Fragmentation mechanisms of oxofatty acids via high-energy collisional activation

Upon high-energy collisional activation, oxofatty-acid ions undergo fragmentations to produce a unique pattern of product ions by which the position of the ketone is revealed. The reactions occurring in the vicinity of the ketone, which are the subject of this article, produce a spectral pattern that is not symmetrical. Although cleavages of α, β, and γ C-C bonds occur on the side proximal to the charge site, giving α, β, and γ ions, respectively, there is only a γ′ ion formed on the side distal to the charge site. The resulting lack of symmetry seemingly contradicts the concept that the reactions are independent of the charge (i.e., that they are charge remote). To eliminate any interaction between the charge and the reaction site, oxofatty acids were linked to glycyrrhetic acid, a steroid with a rigid polycyclic system. The fragmentation pattern remains the same, indicating that the effect does not depend on charge but rather on the ketone. Isotopic labeling and MS/MS/MS studies confirm that the fragmentations of C-C bonds in the vicinity of the ketone are complex, charge-remote processes. Formation of [M-H-H₂O]^? and [M-H-CO₂]^? anions and the ion that is formed by homolytic cleavage of the β bond at the side distal to the charge, however, are charge directed.     

An asymmetric isoxazole annulation

An Asymmetric isoxazole annulation proceeds from the (S)-O-methoxyphenylalaninol imine of (RS)-2-phen-ylpropionaldehyde (3). Deprotonation, quenching with 4-chloromethyl-3,5-dimethylisoxazole, and hydrolysis produced isoxazolylaldehyde (5), whose structure was confirmed by single crystal X-ray diffractometry. The absolute configuration of (-)-5 was established as (R)-by chemical correlation to the known (S)-(-)-4-methyl-4-phenyl-cyclohex-2-ene-1-one (7).     

Synthesis of new isoxazole aminoalcohols

The preparation of new 1-isoxazolyl-2-amino-1-ethanol derivatives is described starting from the corresponding 1-isoxazolylethanones. It is also reported the synthesis of 1-(5-isoxazolyloxy)-3-amino-2-propanol compounds starting from the corresponding 5-haloisoxazoles and the obtainment of 1-(3-isoxazolyloxy)-3-amino-2-propanol compounds starting from the methyl 3-hydroxy-5-isoxazolecarboxylate.     

Ortho effects–I: Fragmentation mechanisms in some ortho-substituted nitroarenes

The mass spectra of o-nitrobenzoic acid, o-nitroanisole, o-nitrosobenzoic acid, o-nitrobenzamide, o-nitrobenzyl alcohol and o-nitrosobenzaldehyde have been studied. Fragmentation mechanisms are proposed for the above compounds; their elucidation was aided by isotopic labeling with D and O¹⁸. Two ‘ortho-effects’ are discussed; one involving H atom transfer between substituents and the other migration of an atom or group to a charge carrying vacant ortho position. The importance of nitro to nitrite conversion in molecular and fragment ions is discussed.     

Research in the isoxazole series

The ionization constants of 14 phenylisoxazoles in acetic acid were determined by a spectrophotometric method. The ionization constants of 4-R-3,5-diphenylisoxazoles correlate well with the Hammett _m constants of substituents R.See [1] for communication XXX.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1029–1031, August, 1976.     

Research in the isoxazole series

3,5-Diarylisoxazoles in acetic acid are smoothly converted to 4-chloro derivatives by the action of chlorine in situ. A side reaction is subsequent addition of hypochlorous acid, which proceeds under the influence of excess chlorine. It is convenient to use tert-butyl hypochlorite for the chlorination of more reactive arylisoxazoles.See [1] for communication XXV.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1325–1328, October, 1973.     

Research in the isoxazole series

The thermal decomposition of phenylazotriphenylmethane in 3,5-dimethyl- and 3,4,5-trimethylisoxazole was studied. In 3, 5-dimethylisoxazole only the hydrogen atom of the methyl group in the 3 position is replaced by the (C₆H₅)₃C radical. The activities of the methyl groups of 3,4,5-trimethylisoxazole decrease in the order 3-C>4-C 5-C. The specific direction of the reaction is associated with the orientation of the phenylazotriphenylmethane in the vicinity of the 3-C atom of the isoxazole ring owing to complexing of the azo group with the nitrogen atom. Complexes of 3, 5-dimethyl- and 3, 4, 5-trimethylisoxazole with Eu⁺ have a similar structure. The structures of the reaction products were established by means of their PMR and mass spectra.See [1] for communication XXXII.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 608–610, May, 1977.     

Research in the isoxazole series

The bromination of phenylisoxazoles in 85% acetic acid is a second-order reaction. The ratios of the rate constants for the bromination of benzene and the investigated compounds are 1∶100–10,000. The maximum reaction rate was observed when a twofold excess of the heterocycles was present, and this constitutes evidence for the intermediate formation of complexes of isoxazoles with bromine.     

Research in the isoxazole series

The 4-nitro derivative is formed in the nitration of 3,5-diphenylisoxazole (I) in acetic anhydride. Mononitration of isoxazole I in concentrated H₂SO₄ gave 3-phenyl-5-(p-nitrophenyl)isoxazole, while polynitration gave a mixture of dinitro derivatives, among which 3- (m-nitro-phenyl)-5-(p-nitrophenyl)isoxazole was identified. The structures of the isolated products were established by means of the spectra, by reaction-chromatography methods, and gasliquid chromatography, as well as by a comparison with genuine samples of the two mononitro and four dinitro derivatives of isoxazole I.     

Microwave spectrum and structure of isoxazole

The investigation of the microwave spectrum of isoxazole ($\text{ONCHCHC}$H) has been continued. The assignment of transitions up to J = 42 gave accurate rotational and distortion constants. The hyperfine splitting of the J = 0 → 1 transitions could be partially resolved and values for the quadrupole coupling constants were obtained.The use of microwave-microwave double resonance modulation in place of Stark effect modulation allowed the assignment of six vibrationally excited states and of the monosubstituted isotopic species containing ¹³C, ¹⁵N and ¹⁸O in their natural abundances. Kraitchman's equations for planar molecules were used to derive the r_s-structure of the isoxazole ring. Application of a least squares technique for singular systems of normal equations gave structure parameters which optimally reproduce the observed changes of all three moments of inertia under isotopic substitution.     

Research in the isoxazole series

The ionization constants of arylisoxazoles in acetic acid were determined by a spectrophotometric method. The effect of substituents on the conjugation in the arylisoxazole system is discussed.See [1] for communication XXXIII.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 327–328, March, 1978.     

Dipole moments of some isoxazole derivatives

The dipole moments of isoxazole and 13 of its halo, amino, and nitro derivatives were measured. A method is proposed for vector calculation for estimating the direction of the dipole moment of the isoxazole ring. It is demonstrated that phenyl substituents in the 3 and 5 positions are electron donors with respect to the isoxazole ring. It was found that the dipole moments of 4-substituted 3,5-dimethylisoxazoles correlate satisfactorily with the Hammett constants.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 460–463, April, 1972.     

An investigation in the isoxazole series

The hydrogen atoms in the CH₃ groups in position 5 of 3,5-dimethyl-4-nitroisoxazole (I) and 3,5-dimethyl-4-phenylazoisoxazole (II)undergo isotopic exchange with diethyl[D]amine. The position of entry of the deuterium has been established and the CH₃ groups of compounds I and II have been characterized by NMR spectroscopy. The possibility of a correlation of the reactivities of the methyl groups with their chemical shifts is discussed.For part XX, see [1].     

New synthesis of pyrazole and isoxazole derivatives

A convenient synthesis of 5-aryl-1-phenylpyrazoles and 5-arylisoxazoles, from readily available ketimine 1 dimethylformamide dimethylacetal and phenylhydrazine or hydroxylamine, is described.