bi400873r_si_001.pdf (770.12 kB)
Kinetics of Action of a Two-Stage Pro-Inhibitor of Serine β‑Lactamases
journal contribution
posted on 2016-02-18, 17:10 authored by Ronak Tilvawala, R. F. Prattβ-Lactamase inhibitors are
important in medicine in the protection
of β-lactam antibiotics from β-lactamase-catalyzed destruction.
The most effective inhibitors of serine β-lactamases covalently
modify the enzyme active site. We have recently studied O-acyl and O-phosphyl hydroxamates as a new class
of such inhibitors. In this paper, we describe our studies of the N-acyl derivatives of a cyclic O-acyl hydroxamic
acid, 3H-benzo[d][1,2]oxazine-1,4-dione,
and, in particular, the N-tert-butoxycarbonyl
derivative. This compound is not a β-lactamase inhibitor itself
but undergoes spontaneous hydrolysis in aqueous solution, yielding
an O-phthaloyl hydroxamic acid, which is a β-lactamase
inhibitor. This compound spontaneously, but reversibly, cyclizes in
solution to form phthalic anhydride, which is also a β-lactamase
inhibitor. Both inhibitors react to form the same transiently stable
phthaloyl–enzyme complex. Thus, we have a two-step cascade,
beginning with a pro-inhibitor, in which each step leads to a different
inhibitor, presumably with different enzyme specificities. The kinetics
of these transformations have been elucidated in detail. The phthaloyl
derivatives, where the free carboxylate is important for facile reaction
with the enzyme, represent a new lead for serine β-lactamase
inhibitors. Analogues can be conveniently constructed in situ by reaction of nucleophiles with phthalic anhydrides and then screened
for activity. Active hits may then become new leads.