Synthesis and physical-chemical properties of (3-benzyl-8-propylxanthin-7-yl)acetohydrazide derivatives and their evaluation for antimicrobial and diuretic activities

One of the most important tasks of our indigenous pharmaceutical science is the necessity for new medicines because existing drugs are characterized by various side effects, resistance, high toxicity, and so on. New bioactive molecule synthesis utilizes substances of natural origin as well as chemically modified ones. Thus, the researcher’s attention is mainly focused on 3-,7-,8-substituted derivatives of the natural heterocyclic xanthine system, which possess a wide range of pharmacological action. Synthesis of a novel of (3-benzyl-8propylxanthin-7-yl)acetohydrazides with antimicrobial and diuretic activities described in the paper.

Xanthines, as important members of the purine family, are considered as key intermediates in the metabolism of nucleobases, because metabolic interconversions of adenine and guanine result in their formation [6,7]. In addition, xanthine, and its derivatives act as precursors in the synthesis of GMP, GDP, and GTP through the salvage pathways within cells [8]. Due to the aforementioned reasons, it is important to explore the use of xanthine derivatives in developing novel synthetic methods. Our interest is in finding effective acetohydrazides of (3-R-xanthine-7(8)-yl)alkanoic acids, and their structural analogs, because such compounds have been reported in the literature by their diverse biological activities.

Aim
Considering the abovementioned evidence, we made endea vors to synthesize a set of novel (3-benzyl-8-propylxanthin-7-yl) acetohydrazide derivatives and to study their physical-chemical properties.

Materials and methods
Unless otherwise indicated, reagents and solvents were purchased from commercial suppliers and used without further purification.
The study of physical-chemical properties of the synthesized compounds was performed according to the State Pharmacopoeia of Ukraine (ed. 1). The melting point was determined by capillary method (2.2.14) on the PTP(M) device.
Infrared spectra were recorded on a Bruker Alpha (Bruker, Germany) in 4000-400 cm -1 with ATR (direct material input). 1 H-NMR spectra were recorded on Varian Mercury VX-200 spectrometer (Varian, USA) in DMSO-d 6 with TMS as an internal standard. Elemental analysis was performed on a Elementar Vario L cube analyzer (Elementar Analysensysteme, Germany). Binary mobile phase of benzene and propan-2-ol in 10 : 1 and 1 : 10 was used for chromatography. Chromatographic spots were visualized by UV light (200-300 nm).

General procedure for the synthesis of (3-benzyl-8propylxanthin-7-yl)acetohydrazide derivatives (2-18).
To a solution of 3.56 g (0.01 mol) of 1 in 70 ml of aqueous dioxane (1:1) and heated to 50 °C was added 1 ml of glacial acetic acid and 0.011 mol of the corresponding aldehyde or ketone. The mixture was heated under a reflux condenser for 15-25 minutes. After cooling, the resulting product was precipitated. The crude product was filtered, washed with water, and dried at 80-85 °C.
Compounds 2-18 were pale-yellow, yellow or orange amorphous substances, insoluble in water, ethanol, diethyl ether, acetone, and soluble in DMF.
The structure of the synthesized compounds was confirmed by elemental analysis data ( Table 1), and by IR-and 1 H NMR spectroscopy (Tables 2, 3).
In the IR spectra of compounds 2-18 ( Table 2) The 1 H NMR spectra of compounds 2-18 ( Table 3) showed absence of the NH 2 -group protons of the hydrazide residue, and NH-groups signal of the ylidene hydrazide residue was appeared as downfield singlet at δ 12.08-11.08 ppm. Signals of protons of methylidene groups were appeared as singlet at δ 8.61-7.85 ppm, protons of benzyl, propyl residue and uracil fragment of the molecule were recorded with the appropriate intensity and characteristic chemical shift.

Discussion
Biological activity of synthesized (3-benzyl-8-propylxanthin-7-yl)acetohydrazide derivatives was predicted by using PASS software [9]. All the compounds showed a good probability of antimicrobial activity (compounds 4-6, 8-10, 14), which makes a good foundation for the in-depth investigation for compounds with high antimicrobial activity. The results of the study of antibacterial and fungicidal activities were described in our previous work [10].
The reason for an in-depth study of the diuretic activity of the synthesized compounds was based on a molecular docking investigation. Interaction of (3-benzyl-8-propylxanthin-7-yl) acetohydrazide (1) and its derivatives (2-5, 7-9, 12-14, 16, 17) with the A 1 adenosine receptor has resulted in high affinity values. This result confirms the trend discovered in earlier in vitro study of diuretic activity of the compound 1 [11]. In conclusion, derivatives of (3-benzyl-8-propylxanthin-7-yl)acetohydrazide could be a promising starting material for further structural optimization to obtain new and more potent diuretic agents [12].
2. The structures of the synthesized compounds was confirmed by various physical-chemical methods.
3. Within the investigated substances we identified compounds displayed good antimicrobial and diuretic activity.

Funding
The research is carried out within the RDW of Zaporizhzhia State Medical University: "Synthesis, physicochemical properties of N-substitued purines, xanthines and its heteroannelated derivatives", state registration number 0110U000908.