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Chapter 15 511
Copyright © 2017 Pearson Education, Inc.
The inhibitor of penicillinase is a phosphate ester with an excellent leaving group, so it readily reacts with
nucleophiles. When the CH
2
OH group of penicillinase attacks the inhibitor, a relatively stable phosphonyl-
enzyme is formed, so its OH group is no longer available to react with penicillin. (The two sets of double
arrows indicate formation and collapse of the tetrahedral intermediate.)
N P
O
O
O
O
O
O
_
H
H–B
+
_
N P
O
CH
HO
COO
2
O
O
O
_
H
−
+
a phosphonyl-enzyme
Hydroxylamine (H
2
NOH) reactivates penicillinase by liberating the enzyme from the phosphonyl-enzyme.
(Unlike alkylation reactions with hydroxylamine where nitrogen is the nucleophile, it is known that oxygen
is the nucleophile when hydroxylamine reacts with phosphate esters.) Again, the two sets of double arrows
indicate formation and collapse of the tetrahedral intermediate.
N
O
CH
2
O
O
_
H
N
O
NH
CH
2
OH
2
O
O
_
H
+
P
O
P
O
90.
NHCO
2
CH
3
HO
NHCO
2
CH
3
HO
H
+
N H
+
B
N
HB
+
CO
2
CH
3
CO
2
CH
3
HCl