1. Introduction

2. Materials and Methods

3. Results and discussion

3.1. Synthesis of the metal complexes

The interaction of metal ions with L1 and L2 in molar ratio of metal:ligand:base (1:4:2) resulted in the formation of the complexes with suggested formulas given in Table 1. The results of elemental analysis for the metal ions were determined by Microwave Plasma – Atomic emission spectrometry. They allow to suppose the tentative average composition of different complexes.

All of the complexes are stable in air and moisture and their solubility is limited. We found that the reaction of L1 and L2 with the transition metal ions afforded a 40-72 % yield of a stable solid compound. The obtained complexes have a yellow-green or brown colour and are limited solubility in DMSO and DMF, except Cu(II)L2 (soluble in DMSO only) and insoluble in water, THF, C₂H₅OH, EtOAc, and cyclohexane. The analytical data including the yield percentage of the complexes are presented in Table 2.

Table 2. Analytical and physical characteristic of metal complexes with 6-methyl-2-thiouracil.

Table 2. Analytical and physical characteristic of metal complexes with 6-methyl-2-thiouracil.

complexes	Colour	Yield (%)	Melting point (°C)	Solubility
L1	colorless		330	soluble in DMSO
Cu(II)L1	yellow-green	61	>350 ᵒC	soluble in DMSO, DMF, C2H5OH, H2O and insoluble in THF, EtOAc and C6H12.
Pd(II)L1	brown	72	>350 ᵒC	soluble in DMSO, DMF and insoluble in H2O, THF, C2H5OH, EtOAc and C6H12.
L2	colorless		218-220	soluble in DMSO
Cu(II)L2	yellow-green	43	260-263 ᵒC	soluble in DMSO and insoluble in H2O, THF, C2H5OH, EtOAc and C6H12.
Pd(II)L2	brown	70	255-257 ᵒC	soluble in DMSO, DMF and insoluble in H2O, THF, C2H5OH, EtOAc and C6H12.

IR Verification of the structures of the metal complexes can be easily achieved by comparing the IR spectra of the free ligands with that of their metal complexes. The selected experimental data from the IR spectra of the complexes Cu(II)L1 and Pd(II)L1 and of the free ligand, cm^-1 is given in Table 3.

Table 3. Selected experimental IR data (in KBr, wavenumber in cm^-1) for 6-methyl-2-thiouracil and its complexes.

Table 3. Selected experimental IR data (in KBr, wavenumber in cm^-1) for 6-methyl-2-thiouracil and its complexes.

assignment	L1	Cu(II)L1	Pd(II)L1
ν(OH)	-	-	3442
ν(NH)	3115 sh	3115	3111
ν(NH)	3080	3080	3071
ν(=CH)	3014	3003	3052
ν(C=O)	1676 m	1637	1678
	1560 w	1559	1559
ν(C=S)	1242	1242	1244
	1167 s	1167	1168

In the IR spectra of the free ligand L1 the bands at 3115 cm^-1 and 3080 cm^-1 are observed which may refer to the stretching vibrations of N-H groups. In the spectrum of the Cu(II) complex the same bands are observed at the same frequencies. In the IR spectrum of the Pd(II)L1 these bands are shifted to the lower frequencies as compared to the free ligand bands with 4 cm^–1 and 9 cm^–1, respectively. This fact shows that the two NH groups of the ligand participate in the coordination for palladium complex. The L1 IR bands at 1676 and 1242 сm^-1 can be attributed to the stretching vibration of C⁴=O and C²=S groups, respectively. The stretching vibration of C⁴=O in CuL1 complex is shifted to the lower frequency with 39 сm^-1 as compared to this stretching in the free ligand. The same bands in IR spectrum of the PdL1 complex are not changed. In the ATR spectrum of PdL1 complex the band at 3400 cm^–1 may refer to the stretching vibrations of molecular H₂O. This band missed for CuL1 complex.

In the IR spectrum of the free ligand L2 the bands at 3112 cm^-1 and 3093 cm^-1 are observed which may refer to the stretching vibrations of N-H groups. In the spectrum of the copper complex the same bands are observed at the same frequencies. In the IR spectrum of the PdL2 complex these bands are shifted; the first with +5 cm^–1 and the second with -13 cm^–1 as compared to those in the free ligand spectrum. This fact shows that the two NH groups of the ligand participate in the coordination for PdL2. In the IR spectrum of L2 the bands at 1656 and 1243 сm^-1 can be attributed to the stretching vibrations of C⁴=O and C²=S groups, respectively. The band for C²=S group is shifted to the lower frequencies as compared to the free ligand spectrum with 11 cm^-1 and to the higher frequencies with 18 сm^-1 for the CuL2 and PdL2 complexes, respectively. The band at 3451 and 3437 cm^–1 in the IR spectrum of the two complexes may refer to the stretching vibrations of OH^- (CuL2) and molecular H₂O (PdL2), Table 4. The solid state ATR spectra confirm these findings.

Table 4. Selected experimental IR data (in KBr, wavenumber in cm^-1) for 6-propyl-2-thiouracil and its complexes.

Table 4. Selected experimental IR data (in KBr, wavenumber in cm^-1) for 6-propyl-2-thiouracil and its complexes.

assignment	L2	Cu(II)L2	Pd(II)L2
ν(OH)	-	3451	3437
ν(NH)	3112	-	3117
ν(NH)	3093	3093	3080
ν(=CH)	3042	3042
ν(C=O)	1656	1651	1657
	1557	1553	1545
ν(C=S)	1243	1232	1261
	1165	1166	1175

The stretching vibrations of C⁴=O and C²=S appear at 1635 and 1245 сm^-1 in the Raman spectrum of 6-metyl-2-thiouracil and 1661 and 1243 сm^-1 in that for 6-propyl-2-thiouracil, respectively. In the Raman spectrum of the CuL2 the band for C=S group is shifted with 13 сm^-1 to the lower frequency.

The ¹H NMR spectrum of 6-metyl-2-thiouracil (L1) shows four signals; a singlets at 12.29 ppm is for H-1 and H-3 (overlap resonances). The olefin proton appears at 5.68 ppm (H-5), and 2.06 ppm is for H-1’. These assignments are confirmed by ¹H-¹H COSY, ¹H-broadband decoupled ¹³C-NMR, DEPT-135 and HMBC spectra and are given in Table 5.

Table 5. ¹H and ¹³C NMR spectral data and ¹H-¹H COSY and HMBC correlations for 6-methyl-2-thiouracil [600.13 MHz (¹H) and 150.903 MHz (¹³C)]^a.

Table 5. ¹H and ¹³C NMR spectral data and ¹H-¹H COSY and HMBC correlations for 6-methyl-2-thiouracil [600.13 MHz (¹H) and 150.903 MHz (¹³C)]^a.

Atom	δ (13C) ppm	DEPT-135	δ (1H) ppm	Multiplicity (J, Hz)	1H-1H COSY	HMBC
1 (NH)			12.29	s
2 (C=S)	175.87	C
3 (NH)			12.29	s
4 (C=O)	161.06	C
5	103.72	CH	5.68	d (0.9)	7	4b, 6, 7
6	153.20	C
1’	18.11	CH3	2.06	d (0.7)	5	5, 6

a) In DMSO-d6 solution. All these assignments were in agreement with COSY, HMQC and HMBC spectra. b) These correlations are weak.

The ¹H NMR and ¹³C NMR spectral data of the Cu(II) and Pd(II) complexes are presented in Table 6 and Table 7, respectively.

The ¹H NMR and ¹³C NMR spectra in DMSO-d6 solution of CuL1 show the same values of chemical shift to those of L1 but the solid-state NMR differentiates between them, see Table 6, 7, 11 and Figure 1. The ¹³C NMR spectrum of the L1 registered with crosspolarisation (CP) experiment shows five signals. Two of them, at 174.6 and 163.0 ppm, are for the C=S and C=O, respectively.

Figure 1. Solid-state NMR of the ligand L1 (a) and its complex with copper (b).

Figure 1. Solid-state NMR of the ligand L1 (a) and its complex with copper (b).

In the ¹³C NMR solid state spectrum of CuL1 the two couples at 171.7 / 174.8 ppm and 162.9 / 169.5 ppm are for C=S and C=O groups, respectively. This means that the resonance for C=S is upfield shifted with 2.9 ppm and the signal for C=O is downfield shifted with 6.5 ppm, respectively. This fact shows that the C=S and C=O groups of the ligand participate in the coordination with the copper. The two couples at 104.7 / 105.4 ppm and 154.0 / 156.4 ppm, Table 11, are for the carbon atom in 5 and 6 position, respectively.

The ¹H NMR solution spectrum of PdL1 shows that the signals for the two amine protons (H-1 and H-3) are upfield shifted with 1.49 and 1.43 ppm. Also, all resonances of the free ligand are present in excess; this could be from the remaining reagent, L1, or from the decomposition of PdL1 in the solution. In the ¹³C NMR solution spectrum of the PdL1 only methyl and olefin resonances of the coordinated ligand can be seen; the others are indistinguishable from the noise.

The ¹H NMR spectrum of 6-propyl-2-thiouracil (L2) shows six signals: two broad singlets at 12.20 ppm (H-1) and 12.31 ppm (H-3). The olefin proton appears at 5.67 ppm (H-5), and 2.32 ppm is for H-1’, 1.54 ppm for H-2’, 0.87 ppm for H-3’. These assignments are confirmed by ¹H-¹H COSY, ¹H-broadband decoupled ¹³C-NMR and DEPT-135 spectra and are given in Table 8.

Table 8. ¹H and ¹³C NMR spectral data and ¹H-¹H COSY and HMBC correlations for 6-propyl-2-thiouracil [500.13 MHz (¹H) and 150.903 MHz (¹³C)]^a.

Table 8. ¹H and ¹³C NMR spectral data and ¹H-¹H COSY and HMBC correlations for 6-propyl-2-thiouracil [500.13 MHz (¹H) and 150.903 MHz (¹³C)]^a.

Atom	δ (13C) ppm	DEPT -135	δ (1H) ppm	Multiplicity (J, Hz)	1H-1H COSY
1 (NH)	-	-	12.20	s
2 (C=S)	176.08	C	-
3 (NH)	-	-	12.31	s
4 (C=O)	161.22	C	-
5	103.06	CH	5.67	s
6	156.74	C
1’	33.21	CH2	2.32	t(7.5)	2’
2’	20.58	CH2	1.54	sx(7.4)	1’, 3’
3‘	13.26	CH3	0.87	t(7.4)	2’

a) In DMSO-d6 solution. All these assignments were in agreement with COSY spectra.

In the ¹H NMR and ¹³C NMR solution spectra of CuL2 only the free ligand resonances are presents. In the solid state ¹³C NMR spectrum there are resonances for both free and coordinated ligand. In the proton spectrum of CuL2 in DMSO-d6 appears a singlet at 2.54 ppm for DMSO-h6 that was coordinated to Cu(II) in the process of synthesis. The data about L2 and CuL2 are summarized and shown in Table 9, Table 10 and Table 11 and Figure 2. a,b,c.

Figure 2. Solid-state NMR of the ligand L2 and its complexes: a) ¹³C CP spectrum of L2; b) ¹³C CP spectrum of Cu(II)L2; c) ¹³C CPPI spectrum of Cu(II)L2; d) ¹³C CP spectrum of Pd(II)L2.

Figure 2. Solid-state NMR of the ligand L2 and its complexes: a) ¹³C CP spectrum of L2; b) ¹³C CP spectrum of Cu(II)L2; c) ¹³C CPPI spectrum of Cu(II)L2; d) ¹³C CP spectrum of Pd(II)L2.

Table 11. ¹³C NMR spectral data (in ppm) for L1 and L2 and some of the complexes aquired with crosspolarisation experiments, external reference α-glycine carbonyl C (176.03 ppm).

Table 11. ¹³C NMR spectral data (in ppm) for L1 and L2 and some of the complexes aquired with crosspolarisation experiments, external reference α-glycine carbonyl C (176.03 ppm).

Atom	L1	L2	Cu(II)L1	Cu(II)L2	Pd(II)L2
1 (NH)
2 (C=S)	174.6	175.5	171.7/174.8	168.3/175.4	172.3/172.9/174.0
3 (NH)
4 (C=O)	163.0	164.8	162.9/169.5	164.9/166.1	160.3/166.4/167.0
5 (CH)	104.7	103.8/104.6	104.7/105.4	103.8/104.6/105.4/107.2	95.8/103.1/105.0
6 (C)	156.2	159.9	154.0/156.4	159.9/161.3	153.0/156.0/159.7
1´	20.2	32.7	20.1	32.7/39.3/39.6/40.9	33.4/34.2/38.6
2´		19.6/20.2		18.2/19.7/20.2/24.4	18.2/19.3/19.7
3´		13.1/14.7		13.1/13.6/14.7/15.7	12.9/15.4
DMSO				40.3

The ¹³C NMR spectrum of the L2 registered with crosspolarisation experiment shows seven signals. The two signals at 175.5 and 164.8 ppm are for the C=S and C=O, respectively. In the ¹³C NMR spectrum with crosspolarisation experiment of CuL2 the signal for C=S is upfield shift of 7.2 ppm. This fact showed that the C=S group of the ligand participate in the coordination with the copper. Also, there appears a signal at 40.3 ppm that confirms the coordination of DMSO-h6 to Cu(II).

There are six couples of signals in ¹H NMR spectrum of Pd(II) complex with 6-propyl-2-thiouracil. In each couple one of the resonances is for the free ligand (the L2) other for the coordinated L2. The couples at 12.20 / 10.77 ppm and 12.32 / 10.87 ppm are for NH at first and third position. The couple at 5.68 / 5.31 ppm is for olefin proton 5. The three couples at 2.32 ppm (t,7.3) / 2.25 (t,7.3) ppm, 1.54 ppm (sx, 7.6) / 1.48 ppm (m) and 0.87 ppm (t, 7.3) / 0.82 ppm (m) are for propyl protons (H-1’), (H-2’) and (H -3’), respectively. There appears a singlet at 2.54 ppm that is for DMSO-h6. It is interesting to note that all resonances are shifted for coordinated L2 as compared to free L2 but the shifts are higher for NHs. In PdL2 the singlets for NH-1 and NH-3 are upfield shifted with 1.43 and 1.44 ppm, respectively.

The ¹³C NMR solution spectrum of PdL2 shows seven groups of signals. The two signals with the highest chemical shift, at 176.02 ppm and 164.19 ppm, are for the C=S and C=O in PdL2, respectively. There is also a resonance at 161.09 ppm (free ligand), a.e. there is downfield shift of 2.97 ppm. This fact shows that the C=O group of the ligand participate in the coordination with Pd(II).

In the CP NMR spectrum of PdL2 the signal for C=S is upfield shifted with 3.2 and 2.6 ppm. In the same spectrum there are three signals for C=O, Table 11. One is upfield shifted with 4.5 ppm and the other downfield shifted with 2.2 ppm. This fact showed that the C=S and C=O groups of the ligand participate in the coordination with the palladium in two different ways.

The ATR spectra of CuL2 and PdL2 show the presence of H₂O and/or OH^-.

According to the solid-state NMR, clear shifts in the signals of the carbon atoms were observed in the complex of Cu(II) with L1, indicating the presence of the complex. There are also signals corresponding to the starting ligand L1, which may or may not be included in the second coordination sphere.

In the case of ligand L2 the situation is more complicated. The ligand itself shows doubled signals for the carbon atoms C-5, C-2´ and C-3´ possibly due to a different spacial arrangement of these atoms in the crystalline lattice of the ligand (Figure 2, a). In the case of the Cu(II)L2 complex, the ligand signals can still be observed, accompanied by the complex signals. What is different in this case is the presence of DMSO included in the complex as a ligand. Despite the presence of many C-1´ signals around it in the CP spectrum (Figure 2, b), the DMSO signal can be easily identified in the CPPI spectrum (Figure 2, c).

The ¹³C spectrum of Pd(II)L2 obtained by cross-polarisation (CP) (Figure 2, d) presents other complications. There are multiple signals for each type of carbon atom in the ligand, indicating the presence of more than one palladium complex or a palladium complex with two ligands in the coordination sphere simultaneously.

5. Conclusions

References

1. Abou El E. D., A.; Ghorab, M.M.; Noaman, E.; Heiba, H.I.; Khalil, A.I. Molecular modeling study and synthesis of novel pyrrolo[2,3-d]pyrimidines and pyrrolotriazolopyrimidines of expected antitumor and radioprotective activities. Bioorg. Med. Chem. 2008, 16, 2391–2402. [Google Scholar] [CrossRef] [PubMed]
2. Renau, T.E.; Wotring, L.L.; Drach, J.C.; Townsend, L.B. Synthesis of Non-nucleoside Analogs of Toyocamycin, Sangivamycin, and Thiosangivamycin: Influence of Various 7-Substituents on Antiviral Activity. J. Med. Chem. 1996, 39, 873–880. [Google Scholar] [CrossRef] [PubMed]
3. Kuyper, L.F.; Garvey, J.M.; Baccanari, D.P.; Champness, J.N.; Stammers, D.K.; Beddell, C.R. Pyrrolo [2,3-d] pyrimidines and Pyrido [2,3-d] pyrimidines as Conformationally Restricted Analogues of the Antibacterial Agent Trimethoprim. Bioorg. Med. Chem. 1996, 4, 593–602. [Google Scholar] [CrossRef] [PubMed]
4. Andrus, P.K.; Fleck, T.J.; Oostveen, J.A.; Hall, E.D. Neuroprotective Effects of the Novel Brain-Penetrating Pyrrolopyrimidine Antioxidants U-101033E and U-104067F Against Post-Ischemic Degeneration of Nigrostriatal Neurons. J. Neurosci. Res. 1997, 47, 650–654. [Google Scholar] [CrossRef]
5. Chamberlain S., D.; Redman A., M.; Wilson J., W.; Deanda, F.; Shotwell J., B.; Gerding, R.; Lei, H.; Yang, B.; Stevens K., L.; Hassell A., M.; Shewchuk L., M.; Leesnitzer M., A.; Smith J., L.; Sabbatini, P.; Atkins, C.; Groy, A.; Rowand J., L.; Kumar, R.; Mook Jr R., A.; Moorthy, G.; Patnaik, S. ; Optimization of 4,6-bis-anilino-1H-pyrrolo[2,3-d]pyrimidine IGF-1R tyrosine kinase inhibitors towards JNK selectivity. Bioorg. Med. Chem. Lett. 2009, 19, 360–364. [Google Scholar] [CrossRef] [PubMed]
6. Amin, K.M.; Hanna, M.M.; Abo-Youssef, H.E.; George, R.F. Synthesis, analgesic and anti-inflammatory activities evaluation of some bi-, tri- and tetracyclic condensed pyrimidines. Eur. J. Med. Chem. 2009, 44(11), 4572–4584. [Google Scholar] [CrossRef] [PubMed]
7. Meade, E.A.; Sznaidman, M.; Pollard, G.T.; Beauchamp, L.M.; Howard, J.L. Anxiolytic activity of analogues of 4-benzylamino-2-methyl-7H-pyrrolo[2,3-d]pyrimidin. Eur. J. Med. Chem. 1998, 33, 363–374. [Google Scholar] [CrossRef]
8. Cooper D., S. ; Antithyroid Drugs. The New England Journal of Medicine 2005, 352, 905–917. [Google Scholar] [CrossRef] [PubMed]
9. Volpé, R. ; The Immunomodulatory Effects of Anti-thyroid Drugs are Mediated via Actions on Thyroid Cells, Affecting Thyrocyte-immunocyte Signalling: A Review. Curr. Pharm. Des. 2001, 7, 451–460. [Google Scholar] [CrossRef]
10. Burch H., B.; Cooper, D.S. Antithyroid drug therapy: 70 years later. Eur. J. Endocrinol. 2018, 179, R261–R274. [Google Scholar] [CrossRef]
11. Mao, X.-M.; Li, H.-Q.; Li, Q.; Li, D.-M.; Xie, X.-J.; Yin, G.-P.; Zhang, P.; Xu, X.-H.; Wu, J.-D.; Chen, S.-W.; Wang, S.-K. Prevention of Relapse of Graves’ Disease by Treatment with an Intrathyroid Injection of Dexamethasone. J Clin Endocrinol Metab. 2009, 94, 4984–4991. [Google Scholar] [CrossRef] [PubMed]
12. Rosenfeld, H.; Ornoy, A.; Shechtman, S.; Diav-Citrin, O. Pregnancy outcome, thyroid dysfunction and fetal goitre after in utero exposure to propylthiouracil: a controlled cohort study. B. J. Clin. Pharmacol. 2009, 68, 609–617. [Google Scholar] [CrossRef] [PubMed]
13. Fernandez, M.G. Hyperthyroidism and pregnancy. Endocrinol Nutr. 2013, 60, 535–543. [Google Scholar]
14. Shaban N., Z.; Masoud M., S.; Awad, D.; Mawlawia M., A.; Sadek O., M. Effect of Cd, Zn and Hg complexes of barbituric acid and thiouracil on rat brain monoamine oxidase-B (in vitro) Chem. -Biol. Interact. 2014, 208, 37–46. [Google Scholar] [CrossRef] [PubMed]
15. Gülcan, M.; Sönmez, M.; Berber, İ. Synthesis, characterization, and antimicrobial activity of a new pyrimidine Schiff base and its Cu(II), Ni(II), Co(II), Pt(II), and Pd(II) complexes. Turk. J. Chem. 2012, 36, 189–200. [Google Scholar] [CrossRef]
16. Teleb S., M.; Askar M., E.; El-Kalyoubi S., A.; Gaballa, A.S. Synthesis, characterization and antimicrobial activities of some 5-bromouracil−metal ion complexes. Bull. Chem. Soc. Ethiop. 2019, 33, 255–268. [Google Scholar] [CrossRef]
17. Golubyatnikova L., G.; Khisamutdinov R., А.; Grabovskii S., А.; Kabal’nova N., N.; Murinov Yu., I. Complexes of Palladium(II) and Platinum(II) with 6-tert-Butyl-2-thiouracil. Russ. J. Gen.Chem. 2017, 87, 117–121. [Google Scholar] [CrossRef]
18. Oladipo, M. A.; Isola, K. T. , Coordination Possibility of Uracil and Applications of Some of Its Complexes: A Review — Res. J. Pharm., Biol.Chem. Sci. 2013, 4, 386–394. [Google Scholar] [CrossRef]
19. Lusty J., R.; Peeling, J.; Abdel-Aal M., A. Complexes of 6-Methyl-2-thiouracil with Rhodium, Iridium, Platinum and Palladium Inorg. Chim. Acta, 1981, 56, 21–26. [Google Scholar] [CrossRef]
20. Paizanos, K.; Charalampou, D.; Kourkoumelis, N.; Kalpogiannaki, D.; Hadjiarapoglou, L.; Spanopoulou, A.; Lazarou, K.; Manos M., J.; Tasiopoulos A., J.; Kubicki, M.; Hadjikakou S., K. Synthesis and Structural Characterization of New Cu(I) Complexes with the Antithyroid Drug 6-n-Propyl-thiouracil. Study of the Cu(I)-Catalyzed Intermolecular Cycloaddition of Iodonium Ylides toward Benzo[b]furans with Pharmaceutical Implementations. Inorg. Chem. 2012, 51, 12248–12259. [Google Scholar] [CrossRef]
21. Sarkar A., R.; Sarkar, M. ; Cadmium(II) Complexes of 1, 3-Propanediamine with 2- Thiouracil and its 6-Methyl Derivative. Synth. React. Inorg. Met.-Org. Chem. 1998, 28, 51–60. [Google Scholar] [CrossRef]
22. Sarkar A., R.; Mandal, S. Mixed-Ligand Peroxo Complexes of Vanadium Containing 2-Thiouracil and its 6-methyl Derivative. Syntli. React. Inorg. Met.-Org. Chem, 2000; 30, 1477–1488. [Google Scholar] [CrossRef]
23. Bomfim, L.M.; de Araujo F., A.; Dias R., B.; Sales C. B., S.; Gurgel Rocha, C.A.; Correa R., S.; Soares M. B., P.; Batista A., A.; Bezerra D., P. Ruthenium(II) complexes with 6-methyl-2-thiouracil selectively reduce cell proliferation, cause DNA double-strand break and trigger caspase-mediated apoptosis through JNK/p38 pathways in human acute promyelocytic leukemia cells. Sci. Rep. 2019, 9, 11483. [Google Scholar] [CrossRef] [PubMed]
24. Abou-Melha K., S. Elaborated studies for the ligitional behavior of thiouracil derivative towards Ni(II), Pd(II), Pt(IV), Cu(II) and UO₂² 2 ions. Spectrochim. Acta Part (A): Molecular and Biomolecular Spectroscopy 2012, 97, 6–16. [Google Scholar] [CrossRef] [PubMed]
25. Masoud, M.S.; Amira, M.F.; Ramadan, A.M.; El- Ashry, G.M. Synthesis and characterization of some pyrimidine, purine, amino acid and mixed ligand complexes. Spectrochim. Acta Part(A) 2008, 69, 230–238. [Google Scholar] [CrossRef] [PubMed]
26. Singh U., P.; Ghose, R.; Ghose A., K.; Sodhi, A.; Singh S., M.; Singh R., K. J Inorg Biochem, 1989; 37, 325–329.
27. El-Morsy, F.A.; Jean-Claude, B.J.; Butler, I.S.; El- Sayed, S.A.; Mostafa, S.I. Synthesis, characterization and anticancer activity of new zinc(II), molybdate(II), palladium(II), silver(I), rhodium(III), ruthenium(II) and platinum(II) complexes of 5,6-diamino-4-hydroxy2-mercaptopyrimidine. Inorg. Chim. Acta 2014, 423, 144–155. [Google Scholar] [CrossRef]
28. Abás, E.; Pena-Martínez, R.; Aguirre-Ramírez, D.; Rodríguez-Diéguez, A.; Laguna, M.; Grasa, L. New selective thiolate gold(I) complexes inhibit proliferation of different human cancer cells and induce apoptosis in primary cultures of mouse colon tumors. Dalton Trans. 2020, 49, 1915–1927. [Google Scholar] [CrossRef]
29. Verma, S.; Shrivastva, S.; Rani, P. Synthesis and spectroscopic studies of mixed ligand complexes of transition and inner transition metals with a substituted benzimidazole derivative and RNA bases. J. Chem. Pharm. Res. 2012, 4, 693–699. [Google Scholar]
30. Shobana, S.; Dharmaraja, J.; Kamatchi, P.; Selvaraj, S. Mixed ligand complexes of Cu (II) / Ni (II) / Zn (II) ions with 5-Fluorouracil (5-FU) in the presence of some amino acid moieties: Structural and antimicrobial studies. J Chem Pharm Res 2012, 4, 4995–5004, https://www.jocpr.com/articles/mixed-ligand-complexes-of-cu-ii--ni-ii--zn-ii-ions-with-5fluorouracil-5fuin-the-presence-of-some-amino-acid-moieties-str.pdf. [Google Scholar]
31. Kamalakannan P.; Venkappayya D.; Balasubramanian T. A new antimetabolite, 5-morpholinomethyl-2-thiouracil—spectral properties, thermal profiles, antibacterial, antifungal and antitumour studies of some of its metal chelates. J. Chem. Soc., Dalton Trans, 2002; 3381–3391. [CrossRef]
32. Abou-Melha K., S. A series of Nano-sized metal ion–thiouracil complexes, tem, spectral, γ-irradiation, molecular modeling and biological studies. Orient. J. Chem. 2015, 31, 1897–1913. [Google Scholar] [CrossRef]
33. Singh U., P.; Singh, S.; Singh S., M. Synthesis, characterization and antitumour activity of metal complexes of 5-carboxy-2-thiouraci. Metal-Based Drugs, 1998; 5, 35–39. [Google Scholar] [CrossRef]
34. Papazoglou, I.; Cox, P.J.; Hatzidimitriou, A.G.; Kokotidou, C.; Choli-Papadopoulou, T.; Aslanidis, P. Copper(I) halide complexes of 5-carbethoxy-2-thiouracil: Synthesis, structure and in vitro cytotoxicity. Eur. J. Med. Chem. 2014, 78, 383. [Google Scholar] [CrossRef]
35. Hoeschele J. D.; Piscataway, N.J. Ethylenediamineplatinum(II) 2,4-dioxopyrimidine complexes, US Patent 4 207 416, 1980.
36. Supaluk, P.; Apilak, W.; Ratchanok, P.; Thummaruk, S.; Chartchalerm, I.; Somsak, R.; Virapong, P. Metal Complexes of Uracil Derivatives with Cytotoxicity and Superoxide Scavenging Activity. Lett. Drug Des. Discov. 2012, 9, 282–287. [Google Scholar] [CrossRef]
37. Illán-Cabeza N., A.; García-García A., R.; Moreno-Carretero M., N.; Martínez-Martos J., M.; Ramírez-Expósito M., J. Synthesis, characterization and antiproliferative behavior of tricarbonyl complexes of rhenium(I) with some 6-amino-5-nitrosouracil derivatives: Crystal structure of fac-[ReCl(CO)₃(DANU-N⁵,O⁴ )] (DANU = 6-amino-1,3-dimethyl-5-nitrosouracil). J. Inorg. Biochem. 2005, 99, 1637–1645. [Google Scholar] [CrossRef] [PubMed]
38. Kitagawa, S.; Nozaka, Y.; Munakata, M.; Kawata, S. Synthesis and crystal structures of tetra- and hexanuclear copper(I) complexes of pyrimidine derivatives, [Cu₄(C₄H₈N₂S₄)](ClO₄)₄ and [Cu₆(C₅H₅N₂S)₆]. Inorg. Chim. Acta. 1992, 197, 169–175. [Google Scholar] [CrossRef]
39. Shaheen, F.; Badashah, A.; Gielen, M.; Marchio, L.; Vos D., de; Khosa M, K. ., Synthesis, characterization and in vitro cytotoxicity of homobimetallic complexes of palladium(II) with 2-thiouracil ligands. Crystal structure of [Pd₂(TU)(PPh₃)₃Cl₂]. Appl. Organomet. Chem. 2007, 21, 626–632. [Google Scholar] [CrossRef]
40. Sce, F.; Beobide, G.; Castillo, O.; Pedro I., de; Pérez-Yáñez, S.; Reyes, E. Supramolecular architectures based on p-cymene/ruthenium complexes functionalized with nucleobases. Cryst.Eng.Comm. 2017, 19, 6039–6048. [Google Scholar] [CrossRef]
41. Balas, V.I.; Verginadis, I.I.; Geromichalos, G.D.; Kourkoumelis, N.; Male, L.; Hursthouse, M.B.; Repana, K.H.; Yiannaki, E.; Charalabopoulos, K.; Bakas, T.; Hadjikakou, S.K. Synthesis, structural characterization and biological studies of the triphenyltin(IV) complex with 2-thiobarbituric acid. Eur. J. Med. Chem. 2011, 46, 2835–2844. [Google Scholar] [CrossRef] [PubMed]
42. N.N. Golovnev, M.S. 42. N.N. Golovnev, M.S. Molokeev, S.N. Vereshchagin, V.V. Atuchin, M.Y. Sidorenko, M.S. Dmitrushkov, Crystal structure and properties of the precursor [Ni(H₂O)₆](HTBA)₂.2H₂O and the complexes M(HTBA)₂(H₂O)₂ (M = Ni, Co, Fe). Polyhedron, 2014; 70, 71–76. [Google Scholar] [CrossRef]
43. Pan, Z.R.; Zhang, Y.C.; Song, Y.L.; Zhuo, X.; Li, Y.Z.; Zheng, H.G. Synthesis, structure and nonlinear optical properties of three dimensional compounds. J. Coord. Chem. 2008, 61, 3189–3199. [Google Scholar] [CrossRef]
44. Ruf, M.; Weis, K.; Vahrenkamp, H. ; Pyrazolylborate-Zinc Complexes of RNA Precursors and Analogues Thereof. Inorg. Chem. 1997, 36, 2130–2137. [Google Scholar] [CrossRef]
45. Yamanari, K.; Kida, M.; Fuyuhiro, A.; Kita, M.; Kaizaki, S. Cobalt(III) promoted ligand fusion reactions of thiobarbituric acid and 4,6-diamino-2-thiouracil (or 4-amino-2-thiouracil). Inorganica Chim. Acta. 2002, 332, 115–122. [Google Scholar] [CrossRef]
46. Esteruelas, M.A.; García-Raboso, J.; Oliván, M. ; Reactions of an Osmium-Hexahydride Complex with Cytosine, Deoxycytidine, and Cytidine: The Importance of the Minor Tautomers. Inorg. Chem. 2012, 51, 9522–9528. [Google Scholar] [CrossRef]
47. Chakraborty, S.; Laye, R.H.; Munshi, P.; Paul, R.L.; Ward, M.D.; Kumar Lahiri, G. Dinuclear bis(bipyridine)ruthenium(II) complexes [(bpy)2Ru^II{L}2^-Ru^II(bpy)₂]²⁺ incorporating thiouracil-based dianionic asymmetric bridging ligands: synthesis, structure, redox and spectroelectrochemical properties. J. Chem. Soc. Dalt. Trans. 2002, 2348–2353. [Google Scholar] [CrossRef]
48. Ma, C.; Tian, G.; Zhang, R. New triorganotin(IV) complexes of polyfunctional S,N,O-ligands: Supramolecular structures based on π-π and/or C–H-π interactions. J. Organomet. Chem. 2006, 691, 2014–2022. [Google Scholar] [CrossRef]