N-[(2H-1,3-benzodioxol-5-yl)methyl]-2-(2,2,2-trichloroacetamido)benzamide

Abstract

The structure of N-[(2H-1,3-benzodioxol-5-yl)methyl]-2-(2,2,2-trichloroacetamido)benzamide was verified by using a combination of 1D and 2D NMR techniques. Fully assigned data from 1D NMR (¹H, ¹³C and DEPT 135) and 2D NMR (COSY, HMQC, HMBC) spectra was presented for the compound. The ¹H NMR spectrum of the ABX spin system in the benzodioxol moiety was simulated to predict the corresponding ⁿJ_HH coupling constants. The spectral assignments for the structure were supported by interpretive library search and HOSE predictions.

1. Introduction

2,4(1H,3H)-quinazolinediones were found to act as anticonvulsants and psychosedatives [1]. In addition, they can find application as pharmacophores, serotonin S₂-receptor antagonists usually applied for treating hypertension [2], and also as puromycin-sensitive aminopeptidase-inhibiting antitumor agents [3]. During the development of a synthetic procedure for obtaining 3-substituted 2,4(1H,3H)quinazolinediones, an important stage in the synthesis was the base-induced intramolecular cyclization of 2-(trichloroacetylamino)benzamides, which led to the production of the corresponding 2,4(1H,3H)-quinazolinediones [4]. One of the reaction intermediates during the synthesis was N-[(2H-1,3-benzodioxol-5-yl)methyl]-2-(2,2,2-trichloroacetamido)benzamide, for which partially assigned ¹H NMR and IR data [4] exists. In addition, fully assigned 1D (¹H, ¹³C) and 2D (HMQC, COSY, HMBC) NMR data can be found for the corresponding compound as a part of the Doctor of Science (DSc) thesis of Prof. Plamen Penchev (University of Plovdiv) [5]. However, the deceptively simple ¹H spectrum of the ABX system in the benzodioxol moiety has never been simulated in order to accurately predict the corresponding ⁿJ_HH coupling constants. Therefore, this work is focused primarily on the ¹H and ¹³C NMR assignments for the benzodioxol moiety supported by the ABX spectrum simulation. Additionally, the NMRShiftDB database [6,7] was used to generate the HOSE predictions with which the chemical shifts in the assigned ¹³C signals were verified. An interpretive library search was also performed in the INFERCNMR database [8]. Partially assigned IR and Raman data was provided to support the structure verification.

2. Results and Discussion

The structure of N-[(2H-1,3-benzodioxol-5-yl)methyl]-2-(2,2,2-trichloroacetamido)benzamide is shown in Figure 1; the atom numbering is used only for the spectral assignments.

The molecular formula of the compound is C₁₇H₁₃N₂Cl₃O₄. The fully assigned NMR data is presented in

Table 1. ¹H and ¹³C NMR data assigned for the compound. [¹H [600.13 MHz] and ¹³C [150.90 MHz]] ^a.

Atom	δ (13C), ppm	DEPT b	δ (1H), ppm	Multiplicity (J, Hz)	1H-1H COSY b	HMBC b
1′	121.54	C
2′	128.67	CH	7.94	dd (7.9, 1.3)	3′, 4′ d	1′ d, 4′, 6′, 10
3′	125.24	CH	7.33	td (7.7, 1.1)	2′, 4′, 5′ d	1′, 5′, 2′ c,4′ d, 6′ d
4′	133.13	CH	7.65	m	2′ d, 3′, 5′	5′ c, 2′, 6′
5′	120.64	CH	8.38	dd (8.2, 0.6)	3′ d, 4′	1′, 3′, 6′ c, 10 d
6′	137.55	C
7′(NH)			13.17	s
8′(C=O)	159.72	C
9′	93.07	C
2	101.22	CH2	5.98	s		3a, 7a
3a	147.60	C
7a	146.55	C
4	108.37	CH	6.92	m	6 c, 7 d, 8 c	6, 8, 7a
5	132.92	C
6	121.05	CH	6.81	m	4 c, 7, 8 d	4, 7a, 8
7	108.45	CH	6.86	m	4 d, 6	3a, 5
8	42.82	CH2	4.41	d (6.0)	4 c, 6 d, 9	4, 6, 5, 10
9(NH)			9.50	t (6.1)	8	8 c, 10
10(C=O)	168.41	C

^a In DMSO-d₆ solution (solvent reference: ¹H δ_ref 2.50 ppm, ¹³C δ_ref 39.51 ppm). All spectral assignments were in agreement with HMQC, 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 Weak correlations. ^d Extremely weak correlations.

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The ¹³C NMR spectrum showed 17 signals and DEPT displayed 9 resonances, consisting of 7 positive CH and 2 negative CH₂ signals. Both signals with the highest chemical shifts in the ¹³C NMR spectrum, 168.41 ppm and 159.72, were for the carbonyl carbons. The signals of the protons H-2′ (7.94 ppm), H-8 (4.41 ppm), and NH-9 (9.50 ppm) showed strong HMBC correlations with the signal at 168.41 ppm, and were correspondingly assigned to the carbon C-10. The two ¹H signals at 13.17 ppm (singlet) and 9.50 ppm (triplet) were for the NH-7′ and NH-9 protons, respectively (Figure 2). The latter ¹H signal has a strong ¹H-¹H COSY correlation with the ¹H signal of the methylene H-8 protons, which is why it was assigned to the NH-9 proton.

For the CH coupling in benzene rings, as described in the literature [9] (p. 27), usually only meta (vicinal) coupling (³J_CH) is resolved. Thus, the strong meta-HMBC correlations—(7.94 ppm–133.13 ppm), (7.33 ppm–120.64 ppm), (7.65 ppm–128.67 ppm), and (8.38 ppm–125.24 ppm)—confirmed the assignment of the signals of the aromatic protons, H-2′, H-3′, H-4′, and H-5′, along with their multiplicity and ¹H–¹H COSY correlations.

Using the Spin Simulation option from Mestrenova software (version 6.0.2-5475, Mestrelab Research SL, Santiago de Compostela, Spain), the results from the ABX spectrum simulation were as follows: δ_H 6.92 ppm for H-4 (⁴J_HH = 1.3 Hz, ⁵J_HH = 0.1 Hz), as well as δ_H 6.81 ppm and δ_H 6.86 ppm for H-6 (⁴J_HH = 1.3 Hz, ³J_HH = 8.0 Hz) and H-7 (⁵J_HH = 0.1 Hz, ³J_HH = 8.0 Hz). The obtained parameters were additionally verified by simulating the ABX spectrum using NMRSim Python library (version 0.6.0). The positions of the protons, H-4, H-6, and H-7, were confirmed by the weak COSY correlations—(6.92 ppm–6.81 ppm), (6.92 ppm–6.86 ppm), (4.41 ppm–6.92 ppm) and (4.41 ppm–6.81 ppm)—indicating the weak interactions of the proton, H-4, and methylene protons with proton H-6, as well as the extremely weak interaction between protons H-4 and H-7. Moreover, there was a strong COSY correlation (6.81 ppm–6.86 ppm), confirming that protons H-6 and H-7 were neighbours. Other useful HMBC correlations (6.81 ppm–42.82 ppm and 6.86 ppm–132.92 ppm) indicated the interactions of protons H-6 and H-7 with methylene carbon C-8 and nonprotonated carbon C-5, respectively. The assignment of the signals of the nonprotonated carbons C-3a and C-7a was based on the HMBC correlations due to the meta-interactions of protons H-4 and H-6 with carbon, C-7a, and of proton H-7 with carbon C-3a—(6.92 ppm–146.55 ppm), (6.81 ppm–146.55 ppm), and (6.86 ppm–147.60 ppm).

INFERCNMR database [8], containing almost 39,000 completely assigned ¹³C NMR spectra, compiled by Prof. Morton Munk (Arizona State University), was used for searching the ¹³C NMR spectrum shown in Table 1. This kind of search method is called an interpretive library search, as it was developed by one of the authors (Prof. Plamen Penchev) and Prof. Munk. Thus, substructures common to both the unknown and reference compounds can be found in the database, accompanied by the estimated probability of its finding and some statistical parameters. The benzodioxole moiety in the compound was found to be a highly probable substructure in the INFERCNMR database. Reference compounds with assigned ¹³C chemical shifts for the benzodioxol moiety close to the ones presented in Table 1 were retrieved. The obtained reference compounds, 5-Nitrofuran-2-carboxylic acid {2-[(pyridin-2-ylmethyl)carbamoyl]phenyl}amide and 5-Nitrofuran-2-carboxylic acid {2-[(thiophen-2-ylmethyl)carbamoyl]phenyl}amide, also had an ortho-substituted benzene ring with two amides attached in the same way as in the compound. The assigned ¹³C NMR data for the corresponding benzene ring is similar to that for the ¹³C NMR assignments proposed by us.

To verify the chemical shifts in the assigned ¹³C signals, HOSE predictions were generated by using the NMRShiftDB database. Good agreement was observed between the experimental and predicted values. The comparison between the experimental and predicted ¹³C chemical shifts is presented in

Table 2. Comparison of the experimental and predicted ¹³C chemical shifts with HOSE code.

Carbon	Experimental δ (13C), ppm	Predicted δ (13C), ppm
C-1′	121.54	119.90
C-2′	128.67	129.40
C-3′	125.24	123.20
C-4′	133.13	132.44
C-5′	120.64	121.11
C-6′	137.55	139.76
C-8′	159.72	161.80
C-9′	93.07	91.95
C-10	168.41	168.50
C-5	132.92	130.30
C-4	108.37	108.00
C-6	121.05	120.35
C-7	108.45	108.50
C-8	42.82	43.63
C-3a	147.60	147.70
C-7a	146.55	146.50
C-2	101.22	101.18

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The assigned IR and Raman bands indicating the presence of NH, C=O, and CH₂; aromatic C=C and C-H groups are presented in

Table 3. Assigned IR and Raman bands.

IR, cm−1	Raman, cm−1
3318 (v(NH))	3076 (v(Csp2-H))
3244 (v(NH))	2942 (vas(CH2))
3075 (v(Csp2-H))	1718 (v(C=O))
2923 (vas(CH2))	1707 (v(C=O))
1718 (v(C=O))	1599 (v(C=C))
1707 (v(C=O))	1587 (v(C=C))
1601 (v(C=C))	1516 (v(C=C))
1587 (v(C=C))	1502 (v(C=C))
1518 (v(C=C))	1448 (v(C=C))
1503 (v(C=C))
1490 (v(C=C))
1447 (v(C=C))
764 (ϒ(C-H)

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3. Materials and Methods

¹H, ¹³C and 2D NMR spectra were recorded on a Bruker Avance II+ 600 MHz NMR spectrometer (Bruker Optics, Billerica, MA, USA) operating at 600.130 MHz (¹H) and 150.903 MHz (¹³C), using TMS as the internal standard and DMSO-d₆ as the solvent. Chemical shifts are expressed in ppm and coupling constants in Hertz. One-dimensional and 2D NMR spectra were recorded using the standard Bruker pulse sequence.

IR spectrum was registered in KBr pellet on a Perkin-Elmer 1750 FT-IR Spectrometer (Bruker Optics, Billerica, MA, USA) from 4000 cm⁻¹ to 450 cm^–1 at a resolution of 2 cm^–1 with 25 scans.

Raman spectrum (stirred crystals placed in aluminium discs) was measured on RAM II (Bruker Optics, Billerica, MA, USA) in the range from 4000 cm⁻¹ to 50 cm⁻¹, with a resolution of 1 cm⁻¹ and laser power of 200 mW, and 100 scans.

4. Conclusions

The structure of N-[(2H-1,3-benzodioxol-5-yl)methyl]-2-(2,2,2-trichloroacetamido)benzamide, whose synthetic procedure was previously described [4], was completely verified using a number of 1D and 2D NMR, IR, and Raman techniques. Computer-assisted approaches, including ABX spectrum simulation with the Spin Simulation tool and NMRSim Python library, interpretive library search in the INFERCNMR database, and the generation of HOSE predictions with NMRShiftDB database, were used to verify the spectral assignments.