These all share a common B-lactam ring. The ring is very strained and the bond between the carbonyl and the nitrogen in the p-lactam ring is very labile and hence makes the molecule reactive. The r-group substitute of the penicillin nucleus can be changed to give the molecule different antibacterial properties. The two naturally occurring penicillins from Penicillium notatum are enicillin G,[Benzyl penicillin,R=CH] and Penicillin V, PHenoxymethyl penicillin,R=CH,O(C6H6)1 X H R NH H COOH
These all share a common β-lactam ring. The ring is very strained and the bond between the carbonyl and the nitrogen in the β-lactam ring is very labile and hence makes the molecule reactive. The R-group substitute of the penicillin nucleus can be changed to give the molecule different antibacterial properties. The two naturally occurring penicillins from Penicillium notatum are Penicillin G, [Benzyl penicillin, R = C6H6 ] and Penicillin V, [Phenoxymethyl penicillin, R = CH2O(C6H6 )] N S O H COOH X H R NH O
The B-lactam structure is derived from two covalently bonded amino acid residues; cysteine and valine. This forms via a tripeptide intermediate where the third amino acid is replaced by the variable r-group SH H2N HN HN OH Cysteine β- actam structure Valine
The β-lactam structure is derived from two covalently bonded amino acid residues; cysteine and valine. This forms via a tripeptide intermediate where the third amino acid is replaced by the variable R-group
Mechanism ofaction N D-Alanyl-D-Alanin Penicillins NAC NAi NAI NAD(NAM(AD
Mechanism of Action O R N N O O O O O O R N N O S D-Alanyl-D-Alanin Penicillins
The peptidoglycan cell wall is a branched polymer made of alternating NAG邗D-N- acetylglucosamine,乙酰葡糖胺]and NAMIβ-D-N- acetylmuramic acid,乙酰壁氨酸] residues Polypeptide chains are attached to the nam residues and these vary depending on the strain of bacteria. The mechanism for cross-linkage is shown below. It is the terminal D-alanyl-D alanine residues of the polypeptide chain off of the nam residues that binds to the transpeptidase which cross-links that chain with the adjacent peptidoglycan strand. Penicillin binds at the active site of the transpeptidase enzyme that cross-links the peptidoglycan strands. It does this by mimicking the D-alanyl-D-alanine residues that would normally bind to this site
The peptidoglycan cell wall is a branched polymer made of alternating NAG [β-D-N-acetylglycosamine,乙酰葡糖胺] and NAM [β-D-N-acetylmuramic acid，乙酰壁氨酸] residues. Polypeptide chains are attached to the NAM residues and these vary depending on the strain of bacteria. The mechanism for cross-linkage is shown below. It is the terminal D-alanyl-Dalanine residues of the polypeptide chain off of the NAM residues that binds to the transpeptidase which cross-links that chain with the adjacent peptidoglycan strand. Penicillin binds at the active site of the transpeptidase enzyme that cross-links the peptidoglycan strands. It does this by mimicking the D-alanyl-D-alanine residues that would normally bind to this site
Peptidoglycan Cell Membrane