The differences between the 1H and 13C NMR data of 3 and 2 were also observed we found a chemical shift of C-9 downfield 2.6 p.p.m., C-10 upfield 2.2 p.p.m., C-11 upfield 1.1 p.p.m. This indicated that streptolidine lactam was converted into acid for compound 3. The hypothesis is also proved by the results of ESI-MS/MS m/z 171, which was assigned to streptolidine, was a characteristic ion peak of STs, whereas the corresponding ion was observed at m/z 189 in the spectrum of 3. Compound 3 was assumed to be the ST acid type compound. By comparing the 1H and 13C NMR data of 3 with those of ST-D acid ( 2), we found that the chemical shift of C-4, C-5 in the 13C NMR spectra and the chemical shift of H-4 and H-5 in the 1H NMR spectra were not different. The spectral characteristics were very similar to those of STs. The NMR spectral data ( Tables 1 and 2) suggested the presence of two amido groups, one carboxylic acid group, one carbamoyl group and one guanidino group. The IR spectra showed the characteristic absorption bands at 16 cm −1, which revealed the existence of a peptide bond. 7, 8Ĭompound 3 was obtained as a colorless amorphous powder. Compounds 1 and 2 were identified as ST-F acid and ST-D acid on the basis of the M.P., IR, MS and NMR data. Two known compounds ( 1, 2) and three novel compounds ( 3– 5) were obtained from the fermentation broth of S. The results indicated that 1–5 exhibited less antibacterial activities when compared with that of ST-D, but the extent of decrease varied with the structures.Ĭompound 4: colorless amorphous powder, m.p. The antibacterial activities of 1–5 against Escherichia coli, Bacillus subtilis, Staphylococcus aureus, Bacillus cereus and Pseudomonas aeruginosa were assayed by means of micro-broth dilution. These compounds were identified as two known compounds, ST-F acid ( 1) and ST-D acid ( 2), and three new compounds, 12-carbamoylstreptothricin E acid ( 3), 12-carbamoylstreptothricin D acid ( 4) and N-acetylstreptothricin D acid ( 5). Here, we report the isolation, structure elucidation and antibacterial activities of five ST acids that were isolated by ion-exchange resin chromatography and preparative RP-HPLC from the fermentation broth of S. 10 A total of 19 ST-like compounds were identified or tentatively characterized on the basis of their mass spectral data among them, 12 were ST acids.
9 In subsequent research, a facile LC-MS/MS method based on RP-HPLC coupled with electrospray ionization tandem mass spectrometry was used for the analysis of STs in the fermentation broth of S. ST-F, ST-D and two other novel compounds, 12-carbamoyl-ST-F and 12-carbamoyl-ST-D, have been isolated from its fermentation broth in our laboratory. qinlingensis, a ST producer, was isolated from soil samples. In the process of screening for new antibiotics, S. 7, 8 In addition, only the bio-activities of ST-F and ST-D acids have been investigated. Attempts at preparing ST acids were made from STs chemically, but only ST-F acid, which bears one β-lysine, was readily obtained, whereas others that bear more β-lysine residues were not prepared successfully. These results suggest that ST-D acid is a potential candidate for clinical development or use as a new lead compound for drug discovery. With the breaking of the amide bond, the antimicrobial activity of streptothricin D (ST-D) was altered from broad-spectrum to bacteria-specific, and its toxicity against eukaryotic cells was also reduced at the same time. 6 isolated a novel ST-resistance gene (sttH) and showed that the hydrolysis of the amide bond of streptolidine lactam could be catalyzed by the enzyme in vitro. Although they were shown to possess strong antimicrobial activity against many species of fungi and bacteria, their application in the therapeutic area has been hampered because of the nephrotoxicity. As streptothricin F was isolated from Streptomyces lavendulae in 1942, 1 dozens of streptothricins (STs) have been isolated from natural resources. Streptothricin antibiotic is a type of broad-spectrum antibiotics.
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