Electron Impact Ionization Mass Spectra of 3-Amino 5,6-dimethoxyl-2-methyl quinazolin-4-(3H)-one Derivative

The synthesis of novel heterocyclic derivatives has attracted considerable attention. The explosive growth of heterocyclic chemistry is emphasized by the large number of research publications, monographs, and reviews. The heterocyclic organic compounds are extensively disseminated in natural and synthetic medicinal chemistry and are vital for human life. Looking at the previous studies on quinazolinones derivatives, only limited information is available on their mass spectral along with the preparation of novel quinazolin-4-(3H)-one derivatives. Objective of this study, was to synthesize a novel 2-Methyl-6, 7-dimethoxy-quinazolin-4-one was synthesized via the reaction between 2-Methyl-6, 7-dimethoxy-benzo-1,3-oxazin-4-one and hydrazine hydrate and study their electron impact (EI) mass spectral fragmentation. The condensation of 2-amino-methyl-4, 5-dimethoxybenzoate with acetic anhydride yielded the cyclic compound 2-methyl-4, 5-disubstituted-1, 3-benzo-oxazine-4-one which further produce a novel 2,3-disubstituted quinazolin-4 ones via the reaction with hydrazine hydrate. The compounds synthesized were unequivocally confirmed by means of Infrared, Nuclear Magnetic Resonance (1H and 13C), Gas Chromatography Mass Spectrophotometer and Elemental analysis. The molecular ion of m/z 235 fragment to give m/z 220 by loss of –NH group. The ion of m/z 220 was broken to give m/z 206 by losing CH2 group and fragment to m/z 177 by loss of HCO. This fragmented to m/z 162 by loss of –CH3 group and then m/z 136 by loss of CN group. The loss of O gave m/z 120 which fragment to give m/z 93 by loss of –HCN and finally gave m/z 65 by loss of CO group. The electron impact ionization mass spectra of compound 2 show a weak molecular ion peak and a base peak of m/z 235 resulting from a cleavage fragmentation. Compound 2 give a characteristic fragmentation pattern. From the study of the mass spectra of compound 2, it was found that the molecular ion had fragmented to the m/z 220. The final fragmentation led to ion of m/z 93 and ion of mass m/z 65, respectively.


Introduction
Heterocyclic compounds are cyclic compounds with the ring containing carbon and other elements, the commonest being oxygen, nitrogen and sulphur (Finar, 2007: 826). Some of the medicinally important heterocyclic compounds are the quinazolines. Quinazoline is a compound made up of two fused six-membered simple aromatic rings, benzene ring and a pirimidine ring. Quinazoline, earlier known as benzo-1 3-diazine was first prepared in the laboratory by Gabriel in 1903, although one of its derivatives was known much earlier (Anti-inflammatory agents, 2008).
Of the many derivatives of quinazoline system known so far, keto-quinazolines also called quinazolinones, are the most important compounds. Depending upon the position of the keto or oxo group, these compounds may be classified into two. The two structural isomers are 2-quinazolinone and 4-quinazolinone, with the 4-isomer being the most common (Quinazolinone encyclopedia, 2010).
Quinazolinone form a large group among the pharmacologically active chemical moieties and are generally of little toxicity without serious side effects to the human body. Quinazolinones are versatile nitrogen heterocyclic compounds, displaying a broad spectrum of biologically and pharmacological activities in animal as well as in human systems. The chemistry and pharmacology of quinazolinones have been of great interest to medicinal chemist (Shradha and Scrivastava, 1994: 143). Quinazolin-4-one and its derivatives possess a diverse range of biological activities including analgesic (Scrivatva et al., 1993), anticancer (Scrivatva et al., 1993 and antidiabetic activity (Hour, 2000: 4479-4487;Hamel et al., 1996: 53-59;Mayer et al., 1997: 8445;Jiang et al., 1990Jiang et al., : 1721. Heterocyclic compounds have a wide range of application: they are predominant among the type of compounds used as pharmaceuticals, as agrochemicals and as veterinary products. They also find applications as sentizers, developers, antioxidants, as corrosion inhibitors, as copolymers, dyestuff (Kozikowski, 1984: 112-121).

General Experimental Procedure
Reagents and solvents were purchased from sigma-Aldrich chemical supplier in Germany. Melting points were determined on a Kofler hot stage apparatus and are uncorrected. IR spectra were recorded on a Buck scientific IR M500 instrument. The 1H and 13C NMR spectra were recorded in DMSO-d6 at 400MHz with HAZ VOLATILE V2.M. Chemical shifts are reported in ppm relative to tetramethylsilane period. Gas chromatography mass (GC/MS) spectra were obtained on a Finingan MAT 44S mass spectrometer operating at electron impact energy of 70eV. Elemental analysis data agreed with the calculated values. Analytical thin layer Chromatography (TLC) was used to monitor the reactions.
Experimental Reagents and solvents were purchased from sigma-Aldrich chemical supplier in Germany. Melting points were determined on a Kofler hot stage apparatus and are uncorrected. IR spectra were recorded on a Buck scientific IR M500 instrument. The 1H and 13C NMR spectra were recorded in DMSO at 400MHz with HAZ VOLATILE V2.M. Chemical shifts are reported in ppm relative to tetramethylsilane. Gas chromatography Mass spectra were obtained on a HAZ VOLATILE V2.M (400MHz) and chemical shifts are reported in ppm relative to tetramethylsilane as reference standard. Elemental analysis agreed favourably with the calculated values. Analytical thin layer Chromatography (TLC) was used to monitor the reactions (Fig.1, Fig.2).

Discussion
Structural elucidations of compounds synthesized were characterized by correct elemental analysis and careful inspections of spectral data. Looking at the 1 H NMR spectra of the compounds synthesized, compound 1 displayed a singlet signal at: δ 3.78 attributed to methoxy group and singlet at δ 3.68 which was due to methyl group. Other singlets appeared at δ7.16 and 6.40 attributed to aromatic protons. Also, 1 H NMR spectrum of compound 2 showed a characteristic signal at δ 2.56 (singlet) corresponding to methyl group and duplet at: δ 3.90 for methoxy group. Two singlets appeared at δ7.41 and 7.10 attributed to aromatic protons. Another signal appeared at 5.80 which was attributed to the protons of the amino group. For the IR spectra, compound 1 was characterized by absence of υ NH2and presence of υ C-O stretch in 1101cm -1 region of the compound. Compound 2 was characterized by absence of υ C-0 and presence of υNH2 in 3301cm -1 region of the compound.
The 13 C NMR spectrum of compound 1, revealed signals at δ16.95, 51.93 and 56.13 attributed to methyl and the two methoxy groups respectively, while the aromatic carbon atoms appeared between δ values 100.05-168.28 with the carbonyl carbon atom appearing as the highest δ value of 168.28. Similarly, compound 2 showed signals at δ22.58, 56.63 and 56.80 attributed to methyl and the two methoxy groups respectively, while the aromatic carbon atoms appeared between δ values 105.64-160.28, with the carbonyl carbon atom appearing as the highest δ value of 160.28.
The 13 C nuclear magnetic resonance revealed low δ values for the aliphatic carbons. This is because the alkyl group is electron donating and hence produces a shielding effect which makes the carbon atom to resonate at low δ values. The aromatic and the carbonyl carbon atoms appeared at high δ values. This is because the aromatic ring is electron withdrawing and the aromatic carbons are highly deshielded and resonate at high frequency. The electronegative effect of the oxygen atom on the carbonyl group makes the carbonyl carbon to appear at higher δ value. Table 4 lists the m/z (relative abundance, %) values of principal fragments of the studied compound, while figure 1 illustrates the mass spectrum of the compound. The mass spectrum of the compound shows a molecular ion of m/z 235 corresponding to the molecular mass of the compound. The molecular ion of m/z 235 fragment to give m/z 220 by loss of -NH group. The ion of m/z 220 was broken to give m/z 206 by losing CH2 group and fragment to m/z 177 by loss of HCO. This fragmented to m/z 162 by loss of -CH3 group and then m/z 136 by loss of CN group. The loss of O gave m/z 120 which fragment to give m/z 93 by loss of -HCN and finally gave m/z 65 by loss of CO group.

Conclusion
The present work shows that the mass spectra of compound 2 has relatively small molecular ion and peaks typical of a cleavage and rearrangement processes type fragmentation. Compound 2 give a characteristic fragmentation pattern with a very stable fragment of benzopyrazolone (m/z 235).