Design, Synthesis, Antifungal Activity, and Molecular Docking of Streptochlorin Derivatives Containing the Nitrile Group.

Based on the structures of natural products streptochlorin and pimprinine derived from marine or soil microorganisms, a series of streptochlorin derivatives containing the nitrile group were designed and synthesized through acylation and oxidative annulation. Evaluation for antifungal activity showed that compound 3a could be regarded as the most promising candidate-it demonstrated over 85% growth inhibition against Botrytis cinerea, Gibberella zeae, and Colletotrichum lagenarium, as well as a broad antifungal spectrum in primary screening at the concentration of 50 µg/mL. The SAR study revealed that non-substituent or alkyl substituent at the 2-position of oxazole ring were favorable for antifungal activity, while aryl and monosubstituted aryl were detrimental to activity. Molecular docking models indicated that 3a formed hydrogen bonds and hydrophobic interactions with Leucyl-tRNA Synthetase, offering a perspective for the possible mechanism of action for antifungal activity of the target compounds.

Discovery of Novel Pimprinine and Streptochlorin Derivatives as Potential Antifungal Agents.

Pimprinine and streptochlorin are indole alkaloids derived from marine or soil microorganisms. In our previous study, they were promising lead compounds due to their potent bioactivity in preventing many phytopathogens, but further structural modifications are required to improve their antifungal activity. In this study, pimprinine and streptochlorin were used as parent structures with the combination strategy of their structural features. Three series of target compounds were designed and synthesized. Subsequent evaluation for antifungal activity against six common phytopathogenic fungi showed that some of thee compounds possessed excellent effects, and this is highlighted by compounds 4a and 5a, displaying 99.9% growth inhibition against Gibberella zeae and Alternaria Leaf Spot under 50 µg/mL, respectively. EC50 values indicated that compounds 4a, 5a, 8c, and 8d were even more active than Azoxystrobin and Boscalid. SAR analysis revealed the relationship between 5-(3'-indolyl)oxazole scaffold and antifungal activity, which provides useful insight into the development of new target molecules. Molecular docking models indicate that compound 4a binds with leucyl-tRNA synthetase in a similar mode as AN2690, offering a perspective on the mode of action for the study of its antifungal activity. These results suggest that compounds 4a and 5a could be regarded as novel and promising antifungal agents against phytopathogens due to their valuable potency.

Streptochlorin analogues as potential antifungal agents: Design, synthesis, antifungal activity and molecular docking study.

Streptochlorin is a small molecule of indole alkaloid isolated from marine Streptomyces sp., it is a promising lead compound due to its potent bioactivity in preventing many phytopathogens in our previous study, but further structural modifications are required to improve its antifungal activity. Our work in this paper focused on the replacement of oxazole ring in streptochlorin with the imidazole ring, to discover novel analogues. Based on this design strategy, three series of streptochlorin analogues were efficiently synthesized through sequential Vilsmeier-Haack reaction, Van Leusen imidazole synthesis and halogenation reaction. Some of the analogues displayed excellent activity in the primary assays, and this is highlighted by compounds 4g and 4i, the growth inhibition against Alternaria Leaf Spot and Rhizoctorzia solani under 50 µg/mL are 97.5% and 90.3%, respectively, even more active than those of streptochlorin, pimprinine and Osthole. Molecular docking models indicated that streptochlorin binds with Thermus thermophiles Leucyl-tRNA Synthetase in a similar mode to AN2690, offering a perspective on the mode of action study for antifungal activities of streptochlorin derivatives. Further study is still ongoing with the aim of discovering synthetic analogues, with improved antifungal activity and clear mode of action.

Pharmacokinetics and Metabolism of Streptochlorin and Its Synthetic Derivative, 5-Hydroxy-2'-isobutyl Streptochlorin, in Mice.

The purpose of this study was to investigate the pharmacokinetics and metabolism of streptochlorin and its derivative 5-hydroxy-2'-isobutyl streptochlorin (HIS) in mice. Plasma concentration of streptochlorin declined rapidly resulting in a high sustemic plasma clearance (CLp) (5.8±1.7 L/h/kg), a large volume of distribution (Vss) (1.4±0.9 L/kg) and a short half-life (t1/2) (0.4±0.1 h) after a single intravenous administration (5 mg/kg). Oral bioavailability (F) was 10.3±3.4% after a single oral administration (10 mg/kg). HIS also showed a rapid plasma decline with a high CLp (11.3±8.8 L/h/kg), a high Vss (0.8±1.0 L/kg) and a short t1/2 (0.070±0.004 h) following intravenous administration. It was not detected in plasma after oral administration. Metabolic stability studies using mouse liver microsomes and S9 fractions predicted a high hepatic clearance for both compounds, consistent with the in vivo data. Metabolite identification studies revealed three metabolic pathways for streptochlorin: monooxygenation, glucuronidation of the indole moiety and oxidative opening of the 4-chlorooxazole ring. HIS was metabolized via monooxygenation of the isobutyl chain and glucuronidation of the indole ring. These results may aid in structural optimization to mitigate the metabolic liability of streptochlorin.

Efficient Preparation of Streptochlorin from Marine Streptomyces sp. SYYLWHS-1-4 by Combination of Response Surface Methodology and High-Speed Counter-Current Chromatography.

Since first isolated from the lipophilic extract of Streptomyces sp. SF2583, streptochlorin, has attracted a lot of attention because of its various pharmacological properties, such as antibiotic, antiallergic, antitumor, and anti-inflammatory activities. For the efficient preparation of streptochlorin from a producing strain Streptomyces sp. SYYLWHS-1-4, we developed a combinative method by using response surface methodology (RSM) and high-speed counter-current chromatography (HSCCC). In the fermentation process, we used RSM to optimize the condition for the efficient accumulation of streptochlorin, and the optimal parameters were: yeast extract 1.889 g/L, soluble starch 8.636 g/L, K2HPO4 0.359 g/L, CaCl2 2.5 g/L, MgSO4 0.625 g/L, marine salt 25 g/L, medium volume 50%, initial pH value 7.0, temperature 27.5 °C, which enhanced streptochlorin yield by 17.7-fold. During the purification process, the preparative HSCCC separation was performed using a petroleum ether-ethyl acetate-methanol-water (9:0.8:5:5, v/v/v/v) biphasic solvent system, where 300 mg of crude sample yielded 16.5 mg streptochlorin with over 95% purity as determined by UPLC. Consequently, the combination method provided a feasible strategy for highly effective preparation of streptochlorin, which ensured the supply of large amounts of streptochlorin for in vivo pharmacological assessments or other requirements.

A novel synthetic derivative of melatonin, 5-hydroxy-2'-isobutyl-streptochlorin (HIS), inhibits inflammatory responses via regulation of TRIF-dependent signaling and inflammasome activation.

Melatonin is substantially reported to possess anti-inflammatory properties. In the present study, we synthesized a novel melatonin derivative, 5-hydroxy-2'-isobutyl-streptochlorin (HIS), which displayed superior anti-inflammatory properties to its parent compound. Further, we explored its underlying mechanisms in cellular and experimental animal models. Lipopolysaccharide was used to induce in vitro inflammatory responses in RAW 264.7 macrophages. LPS-primed macrophages were pulsed with biologically unrelated toxic molecules to evaluate the role of HIS on inflammasome activation. In vivo verifications were carried out using acute lung injury (ALI) and Escherichia coli-induced septic shock mouse models. HIS inhibited the production of proinflammatory mediators and cytokines such as nitric oxide, cyclooxygenase 2, IL-1ß, IL-6 and TNF-α in LPS-stimulated RAW 264.7 macrophages. HIS suppressed the infiltration of immune cells into the lung and the production of pro-inflammatory cytokines such as IL-6 and TNF-α in broncho-alveolar lavage fluid in the ALI mouse model. Mechanistic studies revealed that the inhibitory effects of HIS were mediated through the regulation of the TIR domain-containing, adaptor-inducing, interferon-ß (TRIF)-dependent signaling pathway from toll-like receptors. Further, HIS attenuated IL-1ß secretion via the inhibition of NLRP3 inflammasome activation independent of mitochondrial ROS production. Furthermore, HIS suppressed IL-1ß, IL-6 and interferon-ß production in peritoneal lavage in the Escherichia coli-induced sepsis mouse model. In conclusion, HIS exerted potent anti-inflammatory effects via the regulation of TRIF-dependent signaling and inflammasome activation. Notably, the superior anti-inflammatory properties of this derivative compared with its parent compound could be a promising lead for treating various inflammatory-mediated diseases.

Streptomyces tamarix sp. nov.: antagonism against Alternaria gaisen producing streptochlorin, isolated from Tamarix root soil.

By the end of 2021, the pear yield in Xinjiang reached 1,795,900 tons, accounting for 1/9 of the country. Pear black spot, caused by Alternaria gaisen disease, has had a significant impact on the pear industry. A. gaisen can infect nearly all pear plants, resulting in black spots on the fruit that negatively affect both yield and quality. This study focused on the TRM76323 strain of Streptomyces, which was isolated from the soil of Tamarix chinensis in Xinjiang Province. Through a multiphase classification and identification method, the genetic classification status of the antagonistic strains was determined. The study also identified the antibacterial active components of streptochlorin using modern isolation and purification techniques. The antagonistic activity of Streptomyces against Alternaria was analyzed through in vitro and in vivo experiments. This research not only expanded the resource bank of antagonistic microorganisms in extreme environments in Xinjiang, but also identified active components that could contribute to the development of new drug lead compounds. Additionally, this study presents a novel approach for the prevention and control of pear black spot disease.

Discovery of Novel Benzoxaborole-Containing Streptochlorin Derivatives as Potential Antifungal Agents.

Streptochlorin is a kind of indole alkaloid derived from marine microorganisms. It is a promising lead compound due to its potent bioactivity in preventing many phytopathogens, as shown in our previous study. To explore the potential applications of this natural product, a series of novel benzoxaborole-containing streptochlorin derivatives were designed and synthesized through a one-step and catalyst-free reaction in water at room temperature. All target compounds were first screened for their antifungal profiles in vitro against six common phytopathogenic fungi. The results of bioassay revealed that most of the designed compounds exhibited more significant antifungal activities against Botrytis cinrea, Gibberella zeae, Rhizoctorzia solani, Colletotrichum lagenarium, and alternaria leaf spot under the concentration of 50 µg/mL, and this is highlighted by compounds 4i and 5f, which demonstrated impressive antifungal effects against G. zeae and R. solani, with their corresponding EC50 values 0.2983 and 0.2657 µg/mL, which are obviously better than positive control flutriafol and boscalid (5.2606 and 1.2048 µg/mL, respectively). Scanning electron microscopy on the hyphae morphology showed that compound 5b might cause mycelial abnormalities of G. zeae. 3D-QSAR studies of CoMFA and CoMSIA were carried out on 29 target compounds with antifungal activity against B. cinrea. The analysis results indicated that introducing appropriate electronegative groups at the 5-position of benzoxaborole and the 4,5-positions of the indole ring could effectively improve the anti-B. cinrea activity. Moreover, compound 5b showed good antifungal activities in vivo against Phytophthora capsici. Molecular docking was further explored to ascertain the practical value of the active compound as a potential inhibitor of LeuRS. The abovementioned results indicate that the designed benzoxaborole-containing streptochlorin derivatives could be further studied as template molecules of novel antifungal agents.

An efficient synthesis and antifungal evaluation of natural product streptochlorin and its analogues.

Streptochlorin, a small indole alkaloid isolated from marine Streptomyces sp., exhibits a wide range of potent biological activities. An efficient and economic synthetic protocol for streptochlorin has been developed and validated, 4 steps from indole in a total yield of 45%, and further applied for the synthesis of its analogues. Biological testing showed that most of the target compounds exhibited potential antifungal activity in the primary assays, especially compounds 6, 7 and 9c were the most active ones, representing effective activity against the phytopathogenic fungi screened in preliminary test and might be explored for the study of mode of action in the future.

Synthesis and antifungal activity of novel indole-replaced streptochlorin analogues.

Based on examples of the successful applications in drug discovery of bioisosterism, a series of streptochlorin analogues in which indole has been replaced by other heterocycles has been designed and synthesized, as a continuation of our studies aimed at the discovery of novel streptochlorin analogues with improved antifungal activity. Biological testing showed that most of the indole-replaced streptochlorin analogues were inactive, though compound 6f had a broad spectrum of antifungal activity with significant activity against Alternaria solani. The SAR study demonstrated that indole ring is an essential moiety for the antifungal activity of streptochlorin analogues, promoting the idea of indole ring as a framework that might be exploited in the future.

Anticancer activity of streptochlorin, a novel antineoplastic agent, in cholangiocarcinoma.

BACKGROUND: The aim of this study is to investigate the anticancer activity of streptochlorin, a novel antineoplastic agent, in cholangiocarcinoma. METHODS: The anticancer activity of streptochlorin was evaluated in vitro in various cholangiocarcinoma cell lines for apoptosis, proliferation, invasiveness, and expression of various protein levels. A liver metastasis model was prepared by splenic injection of HuCC-T1 cholangiocarcinoma cells using a BALB/c nude mouse model to study the systemic antimetastatic efficacy of streptochlorin 5 mg/kg at 8 weeks. The antitumor efficacy of subcutaneously injected streptochlorin was also assessed using a solid tumor xenograft model of SNU478 cells for 22 days in the BALB/c nude mouse. RESULTS: Streptochlorin inhibited growth and secretion of vascular endothelial growth factor by cholangiocarcinoma cells in a dose-dependent manner and induced apoptosis in vitro. In addition, streptochlorin effectively inhibited invasion and migration of cholangiocarcinoma cells. Secretion of vascular endothelial growth factor and activity of matrix metalloproteinase-9 in cholangiocarcinoma cells were also suppressed by treatment with streptochlorin. Streptochlorin effectively regulated metastasis of HuCC-T1 cells in a mouse model of liver metastasis. In a tumor xenograft study using SNU478 cells, streptochlorin significantly inhibited tumor growth without changes in body weight when compared with the control. CONCLUSION: These results reveal that streptochlorin is a promising chemotherapeutic agent to the treatment of cholangiocarcinoma.

Synthesis and antifungal activity of novel streptochlorin analogues.

Streptochlorin, first isolated as a new antibiotic in 1988 from the lipophilic extracts of the mycelium of a Streptomyces sp, is an indole natural products with a variety of biological activities. Based on the methods developed for the synthesis of pimprinine in our laboratory, we have synthesized a series of indole-modified streptochlorin analogues and measured their activities against seven phytopathogenic fungi. Some of the analogues displayed good activity in the primary assays, and the seven compounds 10b, 10c, 11e, 13e, 21, 22c and 22e (shown in Figure 1) were identified as the most promising candidates for further study. Structural optimization is still ongoing with the aim of discovering synthetic analogues with improved antifungal activity.