Synthesis and plant growth regulation activity of α-d-ManpNAc-(1→2)-[α-L-Rhap-(1→3)-]α-L-Rhap-(1→4)-β-d-GlupNAc-(1→3)-α-L-Rhap, the repeating unit of O-antigen of Rhizobium trifolii 4s

Steroidal Saponins with Plant Growth Stimulation Effects; Yucca schidigera as a Commercial Source

Plant growth-stimulation bioactivity of triterpenoid saponins is well known, especially for oleanane-type compounds. Nevertheless, a few phytotoxicity bioassays performed on some steroidal saponins have shown hormesis profiles and growth stimulation on Lactuca sativa roots. The focus of the work described here was on the use of the wheat coleoptile bioassay to evaluate plant growth stimulation, and on the search for a commercially available source of active saponins by bio-guided fractionation strategy. Selected saponins were tested and a cluster analysis showed that those saponins with a sugar chain of more than five units had a hormesis profile, while saponins with growth enhancement had fewer sugar residues. Two saponins showed similar activity to the positive control, namely the phytohormone indole-3-butyric acid (IBA). As a potential source of these metabolites, a commercial extract of Yucca schidigera used as a fertilizer was selected. Bio-guided fractionation led to the identification of two fractions of defined composition and these showed stimulation values similar to the positive control. It was observed that the presence of a carbonyl group at C-12 on the aglycone skeleton led to improved activity. A saponin-rich fraction from Y. schidigera could be proposed to enhance crop quality and production.

Enhancing Potency and Selectivity of a DC-SIGN Glycomimetic Ligand by Fragment-Based Design: Structural Basis

Chemical modification of pseudo-dimannoside ligands guided by fragment-based design allowed for the exploitation of an ammonium-binding region in the vicinity of the mannose-binding site of DC-SIGN, leading to the synthesis of a glycomimetic antagonist (compound 16) of unprecedented affinity and selectivity against the related lectin langerin. Here, the computational design of pseudo-dimannoside derivatives as DC-SIGN ligands, their synthesis, their evaluation as DC-SIGN selective antagonists, the biophysical characterization of the DC-SIGN/16 complex, and the structural basis for the ligand activity are presented. On the way to the characterization of this ligand, an unusual bridging interaction within the crystals shed light on the plasticity and potential secondary binding sites within the DC-SIGN carbohydrate recognition domain.

Synthesis of Gibberellic Acid Derivatives and Their Effects on Plant Growth

A series of novel C-3-OH substituted gibberellin derivatives bearing an amide group were designed and synthesized from the natural product gibberellic acid (GA₃). Their activities on the plant growth regulation of rice and Arabidopsis were evaluated in vivo. Among these compounds, 10d and 10f exhibited appreciable inhibitory activities on rice (48.6% at 100 μmol/L) and Arabidopsis (41.4% at 100 μmol/L), respectively. These results provide new insights into the design and synthesis of potential plant growth regulators.

Total Synthesis and Biological Evaluation of Ipomoeassin F and Its Unnatural 11R-Epimer

Ipomoeassin F, a macrolide glycoresin containing an embedded disaccharide, possesses potent in vitro antitumor activity with an unknown mechanism of function. It inhibits tumor cell growth with single-digit nanomolar IC50 values, superior to many clinical chemotherapeutic drugs. To facilitate translation of its bioactivity into protein function for drug development, we report here a new synthesis for the gram-scale production of ipomoeassin F (3.8% over 17 linear steps) from commercially available starting materials. The conformation-controlled subtle reactivity differences of the hydroxyl groups in carbohydrates were utilized to quickly construct the disaccharide core, which, along with judicial selection of protecting groups, made the current synthesis very efficient. The same strategy was also applied to the smooth preparation of the 11R-epimer of ipomoeassin F for the first time. Cytotoxicity assays demonstrated the crucial role of the natural 11S configuration. In addition, cell cycle analyses and apoptosis assays on ipomoeassin F and/or its epimer were conducted. This work has laid a solid foundation for understanding the medicinal potential of the ipomoeassin family of glycolipids in the future.