Data on methods for the construction of the 4-quinolone skeleton and modification of the substituents around it are reviewed. The "structure-activity" relationships of 4-quinolones are examined with respect to antibacterial and antitumor activity.Keywords: 4-quinolones, biological activity. 4-Quinolones have been a subject of research for many scientific teams, and this is reflected in the numerous reviews and monographs devoted to various aspects of the subject. One of the early reviews [1] concerns aspects of the synthesis of individual representatives of the group of 4-quinolones and comparative characterization of their antimicrobial activity. Basic approaches to construction of the fluoroquinolone skeleton and also variation of the substituents at various positions of the ring were examined in the review [2]. The relationship between the structure and antibacterial activity is discussed in [3], and methods for the synthesis of polycyclic derivatives of 4-quinolones based on the annelation of rings to the various faces of the quinoline skeleton are discussed in the review [4]. The reviews [5, 6] were devoted to identification of the structural modifications of 4-quinolones responsible for their conversion from antibacterial agents to antitumor agents. The molecular and biological aspects of the antibacterial action of 4-quinolone-3-carboxylic acids are examined in [7], and issues concerned with the clinical application of 4-quinolones are discussed in the reviews [8][9][10][11][12] and in the monograph [13]. The synthesis and the "structure-activity" relationships of the bioisosteres of 4-quinolones -2-pyridones -are examined in the review [14].The aim of the present review was to classify existing methods for the synthesis not only of fluoroquinolones but also of any 4-quinolones, to demonstrate the effects of modification of the molecule at all positions, to summarize data on the various types of activity, and to examine the "structure-activity" relationship with respect to antibacterial and antitumor activity.

Specific nascent peptides in the ribosome exit tunnel can elicit translation arrest. Such ribosome stalling is used for regulation of expression of some bacterial and eukaryotic genes. The stalling is sensitive to additional cellular cues, most commonly the binding of specific small-molecular-weight cofactors to the ribosome. The role of cofactors in programmed translation arrest is unknown. By analyzing nascent peptide- and antibiotic-dependent ribosome stalling that controls inducible expression of antibiotic resistance genes in bacteria, we have found that the antibiotic is directly recognized as a part of the translation modulating signal. Even minute structural alterations preclude it from assisting in ribosome stalling, indicating the importance of precise molecular interactions of the drug with the ribosome. One of the sensors that monitor the structure of the antibiotic is the 23S rRNA residue C2610, whose mutation reduces the efficiency of nascent peptide- and antibiotic-dependent ribosome stalling. These findings establish a new paradigm of the role of the cofactor in programmed translation arrest in which a small molecule is recognized along with specific nascent peptide sequences as a composite structure that provokes arrest of translation. A similar mechanism could be used by the ribosome to sense a variety of cellular metabolites.

Class II fructose 1,6-bisphosphate aldolases (FBA; E.C. 4.1.2.13) comprise one of two families of aldolases. Instead of forming a Schiff-base intermediate using an ε-amino group of a lysine side chain, class II FBAs utilize Zn(II) to stabilize a proposed hydroxyenolate intermediate (HEI) in the reversible cleavage of fructose 1,6-bisphosphate forming glyceraldehyde 3-phosphate and dihydroxyacetone phosphate (DHAP). As class II FBAs has been shown to be essential in pathogenic bacteria, focus has been placed on these enzymes as potential antibacterial targets. Although structural studies on class II FBAs from Mycobacterium tuberculosis (MtFBA), other bacteria and protozoa have been reported, the structure of the active site loop responsible for catalyzing the protonation/deprotonation steps of the reaction for class II FBAs has not yet been observed. We therefore utilized the potent class II FBA inhibitor phosphoglycolohydroxamate (PGH) as a mimic of the HEI/DHAP bound form of the enzyme and determined the X-ray structure of MtFBA-PGH complex to 1.58 Å. Remarkably, we are able to observe well-defined electron density for the previously elusive active site loop of MtFBA trapped in a catalytically competent orientation. Utilization of this structural information plus site-directed mutagenesis and kinetic studies conducted on a series of residues within the active-site loop revealed that E169 facilitates a water mediated deprotonation/protonation step of the MtFBA reaction mechanism. Also, secondary isotope effects on MtFBA and catalytically relevant mutants were used to probe the effect of loop flexibility on catalytic efficiency. Additionally, we also reveal the structure of MtFBA in its holoenzyme form.

No abstract

No abstract

No abstract

The title compounds (I) are prepared according to a known procedure.

No abstract