Synthesis, Hydrolysis, and Evaluation of 3-Acylamino-3,4-dihydro-2-oxo-2H-1,3-benzoxazinecarboxylic Acids and Linear Azadepsipeptides as Potential Substrates/Inhibitors of β-Lactam-Recognizing Enzymes

Abstract

The title compounds can be considered as stabilized aza analogs of previously studied dihydrobenzopyranones and linear depsipeptides, which behave as substrates or inhibitors of β-lactamases. Treatment of substituted hydrazides 9b and 9b′ with a phosgene substitute resulted in a series of N-methylated 3-acylamino-3,4-dihydro-2-oxo-2H-1,3-benzoxazine-7- and -8-carboxylic acids 2b and 2b′. However, in the case of the corresponding free NH hydrazide 9a(m), a competitive cyclization gave instead a stable 4H-1,3,4-oxadiazol-5-one 10a. To avoid this unwanted cyclization, an N-(p-methoxy)benzylated hydrazide 9b′′ was prepared. After formation of the benzoxazinone ring with carbonyldiimidazole, the removal of this new N1-hydrazide protecting group was achieved with methanesulfonic acid in trifluoroacetic acid to give the expected 3-phenacetamido-3,4-dihydro-2-oxo-2H-1,3-benzoxazine-7-carboxylic acid 2a(m). The corresponding linear azadepsipeptides 5 were generally obtained by reaction of a hydrazide with 3-tert-butoxycarbonylphenyl chlorocarbonate. Hydrolysis of the title compounds in buffer at neutral pH was more rapid than anticipated because of the presence of mechanisms more facile than the classical BAC2. Hydrolysis of the cyclic azadepsipeptide 2a(m), for example, involved intramolecular nucleophilic participation by the amido side chain and a slowly hydrolyzing oxadiazolone intermediate (10a). These compounds, unlike their parent depsipeptides, were not substrates or inhibitors of β-lactamase or DD-peptidase. This result probably arises from a combination of the poor carbonyl electrophilicity and the close to planar geometry of the nitrogen atom of the oxazin-2-one ring.