Istamycin B

A high-performance liquid chromatography with electrospray ionization ion trap tandem mass spectrometry method was developed and validated for the robust profiling and characterization of biosynthetic congeners in the 2-deoxy-aminocyclitol istamycin pathway, from the fermentation broth of Streptomyces tenjimariensis ATCC 31603. Gradient elution on an Acquity CSH C18 column was performed with a gradient of 5 mM aqueous pentafluoropropionic acid and 50% acetonitrile. Sixteen natural istamycin congeners were profiled and quantified in descending order; istamycin A, istamycin B, istamycin A0 , istamycin B0 , istamycin B1 , istamycin A1 , istamycin C, istamycin A2 , istamycin C1 , istamycin C0 , istamycin X0 , istamycin A3 , istamycin Y0 , istamycin B3 , and istamycin FU-10 plus istamycin AP. In addition, a total of five sets of 1- or 3-epimeric pairs were chromatographically separated using a macrocyclic glycopeptide-bonded chiral column. The lower limit of quantification of istamycin-A present in S. tenjimariensis fermentation was estimated to be 2.2 ng/mL. The simultaneous identification of a wide range of 2-deoxy-aminocyclitol-type istamycin profiles from bacterial fermentation was determined for the first time by employing high-performance liquid chromatography with tandem mass spectrometry analysis and the separation of istamycin epimers.

Three strains of istamycin-producing Streptomyces tenjimariensis were isolated over a period of time from soils at the same location and were found to have three different types of plasmid profiles. Protoplast fusion between two of these strains provided a clone harboring a smaller plasmid not present in the parent strains. None of the plasmids had restriction sites for EcoR I and Hind III. Most of the plasmids had one or two restriction sites for BamH I, Bcl I, Bgl II, Kpn I, Pst I and Pvu II, and more than two restriction sites for Sal I and Sst II. Plasmid restriction maps and Southern hybridization experiments revealed that pST2, pST12 and pST22 were identical, as were pST10 and pST20. In addition, it was revealed that pST1, pST1, pST11 and pST21 were related to each other.

3-O-Demethylistamycin B derived from istamycin B was one of the most potent aminoglycoside antibiotics against various bacteria. 3-O-Demethylistamycin B, however, showed considerable acute toxicity in mice. The authors attempted to prepare the derivatives of istamycin B having high potency and low toxicity. The selective N-acylation or N-amidination at the C-2 position of istamycin B could not improve the acute toxicity. The replacement of the amino group at the C-2 position of istamycin B by a hydroxyl group markedly decreased the acute toxicity. Among 2'-deamino-2'-hydroxyistamycins, 4-N-(beta-alanyl)-2'-deamino-3-O-demethyl-2'-hydroxyistamycin B0 (9d) showed good antibacterial activity against Gram-positive and Gram-negative bacteria and a low acute toxicity in mice.