Synthesis and antimicrobial activity of some 2-[ 1-( 4-oxo-3 , 4-dihydrophthalazine-1-yl ) alkyl ]-1 H-isoindole-1 , 3 ( 2 H )-dione and their imidoxy derivatives

In this study, a series of 2-[(4-substituted phthalazine-1-yl)alkyl]-1H-isoindole-1,3(2H)-diones 6a-d and 2-{2-[4-(1,3-dioxo-1,3-dihydro-2H-isoindole-2-yl-alkyl)1-oxo phthalazine-2(1H)yl]alkoxy}-1H-isoindole-1,3(2H)-diones 7a-d have been synthesized from phthalyl derivatives of amino acids 1a-b as starting material. The structures of these compounds were confirmed by IR, H NMR and Mass spectral studies. Synthesized compounds 6a-d and 7a-d showed significant antimicrobial activity.


Introduction
The diverse biological activities of various functional derivatives of 4-substituted alkyl-1-(2H)phthalazinones are well known.Some of the phthalazinone derivatives have found application in clinical medicine 1 due to their pronounced antipyretic, analgesic and tuberculostatic activity while others have shown interesting vasodialator 2 and antihypertensive properties. 3Phthalazine-1(2H)-ones bearing a substitution at C-4 represent key intermediates in the synthesis of various compounds with highly interesting pharmacological properties, such as the blood platelet aggregation inhibitor MV-5445 4 [1-(3-chloroanilino)-4-phenylphthalazine] which has been found to be a selective phosphodiesterase V A inhibitor 5 or the thromboxane A 2 synthetase inhibitor and bronchodilator, 2-[2-(1-imidazolyl)ethyl]-4-[3-pyridyl]-phthalazine-1[2H]-one. 6he phthalazinone nucleus has been proved to be a versatile system in medicinal chemistry.Moreover, a number of established drug molecules like Hydralazine, 7 Budralazine, 8 Azelastine, 9 Ponalrestat 10 or Zopolrestat 11 are accessible starting from the corresponding phthalazinones.The development of new and efficient methodologies for the synthesis of such potentially bioactive phthalazine derivatives is important.3][14][15][16][17][18] Therefore, functionalization of the nucleus continues to be of synthetic interest.In general, most of the structural modifications of the parent system which have been carried out in order to optimize the biological activity of phthalazine-derived drugs can be seen as a variation of the substitution pattern at position 1, 2 and 4, i.e. the substitution pattern of the 1,2-diazine part of the bicyclic system.Considerably less efforts has been devoted in the modification of the benzene part of the phthalazine skeleton. 19n the present paper we are reporting synthesis of some phthalazinones and their imidoxy derivatives.The newly synthesized compounds have been tested for their biological activity evaluation.

Antimicrobial activity
The antimicrobial activity of the synthesized compounds 6a-d and 7a-d was determined in vitro against a variety of bacteria and fungi.Comparative studies between the activity of our prepared compounds and standard drug were also carried out.The tests were carried out using discdiffusion method. 21The compounds were dissolved in DMF, and activity mentioned on 1000 ppm.Agar plates were surface inoculated uniformly from fresh broth culture of the gram +ve and gram -ve bacteria and fungi.The Gram +ve bacteria was Baccilus stablius; the Gram -ve bacteria were Proteus mirabilus, Klebsiella peumoniae, Salmonella typhi and the fungi were Candida albicans (MTCC 227) and Aspergillus fumigatus (MTCC 2550).Flucanazole and Etraconazole were used as standard for antibacterial and antifungal activity respectively.The discs were incubated at 5˚C for 1 h. to permit good diffusion and the incubated at 28˚C for 24 h, the zones of inhibition were measured in mm.
From the data presented in Table 1, it is clear that compound 6a and 6d possess good activity against Proteus mirabilus, Klebsiella peumoniae, but show only moderate activity against Baccilus stablius, Salmonella typhi.Other compounds exhibit low antibacterial activity against all organisms.On the other hand, it was observed that almost all compounds show good activity against both fungal strains as compared to standard Etraconazol.Only compound 6d shows low antifungal activity.Thus it could be concluded that all the tested compounds exhibited relatively better antifungal activity, but weak activity against Gram +ve bacteria than those of Gram -ve bacteria.

Experimental Section
General Procedures.All melting points were determined in open capillary tube and are uncorrected.The IR spectra were recorded on Perkin-Elmer spectrophotometer.The 1 H NMR spectra were registered on a DRX-300 MHz.Spectrometer (300 MHz) in DMSO-d 6 using TMS as internal standard and the chemical shifts are expressed in δ ppm.The mass spectra were recorded on Jeol SX-102 (FAB).m-nitrobenzyl alcohol (NBA) was used as matrix.Purity of synthesized compounds was checked by TLC using silica gel-G.Spots were exposed in an iodine chamber.Compounds 1a-b were prepared according to literature procedure 20 and recrystallized prior to use.

Table 1 .
Antimicrobial activity of compounds 6a-d and 7a-d.(Zone of inhibition) ).A mixture of phthalyloglycine 1a (20.7 g, 0.1 mol), phthalic anhydride (14.8 g, 0.1 mol) and sodium acetate (4 g) was fused at 200 o C on an oil bath for 4 h.The solid obtained was acidified with dil.HCl (5%), washed with water and recrystallized from methanol to give 2a.