Copper-Catalyzed Reductive Ireland-Claisen Rearrangements of Propargylic Acrylates and Allylic Allenoates.

The copper-catalyzed reductive Ireland-Claisen rearrangement of propargylic acrylates led to 3,4-allenoic acids. The use of silanes or pinacolborane as stoichiometric reducing agents and triethylphosphite as a ligand facilitated the divergent and complementary selectivity for the synthesis of diastereomeric anti- and syn-rearranged products, respectively. Copper-catalyzed reductive Ireland-Claisen rearrangement of allylic 2,3-allenoates proceeded effectively only when pinacolborane was used as a reductant to generate various 1,5-dienes in excellent yields and with good diastereoselectivities in some cases. Mechanistic studies showed that the silyl and boron enolates, rather than the copper enolate, underwent a stereospecific rearrangement via a chairlike transition state to afford the corresponding Claisen rearrangement products.

Tetrandrine, an Activator of Autophagy, Induces Autophagic Cell Death via PKC-α Inhibition and mTOR-Dependent Mechanisms.

Emerging evidence suggests the therapeutic role of autophagic modulators in cancer therapy. This study aims to identify novel traditional Chinese medicinal herbs as potential anti-tumor agents through autophagic induction, which finally lead to autophagy mediated-cell death in apoptosis-resistant cancer cells. Using bioactivity-guided purification, we identified tetrandrine (Tet) from herbal plant, Radix stephaniae tetrandrae, as an inducer of autophagy. Across a number of cancer cell lines, we found that breast cancer cells treated with tetrandrine show an increase autophagic flux and formation of autophagosomes. In addition, tetrandrine induces cell death in a panel of apoptosis-resistant cell lines that are deficient for caspase 3, caspase 7, caspase 3 and 7, or Bax-Bak respectively. We also showed that tetrandrine-induced cell death is independent of necrotic cell death. Mechanistically, tetrandrine induces autophagy that depends on mTOR inactivation. Furthermore, tetrandrine induces autophagy in a calcium/calmodulin-dependent protein kinase kinase-ß (CaMKK-ß), 5' AMP-activated protein kinase (AMPK) independent manner. Finally, by kinase profiling against 300 WT kinases and computational molecular docking analysis, we showed that tetrandrine is a novel PKC-α inhibitor, which lead to autophagic induction through PKC-α inactivation. This study provides detailed insights into the novel cytotoxic mechanism of an anti-tumor compound originated from the herbal plant, which may be useful in promoting autophagy mediated- cell death in cancer cell that is resistant to apoptosis.

Virtual screening and optimization of Type II inhibitors of JAK2 from a natural product library.

Amentoflavone has been identified as a JAK2 inhibitor by structure-based virtual screening of a natural product library. In silico optimization using the DOLPHIN model yielded analogues with enhanced potency against JAK2 activity and HCV activity in cellulo. Molecular modeling and kinetic experiments suggested that the analogues may function as Type II inhibitors of JAK2.

Pseudolaric acids: isolation, bioactivity and synthetic studies.

The pseudolaric acids are diterpenoids isolated from the root bark of Pseudolarix amabilis, or the golden larch. Pseudolaric acids A and B are the major antifungal and anti-angiogenic congeners of this family of compounds. This review presents the results of the isolation, biological and synthetic studies of these natural products. 127 references are cited.

Alisol B, a novel inhibitor of the sarcoplasmic/endoplasmic reticulum Ca(2+) ATPase pump, induces autophagy, endoplasmic reticulum stress, and apoptosis.

Emerging evidence suggests that autophagic modulators have therapeutic potential. This study aims to identify novel autophagic inducers from traditional Chinese medicinal herbs as potential antitumor agents. Using an image-based screen and bioactivity-guided purification, we identified alisol B 23-acetate, alisol A 24-acetate, and alisol B from the rhizome of Alisma orientale as novel inducers of autophagy, with alisol B being the most potent natural product. Across several cancer cell lines, we showed that alisol B-treated cells displayed an increase of autophagic flux and formation of autophagosomes, leading to cell cycle arrest at the G(1) phase and cell death. Alisol B induced calcium mobilization from internal stores, leading to autophagy through the activation of the CaMKK-AMPK-mammalian target of rapamycin pathway. Moreover, the disruption of calcium homeostasis induces endoplasmic reticulum stress and unfolded protein responses in alisol B-treated cells, leading to apoptotic cell death. Finally, by computational virtual docking analysis and biochemical assays, we showed that the molecular target of alisol B is the sarcoplasmic/endoplasmic reticulum Ca(2+) ATPase. This study provides detailed insights into the cytotoxic mechanism of a novel antitumor compound.

Herbal diterpenoids induce growth arrest and apoptosis in colon cancer cells with increased expression of the nonsteroidal anti-inflammatory drug-activated gene.

Novel chemotherapeutic agents derived from active phytochemicals could be used as adjuvants and improve the anti-carcinogenicity of standard drug treatments. However, their precise mechanisms of action are sometimes unclear. In this study, the anti-carcinogenic effect of the herbal diterpenoid pseudolaric acid B (PAB) on the growth and apoptosis of colon cancer cells was investigated, and to compare that with the more toxic compound triptolide. PAB induced growth inhibition and apoptosis in HT-29 cells, which were associated with cell cycle arrest at the G(2)/M phase, modulation of cyclin expression and downregulation of the protooncogene c-myc. In addition, PAB also inhibited bcl-x(L) expression, induced cleavage of procaspase-3 and its substrate poly(ADP-ribose) polymerase (PARP), which together caused DNA fragmentation and nuclear chromatin condensation. Concomitantly, the modulation of the growth-related and apoptotic factors by PAB was accompanied by the increased protein and gene expression of the nonsteroidal anti-inflammatory drug-activated gene (NAG-1), which occurred along with cyclooxygenase-2 inhibition. The effects of PAB on PARP cleavage and NAG-1 overexpression were not reversible upon removal of the drug from the culture medium. Similar cytotoxic and pro-apoptotic effects were also attained by treating the HT-29 cells with another diterpenoid triptolide, but its actions on cell cycle progression and on the upstream transcriptional regulation of NAG-1 both took place in a less coherent manner. These findings exemplify the potential of herbal terpenoids, particularly PAB, in modulating colon cancer carcinogenesis through known molecular targets and precise mechanism of action.

Pseudolaric acid B, a novel microtubule-destabilizing agent that circumvents multidrug resistance phenotype and exhibits antitumor activity in vivo.

PURPOSE: Pseudolaric acid B (PAB) is the major bioactive constituent in the root bark of Pseudolarix kaempferi that has been used as an antifungal remedy in traditional Chinese medicine. Previous studies showed that PAB exhibited substantial cytotoxicity. The aims of this study were to elucidate the molecular target of PAB, to examine its mechanism of action, and to evaluate the efficacy of this compound in vivo. EXPERIMENTAL DESIGN: The effect of PAB on cell growth inhibition toward a panel of cancer cell lines was assayed. Cell cycle analysis, Western blotting, immunocytochemistry, and apoptosis analysis were carried out to examine the mechanism of action. Tubulin polymerization assays were conducted to examine the interaction between PAB and tubulin. A P-glycoprotein-overexpressing cell line was used to evaluate the efficacy of PAB toward multidrug-resistant phenotypes. In vivo efficacy of PAB was evaluated by the murine xenograft model. RESULTS: PAB induces cell cycle arrest at G2-M transition, leading to apoptosis. The drug disrupts cellular microtubule networks and inhibits the formation of mitotic spindles. Polymerization of purified bovine brain tubulin was dose-dependently inhibited by PAB. Furthermore, PAB circumvents the multidrug resistance mechanism, displaying notable potency also in P-glycoprotein-overexpressing cells. Finally, we showed that PAB is effective in inhibiting tumor growth in vivo. CONCLUSIONS: We identified the microtubules as the molecular target of PAB. Furthermore, we showed that PAB circumvents P-glycoprotein overexpression-induced drug resistance and is effective in inhibiting tumor growth in vivo. Our work will facilitate the future development of PAB as a cancer therapeutic.

Dihydrochalcones from the leaves of Pieris japonica.

Six new dihydrochalcones, 3-hydroxyasebotin (5), asebogenin 2'-O-beta-D-ribohexo-3-ulopyranoside (6), 2' '-acetylasebotin (7), 3',4,5'-trihydroxy-4'-methoxydihydrochalcone 3',5'-di-O-beta-D-glucopyranoside (8), and pierotins A (9) and B (10), along with four known dihydrochalcones, phloretin (1), phlorizin (2), asebogenin (3), and asebotin (4), were isolated from the leaves of Pieris japonica. Their structures were elucidated on the basis of spectroscopic analysis including HMQC, HMBC, NOESY, and X-ray crystal diffraction. Compounds 1, 3-5, and 7-10 inhibited the proliferation of murine B cells and compounds 5 and 10 inhibited the proliferation of murine T cells in vitro significantly.