The structures of new antitumor antibiotics, glidobactins A (la), B (Ib) and C (Ic) were elucidated by a combination of chemical and enzymatic degradations and spectral analyses. They have in common a cyclized tripeptide nucleus composedof L-threonine, 4(S)-amino-2CE>pentenoic acid and (?ry^r-4-hydroxy-L-lysine, and differ from each other in the unsaturated fatty acid moiety attached to the peptide. In the course of continuing search for novel antitumor antibiotics in the microbial metabolites, Polyangium brachysporum sp. nov. No. K481-B101 (ATCC 53080) collected in Greece was found to produce novel antibiotic complex with antifungal and antitumor activity1~3). The antibiotic complex named glidobactin was extracted and separated into three active components, glidobactins A (la), B (Ib) and C (Ic). In addition to their broad antifungal activity, all the components exhibited potent antitumor activity against P388 leukemia implanted in mice with the T/C values in the range of 200 to 250%. In this report, we present structural studies of la, Ib and Ic, which have shown unique acylated 1 2 memberedcyclic peptide structures. Spectral Characteristics Glidobactins A (la), B (Ib) and C (Ic) were isolated from the fermentation broth of strain K481-B101 by butanol extraction followed by column chromatographies on silica gel and reversed phase silica gel. la and Ic were obtained as colorless needles from aqueous methanol and methanol, respectively, while Ib was isolated as crystalline powder. la: C27H44N4O6;mlz 520 (M+); mp 2592 61°C; M2D4-111°(c 0.5, MeOH). Ib: C29H46N4O6; m/z 546 (M+); mp 232~234°C; M2D4-92°(c 0.5, MeOH). Ic: C29H48N4O6; m\z 548 (M+); mp 273~275°C; M2D4-104°(c 0.5, MeOH). The UVspectra of the three components exhibited the same absorption maximumat 261 nm in methanol suggesting the presence of an a^^d-unsaturated carbonyl functionality. The IR absorption at around 1630 and 1540 cm"1 indicated amide group in their molecules, as described in the preceding paper3).
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