Aromatic acids mass spectra

Peaks seen in the mass spectrum, due to loss of H20 from ions 18 mass units larger than 278 and 337 (favoured by glycine, and aromatic and heteroaromatic amino acids)... 

Sanchez and Brown have obtained a new harman derivative from Aspi-dosperma exalatum Monachino (121). The alkaloid was obtained from a butanol extract, and in the IR spectrum it showed principal absorptions at 1925 cm-1 for an immonium ion, at 1610 cm-1 for a carboxylate anion, and at 748 cm-1 for a disubstituted benzene. In the mass spectrum a molecular ion was observed at m/e 226 and a base peak at m/e 182 (M+ —44). An aromatic methyl group and five aromatic protons were observed in the PMR spectrum. Consideration of this data together with the UV spectrum led to deduction of the structure of the alkaloid as 268, harman carboxylic acid. The ethyl ester (269) was also isolated but it was probably an artifact. 

Lochnerinine (LXXXIX) was shown to be an aromatic methoxy-lochnericine by the 30 mass unit shift of the indolic peaks in its mass spectrum as compared with those of lochnericine 22). Reduction with zinc and acetic acid gave a dihydroindole whose UV-spectrum was closest to that of 7 -methoxyhexahydrocarbazole and the methoxy group was therefore placed at the 16-position 21, 22). Lochnerinine is the epoxide of 16-methoxy-( — )-tabersonine with which it co-occurs in Vinca herbacea 22a). 

Aromatic carboxylic acids produce intense molecular ion peaks. The most important fragmentation pathway involves loss of OH to form the CgHsCO" ion m e = 105), followed by loss of CO to form the CgHs ion. In the mass spectrum of para- m%ic. acid (Fig. 8.38), loss of OH gives rise to a peak at m/e = 135. Further loss of CO from this ion gives rise to a peak at m/e = 107. 

Dreyer and Brenner 62) isolated two new quinazoline alkaloids from seed husks of Zanthoxylum arborescens. The major compound, C17H16N2O2 exhibits a blue fluorescence on TLC. In the H-nmr spectrum the downfield aromatic quartet at 8 8.12 (J = 7.1 Hz) and a one-proton triplet at 8 7.8 (J = 7 Hz), each further split (J = 1 Hz) suggest the presence of four adjacent aromatic protons on an ortho-substituted benzene ring. The aromatic quartet farthest downfield at 8 8.12 indicates the presence of a / r/-related carbonyl group. Two two-proton multiplets (8 2.93—4.40) are consistent with the presence of a 2-phenylethyl system. Other nmr data, in light of the mass spectrum, suggest the presence of an N-methylanthranilic acid system. These characteristics could be assembled in two different ways, leading to structures (7) (Chart 1) and (31). C-spectroscopy and synthesis from N-methylisatoic anhydride and 2-phenylethylamine finally allowed elucidation of the structure. The synthetic product, l-methyl-3-(2 -phenylethyl)-lH,3H-quinazolin-2,4-dione (7) was identical with the alkaloid. 

The mass spectrum gave a base peak at m/e 121, which was considered to be due to the ion CXXV in agreement with the isolation of anisic acid by Manske by oxidation of the original corpaverine. The two pairs of aromatic protons derive from this moiety of the molecule. The other main peaks were due to the m/e 150 and 178 ions. The last peak was assigned to ion CXXVI which is transformed into the ion m/e 150 (CXXVII). That the peak m/e 178 was due mainly to ion CXXVI and not to CXXIX received support when the mass spectrum of sendaverine was compared with that of the 1-benzyltetrahydroisoquinoline (CXXVIII) (195). In this case the base peak is the ion m/e 178, to which structure CXXIX is assigned and which is transformed into the radical ion m/e 163 (CXXX), of low abundance in the case of sendaverine. On the other hand, the ion m/e 150 (CXXVII) is not detectable in the spectrum of CXXVIII. 

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