Mass spectra of some quinoline hydroxamic acids and related compounds

Abstract

Abstract-The mass spectia of some 3-and 4-substituted quinoline hydroxaniic acids and related compounds have been interpreted, and proposed fragmeniations substantiated by ineans of deuterium-labeling and accurate m a s deteiniinations. AIl compounds examincd gave abundant molecular ions; most showed strong [M -16Ik ions and weak [M -17]+ ions. The expulsion of CO and HCN molccules and H and HCO radicals were coninion subsequcnt decompositions. The spectrum of 4-hydroxy-2-n1ethylquinazoline-3-oxide (Vi 1) was unique and showed that nitric oxide was expelled from the molecular ion.A SELECTION of 3-and 4-substituted quinoline hydroxaniic acids and related coiiipounds were synthesized for antimierobial evaluation. Mass spectrometry was used to characterize the products and this revealed some interesting fragmentation pathways. This is the subject of this prccent communication.The m a s spectra of alkylquiiiolines,1~2 oxygenated quinoline~,~ tetrahydroquiiioline~,~ quinoline and isoquinoline N-oxides5s6 and other N-oxides7-'" have been recordcd aiid interpreted. Although cyclic hydroxamic acids are o-hydroxy Noxides, no detailed study of the effect of electron-impact upon these compounds ha5 been reported. There are three isolated reports on the mass spectra of individual cyclic hydroxamic a~i d s .~*~~,~~ In each instance, the suitability of a cyclic hydroxamate structure was inferred from the presence of an [M -161' ion in the spectrum.From the studies on N-oxides just referred to, it can be concluded that aromatic N-oxides give large [M -16]+ ions (>15:( abundance), whereas large [!vi -161' ions are not characteristic of non-aromatic N-oxides. If the operation of an ovtlzoeffect is possible as in the case of 2-alkyl pyridiiie N-oxides, then re!atively abundant [M -17]+ ioiis are formed as a result of a one-step eliinination of an OH radical.In the prescnt study, the m a s spectra of ten quinoline hydroxaniic acids possessing various siibstituents in the 3 or 4 positions (la to Ih; IIIa, Ilib), aiid four related compounds (iV to ViI) were examined to determine whether compounds of this class fragmented predictably and were capable of characterization i i i this way. Mass spectral data of the majority of these compounds are listed in Table 1

The yellow pigments of Beauveria species. Structures of tenellin and bassianin

“…Apart from replacement of the A(H-8)B(H-9) system of 1 by an A(H-8)B(H-9)M(H-IO)N(H-11) sub-spectrum, the 'Hmr spectrum of bassianin (8) matched that of tenellin very closely ( Table 1). The magnitudes of the three vicinal coupling constants, obtained by analysis of the ABMN system, indicated that adjacent olefinic hydrogens in 8 were trans-oriented (7).…”

“…High resolution mass spectral studies together with precursor ion experiments showed that a major fragmentation pathway for both metabolites involved initial loss of an oxygen atom; in contrast the methyl ether derivatives 2, 3, and 4 lost CH20. These uncommon reactions suggested that the metabolites possessed a cyclic hydroxamic acid unit (8), and the combination of mass spectral and nmr results established that the hydroxamate hydroxyl group (6 11.67) of 1 was methylated preferentially. Similarly, the monoacetate derivative (acetyl methyl 6 2.22, Table I) was assigned structure 5 because the acetoxyl substituent was clearly not on C-4 (OH, 6 17.1), and a hydroxamic acid hydroxyl group, like those of the aspergillic acids (9), should be preferentially acetylated because of its acidic properties.…”

Quinoline N-oxides and hydroxamic acids with antibacterial properties

“…The tubes were then incubated at 37" and observed for growth at [16][17][18]24, and 42 h intervals. Appropriate controls were performed also.…”

Mass spectra of 2H‐1,4‐benzoxazine and‐benzothiazine hydroxamic acids

“…All showed abundant molecular ions. The 3,4-dihydr0-4-hydroxy-3-0~0-2H- 1 The benzoxazine hydroxamic acids (Ia) examined are characterized by the formation, on electron-impact, of a strong [M -45]f ion, the result of the loss of a COOH radical from the molecular ion. In the spectra of all five benzoxazines examined (IIa to e), the [M -45]+ ion was the base peak.…”