William Henry Koster

4-Alkylated monobactams : Chiral synthesis and antibacterial activity

Abstract The synthesis of 4-alkylated monobactams by a variety of procedures is described. Two complementary procedures have been developed for the chiral synthesis of rnonobactams. (1) sulfonation of 4-alkyl-3-(protected)amino-2-azetidinones with vanous complexes of SO3, and (2) cyclization of β mesyloxyacyl sulfamates derived from β-alkyl-β-hydroxy-α-amino acids The most general procedure involves introduction of the alkyl group via a Grignard reaction on 6-APA-derived sulfones 23 or 24 followed by sulfonation. For the specific case of (3S,trans)-3-amino-4-methylmonobactamic acid (48). cyclization of the β-mesyloxyacyl sulfamate 40 derived from (L)-threonine is the preferred route. The introduction of 4-alkyl groups into monobactams results in a decrease in activity against gram-positive bacteria, an increase in activity against gram-negative bacteria, and an increase in β-lactamase stability. Increasing the size of the alkyl group beyond methyl results in diminished intrinsic antibacterial activity. 4β-Alkylmonobactams display better β-lactamase stability than their 4α-counterparts.

Beta-lactam antibiotics

Beta-lactam drugs, whose mechanism of action is inhibition of the last stage of bacterial cell wall synthesis, are the largest family of antimicrobial agents and the most widely used in current clinical practice. These drugs have a slow, time-dependent bactericidal action, generally good distribution in the body, and low toxicity. Modifications of the original molecule have led to new compounds with a greater antimicrobial spectrum and activity; nonetheless, the use and efficacy of beta-lactams is limited in some clinical settings, owing to the increasing emergence of antimicrobial resistance. Despite this problem, penicillin remains the treatment of choice in a large number of infections, cephalosporins have a wide range of indications, carbapenems are used in nosocomially-acquired infection and infection caused by multiresistant microorganisms, and beta-lactam inhibitors restore the spectrum of activity of their companion penicillins (aminopenicillins, ureidopenicillins) when resistance is caused by beta lactamase production.

The New Monobactams: Chemistry and Biology

The discovery of the monobactams led to the successful development of aztreonam as the first of this novel class of beta‐lactam antibiotics to enter the clinical field. Continued structural modification on the monobactam nucleus has resulted in two additional compounds from this class that show interesting biologic properties. The first, SQ 83,360, is like aztreonam in exhibiting high activity against members of the Enterobacteriaceae but has the added characteristic of being exceptionally active against strains of Pseudomonas aeruginosa. Also, significant gains are made with SQ 83,360 in activity against Pseudomonas spp. and Acinetobacter. The second compound, tigemonam, is also like aztreonam, having good activity against Enterobacteriaceae, Haemophilus influenzae, and Neisseria gonorrhoeae and showing good beta‐lactam stability. Tigemonam differs from aztreonam in being well absorbed orally by experimental laboratory animals.