Guangmin Yao

Bioactive Acylphloroglucinols with Adamantyl Skeleton from Hypericum sampsonii

Hyperisampsins A-D (1-4), with tetracyclo[6.3.1.1(3,10).0(3,7)]tridecane skeletons and seven biogenetically related congeners (5-11), were isolated from Hypericum sampsonii. Their structures were elucidated by comprehensive spectroscopic techniques. The absolute configuration of 1 was established by ECD calculations, and those of 5 and 9 were confirmed by single X-ray crystallographic analyses. Hyperisampsins A and D showed potent anti-HIV activities with EC50 of 2.97 and 0.97 μM and selectivity index of 4.80 and 7.70, respectively.

Cytotoxic alkaloids from the whole plants of Zephyranthes candida.

Seven new alkaloids, N-methylhemeanthidine chloride (1), N-methyl-5,6-dihydroplicane (5), O-methylnerinine (6), N-ethoxycarbonylethylcrinasiadine (7), N-ethoxycarbonylpropylcrinasiadine (8), N-phenethylcrinasiadine (9), and N-isopentylcrinasiadine (10), together with eight known alkaloids, hemeanthamin (2), 3-epimacronine (3), (+)-tazettine (4), N-methylcrinasiadine (11), trisphaeridine (12), 5,6-dihydrobicolorine (13), lycorine (14), and nigragillin (15), were isolated from the whole plants of Zephyranthes candida. The structures of the new compounds were established by spectroscopic data interpretation, with single-crystal X-ray diffraction analysis performed on 1. The absolute configuration of 3-epimacronine (3) was determined by single-crystal X-ray diffraction analysis with Cu Kα irradiation. Compounds 1-15 were evaluated for their in vitro cytotoxicity against five human cancer cell lines and the Beas-2B immortalized (noncancerous) human bronchial epithelial cell line. Compounds 1, 2, 9, and 14 exhibited cytotoxicity with IC(50) values ranging from 0.81 to 13 μM with selectivity indices as high as 10 when compared to the Beas-2B cell line.

Transition-metal-free synthesis of phenanthridinones from biaryl-2-oxamic acid under radical conditions.

Na2S2O8-promoted decarboxylative cyclization of biaryl-2-oxamic acid for phenanthridinones has been developed. This work illustrates the first example of intramolecular decarboxylative amidation of unactivated arene under transition-metal-free conditions. Additionally, this approach provides an efficient and economical method to access biologically interesting phenanthridinones, an important structure motif in many natural products.

The influence of temperature on low cycle fatigue behavior of nickel base superalloy GH4049

Low cycle fatigue tests on nickel base superalloy GH4049 were conducted at various temperatures from 500 to 850°C in laboratory air. The strain-life and cyclic stress-strain data were analyzed and the change in fatigue life behavior and fatigue parameters with increasing temperature was discussed. At low and intermediate total strain amplitudes, the fatigue life was found to decrease with increasing temperatures. The fracture surface of the fatigue specimens was studied using scanning electron microscopy. It was found that fatigue crack initiation is transgranular, however, fatigue crack growth exhibits a strong dependence on temperature. The cyclic deformation process, creep and oxidation are thought to be the main causes of fatigue life reduction and intergranular cracking.

Asperchalasine A, a Cytochalasan Dimer with an Unprecedented Decacyclic Ring System, from Aspergillus flavipes

Asperchalasine A (1), the first cytochalasan dimer featuring a unique decacyclic 5/6/11/5/5/6/5/11/6/5 ring system consisting of 20 chiral centers, was isolated from the culture broth of Aspergillus flavipes. Three biogenetically related intermediates, asperchalasines B-D (2-4), were also isolated. Their structures, including their absolute configurations, were elucidated using a combination of HRESIMS, NMR, ECD, molecular modeling, and single-crystal X-ray diffraction techniques. Compound 1, which possesses an unprecedented 13-oxatetracyclo[7.2.1.1(2,5).0(1,6)]tridec-8,12-dione core structure, is the first example of a dimeric cytochalasan alkaloid. The biogenetic pathways of 1-4 were described starting from the co-isolated compounds 5 and 6. More importantly, 1 induced significant G1-phase cell cycle arrest by selectively inhibiting cyclin A, CDK2 and CDK6 in cancerous, but not normal, cells, highlighting it as a potentially selective cell cycle regulator against cancer cells.

Hyperattenins A–I, bioactive polyprenylated acylphloroglucinols from Hypericum attenuatum Choisy

Nine new polyprenylated acylphloroglucinols (PPAPs), hyperattenins A-I (1-9), together with thirteen known analogues (10-22), were isolated from the aerial parts of Hypericum attenuatum Choisy. The structures of 1-9 were elucidated by extensive spectroscopic analysis. The absolute configuration of 1 was determined by a single X-ray crystallographic analysis, and the absolute configurations of 2-9 were determined by comparison of experimental and calculated electronic circular dichroism (ECD) spectra. Compound 1 was characterised as a bicyclo[3.3.1] nonane derivative containing an unusual hemiacetal functionality formed by a series of redox reactions on its side chains, which occurs rarely in nature. All new isolates were evaluated for cytotoxic activities against several human cancer cell lines. Compound 9 exhibited significant inhibitory activity against the HL-60 and A-549 cell lines, with IC50 values of 2.04 and 3.26 mu M, respectively. Compound 9 also showed low toxicity to Beas-2B cells (IC50 = 14.36 mu M), suggesting that it could be a selective anti-tumour agent for leukaemia and lung cancer. Compounds 2-8 were also screened for their anti-HIV-1 activities.

Epicochalasines A and B: Two Bioactive Merocytochalasans Bearing Caged Epicoccine Dimer Units from Aspergillus flavipes

Two bioactive merocytochalasans, epicochalasines A (1) and B (2), a new class of cytochalasans bearing unexpected scaffolds consisting of fused aspochalasin and epicoccine dimer moieties, were isolated from the liquid culture broth of Aspergillus flavipes. Both 1 and 2 possess a hendecacyclic 5/6/11/5/6/5/6/5/6/6/5 ring system containing an adamantyl cage and as many as 19 stereogenic centers; however, the fusion patterns of 1 and 2 differ greatly, thus resulting in different carbon skeletons. The absolute configurations of 1 and 2 were determined by X-ray diffraction and calculated ECD, respectively. The biogenetic pathways of 1 and 2 are proposed to involve Diels-Alder and nucleophilic addition reactions. Both 1 and 2 induced significant G2/M-phase cell-cycle arrest. Furthermore, we found that merocytochalasans induce apoptosis in leukemia cells through the activation of caspase-3 and the degradation of PARP.

Armochaeglobines A and B, Two New Indole-Based Alkaloids from the Arthropod-Derived Fungus Chaetomium globosum

Armochaeglobines A (1) and B (2), two indole-based cytochalasan alkaloids with new carbon skeletons, were obtained from the fungus Chaetomium globosum TW1-1, which was first isolated from the arthropod Armadillidium vulgare. Their structures were elucidated by extensive spectroscopic analyses, ECD calculation, and single-crystal X-ray diffraction analysis. Interestingly, compound 1 featured a unique tetracyclic 5/6/7/5 fused ring system and 2 possessed a rare 12-membered carbon scaffold.

Hyperascyrones A-H, polyprenylated spirocyclic acylphloroglucinol derivatives from Hypericum ascyron Linn.

Eight polyprenylated spirocyclic acylphloroglucinol derivatives (PSAPs), hyperascyrones A-H, were isolated from the aerial parts of Hypericum ascyron Linn., together with six known analogs. Their structures were established by spectroscopic analyses including HRESIMS, 1D and 2D NMR, and their absolute configurations were determined by electronic circular dichroism calculations (ECD, Gaussian 09). Structures of previously reported tomoeones C, D, G, and H were revised. Hyperascyrones A-H were evaluated for their cytotoxic and anti-HIV-1 activities, with hyperascyrones C and G exhibiting significant cytotoxicities against HL-60 cell lines with IC50 values of 4.22 and 8.36 μM, respectively. In addition, the chemotaxonomic significance of these compounds was also discussed.

Interrupted Pummerer Reaction in Latent-Active Glycosylation: Glycosyl Donors with a Recyclable and Regenerative Leaving Group

Latent O-glycosides, 2-(2-propylthiol)benzyl (PTB) glycosides, were converted into the corresponding active glycosyl donors, 2-(2-propylsulfinyl)benzyl (PSB) glycosides, by a simple and efficient oxidation. Treatment of the PSB donor and various acceptors with triflic anhydride provided the desired glycosides in good to excellent yields. The leaving group, which was activated by an interrupted Pummerer reaction, can be recycled (PSB-OH) and regenerated as the precursor (PTB-OH). A natural hepatoprotective glycoside, leonoside F, was efficiently synthesized in a convergent [3+1] manner with this newly developed method. The present total synthesis also led to a structural revision of this phenylethanoid glycoside.