Creatinine is generated when creatine is broken down in the body, and then passed through the kidneys . A creatinine serum test can be used to determine the amount of creatinine in the blood. Men have a normal percentage of 1.14 mg/dL and women have a normal percentage of 0.93 mg/dL . 1,3,4-Oxadiazole derivatives are important compounds in many fields, including medicine. Anticancer, antimicrobial, and anti-inflammatory activities have been described for these compounds . 1,3,4-oxadiazoles were important for the development of heterocyclic chemistry theory and are widely used in organic synthesis . Schiff bases prepared from the reaction of carbonyl group with primary amine in the carbonyl group reacts with a primary amine in the acids presence to create Schiff bases. Schiff bases, especially those with a heterocyclic moiety, such as 1,3,4-oxadiazole, have cytotoxic, antibacterial, and antifungal properties [5, 6]. Diazetidine is one of the most important nitrogen-containing compounds, and it has become extremely important in medical and pharmaceutical applications such as antibacterial activity [7-9].
Materials and Methods
Sigma-Aldrich and Fluka supplied all of the starting materials and solvents that were used without further purification. Uncorrected melting points were recorded with a Gallen Kamp capillary melting point apparatus, and FT-IR measurements taken with a SHIMADZU model FTIR-8400S. 1H-NMR spectra were recorded in DMSO solution with TMS as an internal standard using a Bruker spectrophotometer model ultra-shield at 400 MHz.
Synthesis of ester 1a 
In round-bottomed flask creatinine (0.01 mol, 1.13 g), (0.01 mol, 1 mL) ethyl chloroacetate, and potassium carbonate (0.015 mol, 2.07 g) in 1,4-dioxane (20 mL) were refluxed at 70 °C for 24 hours. The reaction mixture was cooled, filtered, and recrystallized from ethanol.
Synthesis of compound 2a-2b 
Compound 1a (0.01 mol, 1.99 g), (0.01 mol) of benzyl chloride/ n-propyl bromide and potassium carbonate (0.015 mol, 2.07 g) in 20 mL 1,4-dioxane were refluxed at 70 °C for 24 hours. The reaction mixture was cooled and filtered and the product was recrystallized from ethanol.
Synthesis of derivatives 3a-3b 
These compounds were produced using the procedure described in the literature with some modifications. Compounds 2a-2b (0.01 mol) were dissolved in 20 mL ethanol, followed by the addition of semicarbazide hydrochloride (0.06 mol) and sodium acetate (0.036 mol). After 3 hours of refluxing the reaction mixture, the precipitate was filtered and recrystallized from ethanol. Synthesis of 1,3,4-oxadiazole derivatives 4a-4b 
In a round-bottomed flask, (0.003 mol) of compounds 3a-3b, 40 mL of 5 percent of sodium hydroxide was placed. The mixture was refluxed for 5 hours. The solution was cooled and naturalized with dil. HCl. The separated precipitate was filtered and recrystallized from ethanol.
Synthesis of Schiff bases 5a-5d 
To prepare the solution of aromatic aldehyde (0.01 mol) (dimethylaminobenzaldehyde/benzaldehyde), glacial acetic acid as a catalyst, (0.01 mol) of compounds 4a-4b was added to 15 ml of ethanol absolute. This mixture was refluxed for 12 hours. Then, the excess solvent was evaporated and the products were recrystallized from ethanol.
Synthesis of diazetidine derivatives 6a-6h 
These compounds were prepared according to the literature procedure with some modifications. Phenyl isocyanate/phenyl isothiocyanate (0.04 mol) was added to a solution of Schiff bases (0.01 mol) 5a-5d in 50 mL dimethyl formamide, and the mixed reaction was heated for 10 hours at 60-65 °C. After cooling the reaction mixture, the precipitate was formed, and then recrystallized from ethanol.
Synthesis of β-lactam derivatives 7a-7d 
To a solution of Schiff bases compounds 5a-5d (0.002 mol) in 20 ml 1,4-dioxane chloroacetylchloride (0.002 mol, 0.15 mL) was added dropwise to the mixture at 0-5 °C in triethylamine, and then stirred at room temperature for 8 hours. After that, the precipitate was filtered, dried, and recrystallized from diethyl ether. All physical properties of the synthesized compounds are presented in Table 1.
Antioxidant activity [17, 18]
The DPPH radical scavenging activity of the samples was tested using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical. At a concentration of 20 mg/L, the DPPH solution in ethanol was made on a regular basis. 0.75 mL sample or standard solution (250-1000 g/mL) was put on top of 1.5 mL DPPH solution. After 30 minutes in the dark, the absorbance readings were measured at 517 nm against a blank, and calculations were made using the following formula.
DPPH Radical Scavenging Activity (percent) = [(A0-A1) / (A0)] ×100
A0 is the absorbance control value, while A1 is the absorbance sample or the standard value.
Results and Discussion
In this study, several novel heterocyclic compounds obtained from creatinine were synthesized, as displayed in Scheme 1.
The FT-IR spectrum of compound 1a shows the appearance of a new band at 1745 cm-1 that corresponds to the (C=O) ester group, 3278 cm-1 that corresponds to NH, and the disappearance of the NH2 band, as listed in Table 2. The appearance of the ester group and N-H band, as well as the disappearance of the NH2 band indicates that a reaction has occurred. The FT-IR spectra of compounds 2a-2b indicated that it disappeared from NH, as provided in Table 2.
The FT-IR of compounds 3a-3b demonstrated the disappearance of ester bands and the appearance of NH band and NH2 band.
Scheme 1: Synthetic rote of synthesized compounds
Compounds 4a-4b showed special bands due to (N-N) band and C-O-C band, as depicted in Table 2 . These bands and others are illustrated in Table 2.
Schiff bases 5a-5d showed the appearance of special bands due to (C=N), as shown in Table 3.
Compounds 6a-6d showed the disappearance of imine bands and appearance of special bands at 1703-1708 cm-1 due to C=O 1,3-diazetidine, while compounds 6e-6h showed the disappearance of imine bands and appearance of special band at 1230 cm-1 due to C=S and compounds 7a-7d indicated disappearance of imine bands and appearance of special bands at 1701-1708 cm-1 due to C=O β-lactam, these bands and others are displayed in Table 4.
Table 3: FT-IR Spectral data of synthesized compounds 5a-5d in cm-1
The 1H-NMR spectrum of compounds 1a,2b showed signals δ at 1.6-1.7 ppm due to (s, 3H-CH3), δ at 3.6 ppm due to (s, 2H, CH3-N-CH2), and δ at 3.3 ppm belong to (d, 2H, NH-CH2).
Compounds 5a and 5d showed at δ 1.2-1.7 ppm due to (s, 3H-CH3), δ at 3.3-3.4 ppm due to (s, 2H, CH3-N-CH2), δ at 4.3 ppm due to (s, 2H, benzyl), and δ at 6.3-6.5 ppm due to (s, 1H, N=CH).
Compounds 6c and 6d showed δ at 1.6-1.7 ppm due to (s, 3H-CH3), δ at 3.3 ppm due to (s, 2H,
CH3-N-CH2), δ at 6.4-6.5 ppm belong to (s, 1H, Ph-CH), and δ at 2.9 ppm due to (s, 6H, N-(CH3 )2.
Compound 6e and 6h observed δ at 1.2-1.7 ppm due to (s, 3H-CH3), δ at 3.4 ppm due to (s, 2H, CH3-N-CH2), and δ at 6.3-6.5 ppm due to (s, 1H, CH-Ph).
Compound 7a,7d showed δ at 1.2-1.8 ppm due to (s, 3H-CH3), at 6.3-6.5 ppm due to (s, 1H, CH-Ph), and δ at 4.2-4.3 ppm due to (d,1H, CH-Cl). These bands and others are listed in Table 5 [20, 21].
Antioxidant activities 
The DPPH method was used to evaluate some newly synthesized compounds for vitamin C as a reference. As indicated in Table 6, the newly prepared compounds 5d, 6e, 6h, and 7d were given a highly antioxidant assay, whereas compound 7a had a high antioxidant capacity at a dose of 50 mg/mL, as exhibited in Table 6 and Figure 1.
Figure 1: Antioxidant activity for some synthesized compounds 5d, 6e, 6h, 7a and 7d
The new 2-substituted 1,3,4-oxadiazole compounds were synthesized in the present research. In the first step, 1,3,4-oxadiazole was produced by cyclizing hydrazide derivatives, and in the second step, Schiff bases were synthesized by reacting with various aldehydes. These Schiff bases were used to synthesize diazetidine and β-lactam, by reacting with various reagents (phenyl isocyanate/phenyl isothiocyanate and chloroacetyl chloride), respectively. Spectral data was used to establish these new substances (FT-IR and 1H-NMR). In addition, in vitro synthetic molecules exhibit good antioxidant activity.
The authors thankful the Deanship at Baghdad University, College of Science, Chemistry Department and also, they would like to thank for everyone who helped to complete this research.
This research did not receive any special grant from funding agencies in the public, commercial, or not or-profit sectors.
All Authors contributed toward data analysis, drafting, and revising the paper and agreed to be responsible for all the aspects of this work.
Conflict of Interest
We have no conflicts of interest to disclose.
Rana Abid Ali Alkalidi
Entesar Obaid Al-Tamimi
Shatha Abdul-Wadood Al-Shammaree
HOW TO CITE THIS ARTICLE
Rana Abid Ali Alkalidi, Entesar Obaid Al-Tamimi, Shatha Abdul-Wadood Al-Shammaree. Synthesis and Identification of New 2-Substituted-1,3,4-Oxadiazole Compounds from Creatinine and Study Their Antioxidant Activities. J. Med. Chem. Sci., 2023, 6(6) 1216-1229