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Synthesis of Mesoionic 1,3,4-Thiadiazole-2-Thiolates
 
 
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4-(8-Propyl-2,4-dithioxo-1,3-diazaspiro[4.5]decan-3-yl)spiro[1,5-dihydro-1,5-benzodiazepine-2,3′-indoline]-2′-one)

by
Dimitar Stoitsov
1,
Marin Marinov
2,
Plamen Penchev
1,* and
Neyko Stoyanov
3
1
Department of Analytical Chemistry and Computer Chemistry, Faculty of Chemistry, University of Plovdiv “Paisii Hilendarski”, 4000 Plovdiv, Bulgaria
2
Department of Chemistry, Phytopharmacy, Ecology and Environmental Protection, Faculty of Plant Protection and Agroecology, Agricultural University—Plovdiv, 4000 Plovdiv, Bulgaria
3
Department of Chemical, Food and Biotechnologies, Razgrad Branch, “Angel Kanchev” University of Ruse, 7200 Razgrad, Bulgaria
*
Author to whom correspondence should be addressed.
Molbank 2025, 2025(2), M2011; https://doi.org/10.3390/M2011 (registering DOI)
Submission received: 30 April 2025 / Revised: 19 May 2025 / Accepted: 21 May 2025 / Published: 23 May 2025
(This article belongs to the Section Structure Determination)
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Versions Notes

Abstract

:
A number of 1D and 2D NMR techniques, such as 1H, 13C, DEPT 135, 1H-1H COSY, HSQC, and HMBC, were utilized for the structure verification of 4-(8-propyl-2,4-dithioxo-1,3-diazaspiro[4.5]decan-3-yl)spiro[1,5-dihydro-1,5-benzodiazepine-2,3′-indoline]-2′-one). The NMR spectra provided evidence for the tautomeric conversion of the compound. The completely assigned NMR data was supported additionally by ATR.

1. Introduction

Isatin, 1,5-benzodiazepine, and 5-spirocyclohexyl-2,4-dithiohydantoin are chemical building blocks possessing several reaction centers, which allow them to be used as precursors in numerous organic syntheses of heterocyclic compounds [1,2,3,4,5]. For example, the carbonyl groups in isatin can participate in addition reactions at the C-O bond as well as in condensation reactions. Meanwhile, the NH group in isatin enters into N-alkylation and N-acylation reactions. Various polar (e.g., hydroxyl, carbonyl) and non-polar groups (e.g., alkyl) can be incorporated into the benzene and diazepine rings of the 1,5-benzodiazepine fragment, leading to the production of a broad range of derivatives with versatile biological activity. Furthermore, 1,5-benzodiazepines are famous for their tautomerism due to the presence of NH groups in their structure, which additionally modifies their biochemical properties [6,7,8]. The 5-spirocyclohexyl-2,4-dithiohydantoin fragment has two NH and two C=S groups, which can participate in substitution and addition organic reactions, respectively. Most of the heterocycles produced containing some or all of the abovementioned fragments possess antimicrobial [3,9,10,11,12,13,14], antifungal [14], antiepileptic [15], and anticancer [16] activity. The high interest towards the isatin-, 1,5-benzodiazepine- and/or 5-spirocyclohexyl-2,4-dithiohydantoin-based derivatives have led to a significant amount of reported IR, NMR, and MS data supporting their structures [1,2,3,4,5,9,10,11,12,13,14]. Thus, spectral or structural data for such newly synthesized compounds can be found in some spectral databases and interpretative libraries [17,18,19].
The main aim of the work was to verify the structure of 4-(8-propyl-2,4-dithioxo-1,3-diazaspiro[4.5]decan-3-yl)spiro[1,5-dihydro-1,5-benzodiazepine-2,3′-indoline]-2′-one) synthesized by combining isatin, 1,5-benzodiazepine, and 5-spirocyclohexyl-2,4-dithiohydantoin. The structure verification was performed mainly by using 1D and 2D NMR techniques—1H, 13C, DEPT 135, 1H-1H COSY, HSQC, and HMBC.

2. Results and Discussion

The suggested structures of the synthesized compound and its tautomer are presented in Figure 1.
The molecular formula of compound I and its tautomer II is C27H29N5S2O. The reason for presenting the tautomer of compound I was the missing signal of NH-iv proton in the 1H NMR spectrum (Table 1) (Figure S1). However, the 1H singlet at 2.72 ppm, with an area of 1.81, indicated the transfer of the NH-iv proton to the C-vi carbon, forming the CH2 group in the structure of tautomer II. Moreover, the HSQC spectrum showed two correlations involving the signal at 2.72 ppm–(2.72–28.90 ppm) and (2.72–32.09 ppm). The former HSQC correlation was positive, indicating the presence of the H-vi proton and C-vi carbon in the CH group in compound I. The latter HSQC correlation was negative, including the chemical shifts of the signals of the methylene protons and carbon in the CH2-vi group that is present in compound II. Thus, the 1H singlet at 2.72 ppm was assigned to both protons in CH2-vi in tautomer II. Also, instead of observing 25 signals in the 13C spectrum (Figure S2), there were 26 signals, where those at 29.17 ppm and 32.14 ppm, as already suggested by the HSQC spectrum, corresponded to the carbon C-vi in the tautomers I and II. Meanwhile, the DEPT 135 spectrum (Figure S3) showed a positive 13C signal at 29.17 ppm as there was not any signal at 32.14 ppm. Consequently, the 1H NMR spectrum showed the resonances specifically for compound II while the 13C NMR and HSQC spectra showed some resonances for both tautomers. The DEPT 135 spectrum included the CH and C6H2, C7H2, C8H2, C9H2, C11H2, and C12H2 signals only for tautomer I. Evidently, the NMR data indicated the mutual presence of both tautomers I and II in the reaction mixture, as the mobile NH-iv proton participated in the tautomeric interconversion. For this reason, there was no NH-iv signal detected in the 1H NMR spectrum (Table 1).
The 1H singlet at 13.91 ppm was assigned to the NH-1 proton that is close to the C2=S group, while the 1H singlets at 10.34 ppm and 7.26 ppm were assigned to the NH-i′ and NH-i protons, respectively. Additionally, the strong HMBC correlations—(10.34–74.30 ppm), (10.34 ppm–141.30 ppm) and (10.34–129.78 ppm)—indicating the interaction of the NH-i′ proton with the C-iii′, C-viii′, and C-ix′ carbons, respectively, supported the assignment of the 1H signal at 10.34 ppm to the NH-i′ proton.
The DEPT 135 spectrum showed four negative signals at 20.05 ppm, 20.88 ppm, 30.51 ppm, and 34.79 ppm that were for the carbons of the six CH2 groups in the 4-(8-propyl-2,4-dithioxo-1,3-diazaspiro[4.5]decan-3-yl) fragment—C6H2, C7H2, C8H2, C9H2, C11H2 and C12H2. The carbon and both protons in C6H2 are chemically equivalent to the corresponding carbon and protons in C7H2. Similarly, the protons and carbons in C8H2 are chemically equivalent to the protons and carbon in the C9H2 group. However, the protons in each of these CH2 groups are not chemically equivalent. Therefore, four HSQC correlations were found specifically for the C6H2, C7H2, C8H2, and C9H2 groups (Figure S4). The strong HMBC correlations, (2.66–79.79 ppm) and (2.66–208.63 ppm), indicated for the two-bond and three-bond interactions of the protons Ha in C6H2 and C7H2, respectively, with the spirocarbon, C-1′, and thiocarbonyl carbon, C-4. The COSY spectrum indicated that the protons Hc and Hd in C8H2 and C9H2, whose signals can be found at 2.20 ppm and 1.59 ppm, are neighbors to the protons Ha and Hb (Figure S5). Furthermore, a strong COSY correlation can be found for each of the signals of the protons, Hc and Hd, with the signal of the proton H-10. Additionally, HMBC correlations, (2.66–21.13 ppm), (2.20–30.77 ppm) and (2.20–45.05 ppm), indicated the interactions of the methylene protons Ha with the carbons C-8/9 as well as those interactions of the protons Hc with the carbons, C-6/7 and C-10. The strong COSY correlations of the signals of the methylene protons He and Hf with the signal of the proton H-10 indicated that He and Hf are bonded with the carbon atom, C-11. Consequently, the signals with the chemical shifts, 1.86 ppm and 1.63 ppm, were assigned to the signals of the protons Hg and Hh that were bonded with the carbon, C-12. The 1H singlet of methyl protons has a chemical shift of 0.86 ppm. While there was one HMBC correlation (Figure S6), (0.86–45.05 ppm), indicating the interaction of the methyl protons with the C-10 carbon, there were no observable COSY correlations involving the signal of methyl protons.
The signals of all aromatic protons and carbons were assigned according to their strong HMBC correlations that resulted from the meta (vicinal) interactions between the protons and carbons in each benzene ring [20]. The COSY correlations, as well as the multiplicity of the 1H signals, supported the assignment of the signals of the benzene protons.
The ATR-IR spectrum showed a band at 3313 cm−1 for the v(N-H) (Table 2). In addition, there were some ATR-IR bands for vas(CH2), vas(CH3), and δs(CH2) at 2937, 2953, and 1473 cm−1. The ATR-IR bands for v(C=O) and v(C=S) can be found at 1705 cm−1 and 1257 cm−1, respectively (Figure S7).

3. Materials and Methods

3.1. Synthesis

The reaction of 8-propyl-1,3-diazaspiro[4.5]decane-2,4-dithione (1) with pyridine and acetic anhydride leads to the synthesis of 1-(8-propyl-2,4-dithioxo-1,3-diazaspiro[4.5]decan-3-yl)ethanone (2, m.p. 176–177 °C, yield 93%).
The reaction of compound 2 with isatin (1H-indole-2,3-dione, 3) produced 3-hydroxy-3-[2-oxo-2-(8-propyl-2,4-dithioxo-1,3-diazaspiro[4.5]decan-3-yl)ethyl]indolin-2-one (4, m.p. 201–202 °C, yield 88%), which was converted into 3-[2-oxo-2-(8-propyl-2,4-dithioxo-1,3-diazaspiro[4.5]decan-3-yl)ethylidene]indolin-2-one after a treatment with AcOH/HCl (5, m.p. 217–218 °C, yield 91%).
The interaction of compound 5 with benzene-1,2-diamine produces 4-(8-propyl-2,4-dithioxo-1,3-diazaspiro[4.5]decan-3-yl)spiro[1,5-dihydro-1,5-benzodiazepine-2,3′-indoline]-2′-one (6, m.p. 234–235 °C, yield 85%). The whole synthesis pathway is presented in Figure 2.

3.2. Synthesis of 3-Hydroxy-3-[2-oxo-2-(8-propyl-2,4-dithioxo-1,3-diazaspiro[4.5]decan-3-yl)ethyl]indolin-2-one (4)

A mixture of 1-(8-propyl-2,4-dithioxo-1,3-diazaspiro[4.5]decan-3-yl)ethanone (2, 2.84 g, 0.01 mol), isatin (3, 1.47 g, 0.01 mol) in 100 mL absolute ethanol, and 4 drops of piperidine was shaken for 30 min at room temperature and it was left to stay overnight. The formed solid product was filtrated and recrystallized in ethanol/dioxane.
m.p. 201–202 °C. Yield 3.79 g (88%).

3.3. Synthesis of 3-[2-Oxo-2-(8-propyl-2,4-dithioxo-1,3-diazaspiro[4.5]decan-3-yl)ethylidene]indolin-2-one (5)

Compound 4 (4.31 g, 0.01 mol) was solved in 25 mL glacial CH3COOH and 0.5 mL concentrated HCl. The reaction mixture was heated for 1 h in a boiling bath. A solid product was formed, which was filtered and recrystallized afterwards in ethanol/dioxane.
m.p. 217–218 °C. Yield 3.76 g (91%)

3.4. Synthesis of 4-(8-Propyl-2,4-dithioxo-1,3-diazaspiro[4.5]decan-3-yl)spiro[1,5-dihydro-1,5-benzodiazepine-2,3′-indoline]-2′-one (6)

Benzene-1,2-diamin (0.60 g, 0.0055 mol) and 0.5 mL glacial CH3COOH was added to the solution of compound 5 (2.07 g, 0.005 mol) prepared in 20 mL ethanol The reaction mixture was heated and boiled for 6 h. After cooling, a solid precipitate was produced, filtered, and recrystallized in ethanol/dioxane.
m.p. 234–235 °C. Yield 2.14 g (85%).

3.5. Apparatus

A Bruker Avance III HD spectrometer (Bruker Optics, Billerica, MA, USA)with frequencies 125.76 MHz and 500.130 MHz was used to measure the 1D and 2D NMR spectra. TMS was used as an internal standard and DMSO-d6 as a solvent. ATR spectrum was registered with VERTEX 70 FT-IR instrument (Bruker Optics, Billerica, MA, USA) using MIRacleTM with a one-reflection ZnSe element (PIKE Technology, Madison, WI, USA). ATR data was measured in the range (4000–600) cm−1 with 25 scans and a resolution of 2 cm−1.

4. Conclusions

The combination of isatin, 1,5-benzodiazepine, and 5-spirocyclohexyl-2,4-dithiohydantoin fragments led to the synthesis of 4-(8-propyl-2,4-dithioxo-1,3-diazaspiro[4.5]decan-3-yl)spiro[1,5-dihydro-1,5-benzodiazepine-2,3′-indoline]-2′-one) which, according to the assigned NMR data, exists in tautomeric equilibrium with its deprotonated form II in the reaction mixture. Further attempts to synthesize and verify the structures of new derivatives, including the same heterocyclic building blocks, will be made.

Supplementary Materials

Figure S1: 1H NMR. Spectrometer frequency is 500.13 MHz. DMSO-d6 is the used solvent. The expansion shows the singlet at 2.72 ppm, with area 1.81 corresponding to the protons of the CH2 group in tautomer II; Figure S2: 13C NMR. Spectrometer frequency is 125.76 MHz. DMSO-d6 is the used solvent. The expansion shows the signals at 32.14 ppm and 29.17 ppm that correspond to the carbon C-vi in both tautomers; Figure S3: DEPT 135. Spectrometer frequency is 125.76 MHz. DMSO-d6 is the used solvent; Figure S4: HSQC. The horizontal and vertical traces show 1H NMR and DEPT 135 spectra, respectively. Spectrometer frequencies for 1H NMR and DEPT 135 spectra are correspondingly 500.13 MHz and 125.76 MHz. DMSO-d6 is the used solvent. The expansion shows the positive HSQC correlation, (2.72 ppm–28.90 ppm), registered for C-vi carbon and H-vi proton of the CH group in tautomer I as well as the negative HSQC correlation, (2.72 ppm–32.09 ppm), for the C-vi carbon and H-vi proton of the CH2 group in tautomer II; Figure S5: 1H-1H COSY. The horizontal and vertical traces show the 1H NMR spectrum, respectively. Spectrometer frequency for 1H NMR is correspondingly 500.13 MHz. DMSO-d6 is the used solvent; Figure S6: HMBC spectrum. The horizontal and vertical traces show 1H and 13C NMR spectra, respectively. Spectrometer frequencies for 1H and 13C NMR are correspondingly 500.13 MHz and 125.76 MHz. DMSO-d6 is the used solvent. Figure S7: ATR-IR.

Author Contributions

Conceptualization, D.S., M.M. and P.P.; formal analysis, D.S.; investigation, M.M.; writing—original draft preparation, D.S.; writing—review and editing, P.P., M.M., D.S. and N.S. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

The data associated with the paper are available.

Conflicts of Interest

The authors declare no conflicts of interest.

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Molbank 2025 m2011 g001
Figure 1. Suggested structure of 4-(8-propyl-2,4-dithioxo-1,3-diazaspiro[4.5]decan-3-yl)spiro[1,5-dihydro-1,5-benzodiazepine-2,3′-indoline]-2′-one) (I) and its tautomer (II). The numbering and lettering of the atoms in both structures were used only for the spectral assignments.
Figure 1. Suggested structure of 4-(8-propyl-2,4-dithioxo-1,3-diazaspiro[4.5]decan-3-yl)spiro[1,5-dihydro-1,5-benzodiazepine-2,3′-indoline]-2′-one) (I) and its tautomer (II). The numbering and lettering of the atoms in both structures were used only for the spectral assignments.
Molbank 2025 m2011 g001
Molbank 2025 m2011 g002
Figure 2. Synthesis of 4-(8-propyl-2,4-dithioxo-1,3-diazaspiro[4.5]decan-3-yl)spiro[1,5-dihydro-1,5-benzodiazepine-2,3′-indoline]-2′-one).
Figure 2. Synthesis of 4-(8-propyl-2,4-dithioxo-1,3-diazaspiro[4.5]decan-3-yl)spiro[1,5-dihydro-1,5-benzodiazepine-2,3′-indoline]-2′-one).
Molbank 2025 m2011 g002
Table 1. 1H and 13C NMR data assignment for compounds I and II. [1H [500.13 MHz] and 13C [125.76 MHz]] a.
Table 1. 1H and 13C NMR data assignment for compounds I and II. [1H [500.13 MHz] and 13C [125.76 MHz]] a.
Atomδ (13C), ppmDEPT b δ (1H), ppmMultiplicity (J, Hz)1H-1H COSY bHMBC b
2(C=S)180.25C
4(C=S)208.63C
1(NH) 13.91s
(1′)79.79C
6/730.77CH22.66 c (Ha) ftd(13.4, 4.7)Hb, Hc, Hd(1′), 8/9, 4
1.80 c (Hb) fmHa, Hc, Hd
8/921.13CH22.20 c (Hc) fqd(13.2, 4.0)Hd, Ha, Hb, 106/7 d, 10 e
1.59 c (Hd) fmHc, Ha, Hb, 10
1045.05CH1.06 cmHc, Hd
1120.31CH22.17 c (He) fqd(13.2, 4.0)Hf, 10, Hg, Hh
1.55 c (Hf) fmHe, 10, Hh, Hg
1235.05CH21.86 c (Hg) fmHe, Hf, Hh
1.63 c (Hh) fmHe, Hf, Hg
1327.38CH30.86 cs 10
ii′(C=O)176.15C
v171.30C
i(NH) 7.26s
(iii′)74.30C
iv(NH)
i′(NH) 10.34s (iii′), viii′, ix′
viii′141.30C
ix′129.78C
iv′125.59CH7.55d(7.4)v′, vi′ e(iii′), viii′, vi′
v′122.44CH7.07 ctd(7.6, 0.9)iv′, vi′, vii′ evii′, ix′
vi′130.46CH7.29td(7.7, 1.2)v′, vii′, iv′ eiv′, viii′
vii′110.03CH6.84d(7.8)v′ e, vi′v′, ix′
vi29.17/32.14CH/CH22.72s v
a121.07CH7.04 c,fdd(7.5,0.8)b, c ec, e
b118.63CH6.63 ftd(7.5, 1.0)a, c, d ed, f
c125.68CH6.90 ftd(7.7, 1.2)a e, b, da, e
d108.41CH6.53 fdd(7.8, 0.8)b e, cb, f
e147.19C
f124.10C
a In DMSO-d6 (solvent reference: 1H δref 2.50 ppm, 13C δref 39.51 ppm). All spectral assignments are in accordance with HSQC, HMBC, and COSY spectra. b Abbreviations: DEPT, Distortionless Enhancement by Polarization Transfer spectrum; 1H-1H COSY, proton–proton homonuclear correlation spectrum; HMQC, Heteronuclear Multiple Quantum Correlation experiment; HMBC, Long-range 1H-13C Heteronuclear Multiple Bond Correlation experiment. c The chemical shift was assigned from the HSQC spectrum. d Correlations are weak. e Correlations are extremely weak. f H-a, H-b, H-c, and H-d are the benzene protons while the chemically inequivalent methylene protons were expressed with capital letter H, accompanied by a letter as a lower subscript.
Table 2. Key ATR-IR bands.
Table 2. Key ATR-IR bands.
ATR-IR BandWavenumber, cm−1
v(N-H)3313
v(C-H)3136, 3085, 3070, 3060
vas(CH3)2953
vas(CH2)2937
v(C=O)1705
v(C=C)1603, 1493
δs(CH2)1473
v(C=S)1257
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MDPI and ACS Style

Stoitsov, D.; Marinov, M.; Penchev, P.; Stoyanov, N. 4-(8-Propyl-2,4-dithioxo-1,3-diazaspiro[4.5]decan-3-yl)spiro[1,5-dihydro-1,5-benzodiazepine-2,3′-indoline]-2′-one). Molbank 2025, 2025, M2011. https://doi.org/10.3390/M2011

AMA Style

Stoitsov D, Marinov M, Penchev P, Stoyanov N. 4-(8-Propyl-2,4-dithioxo-1,3-diazaspiro[4.5]decan-3-yl)spiro[1,5-dihydro-1,5-benzodiazepine-2,3′-indoline]-2′-one). Molbank. 2025; 2025(2):M2011. https://doi.org/10.3390/M2011

Chicago/Turabian Style

Stoitsov, Dimitar, Marin Marinov, Plamen Penchev, and Neyko Stoyanov. 2025. "4-(8-Propyl-2,4-dithioxo-1,3-diazaspiro[4.5]decan-3-yl)spiro[1,5-dihydro-1,5-benzodiazepine-2,3′-indoline]-2′-one)" Molbank 2025, no. 2: M2011. https://doi.org/10.3390/M2011

APA Style

Stoitsov, D., Marinov, M., Penchev, P., & Stoyanov, N. (2025). 4-(8-Propyl-2,4-dithioxo-1,3-diazaspiro[4.5]decan-3-yl)spiro[1,5-dihydro-1,5-benzodiazepine-2,3′-indoline]-2′-one). Molbank, 2025(2), M2011. https://doi.org/10.3390/M2011

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