HETEROCYCLIC SYNTHESIS USING NITRILIMINES : PART 18 . SYNTHESIS OF NEW FUSED HETEROCYCLES CONTAINING TRIAZINONE MOIETY

A series of new 4,5-dihydro-6-oxo-1,2,4-triazino[4,5-b]1,2,3,4-tetrahydro-β-carbolines were synthesized by the reaction of methyl 1,2,3,4-tetrahydro-β-carboline-3-carboxylate and the appropriate hydrazonoyl halide in presence of triethylamine. The structures of the title compounds have been established by their elemental analyses and spectroscopecal data. The microbial features of some of the synthesized compounds were studied by a known method.


Experiment
Melting points were determined on a Stuart Electrothermal Apparatus and are uncorrected.The IR spectra were obtained by using Satellite 3000 Mid infrared spectrophotometer in potassium bromide pellets. 1 H and 13 C NMR spectra were recorded on a Bruker spectrometer (400.13MHz) at room temperature in CDCl3 if not noted otherwise stated, using tetramethylsilane (TMS) as an internal reference.All chemical shifts) were reported in ppm from TMS. Electron impact (EI) mass spectra were measured on Finnigan MAT 8200 and 8400 Mass spectrometers at 70  [27] and hydrazonoyl halides 4 [28][29][30], used in this study, were prepared according to previously described procedures.
Synthesis of 4,5-dihydro-6-oxo-1,2,4-triazino[4,5b]1,2,3,4-tetrahydro-β-carbolines 6a-l.To a stirred solution of the appropriate hydrazonoyl halides (0.012 mol) in chloroform (50 mL) was added a solution of methyl ester hydrochloride (2.5 g, 0.01 mol) in methanol (40 mL).To the resulting reaction mixture, cooled in an ice-salt bath (-5-0 o C), was dropwise added triethylamine (0.05 mol).After addition was complete, stirring was continued for 1 h at 0 o C, and then at room temperature for 6-8 h.The solvent was removed under reduced pressure, and the residue was washed with water.The resulting solid product was collected and recrystallized from methanol or ethanol to give the desired products 6a-l.The physical and analytical data of the title compounds are provided in Table 1.
Spectroscopic data analysis.The electron impact (EI) mass spectra of compounds 6a-l displayed the correct molecular ions (M +• ) in accordance with the suggested structures (Table 1).Their IR spectra of in KBr showed strong absorption bands of N-H in the 3370-3350 cm -1 region, a lactam carbonyl band in the 1680-1670 region, at 1680-1670 cm -1 for R-C=O, and at 1625-1600 cm -1 was assignable to C=N.The 1 H NMR spectra of compounds 6a-l showed all the signals of the proposed structures, indicating that, all compounds have N-H proton of the ring appeared as singlet at 8.0-7.90 ppm and the methine proton at position 12a appeared as two doublets in the range 4.50-4.40ppm due to its coupling with the two diastereotopic protons at position 12 (J = 5 Hz).Correspondingly, the later H-12 protons appeared as two doublets of doublets due to further geminal coupling (J = 1.4 Hz).The diastereotopic H-6 methylene protons are also mutually coupled to each other (J = 1.5 Hz) and hence are displayed as two doublets.The 1 HNMR spectral data of compounds 6a-l are given in Table 2.
The 13 CNMR spectra of compounds 6a-l displayed the characteristic signals of the suggested structures.The signal of the lactam appeared in the range of 162-160 ppm, and that of the carbonyl carbon of R-C=O group resonated in the range of 1660-1640 ppm.The signal at 142-140 ppm, is attributed to C=N of the triazinone ring.The 13 C NMR spectral data of compounds 6a-l are given in Table 3.
Antimicrobial activity.Six of the newly synthesized compounds were screened in vitro for their antimicrobial activity against a variety of bacterial strains such as Euterococci, Escherichia coli, Staphylococcus aureus, Klebsiella spp, Proteus spp, and fungi such as Aspergillus niger, Candida albicans, employing the nutrient agar disc diffusion method [38][39][40] at 10 mg/mL concentration in dimethyl formamide (DMF) by measuring the average diameter of the inhibition zone in mm (Table 4).The data reported in Table 1 represent average of three experiments.The results showed that all the tested compounds exhibited a marked degree of activity against bacteria and fungi compared with well known antibacterial and antifungal substances such as tetracycline and fluconazole.
According to NCCLS (2004), zones of inhibition for tetracycline and fluconazole <14 mm were considered resistant, between 15 and 18 mm were considered weakly sensitive and >19 mm were considered sensitive.Also, the results showed the degree of inhibition varied with the tested compounds (Table 4).

Conclusion
In conclusion, the cyclocondensation of several nitrilimines with β-carboline leads to formation of triazine-β-carboline derivatives, and some of them proved to have potent antibacterial and antifungal activity.The results confirm that the antimicrobial activity is strongly dependent on the nature of the substituents at N-2 and C-4 of the 1,2,4-triazinone ring.

Table 1 . Physical Data, Molecular Ion Peaks and Elemental Analysis for Compounds 6a-l
484eV.Elemental analysis are performed at Cairo University, Egypt and the results agreed with the calculated values within experimental errors.The methyl 1,2,3,4-tetrahydro-β-carboline-3-carboxylate 3

Table 4 . Antimicrobial Screening Results of the Tested Compounds *
* Zone of inhibition in mm