A potent inhibitor of seryl tRNAsynthetase, designated SB-217452 has been isolated from Streptomyces sp. ATCC 700974. The fermentation, isolation, structure elucidation and some properties are described. SB-217452 showed inhibitory activity against both Staphylococcus aureus and rat seryl tRNA synthetases, with similar IC50 values of approximately 8 nM. The inhibitor is the serine linked nucleoside moiety of the antibiotic albomycin 82. In contrast to albomycin 52, SB-217452 showed only very weak antibacterial activity against a limited range of microorganisms. The compoundhas not been previously reported as a naturally occurring metabolite. In addition to SB-217452, albomycin S2 Fe3+ complex and the novel Al3+ complex were isolated from the fermentation. These complexes had no seryl tRNAsynthetase inhibitory activity. Aminoacyl-tRNA synthetases catalyze one of the most critical steps in protein biosynthesis. They attach one of twenty amino acids to one of about sixty tRNAs. Their specificities with regard to amino acids and tRNAs are responsible for the accurate primary structures of proteins. The enzymes are essential for cell viability, and are

Labelling experiments are described that identify three new compounds, N*-(2-carboxyethyl)arginine, 5-guanidino-(2-oxoazetidin-l-yl)pentanoic acid, and 3-hydroxy-5-guanidino-2-( 2-oxoazetidin-I -yl)pentanoic acid as biosynthetic precursors of proclavaminic acid and hence clavulanic acid in Streptom yces clavuligerus ATCC 27064 and a new amidino hydrolase, which hydrolyses 3-hydroxy-5-guanidino-2-(2-oxoazetidin-l -yl)pentanoic acid to proclavaminic acid has been characterised. As part of our goal to elucidate the biosynthesis of clavulanicAlso we reported4 on the production of two new arginine acid 11** we demonstrated3 that arginine 2 and not ornithine is derivatives 3 and 4 by the mutant S . clavuligerus dclH 65 which the amino acid that is processed into the biosynthetic pathway.is blocked in clavulanic acid biosynthesis. In addition, sequencing of the DNA of the clavulanic acid gene cluster identified an open reading frame, which showed homology to arginaseaS From these data we can postulate a number of possible biosynthetic sequences prior to prOClaVaminiC acid 5 which are shown in Scheme 1.

Two novel metabolites, SB 212021 and SB 212305, have been isolated from a Streptomyces and shown to have molecular formulae of C15H10N2O5 and C20H17N3O8S, respectively. The structures were deduced by a combination of NMR techniques and mass spectral fragmentation patterns and shown to be novel membersof the phenazine group of antibiotics. In the absence of added zinc, both compounds had IC50's of 1^75^for the Bacteroides fragilis 262 CfiA and Xanthomonas maltophilia h-l metallo-/Mactamases. The compounds also inhibited ACEwith IC50's of 55 and 68 fiM, respectively. Mode of action studies illustrate that the compounds inihibit some metalloenzymes by chelation of the active site metal ion. They exhibit poor antibacterial activity.Metallo/Mactamases, whilst not as prevalent in nature as their serine counterparts, do constitiute a possible threat to /Mactam chemotherapy due to the unavailability of effective inhibitors.Although only produced by a limited number of organisms they are potentially transferable by plasmids and could therefore pose a wider threat1*. The search for inhibitors of this enzyme is thus aimed at identifying structural types from natural product screening that could provide leads for chemical modification/synthesis.We report on the isolation of two novel phenazines, designated SB 212021 (1) and SB 212305 (2), produced by an unidentified Streptomyces sp. and found to inhibit zinc-dependent metallo-/Mactamase from Bacillus cereus. This paper describes the isolation, physico-chemical properties, structure determination and biological activity of SB 212021 and SB 212305. Materials and Methods Fermentation ConditionsThe unidentified Streptomyces sp. was maintained as a vegetative cell suspension stored in glycerol 10% under liquid nitrogen. Vegetative cell and spore suspension (1 ml) was used to inoculate seed medium (100ml) containing 1.5% agar. The seed stage medium consisted of yeast extract (Oxoid) 0.5%, malt extract (Oxoid) 1.0%, glycerol 1.0% and peptone soya (Oxoid) 0.5% dissolved in distilled water and adjusted to pH 6.5 before sterilisation in an autoclave at 121°C for 15 minutes. Four spiked 500 ml flasks, each containing 60 ml of seed stage mediumas defined above, were inoculated with 3 plugs from a culture plate. The inoculated flasks were incubated on a gyratory shaking table at 240 rpm for 60 hours at 28°C and after this time were used to inoculate 70 spiked 500ml flasks, each containing 60ml of seed stage medium as defined above (inoculum level ca. 5%, 3ml/flask).These inoculated flasks were shaken at 240rpm for 4.5 days at 28°C. The harvested broth was

Clavulanate-9-aldehyde 1 has been detected in Streptomyces clavuligerus and an NADPH dependent dehydrogenase capable of reducing 1 to clavulanic acid 2 has been isolated from this organism.

Twonew classes of inhibitors of LpPLA2 have been identified in fermentations ofPseudomonasfluorescens. The two structurally isomeric series differ in the geometry of closure of the bicyclic carbamate and comprise a range of compounds varying only in length of their lipophilic sidechain. The most abundant species were extracted from the cells and purified by silica and C18 chromatography. Membersof the more stable class were shown to be potent and selective competitive inhibitors of LpPLA2.Lipoprotein-associated phospholipase A2 (LpPLA2) is responsible for the conversion of phosphatidylcholine to lysophosphatidylcholine and oxidised free fatty acids during the conversion of low density lipoprotein to its oxidised form1^Both products are potent chemoattractants for circulating monocytes.2) Lysophosphatidylcholine results in rnacrophage proliferation3} and the endolithial dysfunction4'5) observed in patients with atherosclerosis.