Design, Synthesis, and Antibacterial Evaluation of Some Novel 3′-(Phenylamino)-1′H-spiro[indoline-3,2′-quinazoline]-2,4′(3′H)-dione Derivatives

Abstract A combinatorial synthesis and evaluation of antibacterial activity against clinically isolated resistant strains of Gram-positive and Gram-negative bacteria of 3′-(phenylamino)-1′H-spiro[indoline-3,2′-quinazoline]-2,4′(3′H)-dione derivatives is described. GRAPHICAL ABSTRACT

It is noticeable that when the isatoic anhydride 1a and b, isatin 2a-m, and phenyl hydrazine 3 in the presence of alum were stirred at reflux for 1 h, in all cases the reaction led to the formation of the intermediate 8 that could be isolated and characterized by spectroscopic methods. Furthermore, the continuation of reaction for 3 h led to a mixture of 4a-m and intermediates 8 (monitored by thin-layer chromatography, TLC, and spectroscopic methods); meanwhile, after the times indicated in Table 1, just 4a-m were obtained and the intermediates 8 was not detected in the final mixture.
According to the results, the reaction can be mechanistically considered to proceed via the initial formation of the intermediates 8 by the nucleophilic addition of phenyl hydrazine to isatoic anhydride as a key intermediate. Then, the isatin attacks N-atom from 8 to form an intermediate 9, leaving a water to afford 10, which then transforms the final product via nucleophilic attack by the nitrogen group (Scheme 2).
The newly synthesized compounds were screened in vitro for their antibacterial activities against of bacteria Escherichia coli ATCC 25922, Pseudomonas aeruginusa ATCC 85327, and Klebsiella pneumonia ATCC 29655 (Gram-negative bacteria) and Enterococcus faecalis ATCC 29737, Bacillus subtilis ATCC 465, Bacillus pumilus PTCC 1114, Micrococcus luteus PTCC 1110, Staphylococcus aureus ATCC 25923, Staphylococcus epidermidis ATCC 12228, and Sterptococcus mutans PTCC 1601 (Gram-positive bacteria) by the disk diffusion method (IZ) [37] and subsequently the minimum inhibitory concentration method (MIC). [38] Scheme 2. Reasonable mechanism for the formation of Activities of each compound were compared with tetracycline and gentamicin as standards. MIC and IZ results for bacterial strains are shown in Table 2.
The screening results indicate that some of the tested compounds exhibit significant antibacterial activities when compared with the reference drugs. It was observed that the compounds containing R 1 ¼ H and R 3 ¼ Cl substituted groups show better activity than the other test compounds and the reference (tetracycline and gentamicin), drugs.

CONCLUSION
In summary, we have developed a new strategy that provides an efficient entry to 1 0 H-spiro[isoindoline-1,2 0 -quinazoline]-3,4 0 (3 0 H)-dione derivatives via a one-pot, three-component reaction from isatoic anhydride, isatine, and phenyl hydrazine. Our designed process requires mild reaction conditions, has good yields of products, uses very simple accessible starting materials and solvents as well as an inexpensive, nontoxic, and easily available heterogeneous catalyst, and has an easy experimental workup procedure.
Melting points were obtained in open capillary tubes and were measured on an Electrothermal 9200 apparatus. Mass spectra were recorded on a Shimadzu QP 1100 BX mass spectrometer. The IR spectra were recorded on KBr pellets on a Shimadzu IR-470 spectrophotometer. 1 H and 13 C NMR spectra were determined on a Bruker 300 DRX Avance instrument at 300 and 75 MHz. Elemental analyses for C, H, and N were performed using a Heraus CHN rapid analyzer.

SUPPLEMENTARY INFORMATION
General experimenl procedures, IR, 1 H and 13 C NMR, and MS data and experimental analysis for compounds 4a-m are available online.