Yongbo Xue

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.

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.

Schicagenins A-C: Three Cagelike Nortriterpenoids from Leaves and Stems of Schisandra chinensis

Schicagenins A-C (1-3), three unprecedented nortriterpenoids characterized with a tetracyclic oxa-cage motif and C(9) side chain, were discovered from the leaves and stems of Schisandra chinensis. Their structures were determined on the basis of extensive spectroscopic analysis, and the absolute stereochemistries were established by single-crystal X-ray diffraction and CD experiments. A plausible biosynthetic pathway of 1-3 was also discussed.

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.

Henrischinins A-C: three new triterpenoids from Schisandra henryi.

Three novel triterpenoids, henrischinins A-C (1-3), featuring the unique motif of a 3-one-2-oxabicyclo[3.2.1]-octane, were isolated from the leaves and stems of Schisandra henryi. Their structures were elucidated by spectroscopic methods, and the absolute configuration of 2 was confirmed by a single crystal X-ray diffraction. Compounds 1 and 2 showed weak cytotoxicity against HL-60 cell lines.

Cytotoxic triterpene dilactones from the stems of Kadsura ananosma.

Six new triterpene dilactones with a rare rearranged pentacyclic skeleton, longipedlactones K-P (1-6), and seven known analogues (7-13) were isolated from the stems of Kadsura ananosma. Compound 1 was found to possess a unique peroxide bridge between C-1 and C-9 in rings A and B. The structures of these new compounds were established on the basis of spectroscopic data analysis, especially of their 2D NMR spectra. In the evaluation of the in vitro cytotoxicity of these compounds against a small panel of human cancer cell lines, compounds 3, 7, 9, and 13 were found to be the most potent against HL-60 acute leukemia cell.