Synthesis , Characterization and Antimicrobial Activities of Some New Heterocyclic Schiff Bases Derived from Thiocarbohydrazide

The reaction of pyrazolobenzothienopyrimidine-3-carbaldehyde 1 with thiocarbohydrazide afforded the Schiff’s base 3. The latter compound reacted with some electrophilic reagents to give 1,2,4-triazoles 4–6 and 1,2,4-triazines 7–9. Treatment of compound 3 with 2-cyano-3,3-bis(methylthio)acrylonitrile gave the corresponding 5-amino-4-cyano-3methylthiopyrazole derivative 11. The reaction of pyrazole 11 with carbon disulfide afforded dithioxopyrazolopyrimidine 12. Acylation of compound 11 by using acetic anhydride yielded acetamide 13. On the other hand, the cyclocondensation of pyrazole 11 with acetic anhydride in pyridine yielded pyrazolopyrimidine derivative 14. The reactivity of compound 11 towards formamide and phenylisothiocyanate to give the pyrazolopyrimidines 15 and 16 was studied. The newly synthesized compounds were screened for their antimicrobial activity.


Introduction
Schiff bases 1,2 of heterocyclic compounds are interesting class of organic compounds possessing a wide spectrum of biological activities, such as antibacterial, antitubercular, antiinflammatory, anthelmintic, antiviral and antioxidant activities.Study of thiocarbohydrazide and its derivatives is of great interest due to the wide use of these compounds and their valuable reactions.Thiocarbohydrazides are an important class of compounds which possess applications in many fields.The chemistry of thiocarbohydrazides has gained increased interest in both synthetic organic chemistry and biological fields and has considerable value in many useful applications, such as the assessment process of the three-dimensional ultra structure examination techniques of interphase nuclei and tissues, besides their therapeutic importance. 35][6] Thiocarbohydrazide [7][8][9] is the clo-sest structural analogue of thiosemicarbazide, derivatives of which are recommended as effective antitubercular and antiviral preparations.1][12] In the view of these observations, we planned to synthesis some novel Schiff bases and to evaluate for antimicrobial activity.

1. Chemistry
Novel Schiff bases were obtained from condensation of thiocarbohydrazide with substituted aldehyde giving the monothiocarbohydrazone.Thus, condensation reaction of 10-oxo-4,6,7,8,9,10-hexahydroprazolo [1,5-a]  [1]benzothieno [2,3-d]pyrimidine-3-carbaldehyde (1) 13 with thiocarbohydrazide 2 14 in boiling absolute ethanol containing a catalytic amount of acetic acid gave the corresponding N'-[ (10-oxo-4,6,7,8,9,10-  The structure of the isolated product was confirmed on the basis of its elemental analysis and spectral data.Thus, the IR spectrum of compound 3 showed absorption bands at 1194, 1684, and 3198-3422 cm -1 corresponding to C=S, C=O, NH and NH 2 functions, respectively.Its 1 H NMR spectrum showed four D 2 O-exchangeable signals at δ 3.32, 9.50, 11.36 and 12.05 ppm assigned to NH 2 and three NH protons, respectively. Further, it is of interest to note that the thiocarbohydrazide 3 is a convenient intermediate for the synthesis of a novel isolated heterocyclic system.Thus, heating thiocarbohydrazone 3 under reflux with benzoyl chloride in pyridine gave The structures of compounds 7-9 were characterized from their spectroscopic as well as elemental analytical data.Thus, the IR spectrum of compound 7 revealed absorption bands at 1171, 1674 and 3200-3415 cm -1 corresponding to C=S, C=O and NH functions, respectively.Its  The structures of compounds 12-14 were determined using spectroscopic as well as elemental analytical data.Thus, no evidence for the presence of an amino (NH 2 ) group was seen in both the IR and 1 H NMR spectra.The IR spectrum of compound 13 showed absorption bands at 1254, 1701, 1684, 2205 and 3447 cm -1 corresponding to C=S, C=O, C≡N and NH functions, respectively.Its The 1 H NMR spectrum of compound 15 showed a characteristic singlet at δ 7.62 assigned to pyrimidine-H-6, in addition to three D 2 O-exchangeable signals at δ 3.38, 7.52 and 7.99 ppm attributed to NH 2 and two NH protons, respectively.Also, the structure of 15 was confirmed by its mass spectrum which exhibited the molecular ion peak at m/z 510 (M + , 2%) with a base peak at m/z 336 (100%).On the other hand, the 1 H NMR spectrum of compound 16 showed four D 2 O-exchangeable signals at δ 8.06, 8.20, 8.33 and 8.38 ppm assigned to four NH protons, in addition to an aromatic multiplet in the region δ 6.96-7.60.The structure of 16 was also supported by its mass spectrum which showed the molecular ion peak at m/z 618 (7.5%) corresponding to the molecular formula C 26 H 22 N 10 OS 4 , which agrees well with the molecular weight (618.77) and supports the identity of the structure and the base peak at m/z 336 (100%).

Biological Activities
The standardized disc agar diffusion method 15 was followed to determine the activity of the synthesized compounds against the sensitive organisms Staphylococcus  The compounds were dissolved in DMSO which has no inhibition activity to obtain concentration of 100 μg mL -1 .
The test was performed on medium potato dextrose agars (PDA) which contains infusion of 200 g potatoes, 6 g dextrose and 15 g agar. 16Uniform size filter paper disks (3 disks per compound) were impregnated by equal volume (10 μL) from the specific concentration of dissolved tested compounds and carefully placed on inoculated agar surface.After incubation for 36 h at 27 °C in the case of bacteria and for 48 h at 24 °C in the case of fungi, inhibition of the organisms was measured and used to calculate mean of inhibition zones.
The results depicted in Table 1 show various activities against all species of microorganisms which suggest that the variations in the structures affect the growth of the microorganisms.Thus, we can conclude from these results that some of the prepared compounds showed a low to high antimicrobial activity towards Gram-positive bacteria, Gram-negative bacteria and the fungal strain (Table 1).

1. General
Melting points are uncorrected and were recorded in open capillary tubes on a Stuart SMP3 melting point apparatus.Infrared spectra were recorded on FT-IR Jasco 4100 spectrophotometer using a KBr wafer technique.The 1 H and 13 C NMR spectra were recorded in DMSO-d 6 or CDCl 3 on Gemini spectrometer (300 MHz for 1 H NMR and 75 MHz for 13 C NMR) and the chemical shift ar given as δ downfield from TMS as an internal standard, measured at the Main Laboratories of the War Chemical.Elemental microanalyses were recorded on a Perkin Elmer series II CHNS analyzer 2400.Mass spectra were obtained using gas chromatography GCMS qp-2010 and on a Shimadzu instrument mass spectrometer (70 eV) at the Cairo University Microanalytical Center.10-Oxo-4,6,7,8,9,10-hexahydroprazolo[1,5-a][1]benzothieno[2,3-d]pyrimidine-3-carbaldehyde (1) has been prepared according to the reported method.
A mixture of compound 1 (0.273 g, 1 mmol) and thiocarbohydrazide 2 (0.106 g, 1 mmol) in absolute ethanol (10 mL) containing a few drops of acetic acid was heated under reflux for 1 h.After cooling, the precipitated solid was filtered off, air dried and recrystallized from ethanol to give 3 as yellow crystals.Yield 81%, mp

Table 1 .
The antimicrobial activity of the synthesized compounds