Synthesis, anti-fungal activity evaluation and QSAR studies on podophyllotoxin derivatives

Discovery of Epipodophyllotoxin-Derived B2 as Promising XooFtsZ Inhibitor for Controlling Bacterial Cell Division: Structure-Based Virtual Screening, Synthesis, and SAR Study

The emergence of phytopathogenic bacteria resistant to antibacterial agents has rendered previously manageable plant diseases intractable, highlighting the need for safe and environmentally responsible agrochemicals. Inhibition of bacterial cell division by targeting bacterial cell division protein FtsZ has been proposed as a promising strategy for developing novel antibacterial agents. We previously identified 4'-demethylepipodophyllotoxin (DMEP), a naturally occurring substance isolated from the barberry species Dysosma versipellis, as a novel chemical scaffold for the development of inhibitors of FtsZ from the rice blight pathogen Xanthomonas oryzae pv. oryzae (Xoo). Therefore, constructing structure-activity relationship (SAR) studies of DMEP is indispensable for new agrochemical discovery. In this study, we performed a structure-activity relationship (SAR) study of DMEP derivatives as potential XooFtsZ inhibitors through introducing the structure-based virtual screening (SBVS) approach and various biochemical methods. Notably, prepared compound B₂, a 4'-acyloxy DMEP analog, had a 50% inhibitory concentration of 159.4 µM for inhibition of recombinant XooFtsZ GTPase, which was lower than that of the parent DMEP (278.0 µM). Compound B₂ potently inhibited Xoo growth in vitro (minimum inhibitory concentration 153 mg L^-1) and had 54.9% and 48.4% curative and protective control efficiencies against rice blight in vivo. Moreover, compound B₂ also showed low toxicity for non-target organisms, including rice plant and mammalian cell. Given these interesting results, we provide a novel strategy to discover and optimize promising bactericidal compounds for the management of plant bacterial diseases.

Preparation, characterization and biological evaluation of β-cyclodextrin-biotin conjugate based podophyllotoxin complex

Podophyllotoxin is a natural occurring aryltetralin lignin with pronounced cytotoxic activity. However, its clinical application for cancer treatment has been blocked due to its poor water solubility and selectivity. In this work, biotin as a tumor specific ligand was coupled with β-cyclodextrin and the resulting biotin modified β-cyclodextrin was used to complex with podophyllotoxin to improve its aqueous solubility and tumor selectivity. The solubility of β-cyclodextrin was greatly enhanced(>16 times) by conjugating with biotin. podophyllotoxin/ mono-6-biotin-amino-6-deoxy-β-cyclodextrin inclusion complex was prepared by freeze-drying method and the complex behavior between mono-6-biotin-amino-6-deoxy-β-cyclodextrin and podophyllotoxin was studied by water solubility, phase solubility, Job's plot, UV spectroscopy, Proton Nuclear Magnetic Resonance, Rotating-frame Overhauser Effect Spectroscopy, Powder X-ray diffraction and Scanning electron microscopy. The solubility of podophyllotoxin/ mono-6-biotin-amino-6-deoxy-β-cyclodextrin complex was greatly improved(9 times) compared with Podophyllotoxin. The stability constant of podophyllotoxin/ mono-6-biotin-amino-6-deoxy-β-cyclodextrin complex (K_s= 415.29 M^-1) was 3.2 times that of podophyllotoxin/β-cyclodextrin complex. The possible inclusion mode of podophyllotoxin/mono-6-biotin-amino-6-deoxy-β-cyclodextrin complex was inferred from the Proton Nuclear Magnetic Resonance and Rotating-frame Overhauser Effect Spectroscopy. The cellular uptake study showed that the introduction of biotin increased the cellular uptake of rhodamine-B/mono-6-biotin-amino-6-deoxy-β-cyclodextrin complex. Moreover, cell cytotoxicity study showed that the antitumor activity of podophyllotoxin/ mono-6-biotin-amino-6-deoxy-β-cyclodextrin complex was more potent than podophyllotoxin/β-cyclodextrin complex and free podophyllotoxin. The superior water solubility and enhanced cytotoxicity suggested that the mono-6-biotin-amino-6-deoxy-β-cyclodextrin associated inclusion complex might be a potential and promising delivery system for hydrophobic chemotherapeutics such as podophyllotoxin.

Total Synthesis of (+)-Galbulin and Unnatural Lignans

The total synthesis of (+)-galbulin was achieved in 15% yield and 99% ee over eight steps from commercially available 4-veratraldehyde. The key steps include Meyer's asymmetric tandem addition to a chiral 2-oxazoline-substituted naphthalene, a Pd-catalyzed stereospecific decarboxylative γ-arylation, and a formal anti-Markovnikov hydromethylation. In addition, five unnatural lignans were synthesized using the same synthetic strategy.

Structure-Antifungal Activity Relationship of Fluorinated Dihydroguaiaretic Acid Derivatives and Preventive Activity against Alternaria alternata Japanese Pear Pathotype

The structure-activity relationship of the antifungal fluorinated dihydroguaiaretic acid derivatives was evaluated. Some of the newly synthesized lignan compounds were found to show higher antifungal activity against phytopathogenic fungi such as Alternaria alternata (Japanese pear and apple pathotypes) and A. citri than the lead compound, 3-fluoro-3'-methoxylignan-4'-ol (3). The broad antifungal spectrum of 3'-hydroxyphenyl derivative 16 was observed, and the 3'-fluoro-4'-hydroxyphenyl derivative 38 was found to show the highest activity against the A. alternata Japanese pear pathotype, with an EC₅₀ value of 11 μM. The preventive effect of the potent lignan on the infection of A. alternata in the Japanese pear's leaves was also shown.

Synthesis and insecticidal activity of novel hydrazone compounds derived from a naturally occurring lignan podophyllotoxin against Mythimna separata (Walker)

In continuation of our program aimed at the discovery and development of natural-product-based insecticidal agents, a series of novel hydrazone derivatives of podophyllotoxin, which is a naturally occurring aryltetralin lignan and isolated as the main secondary metabolite from the roots and rhizomes of Podophyllum species, were synthesized and evaluated as insecticidal agents against the pre-third-instar larvae of oriental armyworm, Mythimna separata (Walker) in vivo at 1mg/mL. Especially compounds 8i, 8j, 8t, and 8u showed the more potent insecticidal activity with the final mortality rates greater than 60%.

Synthesis of 4β-acyloxypodophyllotoxin analogs modified in the C and E rings as insecticidal agents against Mythimna separata Walker

To discover the new natural-product-based insecticidal agents, four series of sixty novel 4β-acyloxypodophyllotoxin analogs modified in the C and E rings were prepared, and their insecticidal activity was tested against the pre-third-instar larvae of oriental armyworm, Mythimna separata (Walker) in vivo at the concentration of 1 mg/mL. It demonstrated that the position of the dioxo group on the E-ring of 4'-demethylepipodophyllotoxin was regioselectively controlled by the chlorine atom at its C-2' position when 2'-chloro-4'-demethylepipodophyllotoxin was oxidized by sodium periodate. Among all the derivatives, IIIi exhibited the best potent insecticidal activity with the final mortality rate of 63.3%. To alkylacyloxy series, the proper length of the side chain at the C-4 position of Ia-g, IIa-g and IIIa-g was important for their insecticidal activity.