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Ro 23-9424 is a broad-spectrum antibacterial agent composed of a cephalosporin and a quinolone moiety. Its biological properties were compared with those of its two components and structurally related cephalosporins and quinolones. Like ceftriaxone and cefotaxime but unlike its decomposition product, desacetyl cefotaxime, Ro 23-9424 bound at c2 ,ug/ml to the essential penicillin-binding proteins lb and 3 of Escherichia coli and 1, 2, and 3 of Staphylococcus aureus. In E. coli, Keith, 28th ICAAC, abstr. no. 448, 1988

Novel cyclic lipopeptides with different acyl tails were synthesized via a semisynthetic approach. Structure-activity relationship studies revealed that lipophilicity, chain length, and the location of key aromatic functionalities of the tail modulated activity. The lead compound surotomycin exhibited significantly improved in vitro activity compared with daptomycin (MIC90 0.5 vs 2 μg/mL) against Clostridium difficile including NAP1 epidemic strains. In hamster efficacy studies, surotomycin protected animals at a dose of 0.5 mg/kg, PO.

We have recently reported the structure and synthesis of undecylprodigiosin (II), a C-25 prodigiosin analog isolated from a strain of Streptomyces.1 At that time it was noted that another more complex C-25 prodigiosin-like pigment was formed concurrently with II. In this communication we describe the isolation and structure determination of this product. Formulated as I,1 2 this new tripyrrole pigment incorporates the unusual structural feature of a meta-bridged pyrrole, the first such system to be observed in a natural product. We propose the trivial name metacycloprodigiosin for this new pigment (I),3 the synthesis of which is described in the accompanying report.4 _ OMe ?-^¡^ " \ II (1) .

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