Elansolids A1/A2 (1) [1] and B1-B3 (2-4) and the structurally unusual and highly reactive elansolid A3 (5) [2] are new metabolites from the gliding bacterium Chitinophaga sancti (formerly Flexibacter spec.; Scheme 1). While elansolid A2 (1*) shows antibiotic activity against Gram-positive bacteria in the range of 0.2 to 64 mg mL À1 and cytotoxicity against L929 mouse fibroblast cells with an IC 50 value of 12 mg mL À1 , the atropisomer elansolid A1 (1) is significantly less active. [2,3] The elansolids feature a bicyclo-[4.3.0]nonane core which in the case of elansolids A1/A2 is part of a 19-membered macrolactone. Elansolid B1 is the corresponding seco acid of elansolids A1/A2, while the elansolids B2 and B3 are workup artifacts that result from nucleophilic addition of methanol and NH 3 , respectively, to

The antibiotic elansolid B1 was prepared by a convergent strategy that relied on a highly diastereoselective, biomimetic intramolecular Diels-Alder cycloaddition (IMDA) that furnished the tetrahydroindane unit. Other key features are a double Sonogashira cross-coupling and a substrate-controlled Yamamoto aldol reaction.

A series of novel 7-piperazinyl-1-substituted-6-fluoroquinolones and naphthyridines have been prepared and their antibacterial activities evaluated. These derivatives are characterized by having alkyl, alkenyl, arylalkyl, cycloalkyl, and cycloalkenyl groups at the 1-position. As a result of this study, derivatives 7 and 26, which are substituted with tert-butyl groups at N-1, were found to possess excellent in vitro and in vivo potency, particularly against Staphylococcus aureus, comparable to that of norfloxacin or ciprofloxacin. Structure-activity relationships of N-1 substituted alkyls and cycloalkyls are also discussed.

A number of 7-substituted-1-tert-butyl-6-fluoroquinolone-3-carboxylic acids and 7-substituted-1-tert-butyl-6-fluoro-1,8-naphthyridine-3-carboxylic acids have been prepared and tested for antibacterial activities. Among those the 7-aminopyrrolidinyl 20b and the 7-diazabicyclo naphthyridine 18b are the most potent compounds in vitro and in vivo. Physicochemical data and acute toxicity are also discussed. Compound 18b, BMY 40062, exhibits the most favorable overall properties, considering in vitro and in vivo microbiological activity, its low toxicity, and pharmacokinetic profile, and was selected for clinical evaluation.

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