Synthesis, antimicrobial activity and quantum chemical investigation of novel succinimide derivatives

Article abstract of DOI:10.1016/j.molstruc.2018.12.083

In the present study, twelve new 1-aryl-3-ethyl-3-methylpyrrolidine-2,5-diones were synthesized and their structures were characterized by FT-IR, ¹H NMR, ¹³C NMR spectroscopy and elemental analysis. In the final step of synthetic rout, condensation between corresponding succinic acid and substituted anilines has been improved using the microwave irradiation. Significantly higher yields compared to conventional condensation have been observed. The preliminary biological results indicated that some of the synthesized compounds showed promising in vitro antifungal activities towards several test fungi. 1-(4-Bromophenyl)-3-ethyl-3-methylpyrrolidine-2,5-dione (8) exhibited significant in vitro inhibitory activities against broad spectra of fungus, and on the basis of obtained data, the investigated bromo derivative has to be observed as novel potential fungicide. The density functional theory (DFT) calculations have been performed in order to study the structure-activity relationship (SAR) of the investigated molecules. In order to prediction of the chemical activity of the molecule, the molecular electrostatic potential (MEP) map was analyzed for the optimized geometry of 1-phenyl-3-ethyl-3-methylpyrrolidine-2,5-dione (4) and 1-(4-bromophenyl)-3-ethyl-3-methylpyrrolidine-2,5-dione (8).

Full text of DOI:10.1016/j.molstruc.2018.12.083

Accepted Manuscript
Synthesis, antimicrobial activity and quantum chemical investigation of novel
succinimide derivatives
Jelena Petković Cvetković, Bojan Đ. Božić, Nebojša R. Banjac, Jovana Petrović,
Marina Soković, Vesna D. Vitnik, Željko J. Vitnik, Gordana S. Ušćumlić, Nataša V.
Valentić
PII:
S0022-2860(18)31516-3
DOI:
https://doi.org/10.1016/j.molstruc.2018.12.083
MOLSTR 26020
Reference:
To appear in: Journal of Molecular Structure
Received Date: 29 October 2018
Revised Date: 20 December 2018
Accepted Date: 20 December 2018
Please cite this article as: Jelena.Petković. Cvetković, Bojan.Đ. Božić, Nebojš.R. Banjac, J. Petrović, M.
Soković, V.D. Vitnik, Ž.J. Vitnik, G.S. Ušćumlić, Nataš.V. Valentić, Synthesis, antimicrobial activity and
quantum chemical investigation of novel succinimide derivatives, Journal of Molecular Structure (2019),
doi: https://doi.org/10.1016/j.molstruc.2018.12.083.
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ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Synthesis, Antimicrobial Activity and Quantum Chemical Investigation of novel
Succinimide Derivatives
Jelena Petković Cvetkovićа, Bojan Đ. Božićb, Nebojša R. Banjacc, Jovana Petrovićd, Marina Sokovićd, Vesna D. Vitnike, Željko
J. Vitnike, Gordana S. Ušćumlićа, Nataša V. Valentić*a
a
Department of Organic Chemistry, Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, P.O. Box
3503, 11120 Belgrade, Serbia.
b
Institute of Physiology and Biochemistry, Faculty of Biology, University of Belgrade, Studentski trg 16, 11000 Belgrade,
Serbia.
c
Faculty of Agriculture, Food Technology and Biochemistry, University of Belgrade, Nemanjina 6, 11080, Belgrade, Zemun,
Serbia.
d
Institute for biological research "Siniša Stanković", University of Belgrade, Blvd. despota Stefana 142, 11000 Belgrade,
Serbia.
e Department of Chemistry, ICTM, University of Belgrade, Studentski trg 12-16, 11000 Belgrade, Serbia.
* Corresponding author: Nataša V. Valentić, E-mail: naca@tmf.bg.ac.rs; Tel: +381113303671; Fax: +381113370387
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ACCEPTED MANUSCRIPT
Abstract
In the present study, twelve new 1-aryl-3-ethyl-3-methylpyrrolidine-2,5-diones were synthesized and their structures
1
were characterized by FT-IR, H NMR, 13C NMR spectroscopy and elemental analysis. In the final step of synthetic rout,
condensation between corresponding succinic acid and substituted anilines has been improved using the microwave irradiation.
Significantly higher yields compared to conventional condensation have been observed. The preliminary biological results
indicated that some of the synthesized compounds showed promising in vitro antifungal activities towards several test fungi. 1-
(4-Bromophenyl)-3-ethyl-3-methylpyrrolidine-2,5-dione (8) exhibited significant in vitro inhibitory activities against broad
spectra of fungus, and on the basis of obtained data, the investigated bromo derivative has to be observed as novel potential
fungicide. The density functional theory (DFT) calculations have been performed in order to study the structure-activity
relationship (SAR) of the investigated molecules. In order to prediction of the chemical activity of the molecule, the molecular
electrostatic potential (MEP) map was analyzed for the optimized geometry of 1-phenyl-3-ethyl-3-methylpyrrolidine-2,5-dione
(4) and 1-(4-bromophenyl)-3-ethyl-3-methylpyrrolidine-2,5-dione (8).
Keyword: Succinimide; Antimicrobial activity; Antifungal activity; DFT calculation; Structure-activity relationship.
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1. Introduction
In the treatment of various diseases caused by different microorganisms there are currently available several drugs [1].
Numerous side effects and toxic effects produced by their application, lead to the addition need for drug improvement or finding
of novel agents. Also, results of increased use and misuse of antimicrobial drugs are development of resistant pathogens, which
caused that the overcoming drug resistance has become an important issue in medicinal chemistry [2]. Moreover, it is known
that the utilization of agrochemicals has led to numerous benefits and significant progress in our lifestyles. Due that, the
problem of multidrug resistant microorganisms and pollution problems associated with conventional agrochemicals have
reached an alarming level in the last decades. Accordingly, synthesis and design of new bioactive compounds with novel
structures, biological activity, high selectivity and eco-friendly properties has become an urgent need in future [3-5].
There are number of five-member heterocyclic molecules which are very useful as pharmaceutical, chemical and
agricultural agents. Succinimdes belong to the class of cyclic imides, which synthetics products exhibits wide spectrum of
biological and pharmacological properties such as antimicrobial [6-10], antiepileptic [11], good electro-convulsion [12],
analgesic [13], antitumor [14] etc. Moreover, cyclic imides like succinimides, maleimides and itaconimide demonstrated the
defensive and restorative antifungal influence against rice blast and kidney bean stem rots [15]. The number of succinimide
derivatives showed the seedling growth stimulator activities against wheat and radish [16].
The present research is directed towards the synthesis and characterization of a series of novel 1-aryl-3-ethyl-3-
methylpyrrolidine-2,5-diones as potentially new heterocyclic compounds with promising bioactivity. Additionally, evaluation of
antifungal and antimicrobial activity and investigation of physico-chemical properties (using the density function theory (DFT))
of newly synthesized compounds have been performed. To estimate chemical and biological activity of the molecule, different
molecular descriptors were calculated for the optimized geometries of the investigated succinimides. The corresponding
structure-activity relationships were proposed and discussed.
2. Experimental
2.1. Chemistry
The chemicals used in the synthesis were purchased from Sigma-Aldrich Chemicals (Sigma-Aldrich Corp., St. Louis,
MO, USA) or Merck Chemicals (Merck KGaA, Darmstadt, Germany). Microwave synthesis was performed in Anton Paar
Monowave 300 (Ashland, VA, USA) microwave reactor. The FT-IR spectra of the compounds (in KBr pellets) were determined
using an ABB Bomem MB Series 100 Fourier transform infrared (FT-IR) (Quebec City, Canada) spectrophotometer. The NMR
spectral measurements have been performed on a Bruker AC 250 spectrometer at 200 MHz for the 1H NMR and 50 MHz for the
1
13C NMR spectra or on a Bruker 300 spectrometer at 400 MHz for the H NMR and 100 MHz for the 13C NMR spectra. The
spectra were recorded at room temperature in deuterated dimethyl sulfoxide (DMSO-d6). In this paper, chemical shifts are
expressed in ppm in reference to TMS. All melting points were uncorrected and are reported here in degrees Celsius. The
elemental analyses of the investigated compounds were carried out by standard analytical micromethods using an Elemental
Vario EL III microanalyzer.
2.1.1. Synthesis of 1-aryl-3-ethyl-3-methylpyrrolidine-2,5-diones (1-12
)
All of the investigated 1-aryl-3-ethyl-3-methylpyrrolidine-2,5-diones were synthesized from the corresponding succinic
acid derivative and substituted anilines under solvent-free conditions using the microwave irradiation (MW). 3-Ethyl-3-methyl
succinic acid derivative was synthesized by previously reported procedures (Scheme 1, part Results and discussion) [17-19].
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Generally, the mixture of the previously synthesized 3-ethyl-3-methyl succinic acid (1 mmol, 160.2 mg) and
substituted aniline (1.1 mmol) have been stirred in a 25 mL reactor tube at 180 °C (MW) for 15min under solvent-free
conditions. After the completion of the reaction, the mixture was cooled to room temperature. The obtained crude mixture has
been dissolved in ethyl acetate and consecutively washed with 10 mL of 5% HCl(aq), 10 mL of saturated NaHCO3(aq) and two
times with 10 mL of distilled water. The organic layer was dried over Na2SO4 and the solvent was evaporated under reduced
pressure. The crude product was recrystallized from acetone.
The structures of the novel succinimides were confirmed by melting point, FT-IR, 1H NMR, and 13C NMR
spectroscopy, as well as by elemental analysis. The data obtained during characterization are given below. The numbering of
carbon atoms for 13C NMR is presented in the Supplementary material (Fig. S1).
1-(4-Hydroxyphenyl)-3-ethyl-3-methylpyrrolidine-2,5-dione (1, C13H15NO3). White solid; Yield: 78%; M.p.: 145-147 °C; FT-
IR (KBr): |ν| cm–1 = 1767 (C=O), 1687 (C=O); 1H NMR (200 MHz, DMSO): |δ| ppm = 9.75 (s, 1H, –OH), 7.03 (d, J = 8.0 Hz,
2H, –C6H4), 6.84 (d, J = 8.0 Hz, 2H, –C6H4), 2.80-2.56 (AB q, JAB = 18.0 Hz, 2H, –CH2–), 1.74-1.52 (m, 2H, –CH2CH3), 1.28
(s, 3H, –CH3), 0.86 (t, J = 8.0 Hz, 3H, –CH2CH3); 13C NMR (50 MHz, DMSO): |δ| ppm = 182.37 (C6), 175.79 (C7), 157.56
(C11), 128.57 (C9, C9'), 123.80 (C8), 115.66 (C10, C10'), 43.74 (C4), 40.13 (C5), 31.15 (C2), 23.37 (C3), 8.73 (C1). Anal.
calcd. for C13H15NO3: C, 66.94; H, 6.48; N, 6.00; Found: C, 66.81; H, 6.40; N, 5.93.
1-(4-Methoxyphenyl)-3-ethyl-3-methylpyrrolidine-2,5-dione (2, C14H17NO3). Black solid; Yield: 77%; M.p.: 75-77 °C; FT-IR
(KBr): |ν| cm–1 = 1766 (C=O), 1703 (C=O); 1H NMR (200 MHz, DMSO): |δ| ppm = 7.18 (d, J = 8,0 Hz, 2H, –C6H4), 7.03 (d, J
= 8,0 Hz, 2H, –C6H4), 3.79 (s, 3H, –OCH3), 2.82-2.58 (AB q, JAB = 18.0 Hz, 2H, –CH2–), 1.76-1.54 (m, 2H, –CH2CH3), 1.29 (s,
3H, –CH3), 0.88 (t, J = 8.0 Hz, 3H, –CH2CH3); 13C NMR (50 MHz, DMSO): |δ| ppm = 182.24 (C6), 175.67 (C7), 159.17 (C11),
128.56 (C9, C9'), 125.27 (C8), 114.35 (C10, C10'), 55.57 (C12), 43.78 (C4), 40.14 (C5), 31.11 (C2), 23.27 (C3), 8.69 (C1).
Anal. calcd. for C14H17NO3: C, 68.00; H, 6.93; N, 5.66; Found: C, 67.89; H, 6.82; N, 5.60.
1-(4-Methylphenyl)-3-ethyl-3-methylpyrrolidine-2,5-dione (3, C14H17NO2). White solid; Yield: 75%; M.p.: 54-56 °C; FT-IR
(KBr): |ν| cm–1 = 1777 (C=O), 1710 (C=O); 1H NMR (200 MHz, DMSO): |δ| ppm = 7.29 (d, J = 8.0 Hz, 2H, –C6H4), 7.14 (d, J
= 8.0 Hz, 2H, –C6H4), 2.77-2.65 (AB q, JAB = 18.0 Hz, 2H, –CH2–), 2.34 (s, 3H, –CH3), 1.76-1.54 (m, 2H, –CH2CH3), 1.29 (s,
3H, –CH3), 0.88 (t, J = 8,0 Hz, 3H, –CH2CH3); 13C NMR (50 MHz, DMSO): |δ| ppm = 182.16 (C6), 175.58 (C7), 138.12 (C11),
130.14 (C8), 129.64 (C10, C10'), 127.16 (C9, C9'), 43.87 (C4), 40.20 (C5), 31.16 (C2), 23.31 (C3), 20.95 (C12), 8.73 (C1).
Anal. calcd. for C14H17NO2: C, 72.70; H, 7.41; N, 6.06; Found: C, 72.55; H, 7.33; N, 6.00.
1-phenyl-3-ethyl-3-methylpyrrolidine-2,5-dione (4, C13H15NO2). White solid; Yield: 79%; M.p.: 53-54 °C FT-IR (KBr): |ν| cm–
1
= 1776 (C=O), 1711 (C=O); 1H NMR (200 MHz, DMSO): |δ| ppm = 7.54–7.42 (m, 5H, –C6H5), 7.28 (d, J = 7.0 Hz, 1H, –
C6H5), 2.85-2.61 (AB q, JAB = 18.0 Hz, 2H, –CH2–), 1.78-1.56 (m, 2H, –CH2CH3), 1.31 (s, 3H, –CH3), 0.89 (t, J = 8,0 Hz, 3H,
–CH2CH3); 13C NMR (50 MHz, DMSO): |δ| ppm = 182.04 (C6), 175.45 (C7), 132.71 (C8), 129.14 (C9, C9'), 128.57 (C11),
127.34 (C10, C10'), 43.89 (C4), 40.21 (C5), 31.12 (C2), 23.24 (C3), 8.70 (C1). Anal. calcd. for C13H15NO2: C, 71.87; H, 6.96;
N, 6.45 Found: C, 71.77; H, 6.86; N, 6.39.
1-(4-Fluorophenyl)-3-ethyl-3-methylpyrrolidine-2,5-dione (5, C13H14NO2F). White solid; Yield: 72%; M.p.: 63-64°C FT-IR
(KBr): |ν| cm–1 = 1776 (C=O), 1704 (C=O); 1H NMR (200 MHz, DMSO): |δ| ppm = 7.335 (d, J = 6.0 Hz, 4H, –C6H4), 2.79-
2.65 (AB q, JAB = 18.0 Hz, 2H, –CH2–), 1.79-1.52 (m, 2H, –CH2CH3), 1.30 (s, 3H, –CH3), 0.88 (t, J = 8.0 Hz, 3H, –CH2CH3);
13C NMR (50 MHz, DMSO): |δ| ppm = 181.99 (C6), 175.40 (C7), 161.63 (d, J = 237.9 Hz, C11,11’), 129.53 (d, J = 8.50 Hz,
C9,9’), 129.91 (d, J = 3.0 Hz, C8), 116.05 (d, J = 22.5 Hz, C10,10’), 43.88 (C4), 40.20 (C5), 31.06 (C2) 23.28 (C3), 8.82 (C1).
Anal. calcd. for C13H14FNO2: C, 66.37; H, 6.00; N, 5.95; Found: C, 66.35; H, 5.96; N, 5,92.
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1-(4-Chlorophenyl)-3-ethyl-3-methylpyrrolidine-2,5-dione (6, C13H14NO2Cl). White solid; Yield: 76%; M.p.: 50-52 °C FT-IR
(KBr): |ν| cm–1 = 1775 (C=O), 1702 (C=O); 1H NMR (200 MHz, DMSO): |δ| ppm = 7.57 (d, J = 8.0 Hz, 2H, –C6H4), 7.33 (d, J
= 8.0 Hz, 2H, –C6H4), 2.79-2.65 (AB q, JAB = 18.0 Hz, 2H, –CH2–), 1.73-1.55 (m, 2H, –CH2CH3), 1.30 (s, 3H, –CH3), 0.87 (t, J
= 8,0 Hz, 3H, –CH2CH3); 13C NMR (50 MHz, DMSO): |δ| ppm = 181.89 (C6), 175.29 (C7), 133.07 (C8), 131.54 (C11), 129.23
(C10, C10'), 129.17 (C9, C9'), 43.97 (C4), 40.27 (C5), 31.09 (C2), 23.13 (C3), 8.72 (C1). Anal. calcd. for C13H14ClNO2: C,
62.03; H, 5.61; N, 5.56; Found: C, 61.92; H, 5.45; N, 5.49.
1-(3-Chlorophenyl)-3-ethyl-3-methylpyrrolidine-2,5-dione (7, C13H14NO2Cl). White solid; Yield: 60%; M.p.: 58-59°C FT-IR
1
(KBr): |ν| cm–1 = 1779 (C=O), 1698 (C=O); H NMR (400 MHz, DMSO): |δ| ppm = 7.56-7.45 (m, 3H, –C6H4), 7.31-7.29 (m,
2H, –C6H4), 2.82-2.64 (AB q, JAB = 16.0 Hz, 2H, –CH2–), 1.77-1.58 (m, 2H, –CH2CH3), 1.32 (s, 3H, –CH3), 0.90 (t, J = 8.0 Hz,
3H, –CH2CH3); 13C NMR (100 MHz, DMSO): |δ| ppm = 181.90 (C6), 175.30 (C7), 134.26 (C8), 133.43 (C10 along –Cl),
130.97 (C10’), 128.78 (C9 close to –Cl), 127.51 (C11), 126.37 (C9’), 44.22 (C4), 40.58 (C5), 31.25 (C2) 23.32 (C3), 8.95 (C1).
Anal. calcd. for C13H14ClNO2: C, 62.03; H, 5.61; N, 5.56; Found: C, 61.90; H, 5.47; N, 5.48.
1-(4-Bromophenyl)-3-ethyl-3-methylpyrrolidine-2,5-dione (8, C13H14NO2Br). White solid; Yield: 75%; M.p.: 60-63 °C FT-IR
(KBr): |ν| cm–1 = 1775 (C=O), 1702 (C=O); 1H NMR (200 MHz, DMSO): |δ| ppm = 7.70 (d, J = 8.0 Hz, 2H, –C6H4), 7.26 (d, J
= 8.0 Hz, 2H, –C6H4), 2.78-2.66 (AB q, JAB = 18.0 Hz, 2H, –CH2–), 1.76-1.55 (m, 2H, –CH2CH3), 1.30 (s, 3H, –CH3), 0.87 (t, J
= 8.0 Hz, 3H, –CH2CH3); 13C NMR (50 MHz, DMSO): |δ| ppm = 181.83 (C6), 175.24 (C7), 132.18 (C10, C10'), 131.97 (C8),
129,46 (C9, C9'), 121.56 (C11), 43.98 (C4), 40.28 (C5), 31.10 (C2) 23.13 (C3), 8.72 (C1). Anal. calcd. for C13H14BrNO2: C,
52.72; H, 4.76; N, 4.73; Found: C, 52.59; H, 4.63; N, 4,65.
1-(3-Bromophenyl)-3-ethyl-3-methylpyrrolidine-2,5-dione (9, C13H14NO2Br). White solid; Yield: 63%; M.p.: 72-73°C FT-IR
(KBr): |ν| cm–1 = 1779 (C=O), 1698 (C=O); 1H NMR (200 MHz, DMSO): |δ| ppm = 7.67-7.56 (m, 2H, –C6H4), 7.47 (t, J = 6.0
Hz, 1H, –C6H4), 7.35-7.30 (m, 1H, –C6H4), 2.84-2.59 (AB q, JAB = 18.0 Hz, 2H, –CH2–), 1.81-1.52 (m, 2H, –CH2CH3), 1.30 (s,
3H, –CH3), 0.88 (t, J = 8.0 Hz, 3H, –CH2CH3); 13C NMR (50 MHz, DMSO): |δ| ppm = 181.73 (C6), 175.14 (C7), 134.13 (C8),
131.44 (C10 along –Br), 131.04 (C10’), 130.06 (C9 close to –Br), 126.57 (C11), 121.38 (C9’), 43.94 (C4), 40.28(C5), 30.96
(C2) 23.18 (C3), 8.83 (C1). Anal. calcd. for C13H14BrNO2: C, 52.72; H, 4.76; N, 4.73; Found: C, 52.56; H, 4.60; N, 4.64.
1-(4-Carboxyphenyl)-3-ethyl-3-methylpyrrolidine-2,5-dione (10, C14H15NO4). White solid; Yield: 72%; M.p.: 152-154 °C FT-
IR (KBr): |ν| cm–1 = 1779 (C=O), 1717 (C=O); 1H NMR (200 MHz, DMSO): |δ| ppm = 8.06 (d, J = 8.0 Hz, 2H, –C6H4), 7.44
(d, J = 8,0 Hz, 2H, –C6H4), 2.87-2.63 (AB q, JAB = 18.0 Hz, 2H, –CH2–), 1.78-1.56 (m, 2H, –CH2CH3), 1.31 (s, 3H, –CH3),
0.88 (t, J = 8,0 Hz, 3H, –CH2CH3); 13C NMR (50 MHz, DMSO): |δ| ppm = 181.81 (C6), 175.20 (C7), 166.99 (C12), 136.51
(C8), 130.73 (C11), 130.19 (C10, C10'), 127.34 (C9, C9'), 44.05 (C4), 40.34 (C5), 31.15 (C2), 23.15 (C3), 8.73 (C1). Anal.
calcd. for C14H15NO4: C, 64.36; H, 5.79; N, 5.36; Found: C, 64.48; H, 5.89; N, 5.34.
1-(4-Cyanophenyl)-3-ethyl-3-methylpyrrolidine-2,5-dione (11, C14H14N2O2). White solid; Yield: 76%; M.p.: 93-96 °C FT-IR
(KBr): |ν| cm–1 = 1772 (C=O), 1714 (C=O); 1H NMR (200 MHz, DMSO): |δ| ppm = 7.98 (d, J = 8.0 Hz, 2H, –C6H4), 7.55 (d, J
= 8.0 Hz, 2H, –C6H4), 2.87-2.63 (AB q, JAB = 18.0 Hz, 2H, –CH2–), 1.78-1.56 (m, 2H, –CH2CH3), 1.31 (s, 3H, –CH3), 0.88 (t, J
= 8.0 Hz, 3H, –CH2CH3); 13C NMR (50 MHz, DMSO): |δ| ppm = 181.56 (C6), 174.95 (C7), 136.75 (C8), 133.26 (C10, C10'),
128.11 (C9, C9'), 118.57 (C12), 111.12 (C11), 44.07 (C4), 40.35 (C5), 31.06 (C2), 22.99 (C3), 8.68 (C1). Anal. calcd. for
C14H14N2O2: C, 69.41; H, 5.82; N, 11.56; Found: C, 69.30, H, 5.68, N, 11.49.
1-(4-Nitrophenyl)-3-ethyl-3-methylpyrrolidine-2,5-dione (12, C13H14N2O4). Yellow solid; Yield: 73%; M.p.: 115-117 °C FT-IR
(KBr): |ν| cm–1 = 1782 (C=O), 1713 (C=O); 1H NMR (200 MHz, DMSO): |δ| ppm = 8.36 (d, J = 10.0 Hz, 2H, –C6H4), 7.63 (d, J
= 10.0 Hz, 2H, –C6H4), 2.89-2.65 (AB q, JAB = 18.0 Hz, 2H, –CH2–), 1.79-1.58 (m, 2H, –CH2CH3), 1.32 (s, 3H, –CH3), 0.89 (t,
J = 8,0 Hz, 3H, –CH2CH3); 13C NMR (50 MHz, DMSO): |δ| ppm = 181.58 (C6), 174.97 (C7), 146.85 (C11), 138.29 (C8),
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128,27 (C10, C10'), 124.45 (C9, C9'), 44.12 (C4), 40.38 (C5), 31.09 (C2), 22.97 (C3), 8.70 (C1). Anal. calcd. for C13H14N2O4:
C, 59.54; H, 5.38; N, 10.68; Found: C, 59.44; H, 5.31; N, 10.62.
2.2. Antimicrobial Activity
2.2.1. Human Pathogens
The newly synthesized succinimides were evaluated for antibacterial activity against eight bacterial species:
Staphylococcus aureus (ATCC 6538), Bacillus cereus (clinical isolate), Micrococcus flavus (ATCC 10240), Listeria
monocytogenes (NCTC 7973) (gram positive bacteria), Pseudomonas aeruginosa (ATCC 27853), Enterobacter cloacae
(clinical isolate), Salmonella typhimurium (ATCC 13311), Escherichia coli (ATCC 35210) (gram negative bacteria).
Antifungal activity were evaluated against eight fungal species: Aspergillus flavus (ATCC 9643), Aspergillus
ochraceus (ATCC 12066), Aspergillus versicolor (ATCC 11730), Aspergillus niger (ATCC 6257), Penicillium ochrochloron
(ATCC 9112), Penicillium funiculosum (ATCC 36839), Penicillium verrucosum var.cycopium (food isolate), Trichoderma
viride (IAM 5061).
2.2.2. Preparation of Cultures of Micromycetes
The micromycetes were cultivated on malt agar (MA) medium for 21 days at 26 °C. Inoculum was prepared via spores
rinsing from the substrate surface using sterile solution 0.85% NaCl and 0.1% Tween 80 (v/v). The preferred concentration of
spores was prepared by dissolving 100 ml of a primary culture in 900 ml of malt broth (MB) growth medium. Dilution was
performed several times until the final concentration has been obtained (1.0 × 105 cells/ml). Inoculum was stored at 4 °C until
further usage.
The bacterial strains were stocked in glycerol and seeded on 2 ml of Tryptic Soy Broth (TSB) medium (Biolife, Milan,
Italy), then incubated in thermostat for 24 h at 37 °C. Overnight cultures have 1.0 × 109 cells/ml each. The final solution of
culture and medium (1.0 × 108 cells/ml) was obtained by dissolving 100 ml of a primary culture in 900 ml of TSB. The numbers
of spores were calculated under a Leica DMLS light microscope using a haemocytometer.
2.2.3. Broth Microdilution Method
The antimicrobial activity was performed by using microdilution method [20-26]. The minimal inhibitory (MICs),
minimal fungicidal (MFCs) and minimal bactericidal concentrations (MBCs) of the synthesized succinimides for each species of
studied microorganisms were determined. The newly synthesized compound were dissolved in 10% DMSO water solution. The
concentration dissolved succinimides is 10 mg/ml. In each well of microplates (“F”-micro-plate with cover, Spektar, Čačak,
Serbia), 20 ꢀl of MB growth medium was added for fungi or TSB for bacteria, 180 ꢀl of compound solution and different
volumes in microlitres of fungal inocula for each fungal strain in particular and 10 ꢀl of bacterial inocula for each bacterial
species. Antimycotics ketoconazole and bifonazole and antibiotics streptomycin and ampicillin were used as positive controls (1
mg/ml in sterile physiological saline). Ten percent DMSO was used as a negative control. Microplates were incubated for 72 h
at 28 °C (micromycetes) and for 24 h at 37 °C (bacteria).
2.2.4. MIC Determination
The minimum inhibitory concentration (MIC) is the lowest concentration of antimicrobial agent that completely
inhibits bacterial and fungal without visible growth, observed under a binocular microscope [27-29]. The MIC values were
determined by counting cell numbers by spectrophotometric methods [23,24]. The MICs obtained from the susceptibility testing
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of various bacteria to the analyzed compound were determined likewise via a colorimetric microbial viability assay based on
reduction of INT (p-iodonitrotetrazoliumviolet) [2-(4-iodophenyl)-3-(4-nitrophenyl)-5-phenyltetrazolium chloride; Sigma-
Aldrich, Munich, Germany] colour and compared to positive controls for each bacterial strain. After staining, the colonies were
incubated for 2 h at 37 °C. Inhibition of growth is indicated Pale yellowish colour23. Microplate reader was used (Tecan Austria
GmbH, Grödig, Austria; Eppendorf AG, Hamburg, Germany), to evaluate the intensity of yellow colour. MIC values were
calculated as milligram per 100 ꢀl, and then, the values were transferred in milligrams per milliliter [23,24].
2.2.5. MFC and MBC Determination
The minimum fungicidal (MFC) and minimum bactericidal concentration (MBC) were determined by serial
subcultivation of 2 ꢀl of inoculum into microtiter plates containing 100 ꢀl of broth per well and the further incubation for 72 h at
26 °C for micromycetes and for 24 h at 37 °C for bacteria, according to the protocol of the Mycological Laboratory, Department
of Plant Physiology, Institute for Biological Research “Siniša Stanković”, University of Belgrade [23,24]. MFC and MBC is
defined as the lowest concentration with no visible fungal/bacterial growth, indicating 99.5% killing of the original inocula31.
Optical density is measurement of fungal/bacterial cultures, at the wavelength of 655 nm by a Microplate Manager (Tecan
Austria GmbH, Grödig, Austria; Eppendorf AG, Hamburg, Germany) and compared to a blank (broth medium plus diluted
extracts) and a positive control. MBC values were determined by a colorimetric microbial viability assay based on reduction of
INT colour and were compared to positive controls for each bacterial strain. After stain was applied (40 ꢀl per well), the stained
colonies were incubated for 2 h at 37 °C. Unstained chambers of microplates have indicated the presence of a bactericidal effect
(CLSI2009).The results of MFC and MBC values were calculated as milligrams per 100 ꢀl, and then, the values were
transferred in milligramme per milliliter.
2.3. Theoretical Calculations
All density functional theory (DFT) calculations were performed using the Gaussian 09 program package [30] with
B3LYP method [31] and 6-311G(d,p) basis set. The default convergence criteria were used without any constraint on the
geometry. The stability of the optimized geometry was confirmed by frequency calculations, which gave real values (no
imaginary frequency) for all the calculated frequencies. The solvent effect was introduced by the Conductor Polarizable
Continuum Model (CPCM) [32].
The frontier molecular orbital energies and energy gap of the investigated compounds are also calculated at the same
level of DFT theory. For obtaining the chemical reactivity of the molecule, the Molecular Electrostatic Potential (MEP) surface
is plotted over the optimized geometry. The GaussView 5.0 graphical interface was used to visualize molecular orbitals and
MEP [33]. The Vega ZZ version 2.4 [34] was used to estimate physicochemical descriptors (log P, polar surface area and molar
refractivity) from geometries previously optimized by DFT.
3. Results and discussion
3.1. Synthesis and spectral analisys
In connection with our study of the structure-property relationship of novel succinimide derivatives, we now in this
paper extend our previous work [35-37] on the synthesis, structure and properties of twelve new 1-aryl-3-ethyl-3-
methylpyrrolidine-2,5-diones.
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The synthesis procedure of the novel compounds (1-12) is shown in Scheme 1. In the last step, 1-aryl-3-ethyl-3-
methylsuccinimides derivatives have been synthesized under microwave irradiation in a moderate yield, while all previous steps
have been proceed by literature data [17-19]. Due to microwave irradiation, the products have been obtained in better yields
(85%-89%) with a shorter reaction time (15 min), while in previously reported procedures the succinimide derivatives have
been obtained in lower yields with longer reaction times (conduction heating, 180 °C, 3h).
<Scheme 1>
The chemical structures of the compounds (1-12) have been confirmed by FT-IR, 1H NMR, 13C NMR spectroscopy and
elemental analyses. On the FT-IR spectra two intensive and characteristic stretching absorptions of the carbonyl groups (C=O)
from the succinimide ring in the regions 1782-1766 cm–1 and 1717-1687 cm–1 have been observed. All aromatic and aliphatic
1
C–H stretchings are on their characteristic absorption positions. H NMR spectrum showed a characteristic aromatic protons
belonging to 3- or 4-substituted phenyl group. Protons in p-substituted phenyl ring gave peaks at 8.36-7.03 and 7.63-6.84 ppm
as two doublets, while for unsubstitued and m-substituted phenyl group multiplet signals have been observed. Moreover,
aliphatic protons of –CH3 and –CH2CH3 are on the characteristic positions. Methyl protons are presented as one strong singlet
(from 1.32 to 1.28 ppm), while ethyl group is observed as multiplet (1.79-1.52 ppm) and triplet (0.89-0.86 ppm) signals. Also,
protones from methylene group in succinimide ring (–CH2–) is observed as characteristic AB quartet in the range 2.87-2.56 with
coupling constant JAB = 18 Hz. Additionally, 13C NMR spectra of investigated compounds exhibited all necessary signals at the
appropriate positions (see Experimental).
3.2. Antimicrobial Activity
The newly synthesized succinimides (1-12) have been tested for antibacterial activity on eight bacterial species,
mentioned previously, and MIC/MBC values are given in Table 1. Compound 2 has better MIC/MBC activity than ampicillin,
except in the case of Escherichia coli, where it has no activity. The compound 3 has no activity to Escherichia coli and
Salmonella typhimurium, but its activity (MIC/MBC) is better for other bacteria then ampicillin. The compound 10 shows
activity to four bacteria: Listeria monocytogenes, Pseudomonas aeruginosa, Enterobacter cloacae, Salmonella typhimurium.
Other compounds did not show any activity on the tested bacteria.
<Table 1>
Also, newly synthesized succinimides have been tested for antifungal activity on eight fungal species, and MIC/MFC
values are given in Table 2. The succinimides showed great activity against different species of fungal. The compound 8, which
should be particularly prominent, have better MIC/MFC activity even then a reference commercially available compound
ketoconazole and bifonazole.
<Table 2>
It can be noticed that tested compounds showed higher antifungal potential then antibacterial effect and reacted against
almost all fungal species, with exception toward Penicillium species. Exactly these obtained antimicrobial results candidate the
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investigated compounds (1-12) as promising antifungal agents, whereby compound 8 have to be specially highlighted due to its
high activity against all investigated fungus even in compare to commercially available drugs.
3.3. Theoretical Calculations
3.3.1. Conformational stability
In order to find all stable conformers, a conformational analysis was carried out for the investigated compounds. The
sucinimide ring of investigated compounds is very rigid so the only conformational changes are possible in the position of its
substituents (methyl, ethyl and phenyl group). As the rotation of methyl group does not contribute significantly to the energy of
investigated systems, only the positions of ethyl and phenyl group are investigated. The positions of phenyl group are
investigated in detail in our previous work [38] and similar findings were noted in this case, too. For a better insight to the
energy changes connected with rotation of ethyl group, the potential energy scans (PES) were done for two possible orientations
of phenyl group. During the calculation, all the geometrical parameters were simultaneously relaxed while the torsion angle of
ethyl group was varied in steps of 5° from 0-360° (Fig. S2, Supplementary material). Results show that six conformers for
molecule with symmetric substituent and 12 conformers for asymmetric substituent are possible.
The full geometry optimizations of these conformers were performed by B3LYP [31] method with 6-311G(d,p) basis
set in the vacuum and solvents (THF, ethanol, DMSO and water). The results provided from these calculations are used for
different analyses in this work. The geometry of the most stable isomer for compound 4 obtained with B3LYP method is shown
in Figure 1.
<Figure 1>
The located conformers have similar energies which differ from the energy of the most stable isomer for less than 0.6
kcal/mol, depending of substituent and according to Boltzmann analysis they are simultaneously present in a mixture.
Regardless of that, the properties of interest are simulated based on the geometry of the most stable conformer only.
DFT calculations indicate non-planar conformations between succinimide and phenyl rings for all investigated
succinimides. The deviation from planarity (expressed in terms of dihedral angle θ between planes of succinimide and phenyl
rings, Table 3 and S1 (Supplementary material)) can serve as a rough measure for the efficient transfer of substituent's resonance
effect from phenyl to succinimide ring. In investigated series of succinimides, it increases with increasing of electron-donating
ability of the substituent R. The B3LYP method predicts a torsion angle θ from 38 to 45° in vacuum while with introduction of
solvents (THF, ethanol, DMSO and water) predict a much larger values for this angle, i.e., from 46 to 67°. It must be noted that
the angle θ increase with higher polarity of solvents.
3.3.2. Electronic analysis
The analysis of energies of frontier molecular orbitals (the HOMO and LUMO) as well as the energy gap between
them, explain the kinetic stability and chemical reactivity of the molecule [39]. The energies of HOMO and LUMO are,
respectively, rough measures of the electron-donating and electron-withdrawing abilities of the molecule.
In order to check possible ways of interactions for investigated succinimides the energies and electron distributions of
the frontier molecular orbitals are computed in different solvents (THF, ethanol, DMSO and water) using B3LYP functional, see
Tables 3 and S1 (Supplementary material). Plots of the HOMO and LUMO molecular orbitals along with their energies and
energy gaps for compounds 2, 4, 8 and 12 in vacuum are shown in Fig. 2.
9

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<Figure 2>
The electron density of HOMO orbital for all investigated molecules is dominantly populated on the aryl group and the
imide part of the succinimide ring. The electron densities of the LUMO orbitals demonstrate great influence of substituents
effects on the intramolecular charge transfer (ICT) process. LUMO orbital density in molecules with electron-donating
substituent is localized on the succinimide ring showing big shift of electron density relative to HOMO orbital and indicates
strong ICT character. Molecules with weak electron-withdrawing substituents show slight shift of electron density from the aryl
group to the imide part of the succinimide ring and indicates weak ICT character. Contrary, strong electron-withdrawing
substituents show slight shift of electron density from the imide part of the succinimide ring to the aryl group and indicate weak
ICT character with opposite direction.
<Table 3>
In the series of succinimides investigated here, the non-substituted compound 4 has the largest energy gap with 6.03 eV
in vacuum, while the presence of electron-donating substituent leads to a small decrease in the energy gap and a larger decrease
for electron-withdrawing substituent. Introduction of solvents effects lead to increasing of energy gap, in absolute values, for all
substituents except –NO2. But, relatively to non-substituted compound 4, introduction of the polar solvents prompts a decrease
in the energy gap for all substituted succinimides. The presence of electron-donating substituent leads to a small decrease in the
energy gap while electron-withdrawing substituent exhibits much larger decrease and this effect is consistent with the increase
of polarity. In non-polar solvent, THF, the electron-donating substituent causes a small increase, while electron-withdrawing
substituent, as in previous case, causes large decrease of the energy gap.
3.3.3. Molecular electrostatic potential
Molecular electrostatic potential (MEP) is related to the electronic density and often helps to predict the reactivity of
chemical systems in electrophilic and nucleophilic reactions, the study of biological recognition process and hydrogen bonding
interaction [40]. In order to predict reactive sites of electrophilic or nucleophilic attack for the investigated molecules, the MEP
at the B3LYP/6-311G(d,p) optimized geometry was calculated. The negative (red and yellow) regions of the MEP are related to
electrophilic reactivity and the positive (blue) region to nucleophilic reactivity, as shown in Fig. 3 (MEP).
<Figure 3>
As it can be seen from the Figure 3, molecule of 1-phenyl-3-ethyl-3-methylpyrrolidine-2,5-dione (4) in vacuum has
two possible sites for electrophilic and one site for nucleophilic attack. Negative regions of the studied molecule are located
around the oxygen atoms of the carbonyl groups and moderate positive region is localized on the hydrogen atoms of the
methylene group from the succinimide ring. Similarly, molecule of 8 has two possible sites for electrophilic attack, with
elongated negative potential from carbonyl groups over phenyl group to bromide substituent on para position (Figs. S3 and S4,
Supplementary material). At the same time positive region localized on the hydrogen atoms of the methylene group from
succinimide ring is elongated over H-atoms of phenyl group to σ-hole of para-bromide. Through such positive σ-hole, molecule
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can interact attractively with negative sites to form noncovalent complex [41]. MEP maps for other investigated compounds are
shown in Fig. S5 (Supplementary material).
3.4. ADMET Factor Profiling and SAR Study
One of the most important factors in design of biologically therapeutic species is their oral bioavailability. Due that,
determination which of the investigated succinimides possesses pharmacokinetic activity, their structural properties have been
tested by the empirical ‘rule of five’ established by Lipinski [42]. In accordance with this rule, compounds which satisfied
following four structural features: (1) molecular weight lower than 500; (2) maximum 5 atoms that are proton-donors of the
hydrogen bonds (–OH and –NH); (3) maximum 10 atoms (N and O) that are hydrogen bond acceptors and (4) calculated value
of the logarithm of the octanol-water partition coefficient (log P) lower than 5, will potentially exhibit good in vivo permeability
[43]. Moreover, additional structural parameters which have to be included in the attempts to propose corresponding SAR model
of investigated molecules are: number of rotatable bonds should be lower than 8, low polar surface area (< 140 Å2) and molar
refractivity in the range from 40 to 130 Å3 [43-45]. All structural parameters mentioned above are presented in the Table 4.
<Table 4>
From the Table 4 it can be noticed that all investigated compounds meet the empirical criteria ‘rule of five’ excluded 10
and 12 (criteria for the polar surface area). These results candidate synthesized succinimides for pharmacodynamic phase
investigations. Since log P is associated with solubility and permeability of the molecule, this physicochemical parameter is one
of the most important in the estimation of the molecule capability of transfer through the cell membranes. The investigated
succinimide derivatives are moderately lipophilic compounds, whereby all substituents, excluding strong electron-donating
hydroxyl group and the moderate electron-accepting carboxyl group, induce an increase of hydrophobic character compared to
the unsubstituted molecule (4). Also, the investigated compounds contain a low number of the rotatable bonds (Table 4), and
thus moderate conformational changes due to binding to a receptor are possible. Additionally, it was observed that polar surface
area (PSA) is a very important descriptor for drug transport properties, so the molecules which not possess corresponding PSA
properties will have difficulties in such important process as its transport. In investigated series, only two molecules did not
exhibit this PSA criterion which has been directly reflecting on their activity.
4. Conclusion
In this work, twelve new 1-aryl-3-ethyl-3-methylpyrrolidine-2,5-diones were synthesized in order to characterize and
study the influence of electronic effects of substituents in 4-position on the phenyl group on their antimicrobial and antifungal
activity. It can be concluded that tested compounds showed higher antifungal potential than antibacterial effect and reacted
against almost all fungal species. Exactly these obtained antimicrobial results candidate the investigated compounds (1-12) as
promising antifungal agents, whereby compound 8 have to be specially highlighted due to its high activity against all
investigated fungus even in compare to commercially available drugs.
With the help of density functional theory (DFT) calculations, the transmission of substituent effects through the
molecular skeletion and the nature of the HOMO and LUMO orbitals were explained. We have demonstrated that substituents
on the phenyl group significantly change the conjugation effect and further affect the intramolecular charge transfer (ICT)
character of the investigated succinimides. The molecular electrostatic potential (MEP) map was analyzed for the optimized
geometry of 1-phenyl-3-ethyl-3-methylpyrrolidine-2,5-dione (4) and 1-(4-bromophenyl)-3-ethyl-3-methylpyrrolidine-2,5-dione
11

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(8). The obtained results suggested that structure of compound 8 is very important for its biological recognition and therefore a
higher antifungal activity. The data presented in this investigation afford guidelines for the preparation of new succinimides with
greater antimicrobial activity.
Acknowledgements
This work has been financially supported by the Ministry of Education, Science and Technological Development of the
Republic of Serbia, under Grants no. 172013, 172035, 173052, TR31006 and 173032. Numerical simulations were run on the
PARADOX cluster at the Scientific Computing Laboratory of the Institute of Physics Belgrade, supported in part by the
Ministry of Education, Science and Technological Development of the Republic of Serbia under project No. ON171017.
Supplementary Data
Additional Supporting Information may be found in the online version of this article.
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Figure Captions
Figure 1. The most stable conformer of compound 4 calculated by B3LYP level of theory.
Figure 2. The HOMO and LUMO molecular orbitals with their energies and the energy gaps for compounds 2, 4, 8 and 12 in
vacuum.
Figure 3. Molecular electrostatic potential map of 1-phenyl-3-ethyl-3-methylpyrrolidine-2,5-dione (4) and 1-(4-bromophenyl)-
3-ethyl-3-methylpyrrolidine-2,5-dione (8) in vacuum from B3LYP/6-311G(d,p) calculation ploted on isosurfaces of 0.002 a.u.
electron density); color coding: red (very negative), orange (negative), yellow (slightly negative), green (neutral), turquoise
(slightly positive), light blue (positive), dark blue (very positive).
Scheme 1. The synthetic route of novel 1-aryl-3-ethyl-3-methylsuccinimides (1-12).
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Table 1. MIC/MBC activity of investigated succinimides. Values expressed in mg/ml (10% DMSO).
Staphyl.
aureus
n.a.
Bacillus
cereus
n.a.
Micrococcus Listeria
Pseudomonas Enterobacter Salmonella
Escherichia
No.
flavus
monocytogenes aeruginosa
cloacae
n.a.
typhimurium coli
n.a.
n.a.
n.a.
n.a.
n.a.
1
0.125/0.25 0.125/0.25 0.25/0.5
0.25/0.5
0.25/0.5
n.a.
0.25/0.5
0.125/0.5
n.a.
0.25/0.5
0.125/0.25
n.a.
0.25/0.5
n.a.
n.a.
2
0.25/0.5
n.a.
0.25/0.5
n.a.
0.25/0.5
n.a.
n.a.
3
n.a.
n.a.
4
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
5
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
6
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
7
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
8
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
9
n.a.
n.a.
n.a.
0.25/0.5
0.25/0.5
n.a.
0.25/0.5
n.a.
0.25/0.5
n.a.
0.25/0.5
n.a.
n.a.
10
11
12
0.25/0.5
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
Streptomycin 0.05/0.1
Ampicillin 0.3/0.4
0.1/0.2
0.3/0.4
0.2/0.3
0.3/0.4
0.2/0.3
0.4/0.5
0.2/0.3
0.8/1.25
0.3/0.5
0.4/0.8
0.2/0.3
0.3/0.5
0.2/0.3
0.3/0.5
*n.a. – no activity
1

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Table 2. MIC/MFC activity of investigated succinimides. Values expressed in mg/ml (10% DMSO).
Aspergillus
flavus
Aspergillus
ochraceus
Aspergillus
versicolor
Aspergillus
niger
Penicillium
Penicillium
funiculosum
Penicillium
Trichoderma
viride
No.
ochrochloron
verr.var.cycl.
0.063/0.125 0.063/0.125 0.125/0.25
0.125/0.25
0.25/0.5
n.a.
0.25/0.5
0.25/0.5
0.25/0.5
0.25/0.5
0.25/0.5
0.25/0.5
0.063/0.125
0.063/0.125
0.125/0.25
0.25/0.5
n.a.
0.25/0.5
0.25/0.5
n.a.
n.a.
0.25/0.5
0.125/0.25
0.25/0.5
0.25/0.5
0.25/0.5
0.25/0.5
0.25/0.5
0.032/0.063
0.25/0.5
n.a.
1
2
3
4
5
6
7
8
0.125/0.25
0.125/0.25
0.25/0.5
0.25/0.5
0.125/0.25
n.a.
0.125/0.25
0.25/0.5
0.25/0.5
0.25/0.5
0.25/0.5
0.25/0.5
0.125/0.25
0.25/0.5
0.125/0.25
0.25/0.5
0.125/0.25
n.a.
0.125/0.25
0.25/0.5
0.25/0.5
0.25/0.5
0.25/0.5
0.125/0.25
0.125/0.25
0.125/0.25
0.25/0.5
0.25/0.5
0.25/0.5
n.a.
0.25/0.5
0.125/0.25
0.5/0.5
n.a.
0.25/0.5
0.25/0.5
0.125/0.25
0.25/0.5
0.125/0.25
0.125/0.25
0.25/0.5
0.25/0.5
n.a.
0.063/0.125
0.25/0.5
n.a.
9
0.063/0.125 0.125/0.25
0.063/0.125 0.25/0.5
10
0.25/0.5
0.25/0.5
0.20/0.50
0.15/0.20
0.25/0.5
0.25/0.5
0.15/0.20
0.15/0.20
0.25/0.5
0.5/0.5
0.25/0.5
n.a.
0.25/0.5
0.25/0.5
0.20/0.30
0.10/0.20
0.25/0.5
0.25/0.5
1.00/1.50
0.15/0.20
11
0.125/0.25
0.20/0.50
0.10/0.20
0.25/0.5
0.20/0.50
0.15/0.20
0.25/0.5
1.00/1.50
0.20/0.25
12
Ketoconazole
Bifonazole
0.20/0.50
0.20/0.25
*n.a. – no activity
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Table 3. The energies of HOMO (EHOMO) and LUMO (ELUMO) molecular orbital, the energy gaps (Egap) in eV, torsion angle θ in
° and dipole moments (ꢀ) in Debye for investigated compounds in vacuum and ethanol as solvent.
Vacuum
EHOMO
-6.18
-6.08
-6.52
-6.77
-6.74
-6.77
-6.90
-6.69
-6.81
Ethanol
No.
R
ELUMO
-0.70
-0.66
-0.69
-0.74
-0.86
-1.04
-1.07
-1.06
-1.06
-1.74
-1.86
-2.66
Egap
θ
ꢀ
EHOMO ELUMO Egap
θ
ꢀ
4-OH
4-OCH3
4-CH3
H
5.48
5.42
5.83
6.03
5.88
5.72
5.83
5.63
5.75
5.32
5.33
4.80
43.65 2.58 -6.48
44.23 1.81 -6.39
43.67 1.36 -6.86
43.91 1.84 -7.10
42.59 3.97 -7.01
40.94 4.52 -6.98
41.51 3.84 -7.11
40.88 4.05 -6.91
41.80 3.44 -7.03
40.65 4.18 -7.25
39.02 7.03 -7.28
38.63 7.91 -7.47
-0.79
-0.78
-0.79
-0.82
-0.86
-1.09
-1.12
-1.11
-1.11
-1.88
-1.91
-2.88
5.69
5.61
6.07
6.28
6.15
5.89
5.99
5.80
5.92
5.37
5.37
4.59
65.72 2.38
64.44 1.93
63.56 1.35
61.56 2.02
59.21 3.97
53.38 4.70
53.26 4.19
53.46 4.54
55.56 4.07
50.77 4.58
48.61 8.37
47.29 8.52
1
2
3
4
5
4-F
4-Cl
3-Cl
4-Br
3-Br
6
7
8
9
4-COOH -7.06
10
11
12
4-CN
-7.20
-7.46
4-NO2
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Table 4. Evaluation of drug candidates.
Hydrogen bonds
Molecular
Rotatable Polar surface
Molar
refractivity/Å3
No.
log P
weigh
233.26
bonds
area/Å2
Donorsa
Acceptorsb
2.64
2.75
3.31
3.03
3.19
3.59
3.59
3.86
3.86
2.59
3.17
3.06
1
0
0
0
0
0
0
0
0
1
0
0
4
4
3
3
3
3
3
3
3
5
4
6
2
3
2
2
2
2
2
2
2
3
2
3
116.82
60.74
65.40
64.85
58.95
59.45
63.06
63.06
66.48
66.48
65.58
66.74
66.45
1
247.29
231.29
217.26
235.25
251.71
251.71
296.16
296.16
261.27
242.27
262.26
77.92
60.49
59.72
59.86
59.03
60.57
60.02
59.16
149.92
117.38
152.50
2
3
4
5
6
7
8
9
10
11
12
Ideal
compound
<500
<5
<5
<10
<8
<140
40-130
a A donor indicates any O–H or N–H group.
b An acceptor indicates any O or N including those in donor groups.
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Highlights
1. The twelve newly synthesized succinimides were evaluated for antimicrobal activity.
2. Tested compounds showed higher antifungal potential than antibacterial effect.
3. The investigated bromo derivative was recognized as novel potential fungicide.
4. DFT calculations were performed in order to study SAR and to predict chemical activity of molecules.
5. Ten investigated compounds are candidates for pharmacodynamic phase investigations.
1