by X-ray diffraction experiments and TDDFT ECD calculation. Compounds 1-15 were identified as eudesmane acids, which represent a kind of lactone ring-opening eudesmane-type sesquiterpenes with an acetoxyl or a hydroxy group attached to C-9. Compounds 1 and 2, 5 and 6, and 7 and 8 are three pairs of epimers isomerized at C-3, C-5, and C-11, respectively. Compounds 1-9, 11-13, 15-19, and 21 could influence the proinflammatory phenotype of the M1 macrophage. Among them, compounds 5, 8, 9, 12, 16, and 19 consistently exhibited anti-inflammatory effects, as evidenced by downregulating classic pro-inflammatory cytokines TNF-α, IL-12, IL-6, and IFN-γ in LPS-induced primary bone marrow derived M1 macrophages.

Qualitatively and quantitatively investigating the metabolism of 20(S)-protopanaxadiol-type ginsenosides by gut microbiota of different species.

Ginsenosides Rb1, Rb2, Rb3 and Rc, four major protopanaxadiol (PPD)-type ginsenosides, can be metabolized by gut microbiota. The composition of gut microbiota varies in different species. Existing publications have reported the metabolite fates of ginsenosides by gut microbiota from single species. However, their microbiota-related metabolic species differences have not been evaluated yet. In current study, in vitro anaerobic incubations of PPD-type ginsenosides with gut microbiota from humans, rabbits and rats were conducted. The metabolites of each ginsenoside were then identified by LC-MS. A total of 15 metabolites from the four ginsenosides were identified. The major metabolic pathways were stepwise removals of the C-20 and C-3 sugar moieties to obtain aglycone PPD. The results showed that the hydrolysis rate of C-20 terminal ß-D-glucopyranosyl was significantly higher than those of α-L-arabinopyranosyl, ß-D-xylopyranosyl and α-L-arabinofuranosyl in different species. The activity of ß-glucosidase, the metabolic rates of parent compounds and the formation rates of their metabolites were significantly higher in gut microbiota from rabbits than from humans and rats. Our research draws researchers' attention to the species differences of microbiota-related drug metabolism.

Neuroprotective and Anti-inflammatory Ditetrahydrofuran-Containing Diarylheptanoids from Tacca chantrieri.

Three new dimeric diarylheptanoids, taccachanfurans A-C (1-3), a new monomeric diarylheptanoid, taccachannoid A (4), and four known diarylheptanoids (5-8) were isolated from the EtOH extract of the rhizomes of Tacca chantrieri. Their structures were established on the basis of comprehensive spectroscopic data analysis. The absolute configuration of taccachanfuran A (1) was confirmed by single-crystal X-ray diffraction. All the diarylheptanoid dimers contain a ditetrahydrofuran moiety, which has not been described previously for diarylheptanoid compounds. A plausible biosynthetic pathway for the diarylheptanoid dimers is proposed. Compounds 2-4 showed significant neuroprotective activity against Aß25-35-induced damage in SH-SY5Y cells at the concentrations of 10 and 1 µM. Compounds 3, 4, 6, 7, and 8 showed anti-inflammatory activity in LPS-stimulated murine microglial BV-2 cells at the concentrations of 10 and 1 µM.

Sesquiterpene lactone dimers from Artemisia lavandulifolia inhibit interleukin-1ß production in macrophages through activating autophagy.

Twelve new sesquiterpene lactone dimers, lavandiolides A-L (1-12), were isolated from the whole plants of Artemisia lavandulifolia. Among them, compounds 1-6 are 1,3-linked Diels-Alder adducts between two guaianolide monomers, and 7-12 are 2,4-linked sesquiterpene lactone dimers. Their structures were elucidated by comprehensive analysis of HRESIMS, 1D and 2D NMR spectra. Their absolute configurations were determined by ECD spectra and single-crystal X-ray diffraction analyses with Cu Kα radiation. The nitric oxide (NO) inhibitory effect of all the isolates was assessed on lipopolysaccharide (LPS)-stimulated RAW264.7 macrophages. Compounds 1, 3, 7 and 9 showed potent inhibitory effects on NO production, with IC50 values of 0.61 ± 0.15, 1.64 ± 0.04, 1.89 ± 0.16, and 1.40 ± 0.23 µM, respectively. Furthermore, compound 1 inhibited NLRP3 (NOD-, LRR- and pyrin domain-containing protein 3) inflammasome-mediated interleukin-1ß (IL-1ß) production through activating autophagy.

Discovery and characterization of natural products as novel indoleamine 2,3-dioxygenase 1 inhibitors through high-throughput screening.

Indoleamine 2,3-dioxygenase 1 (IDO1) is emerging as a promising therapeutic target for the treatment of malignant tumors characterized by dysregulated tryptophan metabolism. However, the antitumor efficacy of existing small-molecule IDO1 inhibitors is still unsatisfactory, and the underlying mechanism remains largely undefined. To identify novel IDO1 inhibitors, an in-house natural product library of 2000 natural products was screened for inhibitory activity against recombinant human IDO1. High-throughput fluorescence-based screening identified 79 compounds with inhibitory activity > 30% at 20 µM. Nine natural products were further confirmed to inhibit IDO1 activity by > 30% using Ehrlich's reagent reaction. Compounds 2, 7, and 8 were demonstrated to inhibit IDO1 activity in a cellular context. Compounds 2 and 7 were more potent against IDO1 than TDO2 in the enzymatic assay. The kinetic studies showed that compound 2 exhibited noncompetitive inhibition, whereas compounds 7 and 8 were graphically well matched with uncompetitive inhibition. Compounds 7 and 8 were found to bind to the ferric-IDO1 enzyme. Docking stimulations showed that the naphthalene ring of compound 8 formed "T-shaped" π-π interactions with Phe-163 and that the 6-methyl-naphthalene group formed additional hydrophobic interactions with IDO1. Compound 8 was identified as a derivative of tanshinone, and preliminary SAR analysis indicated that tanshinone derivatives may be promising hits for the development of IDO1 inhibitors. This study provides new clues for the discovery of IDO1/TDO2 inhibitors with novel scaffolds.

Trigonostemons G and H, dinorditerpenoid dimers with axially chiral biaryl linkage from Trigonostemon chinensis.

Trigonostemons G and H, two novel dimeric dinorditerpenoids, were isolated from the stem barks of Trigonostemon chinensis. Their planar structures and relative configurations were established by extensive analysis of spectroscopic data. Trigonostemons G and H possess a homodimeric biaryl skeleton obtained from two rearranged chiral nonracemic abietane-type dinorditerpenes through an axially chiral biaryl 11,11'-linkage. Torsional scan and computation of the transition states were carried out to estimate the rotational energy barrier, and the axial chirality (aS) was determined by time-dependent density functional theory (TDDFT) electronic circular dichroism (ECD) calculations. The positive n-π* ECD transitions of the isolated carbonyl chromophore above 300 nm could be used to determine the central chirality of trigonostemon G independently by ECD calculations of the diastereomers.

Identification of chemotypes in bitter melon by metabolomics: a plant with potential benefit for management of diabetes in traditional Chinese medicine.

INTRODUCTION: Bitter melon (Momordica charantia, Cucurbitaceae) is a popular edible medicinal plant, which has been used as a botanical dietary supplement for the treatment of diabetes and obesity in Chinese folk medicine. Previously, our team has proved that cucurbitanes triterpenoid were involved in bitter melon's anti-diabetic effects as well as on increasing energy expenditure. The triterpenoids composition can however be influenced by changes of varieties or habitats. OBJECTIVES: To clarify the significance of bioactive metabolites diversity among different bitter melons and to provide a guideline for selection of bitter melon varieties, an exploratory study was carried out using a UHPLC-HRMS based metabolomic study to identify chemotypes. METHODS: Metabolites of 55 seed samples of bitter melon collected in different parts of China were profiled by UHPLC-HRMS. The profiling data were analysed with multivariate (MVA) statistical methods. Principle component analysis (PCA) and hierarchical cluster analysis (HCA) were applied for sample differentiation. Marker compounds were identified by comparing spectroscopic data with isolated compounds, and additional triterpenes were putatively identified by propagating annotations through a molecular network (MN) generated from UHPLC-HRMS & MS/MS metabolite profiling. RESULTS: PCA and HCA provided a good discrimination between bitter melon samples from various origins in China. This study revealed for the first time the existence of two chemotypes of bitter melon. Marker compounds of those two chemotypes were identified at different MSI levels. The combined results of MN and MVA demonstrated that the two chemotypes mainly differ in their richness in cucurbitane versus oleanane triterpenoid glycosides (CTGs vs. OTGs). CONCLUSION: Our finding revealed a clear chemotype distribution of bioactive components across bitter melon varieties. While bioactivities of individual CTGs and OTGs still need to be investigated in more depth, our results could help in future the selection of bitter melon varieties with optimised metabolites profile for an improved management of diabetes with this popular edible Chinese folk medicine.

Callistemonols A and B, Potent Antimicrobial Acylphloroglucinol Derivatives with Unusual Carbon Skeletons from Callistemon viminalis.

A phytochemical investigation on the leaves of Callistemon viminalis resulted in the isolation of two unusual compounds, callistemonols A (1) and B (2). Callistemonol A (1) possesses a novel skeleton of a furan ring fusing both an α,ß-triketone and a phloroglucinol unit, while callistemonol B (2) is an acylphloroglucinol derivative featuring two methyl substituents on a five-membered ring and an isovaleryl side chain. Their structures were fully characterized on the basis of extensive spectroscopic analysis, including 1D and 2D NMR parameters, as well as the IR and HRESIMS data. Callistemonol A (1) represents an example of a natural dibenzofuran with two phenyl moieties, and a plausible biogenetic pathway to generate this novel dibenzofuran through a C-C bond-forming radical SAM enzyme is proposed. Moreover, antimicrobial assays, in conjunction with time-killing and biophysical studies, revealed that 1 and 2 exert potent bactericidal activities against a panel of methicillin-resistant pathogenic microbes.

Cytotoxic Germacrane-Type Sesquiterpene Lactones from the Whole Plant of Carpesium lipskyi.

Ten new sesquiterpene lactones, carlipsines A-J (1-10), and 12 known analogues (11-22) were isolated from the whole plant of Carpesium lipskyi. Their structures were elucidated by using 1D and 2D NMR and HRESIMS analyses, and their absolute configurations were confirmed by X-ray diffraction studies. All compounds were identified as germacranolides with diverse substructural features. Compounds 1-4 are 2,5-hemiacetal-linked germacranolides. Compounds 5 and 6 possess a 1,2-epoxy moiety. Compounds 7 and 8 represent unusual 1,5-hemiacetal-linked germacranolides. Compounds 9 and 10 contain a tetrahydrofuran unit with the oxygen atom bridging C-1 and C-8. Compounds 6, 7, 8, 19, 20, 21, and 22 showed cytotoxicity against HL-60 and A-549 cell lines with IC50 values ranging from 2.8 to 10.3 µM.