Synthesis and primary antiviral activity evaluation of 3-hydrazono-5-nitro-2-indolinone derivatives

A series of 5-nitro-3-[(5-nonsubstituted/methyl-4-thiazolidinone-2-ylidene)hydrazono]-1 H -2- indolinones ( 3a-j and 4a-h ) was synthesized by cyclization of 5-nitro-1 H -indole-2,3-dione-3-thiosemicarbazones ( 1a-k ) with ethyl bromoacetate or ethyl 2-bromopropionate. The primary antiviral activities of the new hydrazonoindolinone derivatives, the previously reported 5-nitro-1 H -indole-2,3-dione-3-thiosemicarbazones ( 1a-k ) and 1-morpholino/piperidinomethyl-5-nitro-indole-2,3-dione-3-thiosemicarbazones ( 2a-l ) were evaluated against some pathogenic viruses in the Rega Institue for Medical Research, Belgium. Among the tested compounds, 1c , 2b and 3b afforded some weak activity against the yellow fever virus (YFV) in vero cells, whereas compounds 2b , 3a , 3f , 4e and 4f inhibited the growth of bovine viral diarrhea virus (BVDV) in MDBK CODA cells.

The structures of 3 and 4 were confirmed by analytical and spectral data (IR, 1 H NMR, 13 C NMR and EIMS) (Table 1).In the IR spectra of 3 and 4, the C=S bands disappeared, a new C=O band (1756-1734 cm -1 ) indicative of the thiazolidinone structure appeared in addition to the lactam C=O stretching (1705-1689 cm -1 ) 6 . 1 H-NMR spectra of 3 and 4 did not display the signals of the thiosemicarbazone protons and exhibited a singlet or two singlets resulting from the indole ARKAT NH (δ 11.28-11.43ppm).The SCH 2 protons of 3 were observed as two singlets (δ 4.09-4.20 ppm and 4.11-4.24ppm) due to anisotropic effect of carbonyl group.The CH 3 (δ 1.60-1.72ppm) and the SCH (δ 4.47-4.58ppm) protons of 4 resonated as a doublet and a quartet, respectively 7 .In EIMS spectrum, 3d, 3f, 3i, 4c and 4e chosen as prototypes showed molecular ions with different intensity and the fragments peculiar to the indole and thiazolidinone moieties 8 .
The new 3-hydrazono-5-nitro-2-indolinone derivatives 3a-j and 4a-h and the previously synthesized 9 5-nitro-1H-indol-2,3-dion-3-thiosemicarbazones 1a-k and N-Mannich bases 2a-l were evaluated for in vitro antiviral activity against the yellow fever virus (YFV) (strain 17D) in vero cells and the bovine viral diarrhea virus (BVDV-strain NADL) in Madin-Dardy bovine kidney (MDBK CODA) cells in Rega Institue for Medical Research, Belgium 4,10,11 .For each compound, the 50% effective concentration (EC 50 ) and the minimal toxic concentration (MTC) or the 50% cytotoxic concentration (CC 50 ) were obtained.Ribavirin (Rib) was used as the standard in the tests.Both antiviral activity and cytotoxicity were determined by means of the MTS method.As can be seen in Table 2, some of the tested compounds afforded some weak activity against YFV, but at subtoxic concentrations.Among the compounds tested, the MTC ARKAT value of 1c, 2b and 3b are 100 µg/mL and the EC 50 of these compounds are 2.18, 11 and 2.52 µg/mL, respectively.The EC 50 and the MTC values of ribavirin are 45 and >100 µg/mL in the tests against YFV, respectively.When these data are examined, it is observed that 1c, 2b and 3b are more active, but more toxic than ribavirin.The most active compound against YFV was R 1allyl substituted thiosemicarbazone derivative 1c.In comparison with 1c, formation of N-Mannich bases (2b, 2c) and 5-methyl-4-thiazolidinone derivatives(4a) caused a decrease in antiviral activity against YFV.5-Nonsubstituted 4-thiazolidinone derivative (3c) exhibited no change in activity when compared to 1c, but demonstrated higher toxicity, whereas compounds 2b, 3a, 3f, 4e and 4f inhibited the growth of BVDV.The EC 50 values of these compounds are 40, 50, 44, 13 and 48 µg/mL, respectively.The EC 50 value of ribavirin is 40 µg/mL in the tests against BVDV.The results of 2b, 3a, 3f, 4e and 4f were compared with ribavirin.Compound 4e showed much higher antiviral activity than that of ribavirin.Among 5-nitro-3-hydrazono-2indolinone derivatives tested against BVDV, 4-thiazolidinone derivatives 3 and 4 were more active than 3-thiosemicarbazones 1 and N-Mannich bases 2. In addition, the presence of the methyl group at C-5 of the thiazolidinone ring also seems to have a significant impact on the resultant antiviral activity.Considering the anti-BVDV effect of substituents on the thiazolidinone ring, R 1 -aryl substituted were more active than the corresponding alkyl substituted ones.In fact, R 1 -(4-bromophenyl) substituted 5-methyl-4-thiazolidinone derivative 4e showed the most favourable antiviral activity against BVDV.3-Hydrazono-5-nitro-2-indolinone derivatives 1-4 were also evaluated against the hepatitis C virus in Huh-5-2 cells, the parainfluenza-3 virus, reovirus-1, sindbis virus, coxsackie virus B4 and punta toro virus in vero cells, herpes simplex virus-1, herpes simplex virus-2, vaccinia virus, vesicular stomatitis virus in human embryonic lung (HEL) cells and vesicular stomatitis virus, coxsackie virus B4 and respiratory syncytial virus in HeLa cells.Whereas, no specific antiviral effects (i.e.minimal antivirally effective concentration ≥ 5-fold lower than minimal cytotoxic concentration) were noted for any of the compounds against any of the viruses.
The obtained preliminary results suggest that some of these compounds might serve as potential candidates for antiviral agents. .

5-Nitro-3-[(3-phenyl-4-thiazolidinone-2-ylidene)hydrazono]-1H-2-indolinone (3f).
IR (ν, cm -1 ): 3320 (NH), 1735, 1698 (C=O), 1524, 1341 (NO 2 ).Antiviral activity assays.Antiviral activity against the yellow fever virus (YFV), hepatitis C virus (HCV), the parainfluenza-3 virus, reovirus-1, sindbis virus, coxsackie virus B4, punta toro virus, herpes simplex virus-1, herpes simplex virus-2, vaccinia virus, vesicular stomatitis virus, coxsackie virus B4 and respiratory syncytial virus was determined essentially as described previously 11 .Antiviral activity assay for BVDV.MDBK cells were seeded at a density of 5 x 10³ per well in 96-well cell culture plates in MEM-FCS.Following 24 h incubation at 37°C and 5% CO 2 medium was removed and 5-fold serial dilutions of the test compounds were added in a total volume of 100 µL, after which the cp BVDV virus inoculum [100 CCID 50 (50% cell culture infective dose) in 100 µL] was added to each well.This inoculum resulted in a greater than 90% destruction of the cell monolayer after 4-5 days of incubation at 37°C.Uninfected cells and cells receiving virus without compound were included in each assay plate.After 5 days, medium was removed, and 90 µL of MEM-FCS supplemented with 10 µL of MTS/PMS solution (Promega, Leiden, The Netherlands) was added to each well.Following a 2 h incubation period at 37°C, the optical density of each well was read at 498 nm in a microplate reader.The 50% effective concentration (EC 50 ) was defined as the concentration of compound of which 50% cell viability was protected from virus-induced cytopathic effect (CPE) 4 .Cytostatic assay for BVDV.MDBK cells were seeded at a density of 5 x 10 3 cells per well of a 96-well plate in MEM-FCS.24 hours later, serial dilutions of the test compounds were added.Cells were allowed to proliferate for 3 days at 37°C, after which the cell number was determined by means of the MTS/PMS method (Promega).The 50% cytotoxic concentration (CC 50 ) was defined as the concentration that inhibited the proliferation of exponentially growing cells by 50%.

Table 1 .
Formulas, physical constants and elemental analyses for 3 and 4

Table 2 .
1ntiviral activity and cytotoxicity on YFV and BVDV of compounds 1-4 M.p.'s were determined on a Büchi 530 apparatus and are uncorrected.Elemental analyses were performed on Carlo Erba 1106 elemental analyzers.IR spectra were recorded on KBr discs, using a Perkin Elmer 1600 FT-IR spectrometer.1HNMR and 13 C NMR spectra were obtained on Bruker AC 200 (200 and 50.3 MHz) spectrophotometer using DMSOd 6 .EIMS (70 eV) were recorded onVG Zab Spec.