Membrane-Targeting Neolignan-Antimicrobial Peptide Mimic Conjugates to Combat Methicillin-Resistant Staphylococcus aureus (MRSA) Infections.

Infections caused by methicillin-resistant Staphylococcus aureus (MRSA) continue to endanger public health. Here, we report the synthesis of neolignan isomagnolone (I) and its isomer II, and the preparation of a series of novel neolignan-antimicrobial peptide (AMP) mimic conjugates. Notably, conjugates III5 and III15 exhibit potent anti-MRSA activity in vitro and in vivo, comparable to that of vancomycin, a current effective treatment for MRSA. Moreover, III5 and III15 display not only fast-killing kinetics and low resistance frequency but also low toxicity as well as effects on bacterial biofilms. Mechanism studies reveal that III5 and III15 exhibit rapid bactericidal effects through binding to the phosphatidylglycerol (PG) and cardiolipin (CL) of the bacterial membrane, thereby disrupting the cell membranes and allowing increased reactive oxygen species (ROS) as well as protein and DNA leakage. The results indicate that these neolignan-AMP mimic conjugates could be promising antimicrobial candidates for combating MRSA infections.

Discovery of Natural Product-Based Fungicides (III): Semisynthesis and Biological Activity of N-Phenylpyrazole Sarisan Hybrids as Antifungal Agents.

Many phytopathogenic fungi can easily infect crops, resulting in crop yield reductions. In continuation of our efforts to develop natural product (NP)-based antifungal agents, a series of N-phenylpyrazole sarisan hybrids 6a-v were prepared via I2 -mediated oxidative cyclization, and their structures were determined by various spectral analyses including IR, 1 H-NMR and ESI-MS. Among all N-phenylpyrazole sarisan hybrids, compounds 6a, 6b, 6e, 6i, 6j and 6r exhibited more encouraging antifungal action against at least two phytopathogenic fungi than the reference fungicide hymexazol. Especially, 6a displayed really encouraging and broad-spectrum antifungal activity against F. graminearum, V. mali, and F. oxysporum f.sp.niveum with the EC50 values of 12.6±0.9, 18.5±0.2, and 37.4±1.8 µg/mL, respectively. Moreover, the structure-activity relationships (SARs) were also observed. Additionally, compounds 6a and 6e also exhibited relative low toxicity on normal LO2 cells. This study indicates that these N-phenylpyrazole sarisan hybrids would shed light on developing novel NP-based antifungal agents.

Development of Membrane-Active Honokiol/Magnolol Amphiphiles as Potent Antibacterial Agents against Methicillin-Resistant Staphylococcus aureus (MRSA).

Currently, infections caused by drug-resistant bacteria have become a new challenge in anti-infective treatment, seriously endangering public health. In our continuous effort to develop new antimicrobials, a series of novel honokiol/magnolol amphiphiles were prepared by mimicking the chemical structures and antibacterial properties of cationic antimicrobial peptides. Among them, compound 5i showed excellent antibacterial activity against Gram-positive bacteria and clinical MRSA isolates (minimum inhibitory concentrations (MICs) = 0.5-2 µg/mL) with low hemolytic and cytotoxic activities and high membrane selectivity. Moreover, 5i exhibited rapid bactericidal properties, low resistance frequency, and good capabilities of disrupting bacterial biofilms. Mechanism studies revealed that 5i destroyed bacterial cell membranes, resulting in bacterial death. Additionally, 5i displayed high biosafety and potent in vivo anti-infective potency in a murine sepsis model. Our study indicates that these honokiol/magnolol amphiphiles shed light on developing novel antibacterial agents, and 5i is a potential antibacterial candidate for combating MRSA infections.

Discovery, biological evaluation and docking studies of novel N-acyl-2-aminothiazoles fused (+)-nootkatone from Citrus paradisi Macf. as potential α-glucosidase inhibitors.

Nowadays, the discovery and development of α-glucosidase inhibitors from natural products or their derivatives represents an attractive approach. Here we reported studies on a series of novel N-acyl-2-aminothiazoles fused (+)-nootkatone and evaluation for their α-glucosidase inhibitory activities. Most of (+)-nootkatone derivatives exhibited more potent α-glucosidase inhibitory ability than the positive drug acarbose. In particular, compounds II7 and II14 showed the most promising α-glucosidase inhibitory ability with IC50 values of 13.2 and 13.8 µM. II7 and II14 also exhibited relatively low cytotoxicities towards normal LO2 cells. Kinetic study indicated that compounds II7 and II14 inhibited the α-glucosidase in a noncompetitive manner, and molecular docking results were in line with the noncompetitive characteristics that II7 and II14 did not bind to the known active sites (Asp214, Glu276 and Asp349). Based on our findings, these (+)-nootkatone derivatives could be used as antidiabetic candidates.

Discovery, Synthesis, and Biological Evaluation of Dunnianol-Based Mannich Bases against Methicillin-Resistant Staphylococcus aureus (MRSA).

Dunnianol, a natural sesqui-neoligan derived from the leaves and stems of Illicium simonsii Maxim, has been found to possess moderate antibacterial activity. To improve the antibacterial activity and solubility of dunnianol, a series of dunnianol-based Mannich bases were prepared and evaluated for their antibacterial activities. The most promising compound, 5a', exhibited excellent antibacterial activity against Staphylococcus aureus and clinically isolated methicillin-resistant Staphylococcus aureus (MRSA) with MIC values of 1 to 2 µg/mL. Structure-activity relationships indicated that the introduction of (dimethylamino)methyl at the ortho position of the phenolic hydroxyl group of dunnianol could obtain a more active compound. A mechanism study revealed that 5a' killed MRSA more rapidly than did vancomycin by disrupting the cell membrane. Moreover, 5a' was not susceptible to drug resistance development and also showed low toxicity and good antibacterial efficacy in vivo. These results indicate that the dunnianol-based Mannich base 5a' could be a promising antibiotic candidate for further research.

Application of natural products as insecticide candidates: Semisynthesis and biological evaluation of some novel osthole-based esters.

Natural products are very important sources for the development of new pesticides. Osthole, derived from many medical plants such as Cnidium, Angelica and Citrus plants, is a naturally occurring coumarin compound. To discover the new natural products-based insecticides, thirty-one osthole-based esters containing O-acyl-hydroxylamine groups were prepared, and their structures were identified by different spectral analysis methods. Derivatives A7, A17, A20 and A25 displayed more potent growth inhibitory (GI) activity than the botanical insecticide, toosendanin. Over half of target osthole derivatives had more effective larvicidal effect on P. xylostella than toosendanin. Among all title derivatives, compound A18 displayed more pronounced larvicidal activity (LC50 = 0.64 µmol mL-1) when compared with toosendanin (LC50 = 0.94 µmol mL-1). Some interesting results of structure-activity relationships (SARs) of these osthole derivatives were also discussed. In addition, the hemolysis and cytotoxicity assays indicated that these osthole derivatives showed very low toxicity toward normal mammalian cells.

Natural Product-Based Fungicides Discovery: Design, Synthesis and Antifungal Activities of Some Sarisan Analogs Containing 1,3,4-Oxadiazole Moieties.

A series of sarisan analogs containing 1,3,4-oxadiazole moieties were synthesized by iodine-mediated oxidative cyclization and screened in vitro for their antifungal activities at 50 µg/mL against five phytopathogenic fungi such as Valsa mali, Curvularia lunata, Alternaria alternate, Fusarium solani and Fusarium graminearum. 1,3,4-Oxadiazole derivatives 7e, 7p, 7r, 7t and 7u exhibited potent and a broad spectrum of antifungal activities against at least three phytopathogenic fungi at the concentration of 50 µg/mL. Especially, compound 7r displayed more potent antifungal activities against five phytopathogenic fungi than the positive control hymexazol. The EC50 of 7r against V. mali, C. lunata and A. alternate were 12.6, 14.5 and 17.0 µg/mL, respectively. Additionally, some interesting results of structure-activity relationships (SARs) were also observed.