Alkaliphilic streptomycetes strains were included in our HPLC-diode array screening program for detection of novel secondary metabolites. Strain AK 623, which was isolated from a pine wood soil collected at Hamsterley Forest, County Durham, UK, became attractive because of the appearance of a prominent peak in the HPLC chromatogram which did not correspond to any of the 700 reference compounds stored in our HPLC-UV Vis-Database2). The structure of the isolated metabolite was elucidated as a new derivative of lactonamycin3-5) and named lactonamycin Z (1). Strain AK 623 was examined for a number of key properties known to be of value in streptomycete systematic6,7). It was apparent from the resultant 16S rRNA gene sequence, and morphological and associated data that the organism should be classified as Streptomyces sanglieri8). Batch fermentations of strain AK 623 were carried out in 20-liter fermentors equipped with an intensor system (b20; Giovanola) with a medium consisting of starch 1%, glucose 1%, glycerol 1%, corn steep powder 0.25%, casein peptone 0.5%, yeast extract 0.2%, and NaCl 0.1% in tap water. The culture reached a maximal biomass of 60 vol-% after 30 hours, and production of 3.2 mg/liter of 1 was obtained after 66 hours. Compound 1 was isolated from 18 liter culture filtrate (adjusted to pH 5) by ethyl acetate extraction (4×1 liter) and separation on a LiChroprep Diol column, Fractogel TSK HW-40 chromatography, and preparative reversed-phase HPLC column, yielding 4.2 mg of pure 1 as a yellow powder soluble in DMSO and MeOH. The molecular formula of 1 was determined as C28H27NO13 (found: m/z [M+H]+ 586.15554, calcd. m/z 586.15551, rel. error: 0.05 ppm) by ESI-FTICR-MS. The structure of 1 was elucidated from its NMR data (Table 1) as a new derivative of lactonamycin with α-2,6-dideoxy ribohexose instead of α-rhodinose as the sugar moiety. The relative stereochemistry of the sugar moiety was assigned as α-2,6-dideoxy-ribohexose from vicinal coupling constant information extracted from 1H NMR and DQF-COSY spectra and corroborated by ROESY data. In summary, the structure elucidation revealed 1 to be closely related to lactonamycin, differing solely by the presence of an hydroxy group at C-3' and the relative stereochemistry at C-4' of the sugar moiety.