The University of the West Indies
*St. Augustine Campus*
Faculty of Medical Sciences
School of Pharmacy
Course: MICROBIOLOGY, IMMUNOLOGY AND GENERAL
PATHOLOGY (PHAR 2401)
07/10/2019
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Prepared By: Dr. Rajiv Dahiya
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ANTIBACTERIAL AGENTS
Antibacterials are class of drugs which
are effective in bacterial infections. They
can be:
 Bactericidal - which kill the bacteria
 Bacteriostatic - which inhibit the
growth of bacteria
Antibiotics
are
the
antimicrobial
agents which destroy microorganisms
within the body.
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Bacteria and Its Cell
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Mechanism of action of
Antibiotics
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-LACTAM ANTIBIOTICS
Antibiotics that possess the -lactam (a
four-membered cyclic amide) ring structure
and are effective agents for chemotherapy
of bacterial infections.
-lactam ring


This ring is named as such because the nitrogen atom is
attached to the β-carbon atom relative to the carbonyl.
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Discovery of Penicillin in 1928
Alexander Fleming
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TYPES OF
-LACTAM ANTIBIOTICS
 Penicillins  Cephalosporins
-Lactam ring
-Lactam ring
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GENERAL STRUCTURE
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STRUCTURES OF PENICILLINS
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AMINOPENCILLINS
GENERALIZED STRUCTURES
e.g. ampicillin
amoxycillin
cyclacillin
Cyclacillin
(1-Aminocyclohexylpencillin)
Ampicillin acts as an irreversible inhibitor of the enzyme transpeptidase which is
needed by bacteria to make their cell walls. Amino group helps the drug
penetrate the outer membrane of Gram-negative bacteria.
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PRODRUGS OF AMPICILLIN
(to improve oral bioavailability)
Bacampicillin
Talampicillin
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PRODRUGS OF AMPICILLIN
(to improve oral bioavailability)
Metampicillin
Hetacillin
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ISOXAZOLYL PENCILLINS
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CARBOXYPENICILLINS
Carbencillin
Carindacillin
(Carbenicillin indanyl)
a prodrug of carbenicillin
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CARBOXYPENICILLINS
Temocillin
Ticarcillin
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UREIDOPENICILLINS
Mezlocillin
Azlocillin
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Piperacillin
Chemistry of Penicillins
Penam ring
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Degradation of Penicillins
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STEREOCHEMISTRY OF PENICILLINS
Penam
Penicillanic acid
 Penicillin molecule contains 3 chiral carbon atoms at C-3, C-5 and C-6.
 C-6 (to which acylamino group is attached) has L-configuration.
 C-3 (to which carboxyl group is attached) has D-configuration.
 Thus, acylamino and carboxyl groups are trans to each other with former
in alpha and latter in beta orientation to the penam ring system.
The absolute stereochemistry of penicillins is designated as 3S:5R:6R.
 Any change in stereochemistry results in loss of activity.
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REFERENCES
 Block JH, Beale JM, Gisvold O. Wilson and Gisvold’s
Textbook of Organic, Medicinal and Pharmaceutical
Chemistry, 11th edition, Lipincott Williams and Wilkins, 2004.
 Lemke TL, Williams DA, Roche VF, Zito WS. Foye’s Principles
of Medicinal Chemistry, 6th edition, Lipincott Williams and
Wilkins, 2008.
 Abraham DJ. Burger’s Medicinal Chemistry and Drug
Discovery, 6th edition, Wiley Interscience, 2006.
 Ashutosh Kar. Medicinal Chemistry, 4th edition, New Age
International Publishers, 2007.
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