Design, Synthesis, and Mode of Action of Thioacetamide Derivatives as the Algicide Candidate Based on Active Substructure Splicing Strategy.

Lakes and reservoirs worldwide are experiencing a growing problem with harmful cyanobacterial blooms (HCBs), which have significant implications for ecosystem health and water quality. Algaecide is an effective way to control HCBs effectively. In this study, we applied an active substructure splicing strategy for rapid discovery of algicides. Through this strategy, we first optimized the structure of the lead compound S5, designed and synthesized three series of thioacetamide derivatives (series A, B, C), and then evaluated their algicidal activities. Finally, compound A3 with excellent performance was found, which accelerated the process of discovering and developing new algicides. The biological activity assay data showed that A3 had a significant inhibitory effect on M. aeruginosa. FACHB905 (EC50 = 0.46 µM) and Synechocystis sp. PCC6803 (EC50 = 0.95 µM), which was better than the commercial algicide prometryn (M. aeruginosa. FACHB905, EC50 = 6.52 µM; Synechocystis sp. PCC6803, EC50 = 4.64 µM) as well as better than lead compound S5 (M. aeruginosa. FACHB905, EC50 = 8.80 µM; Synechocystis sp. PCC6803, EC50 = 7.70 µM). The relationship between the surface electrostatic potential, chemical reactivity, and global electrophilicity of the compounds and their activities was discussed by density functional theory (DFT). Physiological and biochemical studies have shown that A3 might affect the photosynthesis pathway and antioxidant system in cyanobacteria, resulting in the morphological changes of cyanobacterial cells. Our work demonstrated that A3 might be a promising candidate for the development of novel algicides and provided a new active skeleton for the development of subsequent chemical algicides.

Design, Synthesis, and Bioassay for the Thiadiazole-Bridged Thioacetamide Compound as Cy-FBP/SBPase Inhibitors Based on Catalytic Mechanism Virtual Screening.

Cyanobacterial fructose-1,6-/sedoheptulose-1,7-bisphosphatase (Cy-FBP/SBPase) was an important regulatory enzyme in cyanobacterial photosynthesis and was a potential target enzyme for screening to obtain novel inhibitors against cyanobacterial blooms. In this study, we developed a novel pharmacophore screening model based on the catalytic mechanism and substrate structure of Cy-FBP/SBPase and screened 26 S series compounds with different structures and pharmacophore characteristics from the Specs database by computer-assisted drug screening. These compounds exhibited moderate inhibitory activity against Cy-FBP/SBPase, with 9 compounds inhibiting >50% at 100 µM. Among them, compound S5 showed excellent inhibitory activity against both Cy-FBP/SBPase and Synechocystis sp. PCC6803 (IC50 = 6.7 ± 0.7 µM and EC50 = 7.7 ± 1.4 µM). The binding mode of compound S5 to Cy-FBP/SBPase was predicted using the molecular docking theory and validated by sentinel mutation and enzyme activity analysis. Physiochemical, gene transcription level, and metabolomic analyses showed that compound S5 significantly reduced the quantum yield of photosystem II and the maximum electron transfer rate, downregulated transcript levels of related genes encoding the Calvin cycle and photosystem, reduced the photosynthetic efficiency of cyanobacteria, thus inhibited metabolic pathways, such as the Calvin cycle and tricarboxylic acid cycle, and eventually achieved an efficient algicide. In addition, compound S5 had a high safety profile for human-derived cells and zebrafish. In summary, the novel pharmacophore screening model obtained from the current work provides an effective solution to the cyanobacterial bloom problem.

Design, synthesis and mechanism research of novel algicide based on bioactive fragments synthesis strategy.

The frequency and intensity of harmful cyanobacterial blooms (HCBs) are increasing all over the world, their prevention and control have become a great challenge. In this paper, a series of 1,3,4-thiadiazole thioacetamides (T series) were designed and synthesized as potential algaecides. Among them, the compound T3 showed its best algacidal activity against Synechocystis sp. PCC 6803 (PCC 6803, EC50 = 1.51 µM) and Microcystis aeruginosa FACHB 905 (FACHB905, EC50 = 4.88 µM), which was more effective than the lead compound L1 (PCC6803, EC50 = 7.7 µM; FACHB905, EC50 = 8.8 µM) and the commercially available herbicide prometryn (PCC6803, EC50 = 4.64 µM；FACHB905, EC50 = 6.52 µM). Meanwhile, T3 showed a lower inhibitory activity (EC50 = 12.76 µM) than prometryn (EC50 = 7.98 µM) to Chlorella FACHB1227, indicating that T3 had selective inhibition to prokaryotic algae (PCC6803, FACHB905) and eukaryotic algae (FACHB1227). Furthermore, the algacidal and anti-algae activities of T3 were significantly better than those of prometryn, while the toxicity of zebrafish and human cells was less than prometryn. Electron microscope, physiological, biochemical and metabonomic analysis showed that T3 interfered with light absorption and light conversion during photosynthesis by significantly reducing chlorophyll content, thus inhibited metabolic pathways such as the Calvin cycle and TCA cycle, and eventually led to the cell rupture of cyanobacteria. These results afforded further development of effective and safe algaecides.

[Role of melatonin in spatial learning and memory in rats and its mechanism].

It has been suggested that melatonin is involved in learning and memory. In the present study, we investigated the effects of melatonin on spatial learning and memory in rats, using Morris water maze and electrophysiological methods. The results are as follows. (1) During a six-day water maze training, the mean escape latency of melatonin group in the last 4 days was 30.02+/-3.6 s, and that of control group was 18.44+/-2.7 s (P<0.01). The crossing annulus coefficient of melatonin group was 25.68+/-2.32%, and that of control group was 43.33+/-2.85% (P<0.01). (2) Microinjection of melatonin into CA1 area inhibited long-term potentiation (LTP). Sixty minutes after tetanus, the field excitory postsynaptic potentials (fEPSP) slope of group C (n=7 0.5 microliter saline) was 169.71+/-6.48 % of the baseline, and that of group M2 (n=6, 2 microgram melatonin) was 114.28+/-1.80% of the baseline. The difference is significant (P<0.01). (3) We also investigated the effects of melatonin on LTP after administration of scopolamine. Sixty minutes after tetanus, the fEPSP slope of group SM (n=6, 2 microgram scopolamine before 2 microgram melatonin) was 113.70+/-5.55% of the baseline. It showed a significant decrease compared with group C (P<0.01). However, there was no difference between groups SM and M2 (P>0.05, i.v.). The results obtained by applying melatonin after bicuculline were different from those after scopolamine. Sixty minutes after tetanus, the fEPSP slope of group BM (n=7, 1 microgram bicuculline before 2 microgram melatonin) was 162.29+/>10.52% of the baseline. Compared with group C, there is no significant difference (P>0.05); but compared with group M2, the difference is significant (P<0.01). Our results showed that application of melatonin in rats significantly inhibited not only spatial learning and memory, but also LTP in CA1 area. Furthermore, the results indicate that the inhibition of LTP by melatonin may not be mediated by cholinergic system, but may be through the modulation of GABAergic system.