The new cytotoxic agents rakicidins A and B were isolated from cultured broth of a Micromonospora sp. Spectroscopic and amino acid analysis has shown that rakicidin A is a new cyclic lipopeptide, consisting of 4-amino-penta-2,4-dienoic acid, 3-hydroxy-2,4,16-trimethylheptadecanoic acid, sarcosine, and 3-hydroxyasparagine. Rakicidin B differs by one methylene group in the lipid side chain. These compounds exhibited cytotoxicity against the Ml09 cell line. In our continuing search for newantitumor agents from microorganisms, an isolate of Micromonospora was selected for further evaluation. This research led to the discovery of two newcytotoxic lipopeptides, rakicidins A and B (Fig. 1). This paper describes the fermentation, biological evaluation, purification, physico-chemical characterization, and structure elucidation of these compounds. Fermentation Microorganism The producing organism was isolated from a soil sample collected at Andhra Pradesh, India and was identified as a Micromonospora sp., strain No. R385-2. Media and Culture Conditions Micromonospora strain No. R385-2 was grown on slants of modified Bennett's mediumwhich contained the following: 0.5% Japanese potato starch (Generichem DEC. 1995 Corp. Acadama Dextrin No. 3), 0.5% glucose, 0.1% fish meat extract (Mikuni Chem. Industry), 0.1% yeast extract (Difco), 0.2% N-Z Case (Sheffield Products), 0.2% NaCl, 0.1% CaCO3, 1.5% agar. The medium was sterilized at 121°C for 20 minutes. The culture was transferred from the slant into 100ml of GERmedium in a 500ml flask. The medium contained the following: 2.4% Japanese potato starch, 0.1% dextrose, 0.3% beef extract (BBL), 0.5% tryptone (Difco), 0.5% yeast extract (BBL), 0.2% CaCO3 and was adjusted to pH 7.6 before autoclaving. The mediumwas sterilized at 121°C for 20

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Nocathiacin I (BMS-249524) is a highly cross-linked thiazolyl peptide that displays potent activity against Gram-positive bacteria, including a number of antibiotic-resistant strains. This natural product contains 10 chiral centers. NMR studies have been performed to characterize the solution structure of nocathiacin I. A uniformly 13C,15N-labeled sample was used to obtain NMR assignments. Restrained simulated annealing calculations were performed by using accurately determined NOE distance restraints. All of the chiral centers were allowed to float during the simulated annealing protocol. Two clusters of structures were obtained that satisfy the NOE restraints very well and that are reasonably consistent with vicinal J-coupling constants. Within each cluster, all 10 chiral centers are uniquely defined. The two clusters are effectively mirror images of each other: all chiral centers that have the R(S) configuration in one cluster have the S(R) configuration in the other. The single threonine residue in nocathiacin I was subsequently determined to be l-threonine by chiral capillary electrophoresis, allowing the absolute configurations of all 10 chiral centers to be defined.