Qingyi Tong

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.

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.

Indole diketopiperazines from endophytic Chaetomium sp 88194 induce breast cancer cell apoptotic death

Diketopiperazines are important secondary metabolites of the fungi with variety bioactivities. Several species belonging to genus Chaetomium produce compounds of this class, such as chetomin. To identify new antitumor agents, secondary metabolites of fungus Chaetomium sp 88194 were investigated and three new indole diketopiperazines, Chaetocochins G (1), Oidioperazines E (2) and Chetoseminudin E (3), along with two known compounds Chetoseminudins C (4) and N-acetyl-β-oxotryptamine (5), were obtained. Chaetocochins G and Chetoseminudin E were recrystallized in CHCl3 containing a small amount of MeOH, and their structures with absolute configuration were established by spectroscopic data interpretation and single-crystal X-ray diffraction analysis. The absolute configuration of Oidioperazines E was defined by comparing of experimental and calculated electronic circular dichroism spectra. These isolates were also evaluated the anticancer activity, and Chaetocochins G displayed more potent cytotoxicity in MCF-7 cells than the common chemotherapeutic agent (5-fluorouracil) associated with G2/M cell cycle arrest. More importantly, Chaetocochins G induced cell apoptotic death via caspase-3 induction and proteolytic cleavage of poly (ADP-ribose) polymerase, concomitantly with increased Bax and decreased Bcl-2 expression. Our findings suggested that indole diketopiperazines from endophytic Chaetomium sp 88194 may be potential resource for developing anti-cancer reagents.

Asperflavipine A: A Cytochalasan Heterotetramer Uniquely Defined by a Highly Complex Tetradecacyclic Ring System from Aspergillus flavipes QCS12

Asperflavipines A (1) and B (2), two structurally complex merocytochalasans, were isolated from Aspergillus flavipes. Asperflavipine A (1), which contains two cytochalasan moieties and two epicoccine moieties, is the first cytochalasan heterotetramer to be discovered. It is uniquely defined by 5/6/11/5/6/5/6/5/6/5/5/11/6/5 fused tetradecacyclic rings with three continuous bridged ring systems. Asperflavipine B (2) is a cytochalasan heterotrimer containing a cytochalasan and two epicoccine moieties with a 5/6/11/5/5/6/5/6/5 nonacyclic ring system. The hypothetical biosynthesis of 1 and 2 is proposed to involve Diels-Alder and [3+2] cycloaddition reactions as key steps and reveals unparalleled plasticity in the biosynthesis of merocytochalasans. The existence of 1 adds a new dimension to the diversity of the cytochalasan family. Compound 1 showed moderate cytotoxicity and induced apoptosis in Jurkat, NB4, and HL60 cells through the activation of caspase-3 and degradation of poly(ADP-ribose) polymerase (PARP).

Small molecule activation of NOTCH signaling inhibits acute myeloid leukemia

Aberrant activation of the NOTCH signaling pathway is crucial for the onset and progression of T cell leukemia. Yet recent studies also suggest a tumor suppressive role of NOTCH signaling in acute myeloid leukemia (AML) and reactivation of this pathway offers an attractive opportunity for anti-AML therapies. N-methylhemeanthidine chloride (NMHC) is a novel Amaryllidaceae alkaloid that we previously isolated from Zephyranthes candida, exhibiting inhibitory activities in a variety of cancer cells, particularly those from AML. Here, we report NMHC not only selectively inhibits AML cell proliferation in vitro but also hampers tumor development in a human AML xenograft model. Genome-wide gene expression profiling reveals that NMHC activates the NOTCH signaling. Combination of NMHC and recombinant human NOTCH ligand DLL4 achieves a remarkable synergistic effect on NOTCH activation. Moreover, pre-inhibition of NOTCH by overexpression of dominant negative MAML alleviates NMHC-mediated cytotoxicity in AML. Further mechanistic analysis using structure-based molecular modeling as well as biochemical assays demonstrates that NMHC docks in the hydrophobic cavity within the NOTCH1 negative regulatory region (NRR), thus promoting NOTCH1 proteolytic cleavage. Our findings thus establish NMHC as a potential NOTCH agonist that holds great promises for future development as a novel agent beneficial to patients with AML.

Novel small molecule 11β-HSD1 inhibitor from the endophytic fungus Penicillium commune

Two new phenone derivatives penicophenones A (1) and B (2), a new cyclic tetrapeptide penicopeptide A (3), and five known compounds were isolated from the culture broth of Penicillium commune, an endophytic fungus derived from Vitis vinifera. Compounds 1–3 were elucidated by extensive spectroscopic analyses including 1D and 2D NMR and HRESIMS. The absolute configurations of 1 and 3 were determined by comparing its ECD with related molecules and modified Marfey’s analysis, respectively. Penicophenone A (1) possesses a rare benzannulated 6,6-spiroketal moiety, which is a new member of the unusual structural class with peniphenone A as the representative. Compound 3 exhibited significant inhibition activities against 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) in vitro and showed strong binding affinity to 11β-HSD1. Moreover, compound 3 treatments decreased the lipid droplet accumulation associate with the inhibition of 11β-HSD1 expression in differentiate-induced 3T3-L1 preadipocytes. Furthermore, the molecular docking demonstrated that compound 3 coordinated in the active site of 11β-HSD1 is essential for the ability of diminishing the enzyme activity.

Hyperisampsins H–M, Cytotoxic Polycyclic Polyprenylated Acylphloroglucinols from Hypericum sampsonii

Six new polycyclic polyprenylated acylphloroglucinols (PPAPs), named hyperisampsins H–M (1–6), were isolated from the aerial parts of Hypericum sampsonii, together with five known analogs (7–11). The structures of 1–6 were established by extensive spectroscopic analyses, including HRESIMS and NMR. In addition, the absolute configurations of these new compounds were determined by electronic circular dichroism (ECD) calculations. Compounds 1 and 2 represent the first examples of PPAPs possessing a unique γ-lactone ring at C-23, while 3–6 differed from normal PPAPs with an unprecedented 1,2-dioxane ring. Compounds 1–7 were evaluated for their cytotoxic activities against a panel of human cancer cell lines in vitro, of which 3, 4, and 6 exhibited significant cytotoxic activities with IC50 values ranging from 0.56 to 3.00 μM. Moreover, compound 3 induces leukemia cell apoptotic death, evidenced by activation of caspase-3, degradation of PARP, up-regulation of Bax, and down-regulation of Bcl-2 and Bcl-xl.

Aspergilasines A–D: Four Merocytochalasans with New Carbon Skeletons from Aspergillus flavipes QCS12

Aspergilasines A-D (1-4), four merocytochalasans with new skeletons, were isolated from the liquid culture broth of Aspergillus flavipes QCS12. Aspergilasine A (1) possesses a uniquely caged pentacyclo[7.2.0.14,11.02,7.05,10]dodecane skeleton with an unexpected cyclobutane ring that formed by the fusion of two epicoccine moieties via two [3 + 2] cycloadditions. Aspergilasines B-D (2-4) are key biosynthetic intermediates of epicochalasine B that fit well with our previous biosynthetic proposal.

Tricyclic Polyprenylated Acylphloroglucinols from St John’s Wort, Hypericum perforatum

The new polyprenylated acylphloroglucinol derivatives 1-15 and the known furohyperforin (16) were isolated from the stems and leaves of Hypericum perforatum. Their structures were determined by analyses of NMR and HRESIMS data. Their absolute configurations were elucidated by a combination of electronic circular dichroism (ECD) and Rh2(OCOCF3)4-induced ECD, as well as X-ray diffraction crystallography. The new hyperforatin F (9) contains a unique acetyl functionality at C-1 of the bicyclo[3.3.1]nonane core. Hyperforatins G (10) and H (11) are similarly the first examples of naturally occurring [3.3.1]-type polycyclic prenylated acylphloroglucinols possessing a carbonyl functionality at C-32. The compounds were tested for their acetylcholinesterase (AChE) inhibitory activities and cytotoxic activities against a panel of human tumor cell lines. Compounds 3, 5, 6, 8, and 9 exerted moderate inhibitory activities (IC50 3.98-9.13 μM) against AChE.