世界卫星数字音频广播简析

本文简要回顾了世界卫星数字音频广播的源起和发展历程，并解析了卫星数字音频广播陷入困境的原因。     

Structure–antibacterial relationship of nigericin derivatives

Two new polyether antibiotics 3, 5 together with three known ones 1, 2, 4 were isolated from Streptomyces hygroscopicus XM201. Based on the unambiguous NMR data assignments, their structures were determined to be 30-acetyl nigericin (1), 1-O-methyl-30-acetyl nigericin (2), 1,29-O-dimethyl-30-acetyl nigericin (3), nigericin (4), and 29-O-methyl abierixin (5), respectively. The antibacterial activities of the nigericin derivatives 1–4 were studied. Compounds 1 and 4 showed strong activities against Staphylococcus aureus ATCC25923 and Bacillus cereus 1126 with MIC of 0.25 μg/mL and 0.125 μg/mL, respectively. No inhibitory activities were observed against Escherichia coli CMCC44103 at a concentration of 25 μg/mL. Only 1 and 4 showed distinguished effects on the protoplast regeneration clones of B. cereus 1126 and E. coli CMCC44103 at a concentration of 1 μg/mL. Published in Khimiya Prirodnykh Soedinenii, No. 3, pp. 285–288, May–June, 2009.