Synthesis of a New [3-(4-Chlorophenyl)-4-oxo-1, 3-thiazolidin-5-ylidene]acetic Acid Derivative

: The new methyl [3-(4-chlorophenyl)-2-{[(2,4-dichloro-1,3-thiazol-5-yl)methylidene] hydrazinylidene}-4-oxo-1,3-thiazolidin-5-ylidene]acetate was synthesized from 4-(4-chlorophenyl)-1-(2,4-dichloro-1,3-thiazol-5-yl)methylidene-3-thiosemicarbazide using dimethyl acetylenedicarboxylate as thia-Michael reaction acceptor. New compounds ( 3 and 4 ) were characterized by IR, 1 H and 13 C NMR spectroscopy methods.


Introduction
Toxoplasmosis is a common parasitic infectious disease that occurs all over the world. Toxoplasmosis is caused by the protozoan Toxoplasma gondii, whose ultimate host is Felidae. Approximately 30% of people have positive antibodies indicating toxoplasmosis [1]. The basic danger of the disease is the possibility of congenital infections during pregnancy and the reactivation of the disease in immunocompromised persons.
In addition, the currently used drugs are not 100% effective for the treatment of toxoplasmosis, and this has prompted us to look for new synthetic compounds that could be used to combat this common parasite in the future.
In our previous research [12], we identified (4-oxothiazolidin-5-yl/ylidene)acetic acid derivatives with antiparasitic activity against T. gondii ( Figure 1). The highlighted fragments (green and orange color) in Figure 1 are favorable for anti-T. gondii activity. Based on previous studies, we designed a compound which contains both highlighted fragments.
4-(4-chlorophenyl)-3-thiosemicarbazide to give the thiosemicarbazone (3). In the last step of synthesis, the targeted compound was obtained from 4-(4-chlorophenyl)-1-(2,4-dichloro-1,3-thiazol-5-yl)methylidene-3-thiosemicarbazide (3) and dimethyl acetylenedicarboxylate by thia-Michael addition of the sulfur atom to the triple bond and then cyclization to give the (4-oxothiazolidin-5-ylidene)acetic acid derivative 4 (Scheme 1), which illustrates that precursor 3 is also useful for this type of reaction, if other compounds (maleic anhydride, maleimide derivatives etc.) are used as acceptors in the thia-Michael addition.  The structures of compounds 3 and 4 were supported by IR, 1 H, and 13 C NMR spectroscopy methods (see Supplementary Materials). The 1 H NMR spectra exhibit the characteristic signals for para-substituted phenyl ring as two doublets in the range 7.44 to 7.76 ppm with spin-spin coupling J = 8.7Hz. The signals derived from the proton of a CH=N group were observed at 8.29 ppm and 8.30 ppm for compounds 3 and 4, respectively. The characteristic proton signal of methylidene group (CH=) of compound 4 was observed as singlet at 6.94 ppm. All remaining signals arising from other parts of the molecule were present. Similarly, 13 C NMR confirmed present of all carbon atoms in molecule (details were presented in the experimental part).

General
All commercial reagents and solvents were purchased from either Alfa Aesar (Lancaster, UK) or Sigma-Aldrich (St. Louis, MO, USA) and used without further purification. The melting points were determined by using Gallenkamp MPD 350.BM 3.5 apparatus Sanyo (Moriguchi, Japan) and are uncorrected. The purity of the compound was checked by TLC on plates with silica gel Si 60F254, produced by Merck Co. (Darmstadt, Germany). The 1 H NMR and 13 C NMR spectra were recorded by a Bruker Avance 300 MHz instrument (Bruker Corporation, Billerica, MA, USA) using DMSO-d6 as solvent and TMS as an internal standard. Chemical shifts were expressed as δ (ppm). IR spectrum was recorded by Nicolet 6700 spectrometer (Thermo Scientific, Philadephia, PA, USA). Elemental analysis was performed by AMZ 851 CHX analyzer (PG, Gdańsk, Poland) and the results were within ±0.4% of the theoretical value.

General
All commercial reagents and solvents were purchased from either Alfa Aesar (Lancaster, UK) or Sigma-Aldrich (St. Louis, MO, USA) and used without further purification. The melting points were determined by using Gallenkamp MPD 350.BM 3.5 apparatus Sanyo (Moriguchi, Japan) and are uncorrected. The purity of the compound was checked by TLC on plates with silica gel Si 60F 254 , produced by Merck Co. (Darmstadt, Germany). The 1 H NMR and 13 C NMR spectra were recorded by a Bruker Avance 300 MHz instrument (Bruker Corporation, Billerica, MA, USA) using DMSO-d 6 as solvent and TMS as an internal standard. Chemical shifts were expressed as δ (ppm). IR spectrum was recorded by Nicolet 6700 spectrometer (Thermo Scientific, Philadephia, PA, USA). Elemental analysis was performed by AMZ 851 CHX analyzer (PG, Gdańsk, Poland) and the results were within ±0.4% of the theoretical value.