Patent specification for "Nitrogen-containing compounds and their use". Field of the Invention The invention relates to nitrogen-containing compounds, their preparation and their use in preventing or treating bacterial infections. BACKGROUND OF THE INVENTION The emergence of bacterial resistance to known antibacterial agents is becoming a major challenge in treating bacterial infections. An advanced way to treat bacterial infections, and especially those caused by resistant bacteria, is to develop newer antibacterial agents that can overcome bacterial resistance. Coates et al. (Br. J. Pharmacol. 2007； 152 (8), 1147-1154.) reviewed new methods for developing new antibiotics. however, the development of new antibacterial agents is a challenging task. for example, Gwynn et al. (Annals of the New York Academy of Sciences, 2010, 1213: 5-19) reviewed the challenges in discovering antibacterial agents. Another method for overcoming bacterial resistance to known antibacterial agents is to target bacterial mechanisms, which help them acquire and maintain resistance. For example, various bacteria are known to produce enzymes (beta-lactamase enzymes) that hydrolyze the beta-lactam ring into a typical beta-lactam antibacterial agent. Since the beta-lactam ring is hydrolyzed, antibacterial agents become ineffective against these bacteria. Bacteria are known to produce various types of beta-lactamase enzymes. depending on their amino acid sequence homologies, beta-lactamase enzymes are broadly classified into four classes: a, b, c, and d (ambler r. p., phil. trans. r. soc. lon., b289, 321-331, 1980). beta-lactamase enzymes belonging to classes a, c and d use serine as the active site to facilitate catalysis, whereas those belonging to class b contain one or more metal ions (eg zinc ions) at the active site to facilitate catalysis. beta-lactam cleavage. Various compounds, generally known as beta-lactamase inhibitors, are capable of inhibiting the activity of one or more beta-lacta
