Plants sense potential pathogens by recognizing conserved pathogen-associated molecular patterns (PAMPs) that cause PAMP-triggered immunity (PTI). We previously reported that rice recognizes flagellin from the rice-incompatible N1141 strain of Acidovorax avenae and subsequently induces immune responses. Cell extracts isolated from flagellin-deficient N1141 (Δfla1141) still induced PTI responses, suggesting that Δfla1141 possesses an additional PAMP distinct from flagellin. Here, we show that elongation factor Tu (EF-Tu), one of the most abundant bacterial proteins, acts as a PAMP in rice and causes several PTI responses. In Brassicaceae species, EF-Tu and an N-acetylated peptide comprising the first 18 amino acids of the N-terminus, termed elf18, are fully active as inducers of PTI responses. By contrast, elf18 did not cause any immune responses in rice, whereas an EF-Tu middle region comprising Lys176 to Gly225, termed EFa50, is fully active as a PAMP in rice. In the leaves of rice plants, EF-Tu induced H2O2 generation and callose deposition, and also triggered resistance to coinfection with pathogenic bacteria. Taken together, these data demonstrate that rice recognizes EFa50, which is distinct from elf18, and that this epitope induces PTI responses.

Structure-activity relationships of the west amino acid modified analogues of rhodopeptins, novel antifungal tetrapeptide isolated from Rhodococcus species Mer-N1033, have been investigated. Among the analogues synthesized, 2,2-difluoro and 2-hydroxy derivatives retained the antifungal activity with better physical properties, i.e., solubility or acute toxicity.

The substrate activity screening (SAS) method, a substrate-based fragment identification and optimization method for the development of enzyme inhibitors, was previously applied to cathepsin S to obtain a novel (2-arylphenoxy)acetaldehyde inhibitor, 2, with a 0.49 microM Ki value (Wood, W. J. L.; Patterson, A. W.; Tsuruoka, H.; Jain, R. K.; Ellman, J. A. J. Am. Chem. Soc. 2005, 127, 15521-15527). In this paper we disclose the X-ray structure of a complex between cathepsin S and inhibitor 2 which reveals an unprecedented binding mode. On the basis of this structure, additional 2-biaryloxy substrates with greatly increased cleavage efficiency were designed. Conversion of the optimized substrates to the corresponding aldehyde inhibitors yielded a low molecular weight (304 Daltons) and potent (9.6 nM) cathepsin S inhibitor that showed from 100- to >1000-fold selectivity relative to cathepsins B, L, and K.

A series of novel 5-amino-6-fluoro-1-[(1R,2S)-2-fluorocyclopropan-1-yl]-8-methylquinolones bearing fluorinated (3R)-3-(1-aminocyclopropan-1-yl)pyrrolidin-1-yl substituents at the C-7 position (2-4) was synthesized to obtain potent drugs for infections caused by Gram-positive pathogens, which include resistant strains such as methicillin-resistant Staphylococcus aureus (MRSA), penicillin-resistant Streptococcus pneumoniae (PRSP), and vancomycin-resistant enterococci (VRE). These fluorinated compounds 2-4 exhibited potent antibacterial activity comparable with that of a compound bearing a non-fluorinated (3R)-3-(1-aminocyclopropan-1-yl)pyrrolidine moiety at the C-7 position (1) and had at least 4 times more potent activity against representative Gram-positive bacteria than ciprofloxacin (CPFX), gatifloxacin (GFLX), or moxifloxacin (MFLX). Among them, the 7-[(3S,4R)-4-(1-aminocyclopropan-1-yl)-3-fluoropyrrolidin-1-yl] derivative 3 (=DQ-113), which showed favorable profiles in preliminary toxicological and nonclinical pharmcokinetic studies, exhibited potent antibacterial activity against clinically isolated resistant Gram-positive pathogens.

Novel 7-[7-amino-7-methyl-5-azaspiro[2.4]heptan-5-yl]-6-fluoro-1-[(1R,2S)-2-fluorocyclopropyl]- 8-methoxy-1,4-dihydro-4-oxoquinoline-3-carboxylic acid 2a and 2b were designed and synthesized to obtain potent antibacterial drugs for the treatment of respiratory tract infections. Among these, compound 2a possessing (S)-configuration for the asymmetrical carbon on the pyrolidine moiety at the C-7 position of the quinolone scaffold exhibited potent in vitro antibacterial activity against respiratory pathogens including gram-positive (Streptococcus pneumoniae and Staphylococcus aureus), gram-negative (Haemophilus influenzae and Moraxcella catarrhalis), and atypical strains (Chalmydia pneumoniae and Mycoplasma pneumoniae), as well as multidrug-resistant Streptococcus pneumoniae and quinolone-resistant and methicillin-resistant Staphylococcus aureus). Furthermore, compound 2a showed excellent in vivo activity against the experimental murine pneumonia model due to multidrug resistant Streptococcus pneumoniae (MDRSP) and favorable profiles in preliminary toxicological and nonclinical pharmacokinetic studies.