Nucleobase-Coupled Xanthones with Anti-ROS Effects from Marine-Derived Fungus Aspergillus sydowii.

A MS/MS-based molecular networking approach compared to the Global Natural Product Social Molecular Networking library, in association with genomic annotation of natural product biosynthetic gene clusters within a marine-derived fungus, Aspergillus sydowii, identified a suite of xanthone metabolites. Chromatographic techniques applied to the cultured fungus led to the isolation of 11 xanthone-based alkaloids, dubbed sydoxanthones F-M. The structures of these alkaloids were elucidated using extensive spectroscopic data, including electronic circular dichroism and single-crystal X-ray diffraction data for configurational assignments. Among these analogues, sydoxanthones F-K exhibit structure features typical of nucleobase-coupled xanthones, with sydoxanthone H being an N-bonded xanthone dimer. Notably, (±)sydoxanthones F (1a/1b), (±)sydoxanthones H (3b/3a), and (±)sydoxanthones J (5b/5a) are enantiomeric pairs, while sydoxanthones G (2), I (4), and K (6) are stereoisomers of 1, 3, and 5, respectively. Furthermore, (+)sydoxanthone H (3a) demonstrated significant rescue of cell viability in H2O2-injuried SH-SY5Y cells by inhibiting reactive oxygen species production, suggesting its potential for neuroprotection.

Confirmation of the stereochemistry of spiroviolene.

We confirm the previously revised stereochemistry of spiroviolene by X-ray crystallographically characterizing a hydrazone derivative of 9-oxospiroviolane, which is synthesized by hydroboration/oxidation of spiroviolene followed by oxidation of the resultant hydroxy group. An unexpected thermal boron migration occurred during the hydroboration process of spiroviolene that resulted in the production of a mixture of 1α-hydroxyspiroviolane, 9α- and 9ß-hydroxyspiroviolane after oxidation. The assertion of the cis-orientation of the 19- and 20-methyl groups provided further support for the revised cyclization mechanism of spiroviolene.

Enantioselective Divergent Syntheses of Diterpenoid Pyrones.

Capitalizing a synergy between late-stage C(sp3)-H alkynylation and a series of transition metal-catalyzed alkyne functionalization reactions, we reported herein enantioselective divergent synthesis of 10 diterpenoid pyrones within 14-16 steps starting from chiral pool enoxolone, including the first enantioselective synthesis of higginsianins A, B, D, E, and metarhizin C. Our synthesis also highlights an unprecedented biomimetic oxidative rearrangement of α-pyrone into 3(2H)-furanone, as well as applications of Echavarren C(sp3)-H alkynylation reaction and Toste chiral counterion-mediated Au-catalyzed intramolecular allene hydroalkoxylation in natural product synthesis.

Enantioselective Synthesis of the 1,3-Dienyl-5-Alkyl-6-Oxy Motif: Method Development and Total Synthesis.

The 1,3-dienyl-5-alkyl-6-oxy motif is widely found in various types of bioactive natural products. However, present synthesis is mainly non-asymmetric which relied upon different olefination or transition metal-catalyzed cross-coupling reactions using enantioenriched precursors. Herein, based upon a newly developed enantioselective α-alkylation of conjugated polyenoic acids, a variety of 1,3-dienyl-5-alkyl-6-oxy motif (with E-configured internal olefin) was generated as the corresponding α-adducts in a highly enantioselective and diastereoselective manner. Utilizing 1,3-dienyl-5-alkyl-6-oxy motif as key intermediates, we further demonstrated their synthetic potential by expedient total syntheses of three types of natural products (glutarimide antibiotics, α-pyrone polyketides and Lupin alkaloids) within 4-7 steps.

Targeted Isolation of Dolabellane Diterpenoids from the Soft Coral Clavularia viridis Using Molecular Networking.

LC-MS/MS-based molecular networking annotation coupled 1H NMR detection allowed the depiction of the soft coral Clavularia viridis to produce a profile of dolabellane-type diterpenoids. Chromatographic separation of the EtOAc fraction resulted in the isolation of 12 undescribed dolabellane-type diterpenoids, namely, clavirolides J-U (1-12). Their structures were characterized by the extensive analysis of the spectroscopic data, including the calculated ECD and X-ray diffraction for the configurational assignments. Clavirolides J-K are characterized by a 1,11- and 5,9-fused tricyclic tetradecane scaffold fused with a α,ß-unsaturated-δ-lactone, and clavirolide L possesses a 1,11- and 3,5-fused tricyclic tetradecane scaffold, which extend the dolabellane-type scaffolds. Clavirolides L and G showed significant inhibition against HIV-1 without RT enzyme inhibition, providing additional non-nucleosides with different mechanisms from efavirenz.

Sclerotiamides C-H, Notoamides from a Marine Gorgonian-Derived Fungus with Cytotoxic Activities.

Bioassay-guided fractionation in association with LC-MS and NMR detection led to the isolation of six new alkaloids, sclerotiamides C-H (1-6), from the marine gorgonian-derived fungus Aspergillus sclerotiorum LZDX-33-4. Their structures were determined from extensive spectroscopic data, including ECD data and single-crystal X-ray diffraction analysis for configurational assignments. Sclerotiamides C (1) and D (2) are notoamide-type alkaloids with the incorporation of a unique 2,2-diaminopropane unit, and sclerotiamides E (3) and F (4) are unprecedented notoamide hybrids with a new coumarin unit. Sclerotiamide H (6) represents a new highly oxidized notoamide scaffold. Sclerotiamides C and F showed significant inhibition against a panel of tumor cell lines with IC50 values ranging from 1.6 to 7.9 µM. Sclerotiamide C induces apoptosis in HeLa cells by arresting the cell cycle, activating ROS production, and regulating apoptosis-related proteins in the MAPK signaling pathway. The present study extends the scaffold diversity of the notoamides and provides a potential lead for the development of a cytotoxic agent.

Enantioselective Total Synthesis of Hyperforin and Pyrohyperforin.

Capitalizing on the late-stage diversification of an essential 1,3-diene intermediate, we describe herein a 9-step enantioselective total synthesis of (+)-hyperforin and (+)-pyrohyperforin, starting from commercially available allylacetone. Our convergent synthesis features a series of critical reactions: 1) an enantioselective deconjugative α-alkylation of α,ß-unsaturated acid using chiral lithium amides as noncovalent stereodirecting auxiliaries; 2) a HfCl4 -mediated carbonyl α-tert-alkylation to forge the intricate bicyclo[3.3.1]nonane framework; 3) an abiotic cascade pyran formation; and 4) a selective 1,4-semihydrogenation of polyenes. During the course of our synthesis, we also identified a 1,2-cyclopropanediol overbred intermediate which was responsible for the 1,3-diene precursor formation through a controlled fragmentation.

Crystal Structures of Fsa2 and Phm7 Catalyzing [4 + 2] Cycloaddition Reactions with Reverse Stereoselectivities in Equisetin and Phomasetin Biosynthesis.

Fsa2 and Phm7 are a unique pair of pericyclases catalyzing [4 + 2] cycloaddition reactions with reverse stereoselectivities in the biosynthesis of equisetin and phomasetin, both of which are potent HIV-1 integrase inhibitors. We here solve the crystal structures of Fsa2 and Phm7, both of which possess unusual "two-ß barrel" folds. Different residues are evident between the active sites of Fsa2 and Phm7, and modeling experiments provide key structural information determining the reverse stereoselectivities. These results provide a better understanding of how natural pericyclases control the catalytic stereoselectivities and benefit the protein engineering in future.

Discovery of cyclohexadepsipeptides with anti-Zika virus activities and biosynthesis of the nonproteinogenic building block (3S)-methyl-l-proline.

The fungal cyclohexadepsipeptides destruxins (DTXs), isaridins (ISDs), and isariins (ISRs) are nonribosomal peptides whose structures include a 19-membered ring composed of five amino acid residues and one α- or ß-hydroxy acid residue. These cyclohexadepsipeptides contain unusual nonproteinogenic amino acid-building blocks and possess a range of antiviral, antibacterial, and other activities. The biosynthetic gene clusters for ISDs and ISRs have not been identified, and the biosynthesis of the nonproteinogenic (3S)-methyl-l-proline residue, which is found in DTXs, ISDs, and many other natural products, lacks full characterization. In an ongoing effort to identify compounds that can inhibit the Zika virus (ZIKV), we examined the extract of marine-derived fungus Beauveria felina SX-6-22 and discovered 30 DTXs, ISDs, and ISRs (1-30) including seven new compounds (1-7). The anti-ZIKV assays showed that 9-12 and 16-18 possess inhibitory activities against ZIKV RNA replication and NS5 (nonstructural protein 5) production in ZIKV-infected A549 cells. We sequenced the genome of B. felina SX-6-22 and identified three biosynthetic gene clusters detx, isd and isr, which are responsible for the biosynthesis of DTXs, ISDs, and ISRs, respectively. Comparative analyses of the three gene clusters clarified the biosynthetic relationships among these cyclohexadepsipeptides. Finally, we characterized the entire biosynthesis of nonproteinogenic building block (3S)-methyl-l-proline. The Δ1-pyrroline-5-carboxylate reductases (P5CRs), also used in the biosynthesis of l-proline, were demonstrated to catalyze the final reduction step in (3S)-methyl-l-proline formation, suggesting potential cross talk between primary and secondary metabolisms. These results provide opportunities for biosynthetic pathway engineering to generate new anti-ZIKV cyclohexadepsipeptides.

Enantioselective Total Synthesis of Berkeleyone†A and Preaustinoids.

Herein we report the first enantioselective total synthesis of 3,5-dimethylorsellinic acid-derived meroterpenoids (-)-berkeleyone A and its five congeners ((-)-preaustinoids A, A1, B, B1, and B2) in 12-15 steps, starting from commercially available 2,4,6-trihydroxybenzoic acid hydrate. Based upon the recognition of latent symmetry within D-ring, our convergent synthesis features two critical reactions: 1) a symmetry-breaking, diastereoselective dearomative alkylation to assemble the entire carbon core, and 2) a Sc(OTf)3 -mediated sequential Krapcho dealkoxycarbonylation/carbonyl α-tert-alkylation to forge the intricate bicyclo[3.3.1]nonane framework. We also conducted our preliminary biomimetic investigations and uncovered a series of rearrangements (α-ketol, α-hydroxyl-ß-diketone, etc.) responsible for the biomimetic diversification of (-)-berkeleyone A into its five preaustinoid congeners.

Illihenin A: An Antiviral Sesquiterpenoid with a Cage-like Tricyclo[6.2.2.01,5]dodecane Skeleton from Illicium henryi.

Illihenin A (1), a novel sesquiterpenoid, was isolated from the roots of Illicium henryi. The structure was determined by spectroscopic analyses, ECD calculation, and single-crystal X-ray diffraction. Compound 1 represents a class of novel 5/7/6 tricyclic sesquiterpenoids featuring a rare cage-like tricyclo[6.2.2.01,5]dodecane core. A plausible biosynthetic pathway of 1 by rearrangement of allo-cedrane is proposed. Additionally, 1 showed potent antiviral activity against coxsackievirus B3 with an IC50 value of 2.87 µM.

Study on Lubrication Characteristics of Novel Forced Wave Generator of Harmonic Drive without Flexible Bearing.

In contrast to the conventional forced wave generator which consists of cam and flexible bearing in harmonic drive, the novel forced wave generator retains cam but cancels flexible bearing. In this article, the lubrication characteristics of the novel forced wave generator in harmonic drive is studied. First, an elliptical sliding bearing (ESB) model of simplified structure between the novel forced wave generator and the flex spline is established. Further, the computational fluid dynamics (CFD) method is employed to study the effect of some factors on the lubrication characteristics of the ESB model including elliptical gap ratio, width, and rotational speed. According to the analysis, the elliptical gap ratio has a great impact and its optimal value is 3, which is used in the design of the novel forced wave generator. Last, the practical design of the novel forced wave generator in harmonic drive is given, which can provide a basis for design and optimization of a forced wave generator without flexible bearing of the harmonic drive.

Functional characterization and structural bases of two class I diterpene synthases in pimarane-type diterpene biosynthesis.

Pimarane-type diterpenoids are widely distributed in all domains of life, but no structures or catalytic mechanisms of pimarane-type diterpene synthases (DTSs) have been characterized. Here, we report that two class I DTSs, Sat1646 and Stt4548, each accept copalyl diphosphate (CPP) as the substrate to produce isopimara-8,15-diene (1). Sat1646 can also accept syn-CPP and produce syn-isopimaradiene/pimaradiene analogues (2-7), among which 2 possesses a previously unreported "6/6/7" ring skeleton. We solve the crystal structures of Sat1646, Sat1646 complexed with magnesium ions, and Stt4548, thereby revealing the active sites of these pimarane-type DTSs. Substrate modeling and subsequent site-directed mutagenesis experiments demonstrate different structural bases of Sat1646 and Stt4548 for 1 production. Comparisons with previously reported DTSs reveal their distinct carbocation intermediate stabilization mechanisms, which control the conversion of a single substrate CPP into structurally diverse diterpene products. These results illustrate the structural bases for enzymatic catalyses of pimarane-type DTSs, potentially facilitating future DTS engineering and combinatorial biosynthesis.

Aaptodines A-D, Spiro Naphthyridine-Furooxazoloquinoline Hybrid Alkaloids from the Sponge Aaptos suberitoides.

LC-MS-oriented fractionation of the sponge Aaptos suberitoides resulted in the isolation of four heptacyclic alkaloids, aaptodines A-D (1-4), which contain 9,10-dihydrofuro[2,3-f][1,3]oxazolo[5,4-h]quinolone and 7,8-dihydrocyclopenta[de][1,6]naphthyridine subunits with a spiro carbon atom. The structures were determined on the basis of NMR spectroscopic and single-crystal X-ray diffraction data analysis aided by electronic circular dichroism calculations and Mosher's method. A biosynthetic pathway for the formation of aaptodines A-D is postulated. Aaptodine D exhibits potent inhibition against osteoclast formation.

(+)- and (-)-Corydecumbenines A and B, two pairs of novel quaternary protoberberine alkaloid cycloadduct enantiomers with anti-neuroinflammatory and neuroprotective activities from the rhizomes of Corydalis decumbens.

Two novel Diels-Alder [4 + 2] cycloadducts of quaternary protoberberine alkaloids and fumaric acid monoanion, corydecumbenines A and B (1 and 2), and six known isoquinoline analogues (3-8) were isolated from the rhizomes of Corydalis decumbens. The planar structures of 1 and 2 were elucidated by extensive spectroscopic analysis including UV, IR, HRESIMS, 1D and 2D NMR. Chiral chromatography of 1 and 2 afforded two pairs of enantiomers (+)-corydecumbenine A (1a), (-)-corydecumbenine A (1b), (+)-corydecumbenine B (2a), and (-)-corydecumbenine B (2b), respectively, and their absolute configurations were determined by single-crystal X-ray crystallography and comparison of experimental and calculated electronic circular dichroism (ECD) spectra. Compounds 1b and 2b exhibited significant nitric oxide (NO) inhibitory activities in lipopolysaccharide (LPS)-stimulated BV-2 cells with IC50 values of 11.6 and 16.2 µM, respectively, comparable to the positive control indomethacin (IC50 = 10.3 µM), and they could also decrease the level of interleukin (IL)-1ß in BV-2 cells in a dose-dependent manner. Most of the isolates showed neuroprotective effects against the injury of OGD/R-induced PC12 cells at 20 µM.

Insulin-Sensitizing Activity of Sub-Nanoscaled Polyalkoxyvanadate Clusters.

Sub-nanoscaled polyalkoxyvanadates (PAOVs) functionalized with various aliphatic acids are evaluated for their insulin-sensitizing activity in lowering the blood glucose levels of diabetic mice in typical glucose tolerance tests. All the PAOVs can restore the blood glucose to normal levels after a single oral administration of PAOVs. Among them, the myristic acid-modified PAOVs enable the response of insulin to the repeated glucose challenges, lasting for up to 13 h. The combined administration of PAOVs exerts better glucose control over insulin alone, while the capric acid- and myristic acid-modified ones can enhance the responsiveness of insulin to glucose challenge and is comparable to a clinical-used derivative of insulin. Interestingly, continuous glucose monitoring shows that myristic acid-modified PAOV derivatives sensitize the responsiveness of insulin, almost matching with that of a healthy pancreas. These discoveries open up new opportunities for the application of PAOVs to promote glucose-responsive and long-lasting activity of insulin, which are expected to aid the accurate blood glucose control in insulin therapy while reducing the number of insulin administrations.

[Comparison on driving mechanism of county ecological efficiency: With three counties in the mountainous area of southern Ningxia, China as an example]. / 县域生态效率驱动机制对比­­ä»¥å®å—山区3县为例.

With Tongxin, Xiji, and Longde counties in the mountainous area of southern Ningxia as the research area, we used extended-exergy analysis (EEA) to compare their ecological efficiency driving mechanism in 2008-2017 to explore the causes of their variation in ecological degradation. The results showed that the overall difference of ecological efficiency in the three counties was significant during the study period. The ecological efficiency of Tongxin was low, with large inter-annual variation. The ecological efficiency of Xiji was stable, and the overall efficiency of Longde was the highest. The difference of exergy scale was small among the three counties. The exergy proportion in the economic sectors was not coordinated, which were dominated by agricultural and residential sectors. The economic sectors presented significant capital-pull-type and labor-intensive characteristics, indicating the driving force for ecological degradation mainly came from agricultural production and residents' lives in underdeveloped regions. The system's internal exergy conversion rate and the external energy exchange rate of the three counties were extremely low, constituting a simple network circulation path with high input, low storage, low opening and low conversion, which weakened the endogenous development of social economic subsystem and threatened the fragile ecosystem.

[Jasmonate signal pathway involved in phytoalexin biosynthesis in Sorbus aucuparia cell elicited by Hpa1].

The Harpin protein Hpa1 can induce defense responses in plant. This study aimed at investigating the role of jasmonate (JA) signal pathway in the process of biosynthesis of secondary metabolite in Sorbus aucuparia cell eliciting by Hpa1 crude extract (Hpa1 CE). The results showed that Hpa1 crude extract (Hpa1 CE) could induce phytoalexin synthesis in S. aucuparia cell， most of which was noraucuparin and its glycosides. Meanwhile Hpa1 CE treatment resulted in methyl jasmonate (MeJA) production increased and noraucuparin was de novo synthesized in large quantities. Combination of Hpa1 CE and salicylhydroxamic acid (SHAM, JA signaling inhibitor) caused the decreased MeJA and noraucuparin in the S. aucuparia cell compared with that in Hpa1 CE group. Real-time PCR results indicated that Hpa1 CE treatment caused down-regulation of JAZ and up-regulation of mcy2 in transcription level. Therefore Hpa1 CE elicited defense mechanism and JA signaling pathway involved in phytoalexin biosynthesis in S. aucuparia cell. It presented information to elucidate the role of JA signal pathway in stress response in the perspective of secondary metabolism of plant.

Correction: Diversified polyoxovanadate derivatives obtained by copper(i)-catalysed azide-alkyne cycloaddition reaction: their synthesis and structural characterization.

Correction for 'Diversified polyoxovanadate derivatives obtained by copper(i)-catalysed azide-alkyne cycloaddition reaction: their synthesis and structural characterization' by Hongli Jia et al., Dalton Trans., 2018, 47, 577-584.

Diversified polyoxovanadate derivatives obtained by copper(i)-catalysed azide-alkyne cycloaddition reaction: their synthesis and structural characterization.

In this work, we confirmed that the copper-catalysed azide-alkyne cycloaddition (CuAAC) reaction is an effective method for the organic-functionalization of polyoxometalates (POMs). Herein, for the first time, four novel 1,2,3-triazole functionalized polyoxovanadate (POV) organic-inorganic hybrids, (Bu4N)2[V6O13{(OCH2)3C5H6N3O}2]·1.5CH3CN 2, (Bu4N)2[V6O13{(OCH2)3C7H8N3O2}2]·2CH3CN 3, (Bu4N)2[V6O13{(OCH2)3C11H10N3}2] 4 and (Bu4N)2[V6O13{(OCH2)3C10H7N3Cl}2] 5 were prepared through the CuAAC reaction using the azide functionalized hexavanadate, (Bu4N)2[V6O13{(OCH2)3CCH2N3}2]·2.5CH3CN 1, as the precursor, where CuI was used as the catalyst and N,N-diisopropylethylamine (DIPEA) as a stabilizer for CuI. All the four compounds were structurally and compositionally characterized by single-crystal X-ray diffraction, elemental analyses, powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR), 1H NMR, ESI-MS, UV-Vis and thermogravimetric analysis (TGA).