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Two novel seco-polycyclic polyprenylated acylphloroglucinols (PPAPs), hyperbenzones A (1) and B (2), were isolated from the roots of Hypericum beanii, together with one known biosynthetic congener 3. Compound 1 incorporates a 6/5/5 ring system with an unprecedented spiro[bicyclo[3.3.0]octane-3,1ʹ-cyclohexane]-2,2ʹ-dione motif. The structures of 1 and 2 were determined by a combination of high resolution electrospray ionization mass spectroscopy (HRESIMS), nuclear magnetic resonance (NMR) spectroscopic analyses, gauge-independent atomic orbital (GIAO) NMR chemical shift calculation with DP4+ analyses, electronic circular dichroism (ECD) calculation, and X-ray diffraction analysis. A 1,2-seco retro-Claisen rearrangement from a bicyclo[3.3.1]nonane PPAP precursor and following chemodivergent radical cascade cyclizations are proposed as the key steps in the biosynthetic pathway to yield compounds 1 and 2. Biological investigations indicated that compounds 1 and 3 could decrease intracellular lipid accumulation in a palmitic acid-induced nonalcoholic steatohepatitis (NASH) cell model.

Buxrugulosides A-E, four lignan glycosides (1-4) and a protocatechuate derivative (5) featuring a rare (N, N-diethyl)methyl amino group at aromatic rings, were obtained from the aerial parts of Buxus rugulosa, which is famous for treating coronary heart disease. Their structures including absolute configurations were elucidated by HRMS, 1D and 2D NMR, and by comparing their CD data with previous reports. Compound 1 was a rare sesquilignan, and all of these compounds were the first example of lignans with (N, N-diethyl)methyl amino group.

Munrolins A-Q (1-17), 17 new ring C-seco limonoids with diverse oxidative patterns of C-12, together with nine known analogues (18-26), were isolated from the CH2Cl2 extract of Munronia unifoliolata. The planar structures were elucidated by a combination of 1D and 2D NMR and HR-MS analyses, while the absolute configurations were confirmed by ECD calculations and single-crystal X-ray diffraction. Munrolins A (1) and B (2) were first identified as ring C-seco limonoids with a 12,13-ether bridge moiety. Munrolins C-J (3-10) have a rare reduced primary alcohol fragment, while munrolin Q (17) has an unusual ketal fragment formed by dehydration of C-12/14. These limonoids with diverse alcohol and aldehyde type C11/12 branches may be generated through different degrees of reduction after the Baeyer-Villiger oxidation at the C ring, as key intermediates to supplement the biogenetic pathway of ring C-seco limonoids. Compounds 11, 19, and 26 could reverse the multidrug resistance of MCF-7/doxorubicin cells with reversal fold values of 5.2, 4.5, and 18.3, respectively.

Aglatestine A (1), an unprecedented 3/6/6 tricarbocyclic limonoid framework along with four biogenic A/D-seco limonoid analogues with rare β-substituents at C-6 (2-5), was discovered from the fruits of Aglaia edulis. The structures of 1-5 along with their absolute configurations were clarified using methods of HRMS(ESI), NMR, electronic circular dichroism, X-ray diffraction crystallography, and quantum chemical calculations. The plausible biogenetic speculation suggested that an electrophilic cyclization between C-1 carbocation from acetolysis and electron-rich C-5 from enolization of C═O of 2 may play a key role. The biological evaluation showed that 5 exhibited anti-inflammatory activity indicated by inhibiting NO release in LPS-activated RAW 264.7 macrophages (IC50: 35.72 ± 1.96 μM).

Six new oligomeric neolignans including two trimeric neolignans (1 and 2) and four dimeric neolignans (3-6) were isolated from the leaves of Magnolia officinalis var. biloba. Their structures were determined based on HR-ESIMS and NMR data, as well as electronic circular dichroism (ECD) calculations. Compound 1 is formed from two obovatol moieties directly linked to an aromatic ring of the remaining obovatol moiety, which is an unprecedented type of linkage between monomers. All isolates were assessed for their inhibitory effects on NO production in LPS-stimulated RAW 264.7 macrophage cells. Compounds 1 and 3 showed significantly inhibitory activities with IC50 values of 6.04 and 3.26 μmol·L-1, respectively.

Mufolinin A (1), a ring A-seco rearranged limonoid with an unprecedented ethyl at C-10 and novel 6/6/6/5 fused-ring skeleton, together with three new potential precursors (ring A-seco limonoids, 2–4) were isolated from Munronia unifoliolata. Their structures and absolute configurations were confirmed by nuclear magnetic resonance (NMR), high resolution electrospray ionization mass spectroscopy (HRESIMS), X-ray crystallography, electronic circular dichroism (ECD) calculations and NMR calculations with DP4+ analyses. The unprecedented ethyl group of 1 was hypothesized to be derived from methyl migration and ring reduction rearrangement of ring A-seco limonoid 4. Compounds 2 and 4 showed significant multidrug resistance (MDR) reversal activities in MCF-7/DOX cells with reversal fold (RF) values of 13.1 and 8.0, respectively.

Two new type B polycyclic polyprenylated acylphloroglucinols (PPAPs) (1 and 2) and a known biogenetic precursor hyperbeanol Q (3) were isolated from the root extract of Hypericum beanii, a medicinal plant widespread in southwest China. Their chemical structures were elucidated by 1D/2D NMR and HRESIMS data analysis, and absolute configurations were determined through detailed electric circular dichroism (ECD) analysis including ECD exciton chirality, Mo2(OAc)4-induced ECD, and ECD comparison. Of these compounds, hyperbeone A (1) is a typical [3.3.1]-type B PPAP with an unusual C-1 geranyl side chain, and hyperberin C (2) possesses a rare bicyclo[5.3.1]hendecane core. Taking compound 3 as a starting point, a plausible biosynthetic pathway to the bicyclic type B frameworks of 1 and 2 was proposed.

Two novel natural products, beetleane A (1) and epicoane A (2), were obtained from the metabolites of an endophytic Epicoccum nigrum. Compound 1 has a unique beetlelike structure that is constructed by the fusion and further fold of an unusual [5.5.5.6]trioxafenestrane with a cycloheptane ring. Compound 2 possesses a compact cagelike structure with a unique 6/5/5/5/6/6/5 heptacyclic ring system. Both 1 and 2 showed strong antiliver fibrosis activity in vitro.

Aphamines A–C (1–3), three pairs of acyclic diterpene dimer enantiomers with an unprecedent ploymerization pattern, were discovered from Aphanamixis polystachya by NMR-guided isolation and chiral resolution. The elucidation of their novel carbon skeletons was achieved based on spectroscopic analysis, exciton chirality, and calculated electronic circular dichroism (ECD). Plausible Claisen rearrangement, 5-exo-trig cyclization, and reduction reactions may play important roles in the polymeric biosynthesis pathway. Compounds 1 and 3 showed inhibitory effects on nitric oxide (NO) production (IC50: 6.71–15.36 μmol/L) and reduced the expression of iNOS in LPS-induced RAW 264.7 macrophages.

One new alkaloid, 15b-β-hydroxy-16α-hydroxy-5-N-acetylardeemin (1), and one new dimeric derivative of citrinin, penicitrinol Q (5), together with three known alkaloids (2–4) and two citrinin dimers (6–7), were isolated from the solid culture of an endophytic Aspergillus terreus resided in Pinellia ternata. Their structures were established by detailed spectroscopic analysis, and the absolute configurations were determined by single crystal X‑ray diffraction and the comparison of ECD spectra. Penicitrinol Q (5) exhibited inhibitory effects against Staphylococcus aureus and Bacillus subtilis with MIC50 values of 4.3 and 6.2 μg/mL, respectively. When using a concentration of 30 μM, compound 2 showed 2.1-fold enhancement of doxorubicin susceptibility in treating doxorubicin-resistant human breast cancer cell line.

Fortuneicyclidins A (1) and B (2), a pair of epimeric pyrrolizidine alkaloids containing an unprecedented 7-azatetracyclo[5.4.3.0.02,8]tridecane core, were isolated from the seeds of Cephalotaxus fortunei, along with two biogenetically relative known analogues, 3 and 4. The structures were determined by multiple spectral techniques and chemical derivatization methods. Compound 1 showed inhibitory activity against α-glucosidase.

In this work, 26 methylated acylphloroglucinol meroterpenoids with diverse skeletons, including 18 new ones (bellumones A-R, 1-18), were identified from the flowers of Hypericum bellum. Their structures including absolute configurations were elucidated by detailed spectroscopic data, calculated electronic circular dichroism (ECD), and X-ray diffraction (XRD). Through methylation at C-5, prenylation with different chain lengths of the acylphloroglucinol-derived core, along with different types of secondary cyclization, type A bicyclic polyprenylated acylphloroglucinols (BPAPs) (1-5 and 19-24) and dearomatized isoprenylated acylphloroglucinols (DIAPs) (6-18 and 25-26) were obtained. The significant results of anti-inflammatory, antioxidant, and anti-nonalcoholic steatohepatitis (anti-NASH) activities suggest its usefulness in daily health care.

Inspired by a geranyl-originated undecanoate acid ethyl ester (biosynthetic fragment, 9), elodeoidins A–H (1–8), representing four unprecedented rearranged acylphloroglucinol meroterpenoids, were discovered from the herb of Hypericum elodeoides. Their structures were elucidated by HRESIMS, NMR, Mosher, ECD, quantum chemical calculations, and biosynthetic pathways. Structurally, the six-membered acylphloroglucinol core rearranged to a five-membered β-diketone unit possessing an exocyclic carbonyl group (C-1 or C-3) through an α-ketol rearrangement. Subsequently, key cyclizations with C-1 or C-3 established a 2-cyclopentyltetrahydrofuran moiety in 1 and 2, a [5,5]-spiroketal-fused 5–5–5–5 skeleton in 3 and 4, a 1,2-dioxonane-bridged 5–9–5 framework in 5 and 6, and a 2,5-dioxabicyclo[2.2.2]octane caged structure in 7 and 8. (±)-5 and 6 showed significant anti-inflammatory activity (IC50: 6.06 ± 0.41–10.46 ± 0.14 μM). These diversiform skeletons indicated that the biosynthetic fragment inspired discovery and elucidation strategy is valuable for the discovery of novel and unprecedented natural products.

The spatially close and highly reactive ester appendages through the opening of A and B rings of prieurianin-type limonoids would further rearrange into diverse ring system via oxygen-bridges or new C–C bonds. In our current research, two limonoids with an unprecedented 7/6/5 tricyclic skeleton (1) and 2,6-dioxabicyclo[3.2.2]nonan-3-one caged ring A system (2), along with eight other new ones (3–10) were obtained from Aphanamixis polystachya and Aphanamixis sinensis, and the structure of 1 was confirmed by X-ray crystallographic diffraction. Meanwhile, a reliable solution based on biomimetic alkaline hydrolysis to build new oxygen-bridges via OH-1 was established to resolve the difficulties in the structural elucidation of prieurianin limonoids with broad or missing NMR signals and applied for the determination of 9 and 10. Moreover, the potential of Dieckmann reaction as a key biosynthetic step in the formation of C-3/C-6 bonds in the aphanamolide-type backbone was verified by chemical conversions of 13–16. These findings provided new ideas and perspectives for structural elucidation and chemical communication of prieurianin-type limonoids.

Toonayunnanaes A-E (1-5), five B-seco limonoids, along with five known compounds (6-10) were isolated from the bark of Toona ciliata. Compound 1 is a limonoid with a e-7(8)-lactone in the B ring, and compound 2 possesses a 1,14-oxygen bridge and a 15-OH. Their structures were elucidated by extensive spectroscopic analysis including 1D and 2D NMR, and HRESIMS. Compound 1 exhibited significant inhibition effect of NO production in LPS-stimulated RAW264.7 macrophages with an IC50 value of 10.94 ± 0.08 μM.

Eight new germacranolides, minusolides A–H (1–8), along with two known analogues, 9 and 10, were isolated from the whole plant of Carpesium minus. Their structures were elucidated by spectroscopic ...

A new andirobin-type limonoid with modified furan ring, khaysenelide K (1), together with a known analogue (2), was isolated from the stem barks of Khaya senegalensis. The structure and absolute configuration of 1 were elucidated by a combination of 1D and 2D NMR, HRESIMS, and single-crystal X-ray diffraction using mirror Cu-Kα radiation. Compound 1 showed moderate NO inhibitory activity in LPS-activated RAW 264.7 macrophages with IC50 value of 27.74 ± 0.68 μM.[Formula: see text].

(±)-Melipatulinones A–C (1–3), three unique enantiomeric pairs of lignan–phloroglucinol hybrids along with the biogenetically related compound melipatulignan A (4), were isolated from the leaves of Melicope patulinervia. Melipatulinones A (1) and B (2) share a novel spiro[hydrobenzofuran-2,3′-furan] 5/5/6 tricyclic ring system, while melipatulinone C (3) features an unprecedented spiro[cyclopenta[b]hydrofuran-2,3′-furan] 5/5/5 tricyclic framework. Their structures were determined by spectroscopic methods, electronic circular dichroism (ECD) calculations, and X-ray diffraction. Compounds 1–3 exhibited a pancreatic lipase inhibitory effect.

Three unprecedented benzoyl-migrated polycyclic polyprenylated acylphloroglucinols (PPAPs), hyperforones A–C (1–3), were isolated from Hypericum forrestii, together with a new benzoyl-substituted analogue (4) of hyperforin. Compounds 1–3 are the first examples of naturally occurring benzoyl-PPAPs with a unique C-1 H-substituted bicyclo[5.3.1]hendecane scaffold. Their structures and absolute configurations were established by HRESIMS, NMR spectroscopy data, electronic circular dichroism (ECD) exciton chirality method, ECD calculations, and gauge-independent atomic orbital (GIAO) NMR calculations with DP4+ analyses. A plausible biosynthetic formation of the benzoyl-migrated C-1 H-substituted bicyclo[5.3.1]hendecane skeleton in 1–3via a sterically favored hemiketalization/Retro-Claisen cascade was proposed. Bzhyperforin (4) showed significant cytotoxicity against MDA-MB-231 cells with an IC50 value of 6.88 ± 1.37 μM.

Taxodisones A and B, C30-terpenes with an unprecedented tetracyclo[12.4.0.0.2,709,14]octodecane core, were isolated from the seeds of Taxodium distichum. Their structures, including their configurations, were unambiguously determined. Their biomimetic synthesis suggests that they stem from diterpenes and monoterpenes, and not from squalene or oxidosqualene. In addition, their bioactivities were also evaluated.

Five new spirocyclic polycyclic polyprenylated acylphloroglucinols, Hyperpatulones C-G (1–5), were obtained from the leaves of Hypericum patulum. Their structures were characterized by the comprehensive analysis of their IR, NMR, CD spectra and HRESIMS data. All the new compounds were evaluated for the α-glycosidase inhibitory activities. Among them, compounds 3–5 showed α-glucosidase inhibitory activities, with IC50 values of 14.06–37.69 μM.

The first examples of type B polycyclic polyprenylated acylphloroglucinols with a bicyclo[5.3.1]hendecane core, hyperberins A (1) and B (2), were isolated from Hypericum beanii, together with three biosynthetic congeners. Their structures were established by a combination of NMR, electric circular dichroism (ECD), and X-ray diffraction analyses. These isolates indicated divergent cationic cyclization as key steps in the biosynthesis of PPAPs with diverse architectures. Compounds 1 and 2 were moderately cytotoxic and exhibited significant anti-inflammatory activities.

Two uncommon C37 heterodimeric diterpenoids, taicrypnacids A (1) and B (2), and a known labdane-type diterpenoid (3) were isolated from the leaves of Taiwania cryptomerioides. Several techniques, such as comprehensive spectroscopic analysis, chemical conversion, X-ray crystallography, and ECD data, were employed to define the structures. The two new compounds displayed cytotoxicity against human breast cancer (MCF-7), osteosarcoma (U-2 OS), and human colon carcinoma (HCT-116) cell lines, while the methyl ester 1a showed no activity. Compound 1 induced Ca2+-ROS pathway-mediated endoplasmic reticulum stress, and excessive stress led to cell death by activating apoptosis and autophagy.

The theoretical analysis and biomimetic conversion confirmed that the oxidative cleavage of the Δ8,9 double bond of chloranthalactone A (I), an abundant lindenane-type sesquiterpenoid in Chloranthaceae plants, generates 8,9-secolindenane (II) with active aldehyde and maleic anhydride fragments that can capture other fragments and produce oligomeric molecules. A careful phytochemical investigation of the leaves of Sarcandra glabra led to the discovery of eight novel 8,9-secolindenane-type sesquiterpenoid oligomers (sarglalactones A-H, compounds 1-8), including three unprecedented trimers (1-3), five unusual dimers (4-8), and five 8,9-secolindenane monomers (sarglalactones I-M, 9-13). Their structures were determined by comprehensive HRMS, NMR, circular dichroism, and X-ray diffraction analyses. Bioassay results showed that these oligomers significantly reversed the multidrug resistance of MCF-7/doxorubicin (DOX) cells and increased the sensitivity of U2 OS cells to DOX by downregulating the HMGB1 expression.

Withaminimas A-F (1-6), six new withaphysalin-type withanolides were isolated from the aerial parts of Physalis minima L.. The structures of these compounds were elucidated through a variety of spectroscopic techniques including HR-MS, NMR, and ECD. Compound 1 belongs to rare 18-norwithanolides, and 2-3 were 13/14-secowithanolides. According to the traditional usage of P. minima, inhibitory effects on nitric oxide (NO) production in lipopolysaccaride-activated RAW264.7 macrophages were evaluated, and compounds 1-4 exhibited significant inhibitory effects with IC50 values among 3.91-18.46 μmol·L-1.

Screening active natural products, rapid identification, and accurate isolation are of great important for modern natural lead compounds discovery1. We hereby reported the isolation of seven new neotecleanin-type limonoids (17), seven new limonoids with 5-oxatricyclo[5.4.0.11,4]hendecane ring system (814), and two new precursors (1516) together with four known limonoids (1720) from the root barks of Walsura robusta. Their structures, including their absolute configurations, were elucidated based on analyses of HR-ESI-MS, 1D/2D NMR, ECD spectrum calculations and single-crystal X-ray diffraction techniques. Compounds 2, 8, 9, 11, 13, 14, 18 showed significant anti-inflammatory activities in LPS-induced RAW 264.7 cell line, BV2 microglial cells, and Propionibacterium acnes-stimulated THP-1 human monocytic cells. Walrobsin M (11) exhibited anti-inflammatory activity with IC50 value of 7.96±0.36 μmol/L, and down-regulated phosphorylation levels of ERK and p38 in a dose-dependent manner. KEY WORDS: Walsura robusta, limonoid, Neotecleanin-type, ECD spectrum calculation, Single-crystal X-ray diffraction, Anti-inflammatory activity, Propionibacterium acnes, THP-1 human monocytic cell

Three undescribed 3(2H)-furanone derivatives, asperfuranones A-C (1-3), along with one known compound (4) were isolated from the Aspergillus sp. strain obtained from the intestines of centipede. Their structures were determined by NMR and MS spectroscopic analyses, and the absolute configurations were established by the Snatzke's sector rules, modified Mosher's method and electronic circular dichroism (ECD) calculation. Meanwhile, the application of the sector rules led to the reassignment of the absolute configurations of 4 and other seventeen previously reported analogues (5-21).

Ten undescribed phragmalin-type limonoids (Chuktabularoids A-J, 1–10) and four known compounds (11–14) were isolated from the fruit shells of Chukrasia tabularis A. Juss. Their chemical structures were elucidated through a combination of HRESIMS, NMR, and ECD experiments. Their frameworks differed mainly in D-ring, including C-15-acyl, 16-nor C-15 acyl, C-13/14/18-cyclopropane, and Δ14, 15 types. The majority of the isolated compounds were investigated for multidrug resistance (MDR) reversal activity against doxorubicin-resistant human breast carcinoma (MCF-7/DOX) cells, compounds 11 and 12 exhibited a 5.6-fold and 19.7-fold enhancing effect on doxorubicin susceptibility at 30 μM, respectively.

Artemisianins A-D (1–4), four stereoisomers of sesquiterpenoid dimers, forming via [4+2] cycloaddition from a 1, 10-seco-guaianolide dienophile and a guaianolide diene, along with two biosynthetically related precurors 5 and 6, were isolated from the famous traditional Chinese medicine Artemisia argyi. The structures of 1–4, including their absolute configurations, were elucidated by extensive spectroscopic data and ECD/TDDFT calculation analysis. Compounds 1–4 exhibited cytotoxicity with IC50 values ranging from 7.2 to 23.3 μM. The accumulation of Ca2+ in cytoplasm and enlarged endoplasmic reticulum (ER) indicated that 1 mediated HT-29 cancer cell apoptosis through improvement of ER-stress, which was further proved by unfolded protein response (UPR) pathway on basis of the upregulation of IRE1α, p-PERK, ATF6, and CHOP.

Ciliatasecones A-C (1-3), three rearranged limonoids with a novel ring-seco model and an unprecedented cycle system, were isolated from the root bark of Toona ciliata var. yunnanensis. Ciliatasecones A-B (1-2) share a novel cyclopenta[b]furan ring C/D system through C-9/11-seco and C-11/14 ether linkage. Ciliatasecone C (3) was found to possess a rare rearranged six-membered lactone ring B between C-7 and C-9. Plausible biogenetic pathway speculation indicated that C-9/11 cleavage and oxygen bridge formation played the key roles in the framework rearrangement of 1-3.

A pair of novel C23 terpenoid epimers, officinalins A (1) and B (2), together with a biogenetically related known diterpenoid (3), was isolated from the leaves of Salvia officinalis. The epimers feature an unprecedented carbon skeleton with a tetracycline-[9.6.0.03,8.012,16]-heptadecane core and a peroxide bridge. Their structures were unequivocally established by extensive spectroscopic analyses, including electronic circular dichroism (ECD) calculations and ROESY correlation analogy with model compounds for the configuration assignment. Possible biosynthetic pathways of 1 and 2 were proposed. Compound 1 exhibited potent NO inhibitory activity with an IC50 value of 2.02 ± 0.87 μM.

Five new prenylated acetophenones, melicoptelins A-E (1–5), along with one known congener (6) were isolated from the roots of Melicope ptelefolia. Among them, compounds 2a/2b, 3a/3b, and 4a/4b were obtained as inseparable interconverting mixtures of keto and enol tautomers. Their structures were elucidated on the basis of extensive spectroscopic methods, including 1D, 2D NMR and HRESIMS. Compouds 2a/2b, 4a/4b and 5 exhibit protein tyrosine phosphatase 1B (PTP1B) inhibitory activity with IC50 values of 34.4, 55.2 and 66.6 μM, respectively.

Seven undescribed phenylspirodrimane derivatives, stachybochartins A–G (1–7), and four known analogues (8–11) were isolated from the endophytic fungus Stachybotrys chartarum obtained from Pinellia ternata. Stachybochartins A–D are four rare C–C-coupled dimeric derivatives and stachybochartin G features a seco-bisabosqual skeleton. Their structures and configurations were elucidated via spectroscopic analysis, electronic circular dichroism (ECD) calculations, the ECD exciton chirality method and the modified Mosher's method. Stachybochartins A–D and G displayed cytotoxic activities against MDA-MB-231 breast cancer cells and U-2OS osteosarcoma cells, with IC50 values ranging from 4.5 to 21.7 μM. Stachybochartins C and G exerted strong anti-proliferative activities against U-2OS cells in concentration- and time-dependent manners and induced apoptosis.

Six new Cephalotaxus alkaloids, including five cephalotaxine-type alkaloids, and one homoerythrina-type alkaloid, along with six known analogues, were isolated from the seeds of Cephalotaxus fortunei. Their structures were elucidated by combination of spectroscopic data analyses, time-dependent density functional theory (TDDFT) ECD calculation, and single-crystal X-ray diffraction. Cephalofortine B represents the first example of C-5 epi-cephalotaxine-type alkaloid. All isolated compounds were tested for cytotoxicities against HCT-116, A375, and SK-Mel-28 cell lines. Cephalofortine E showed moderate activity against HCT-116 cell line, with an IC50 value of 7.46 ± 0.77 μM.

Harringtonolide (HO), a natural product isolated from Cephalotaxus harringtonia, exhibits potent antiproliferative activity. However, little information has been reported on the systematic structure−activity relationship (SAR) of HO derivatives. Modifications on tropone, lactone, and allyl positions of HO (1) were carried out to provide 17 derivatives (2–13, 11a–11f). The in vitro antiproliferative activity against four cancer cell lines (HCT-116, A375, A549, and Huh-7) and one normal cell line (L-02) was tested. Amongst these novel derivatives, compound 6 exhibited comparable cell growth inhibitory activity to HO and displayed better selectivity index (SI = 56.5) between Huh-7 and L-02 cells. The SAR results revealed that the tropone and lactone moieties are essential for the cytotoxic activities, which provided useful suggestions for further structural optimization of HO.

Two new phthalide dimers (1 and 2) were obtained from the rhizomes of Ligusticum sinense Oliv., along with three known dimeric phthalides (3–5). Their structures were determined with the aid of the spectroscopic data, and their absolute configurations were elucidated based on the comparison of calculated and experimental electronic circular dichroism (ECD) spectra. All the compounds were evaluated in vitro for their inhibitory activities against NO production in LPS-treated RAW264.7 macrophages. Among them, compounds 1 and 3 showed potent NO prohibitive activity with IC50 values at 4.86 ± 0.29 μM and 4.87 ± 0.32 μM, respectively.

Three new β-triketone flavanone hybrids, cajuputones A-C were obtained from Melaleuca cajuputi (the Australian 'tea tree'). The structures of cajuputones A-C were elucidated by 1D/2D NMR spectroscopy and HR-ESI-MS analyses; and their absolute configurations were established by electric circular dichroism (ECD) calculations using TDDFT method. Structurally, cajuputones A-C feature a rare 6/6/6/6 oxatetracyclic ring system fused between an acylphloroglucinol-derived β-triketone and a pinocembrin or strobopinin moiety via an angle-type pyran-like motif. DFT-based conformational optimization in chloroform explained the similarity of the 1D NMR data of cajuputones B and C (C-2 epimers).

Abstract Four new limonoids, toonayunnanaes F − I (1 − 4), and six known compounds (5 − 10) were isolated from the barks of Toona ciliata. Their structures were elucidated by thoroughly analyzing of NMR and HRMS data, and single-crystal X-ray diffraction of 1. The oxetane ring moiety in 1 was rare in limonoids and other natural products. Compound 1 showed nitric oxide (NO) inhibitory effect with an IC50 38.45 ± 0.41 µM in lipopolysaccharide (LPS)-activated RAW 264.7 macrophages. Graphic Abstract

(±)-Patulignans A–C (1–3), three unique pairs of lignan enantiomers were isolated from the leaves of Melicope patulinervia. Patulignan A (1) possesses an unprecedented dimethyloxonane moiety in nature, meanwhile patulignans B (2) and C (3) are epimers carrying a novel dimethyl-1,6-dioxaspiro[4.5]decane skeleton. Their structures were established by spectroscopy methods and electronic circular dichroism (ECD) calculations. Compounds 1–3 showed significant inhibitory activity against α-glucosidase.

Inspired by the diversity-oriented synthesis, some novel formyl phloroglucinol meroterpenoids were synthesized via biomimetic synthesis using essential oils. Eight of them were demonstrated with good in vitro fungicidal activity against Candida albicans and C. glabrata. Compound c2 showed the best anticandidal ability that was powerfully comparable to fluconazole when testing against several strains in vitro. The antibiofilm activity was also found for the c2 treating group which was evidenced to block the hyphal elongation and filamentation of C. albicans. Therefore, compound c2 is a promising candidate for further antifungal-based structure modification.

Aureochaeglobosins A–C (1–3), three novel [4 + 2] cycloaddition heterodimers of chaetoglobosin and aureonitol derivatives, were obtained from the culture of endophytic fungus Chaetomium globosum, representing the first adduct examples of chaetoglobosins. Their structures were elucidated by extensive spectroscopic analyses, single-crystal X-ray diffraction, and a modified Mosher’s method. Compounds 2 and 3 showed significant cytotoxicities against human MDA-MB-231 cancer cells with IC50 values of 7.6 and 10.8 μM, respectively.

Peyronellones A and B (1 and 2), a pair of rare tetracyclic caged adducts of azaphilone with pyruvic acid, along with four new analogues (3–6), were isolated from solid cultures of the endophytic fungus Peyronellaea glomerata. Their structures were elucidated through spectroscopic analysis, and their absolute configurations were unambiguously determined by a combination of single-crystal X-ray crystallography, Rh2(OCOCF3)4-induced ECD experiments, ECD calculations, and modified Mosher methods. Compound 2 (5 μM) was found to have a significant hypoxia-protective effect that improved the survival rate of hypoxia/reoxygenation-treated human umbilical vein endothelial cells from 35% to 70%, which was equal to the potency of the positive control, verapamil. Flow cytometry analysis suggested 2 could inhibit H/R-induced late-stage apoptosis of this cell line.

Phytochemical investigation of the fruits from Trichilia connaroides led to the isolation of four rare 1,2-seco phragmalin-type limonoids (1-4) with C-7/28 δ-lactone ring along with two known triterpenoids (5-6). An oxygen bridge between C-1 and C-2 formed an rare 9-oxa-tricyclo[3.3.2.17,10]undecane-2-ene moiety in structure of 1 and 2, and 3-4 possessed a bicyclo[5.2.14,10]decane skeleton. Their structures were established based on extensive spectroscopic methods and their absolute configurations of 1 were confirmed by TDDFT/ECD calculation and comparative analysis. Compounds 5-6 showed moderate inhibitory effects on Hela tumor cell lines with inhibition ratio values of 83.8% and 87.1% at concentration 40μM, respectively.

The reactivity-based screening (RBS) was developed for directed discovery of cytotoxic withanolides. In this study, a thiol probe, 4-chlorobenzenethiol, was used to selectively attack cytotoxic withanolides containing potential pharmacophore, 2(3)-en-1-one in ring A (AEO) and 5β,6β-epoxy in ring B (BE), from the plant extract of Physalis angulata var. villosa. The screening was performed based on the potential mechanism of 4-chlorobenzenethiol nucleophilic addition to AEO, followed by detection of adducts using liquid chromatography quadrupole-time-of-flight mass spectrometry (LC-Q-TOF-MS). Guided by RBS, eleven target withanolides, including five new compounds, physagulides R-V (10–14) and six known ones (2, 7–9, 15, 16) were discovered. All of them exhibited cytotoxicity against the both tested cell lines, especially, compounds 2, 7, 8 and 14 showed potent activities with IC50 values of 1.57–6.29 μM. The results suggested that RBS was efficient and accurate for rapid identification of cytotoxic withanolides and could guide isolation of target components from the complex medicinal plant extract.

Ten new highly oxidized monomeric (1–8) and dimeric guaianolides (9 and 10), along with two known guaianolide derivatives (11 and 12), were isolated from the aerial parts of Chrysanthemum indicum using a bioassay-guided fractionation procedure. The new compounds were characterized by the basic analysis of the spectroscopic data obtained, and the absolute configurations were determined by both empirical approaches and ECD calculations. Inhibitory effects of 1–12 on nitric oxide production were investigated in lipopolysaccaride (LPS)-mediated RAW 264.7 cells, and most of them (1–8 and 11) displayed IC50 values in the range 1.4–9.7 μM. Moreover, a mechanistic study revealed that the potential anti-inflammatory activity of compound 1 appears to be mediated via suppression of an LPS-induced NF-κB pathway and down-regulation of MAPK activation.

Biogenesis-inspired chemical research of the leaves of Taiwania cryptomerioides afforded four unprecedented dimeric diterpenes, featuring a tetracyclic [7. 75, 9. 4. 05, 10. 08, 9] octodecane core: taiwanoids A-D (1-4). The structures of these compounds were determined on the basis of comprehensive spectral analysis, chemical conversions and X-ray crystallography. A possible biosynthetic pathway for compounds 1-4 was proposed. Compounds 2 and 3 exerted a 5.37 and 6.26-fold potentiation effect on bortezmib (BTZ) susceptibility at a tested concentration of 20 μM, respectively.

Asperones A–E (1–5), five dimeric polyketides with two distinct skeletons generated by the crucial [3 + 2] and [3 + 3] cycloadditions, were isolated from fungal metabolites of an Aspergillus sp. Their structures were established by spectroscopic data, chemical derivatization, single-crystal X-ray diffraction, and electronic circular dichroism calculations. Compounds 2–4 showed significant nitric oxide (NO) inhibition in lipopolysaccharide (LPS)-induced RAW 264.7 macrophage cells, and exhibited IC50 values of 16.0, 13.2, and 6.0 μM, respectively.

Melaleucadines A and B (1 and 2), two rare benzylic phloroglucinol-terpene hybrids (meroterpenoids), have been isolated and identified from the branches and leaves of the Australian “tea tree” Melaleuca leucadendron L. Their structures including absolute configurations were determined by 1D/2D NMR, HR-MS, and the CD exciton chirality method. Compound 1 was a hybrid of a benzylic phloroglucinol and rearranged β-pinene via a rare 2,3,4,5-tetrahydrooxepine ring, and 2 was the adduct of a benzylic phloroglucinol and a humulene-type sesquiterpene via an oxa-heterocycle. Bioactivity screening revealed that compounds 1 and 2 exhibited neuroprotective effects at a concentration of 50.0 μM.

Orthoesters based on phragmalin-type limonoid from Meliaceae family is an important branch of plant orthoesters, and it is mainly existed as 1/8/9-, 8/9/11-, 8/9/14-, or 8/9/30-types. In the process of exploring the biogenetic pathway of the orthoester moiety in phragmalins, the reversible conversion between 8/9/11-orthoerter (tabularisin A, 1) and 8/9/30-orthoester (tabularisin C, 2) under acid-catalyzed condition were found and optimized. The protonated orthoester or ester group triggered sequential transesterifications may be the key steps of this reversible rearrangement. This research not only revealed a novel rearrangement mode involving multiple groups in organic synthesis, but also suggested the close biosynthetic relationship between 8/9/11- and 8/9/30-phragmalin-type orthoesters.