Lactam

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(CC) Image: David E. Volk
Lactam structures.

In chemistry, a lactam is a cyclic amide. The name is derived from two chemical terms, lactone, referring to a cyclic ketone, and amide, a compound containing a nitrogen atom next to a carbonyl group. Lactams are named according to the size of the cyclic ring in the lactam: ${\displaystyle \alpha }$-lactams, ${\displaystyle \beta }$-lactams, ${\displaystyle \gamma }$-lactams and ${\displaystyle \delta }$-lactams contain rings made of three, four, five or six atoms, respectively. ${\displaystyle \alpha }$-lactams are also called aziridinones. Many widely used antibiotic drugs, including the penicillins and cephalosporins, owe their activity to the presence of a ${\displaystyle \beta }$-lactam structure. The lactams may have substitutions added to the nitrogen atom or any of the non-carbonyl carbon atoms in the base structure.

Synthesis of lactams[edit]

Synthesis of alpha-lactams[edit]

(CC) Image: David E. Volk
A general purpose alpha-lactam synthesis

The cyclization reaction of an ${\displaystyle \alpha }$-haloamide precuror in the presence of sodium hydride and 15-crown-5 ether at room temperature in dichloromethane (CH₂Cl₂) is a high-yielding, general route to ${\displaystyle \alpha }$-lactam (aziridinone) products. The hydrogen gas and sodium halide by-products are readily removed.^[1]

Antibiotics[edit]

(CC) Image: David E. Volk
Base structure of all cephalosporins.

The ${\displaystyle \beta }$-lactam forms the center structure of many antibiotic drugs, such as the cephalosporins and the penicillins, as shown above. In the penicillins, the non-lactam ring is one atom smaller compared to the cephalosporins. The activity of cephalosporins, penicillins, and some other antibiotics are due to the presence of the beta-lactam, which binds irreversibly, via acylation, to penicillin-binding proteins, thereby inhibiting the peptidogycan layer of bacterial cell wall synthesis. Cephalosporins and penicillins are often made semi-synthetically, using a core structure obtained from a natural organism, such as a fungus, due to the difficulty and expense of synthesizing these lactams.

References[edit]