Antibacterial Optimization of 4-Aminothiazolyl Analogues of the Natural Product GE2270 A: Identification of the Cycloalkylcarboxylic Acids Matthew J. LaMarche,* ,† Jennifer A. Leeds, ‡ Kerri Amaral, ‡ Jason T. Brewer, † Simon M. Bushell, † Janetta M. Dewhurst, † JoAnne Dzink-Fox, ‡ Eric Gangl, † Julie Goldovitz, ‡ Akash Jain, ∥ Steve Mullin, ‡ Georg Neckermann, ‡ Colin Osborne, ‡ Deborah Palestrant, § Michael A. Patane, † Elin M. Rann, † Meena Sachdeva, ‡ Jian Shao, † Stacey Tiamfook, ‡ Lewis Whitehead, † and Donghui Yu ‡ † Global Discovery Chemistry, ‡ Infectious Disease Area, and § Protein Structure Group, Novartis Institutes for Biomedical Research, Cambridge, Massachusetts 02139, United States ∥ Chemical and Pharmaceutical Profiling, Novartis Pharmaceuticals, Cambridge, Massachusetts 02139, United States * S Supporting Information ABSTRACT: 4-Aminothiazolyl analogues of the antibiotic natural product GE2270 A (1) were designed, synthesized, and optimized for their activity against Gram positive bacterial infections. Optimization efforts focused on improving the physicochemical properties (e.g., aqueous solubility and chemical stability) of the 4-aminothiazolyl natural product template while improving the in vitro and in vivo antibacterial activity. Structure−activity relationships were defined, and the solubility and efficacy profiles were improved over those of previous analogues and 1. These studies identified novel, potent, soluble, and efficacious elongation factor-Tu inhibitors, which bear cycloalkylcarboxylic acid side chains, and culminated in the selection of development candidates amide 48 and urethane 58. ■ INTRODUCTION Clinical resistance to marketed drugs is becoming increasingly common. 1 Therefore, the discovery of antibiotics that act via novel mechanisms of action remains a pressing unmet medical need in infectious disease care. In particular, treating Gram positive skin and soft tissue infections caused by methicillin resistant S. aureus, vancomycin resistant enterococci, and group A streptococci remain distinct clinical challenges. In 1991, Selva and co-workers from Lepetit Research Institute reported the structure and antibiotic activity of GE2270 A (1, Figure 1). This thiopepetide-based natural product was isolated from a fermentation broth of Planobispora rosea and found to inhibit the prokaryotic chaperone elongation factor Tu (EF-Tu). 2 The in vitro antibiotic profile against methicillin resistant staph- ylococci, vancomycin resistant enterococci, and group A streptococci was exquisite, with minimum inhibitory concen- trations below 1 μg/mL. Previously, we described lead finding activities associated with 1 concerning the identification, decomposition, and subsequent stabilization of 4-aminothiazolyl analogues. 3 Because of promising initial in vitro results, the 4-amino- thiazolyl template was selected for further medicinal chemistry optimization. Specifically, a substantial increase in aqueous solubility would be necessary in order to formulate the compounds for infused intravenous drug delivery, as the aqueous solubility of 1 was undetectable in our assays (detection limit, 5 ng/mL). The improved aqueous solubility and formulatability would allow for in vivo efficacy evaluation in murine infection models (vide infra), an important preclinical milestone for this novel antibacterial chemical template, and also allow for comparison to the standards of care for soft tissue infections (i.e., linezolid, daptomycin). As part of the strategy to further chemically stabilize the 4- aminothiazole macrocyclic appendage while increasing intrinsic aqueous solubility and improving cellular antibacterial activity, a variety of linkers, spacers, and termini were examined (Tables 1−5). Four organisms comprised our antibiotic activity characterization efforts: Enterococcus faecalis, Enterococcus faecium, Staphylococcus aureus, and Streptococcus pyogenes. 4 In addition, the antibacterial activity of all analogues against Steptococcus pneumonia (not shown) did not differ significantly compared to Streptococcus pyogenes. In order to confirm that the novel analogues were acting via inhibition of EF-Tu, all Received: July 14, 2011 Published: October 14, 2011 Article pubs.acs.org/jmc © 2011 American Chemical Society 8099 dx.doi.org/10.1021/jm200938f | J. Med. Chem. 2011, 54, 8099−8109