ORGANIC: MASS SPECTROMETRY, VOL. 23, 672-673 (1988)

New Mass Spectra

Electron Impact Mass Spectrometry of 7-(0- and p-R-Pheny1)- lO,lO-dimethyl-8,9,10,1 l-tetrahydrobenz[c]acridin-8-ones'

The synthesis of various series of acridines has been reported.' Explorations of these derivatives have provided a variety of pharmacologically active compound^.^ As part of a prog- ramme directed towards investigation of pharmacological and mass spectral properties of acridine derivatives, we have reported the synthesis of this heterocyclic ~ y s t e m . ~ The few data available in the literature on the mass spectra of such compounds, and their availability with a variety of substit- uents, prompted us to study their mass spectral fragmentation patterns.

In this paper we wish to report the mass spectra of com- pounds 1-10. The relative abundances of the important ions are shown in Table 1. The major fragmentation pathways have been identified by the presence of metastable peaks and by comparison with the fragmentation patterns of model com- pounds.

1: R = H 6: R = p - B r 2: R=o-CI 7: R = p - N O , 3: R = o - O M e 8: R = p - O M e 4: R = o - M e 9: R = p - M e ' 5: R = p - C I 10: R = p - N H ,

Benz[c]acridin-8-ones 1-10 are very stable under electron impact owing to their aromaticity which favours the molecu- lar ion, M", as base peak (Table l), with the exception of o-C1 and o-OMe derivatives. In the case of the 0-C1 compound its molecular ion was recorded by chemical ionization mass spectrometry with methane as reagent gas.

Loss of a hydrogen atom occurs in all the mass spectra analysed. Careful examination of the relative abundances listed in Table 1 showed that:

(i) for the compound with CH3 as the o-R-substituent of the 7-phenyl group, the relative abundance of the [M - I]' ion is the highest;

(ii) when the compounds have the R-substituent of the 7- phenyl group in the ortho position, the relative abundance of [M - 13' is the smallest;

(iii) in the case of compounds with the R-substituent of the 7-phenyl group in the para position, the relative abundance of [M - 11' ion is greater than that of compounds of type (ii) but less than that for the o-Me compound.

One major fragmentation route from the molecular ions of the ortho-R-compounds involves the loss of the R-substituent which gives rise to an ion at m/z [ M - R]+, base peak for the compounds with o-R=CI and -0Me. The relative abun- dance of the [M - R]' peak in all the para-R compounds studied is low. It is the existence of this unique species that makes the identification of benz[c]acridin-8-ones 1-10 a rela- tively easy matter. The ion [M - R]' is considered to lose isobutene, via a retro-Diels-Alder r ea~ t ion ,~ from the 5,5- dimethyl-cyclohexen- 1 -one moiety of the benz[c]acridin-8-one structure, 1-10, yielding the species at m/z 294. The same frag- ment is also formed from the ion at m/z [M - 561' by loss of the R-substituent. The fragment of m/z [M - 561' is formed from M +' through a retro-Diels-Alder reaction with a similar mechanism to produce the ion at m/z 294.

Loss of carbon monoxide from the m/z 294 ion leads to a cation at m/z 266. This ion then goes on to lose one hydrogen atom, giving the m/z 265 ion.

These observations bear a close similarity to those reported by us6 on the mass spectral fragmentation pattern of 1-H- dibenzo[b,e] [1,4]diazepin- 1-ones.

Another significant fragmentation pathway of benz[c]acridin-8-one 1-10 derivatives is the elimination of the 10-methyl group from the molecular ion, giving rise to a frag- ment at m/z [M - 151'. In the case of o-Me and p-Me deriv- atives the relative abundance of the [M - 151' ion is higher, owing to the loss of the CH,-substituent on the 7-phenyl group.

The mass spectra were measured on a Hitachi-Perkin- Elmer RMU-7H double-focusing mass spectrometer and a Hewlett-Packard 5985A quadrupole mass spectrometer using the direct inlet system. The spectra were recorded at an ion- ization chamber temperature of 190 "C and with ionizing elec- tron energy of 70 eV.

Table 1. Relative abundance of principal fragments in the mass spectra of 740- and p-R-phenyl)-lO,lO- dimethyl-8,9,10,1 l-tetrahydrobenz[clacridin-8-ones

Compound no R M f M' 1 M ' - 2 9 M + R 294 M + - 5 6 266 265 M * - 1 5

1 2 3 4 5 6 7' I 9

10

-H 0-CI o - O M e o - M e p-CI p-Br P-NO, p - O M e p - M e P-NH,

100.0

21.4 100.0 100.0 100.0 100.0 100.0 100.0 100.0

a 39.6 30.5 0.8 0.8 0.8 3.3

65.2 7.4 14.8 23.1 25.0 26.6

7.4 24.7 36.3 21.5 39.6 26.4 30.5 9.9

39.6 100.0 100.0

76.8 2.5

10.0 2.5 3.3

11.5 1.6

30.5 54.5 13.2 0.8 1.6 0.8 3.3 14.8

31.4 28.0 63.3 35.0 3.3 36.3 4.9 51.2 3.3 61.1 1.6 28.9

33.0 13.2 2.5 38.0 43.8 1.6 3.3 2.4 0.8

22.3 11.5 76.8 31.4 14.5 2.5 65.0 41.6 3.3 36.3 18.1 1.6

8.3 4.9 3.3 23.1 8.2 11.5 4.1 2.4 1.6

a Determined by chemical ionization mass spectrometry.

003&493X/88/090672-02 $05.00 0 1988 by John Wiley & Sons, Ltd.

Received 19 January 1988 Accepted 29 January 1988

NEW MASS SPECTRA 673

EDUARDO CORTES (to whom correspondence should be addressed), ROBERTO MARTfNEZ and J. GUSTAVO AVILA Instituto de Quimica, Universidad Nacional Autonoma de Mexico, Circuit0 Exterior, Ciudad Universitaria, Coyoacan 04510, Mexico, DF Mexico

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