New possibilities of the functionalization of 6-hydrazino-1,3-dimethyluracils: one-pot synthesis of 5,7-dimethylpyrazolopyrimidine-4,6-dione and 1,3-dimethyl-5-arylidenebarbituric acid derivatives Chimica Techno Acta LETTER published by Ural Federal University 2021, vol. 8(2), № 20218203 eISSN 2411-1414; chimicatechnoacta.ru DOI: 10.15826/chimtech.2021.8.2.03 1 of 4 New possibilities of the functionalization of 6-hydrazino-1,3-dimethyluracils: one-pot synthesis of 5,7-dimethylpyrazolopyrimidine-4,6-dione and 1,3-dimethyl-5-arylidenebarbituric acid derivatives Yu.A. Azev * , O.S. Koptyaeva, T.A. Pospelova Ural Federal University, 19 Mira St., Ekaterinburg, 620002, Russia * Corresponding author: azural@yandex.ru This short communication (letter) belongs to the regular issue. © 2021, The Authors. This article is published in open access form under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). Abstract 3-aryl-5,7-dimethylpyrazolopyrimidine-4,6-diones and 5-benzylidene-1,3-dimethylpyrimidine-2,4,6-triones were obtained by heating hydrazones of 1,3-dimethyl-6 -hydrazinouraciles in tri- fluoroacetic acid (TFA). The same compounds were also obtained by heating the hydrazones of 1,3-dimethyl-6-hydrazinouraciles in aque- ous ethanol in the presence of hydrochloric acid. Keywords 1,3-dimethyl-6- hydrazinouracil hydrazones pyrazolopyrimidine-6,8- diones 1,3-dimethylbarbituric acid Received: 07.04.2021 Revised: 20.04.2021 Accepted: 26.04.2021 Available online: 28.04.2021 1. Introduction Derivatives of pyrimidine (uracil, cytosine, thymine) are part of nucleic acids, which are carriers of hereditary traits in living organisms and are involved in the synthesis of proteins. The pyrimidine core is a component of bicyclic systems such as purine and pteridine. It is known that pyrazolopyrimidine derivatives have a wide spectrum of biological activity, including antimicrobial[1, 2, 3], antivi- ral[4, 5], anti-inflammatory and etc. [6, 7, 8]. As a result of the cyclization of hydrazinouracils with the corresponding reagents, derivatives of pyrimidodia- zoles and pyrimidotriazines were obtained [9]. 5,7-dimethyl-3-phenylpyrazolopyrimidine-4,6-dione was obtained by heating 6-arylidenehydrazine-1,3- dimethyluracils with thionyl chloride in dry benzene from a mixture of reaction products [10]. As a result of boiling the derivatives of 1,3-dimethyl-6-hydrazinouracil with an equimolar amount of N-bromosuccinimide in acetic acid, the derivatives of the corresponding pyrimidoazoles were isolated [11]. The hydrazone of 3-methyl-5-nitro-6- hydrazinouracil was cyclized on heating in DMF to form 3- arylpyrazolopyrimidine-4,6-dione; The same compound was obtained by nitration of hydrazones of 3-methyl-6- hydrazinouracil [12]. Analysis of the literature showed that pyrimidopyra- zoles were obtained in the presence of an easily leaving group in the hydrazinouracil molecule, which undergoes ipso-substitution followed by annulation of the pyrazole ring. In this work, we have studied the transformations of 6-hydrazino-1,3-dimethyluracil to find ways to synthesize new potentially biologically active compounds, as well as to improve the methods for preparing known compounds. 2. Experimental Unless otherwise indicated, all common reagents and sol- vents were used from commercial suppliers without fur- ther purification. The reaction progress and purity of the obtained com- pounds were controlled by TLC method on Sorbfil UV-254 plates, using visualization under UV light. Melting points were determined on a Stuart SMP10 melting point appa- ratus. 1 H, 13 C and 19 F NMR spectra were acquired on Bruker Bruker AVANCE-400 spectrometer in DMSO-d6 solutions, using TMS as internal reference for 1 H and 13 C NMR or CFCl3 for 19 F NMR. Mass-spectra (EI, 70 eV) were recorded on MicrOTOF-Q instrument (Bruker Daltonics) at 250 °C. Elemental analysis was performed using a Perkin- Elmer 2400 Series II CHNS/O analyzer. 1,3-Dimethyl-6-hydrazinopyrimidine-2,4-dione 1 was obtained according to the method described in [13]. http://chimicatechnoacta.ru/ https://doi.org/10.15826/chimtech.2021.8.2.03 http://creativecommons.org/licenses/by/4.0/ Chimica Techno Acta 2021, vol. 8(2), № 20218203 LETTER 2 of 4 The general method for the synthesis of hydrazones 2а-c 1.0 mmol of hydrazine 1 was dissolved in a mixture of 3 ml of water and 3 ml of alcohol, 1.0 mmol of aldehyde dissolved in 5 ml of alcohol was added to the resulting solution, and the mixture was heated for 1-2 minutes. The formed precipitate was filtered off, washed with 1 ml of alcohol. 6-(2-benzylidenehydrazinyl)-1,3- dimethylpyrimidine-2,4(1H,3H)-dione 2а. Yield 85 %, m.p. 260-261 °C. (Ref. 261 °C [12]). 1 H NMR (400 MHz, DMSO-d6, δ, ppm): 3.18 (s, 3H, CH3), 3.43 (s, 3H, CH3), 5.51 (s, 1H, CH), 7.38-7.41 (m, 3H, CHar), 7,70 (d, J = 6.4 Hz, 1H, CHar), 8.34 (s, 1H, CHar), 10.38 (s, 1H, NH). Mass spectrum (EI, 70 eV), m/z (%): 258 (100) [М] + , 142 (35), 104 (38), 90 (49). Found (%): С, 60.51; Н, 5.52; N, 21.71. Calculated for С13Н14N4O2 (%): С, 60.45; Н, 5.46; N, 21.69. 6-(2-(4-(dimethylamino)benzylidene)hydrazinyl)- 1,3-dimethylpyrimidine-2,4(1H,3H)-dione 2b. Yield 80 %, m.p. 251-252 °C. (Ref. 252 °C [14]). 1 H NMR (400 MHz, DMSO-d6, δ, ppm): 3.02 (s, 6H, 2CH3), 3.16 (s, 3H, CH3), 3.40 (s, 3H, CH3), 5.44 (s, 1H, CH), 6.67 (d, J = 8.8 Hz, 2H, CH), 7.50 (d, J = 8.8 Hz, 2H, СH), 8.17 (s, 1H, CH), 10.00 (s, 1H, NH). Mass spectrum (EI, 70 eV), m/z (%): 301 (18) [М] + , 284 (2), 132 (48), 55 (100). Found (%): С, 59.81; Н, 6.40; N, 23.22. Calculated for С15Н19N5O2 (%): С, 59.79; H, 6.36; N, 23.24 1,3-dimethyl-6-(2-(4- nitrobenzylidene)hydrazinyl)pyrimidine-2,4(1H,3H)- dione 2с. Yield 85 %, m.p. 285-286 °C. (Ref. 285 °C [14]). 1 H NMR (400 MHz, DMSO-d6, δ, ppm): 3.18 (s, 3H, CH3), 3.43 (s, 3H, CH3), 5.56 (s, 1H, CH), 7.98 (d, J = 8.8 Hz, 2H, CH), 8.25 (d, J 8.8 Hz, 2H, CH), 8.43 (s, 1H, CH), 10.74 (s, 1H, NH). Mass spectrum (EI, 70 eV), m/z (%): 303 (18) [М] + , 256 (2), 218 (12), 142 (32). Found (%): С, 51.52; Н, 4.27; N, 23.13. Calculated for С13Н13N5O4 (%): С, 51.48; Н, 4.32; N, 23.09. Reactions of hydrazones 2a-c with TFA 0.5 mmol of hydrazone 2 was heated in 1.5 ml of TFA in a closed vessel at 110 ° C for 85-90 hours. The solvent was removed in vacuo. The solid residue was treated with 3 ml of ethanol. The resulting precipitate of product 4 was fil- tered off. The alcoholic mother liquor was treated with 1-2 ml of water, the precipitate that formed was filtered off to obtain product 3. 5,7-dimethyl-3-phenyl-1H-pyrazolo[3,4- d]pyrimidine-4,6(5H,7H)-dione 3а. Yield 20 %, m.p. 256-257 °C. (Ref. 257 °C [11]). 1 H NMR (400 MHz, DMSO- d6, δ, ppm): 3.30 (s,3H, CH3), 3.49 (s, 3H, CH3), 7.46-7.50 (m, 3H, CHar), 8.14-8.16 (m, 2H, CHar), 13.64 (br.s, 1H, NH). Mass spectrum (EI, 70 eV), m/z (%): 256 (92) [М] + , 199 (38), 171 (100). Found (%): С, 60.96; Н, 4.75; N, 21.83. Calculated for С13Н12N4O2 (%): С, 60.93; Н, 4.72; N, 21.86. 3-(4-(dimethylamino)phenyl)-5,7-dimethyl-1H- pyrazolo[3,4-d]pyrimidine-4,6(5H,7H)-dione 3b. Yield 18 %, m.p. 272-273 °C. (Ref. 273 °C [12]). 1 H NMR (400 MHz, DMSO-d6, δ, ppm): 3.05 (s, 6H, 2CH3), 3.29 (s, 3H, CH3), 3.46 (s, 3H, CH3), 6.74 (d, J = 8.8 Hz, 1H, CHar), 8.07 (d, J = 8.8 Hz, 1H, CH), 13.2 (br.s, 1H, NH). Mass spectrum (EI, 70 eV), m/z (%): 299 (100) [М] + , 242 (14), 134 (17). Found (%): С, 60.24; Н, 5.75; N, 23.42. Calculated for С15Н17N5O2 (%): С, 60.19; H, 5.72; N, 23.40. 5,7-dimethyl-3-(4-nitrophenyl)-1H-pyrazolo[3,4- d]pyrimidine-4,6(5H,7H)-dione 3с. Yield .45 % m.p. >300 °C. (Ref. >300 °C [11]). 1 H NMR (400 MHz, DMSO- d6, δ, ppm): 3.31 (s, 3H, CH3), 3.49 (s, 3H, CH3), 8.34 (d, J = 8.8 Hz, 2H, CH), 8.47 (d, J = 8.8 Hz, 2H, CH), 14.08 (s, 1H, NH). Mass spectrum (EI, 70 eV), m/z (%): 301 (100) [М] + , 244 (26), 216 (12), 142 (69). Found (%): С, 51.86; Н, 3.71; N, 23.28. Calculated for С13Н11N5O4 (%): С, 51.83; Н, 3.68; N, 23.25. 5-benzylidene-1,3-dimethylpyrimidine- 2,4,6(1H,3H,5H)-trione 4а. Yield 25 %, m.p. 159-160 °C. (Ref. 160 °C [15]). 1 H NMR (400 MHz, DMSO-d6, δ, ppm): 3.25 (s, 3H, CH3), 3.29(s, 3H, CH3), 7.45-7.53 (m, 3H, 3CHar), 8.05-8.07 (d, 2H, 2CHar), 8.38 (s, 1H, CH). Mass spectrum (EI, 70 eV), m/z (%): 243 (100) [М-1] + , 186 (35), 130 (40), 102 (60). Found (%): С, 63.96; Н, 4.99; N, 11.53. Calculated for С13Н12N2O3 (%): С, 63.93; Н, 4.95; N, 11.47. 5-(4-(dimethylamino)benzylidene)-1,3- dimethylpyrimidine-2,4,6(1H,3H,5H)-trione 4b. Yield 25% m.p. 240-242 °C. (Ref. 241 °C [16]). 1 H NMR (400 MHz, DMSO-d6, δ, ppm): 3.19 (s, 6H, 2CH3), 3.28 (s, 6H, 2CH3), 6.74-6.77 (d, 2H, 2CHar), 8.39-8.41 (d, 2H, 2CHar), 8.24 (s, 1H, CH). Mass spectrum (EI, 70 eV), m/z (%): 287 (100) [М] + , 286(70), 144 (18). Found (%): С, 62.21; Н, 5.99; N, 14.67. Calculated for С15Н17N3O3 (%): С, 62.17; H, 5.96; N, 14.63. 1,3-dimethyl-5-(4-nitrobenzylidene)pyrimidine- 2,4,6(1H,3H,5H)-trione 4с. Yield 17%, m.p. >300 °C. (Ref. >300 °C [16]). 1 H NMR (400 MHz, DMSO-d6, δ, ppm): 3.31 (s, 3H, CH3), 3.50 (s, 3H, CH3), 8.18 (s, 1H, CH), 8.34 (d, J = 9.2 Hz, 2H, CHar), 8.49 (d, J = 9.2 Hz, 2H, CHar). Mass spectrum (EI, 70 eV), m/z (%): 288 (87) [М] + , 288 (100), 272 (64), 242 (58), 156 (55). Found (%): С, 54.01; Н, 3.85; N, 14.64. Calculated for С13Н11N3O5 (%): С, 53.98; Н, 3.83; N, 14.53. Conversions of hydrazones 2a-c in ethanol in the pres- ence of acid. 0.02 Mmol of the corresponding compound 2 in 3 ml of ethanol and the presence of 0.25 ml of concentrated hy- drochloric acid was kept at reflux for 2.5-3 hours. The re- action mixture was cooled, precipitate 4 was filtered off. The melting points and spectral characteristics of the obtained compounds 4a-c were similar to those obtained earlier. 5-benzylidene-1,3-dimethylpyrimidine- 2,4,6(1H,3H,5H)-trione 4а. Yield 48%. 5-(4-(dimethylamino)benzylidene)-1,3- dimethylpyrimidine-2,4,6(1H,3H,5H)-trione 4b. Yield 53%. Chimica Techno Acta 2021, vol. 8(2), № 20218203 LETTER 3 of 4 1,3-dimethyl-5-(4-nitrobenzylidene)pyrimidine- 2,4,6(1H,3H,5H)-trione 4с. Yield 54%. Reaction of 1,3-dimethylbarbituric acid with aldehydes. 0.05 mmol of barbituric acid 5 was heated in 5.0 ml of ethanol with 0.05 mmol of the corresponding aldehyde in the presence of 0.25 ml of HCl for 25-30 minutes. The re- action mixture was cooled, the precipitate of the corre- sponding product 4 was filtered off. The melting points and spectral characteristics of the obtained compounds 4a-c were similar to those obtained earlier. 5-benzylidene-1,3-dimethylpyrimidine- 2,4,6(1H,3H,5H)-trione 4а. Yield 60%. 5-(4-(dimethylamino)benzylidene)-1,3- dimethylpyrimidine-2,4,6(1H,3H,5H)-trione 4b. Yield 54%. 1,3-dimethyl-5-(4-nitrobenzylidene)pyrimidine- 2,4,6(1H,3H,5H)-trione 4с. Yield 70%. 3. Results and Discussion We used hydrazones 2a-c, as objects of study, obtained by short-term heating of 1,3-dimethyl-6-hydrazinouracil 1 in aqueous-alcoholic solutions with the corresponding alde- hydes in the presence of HCl (Scheme 1). We found that heating hydrazones 2а-c in TFA gave 5,7-dimethylpyrazolopyrimidine-4,6-diones 3а-c and 5- benzylidene-1,3-dimethylpyrimidine-2,4,6-trione deriva- tives 4а-c. Considering the literature data, it can be as- sumed that the formation of pyrazolopyrimidines 3a-c occurs through the 5-trifluoroacyl intermediate A. The formation of intermediate A occurs as a result of acylation of the starting hydrazones 2a-c of TFA. During this pro- cess, water is released and the process of cleavage of hy- drazones with the formation of compounds 4a-c is started. To confirm the proposed reaction mechanism, we in- vestigated the transformations of hydrazones 2 upon heat- ing in aqueous ethanol in the presence of hydrochloric acid. As a result of the reactions, derivatives of barbituric acid 4a-c were obtained (Scheme 2). The formation of arylidene derivatives apparently oc- curred as a result of the transfer of the aldehyde group from the hydrazine fragment to the 5-position of the py- rimidine nucleus with the formation of intermediate A. Then, acid hydrolysis of the hydrazino group of intermedi- ate A took place, giving derivatives of barbituric acid 4. Products 4a-c were also obtained by heating 1,3- dimethylbarbituric acid 6 with the corresponding alde- hydes. 4. Conclusions Thus, as a result of the conducted studies, a new one-pot method for the synthesis of derivatives of 5,7- dimethylpyrazolopyrimidine-4,6-dione and 5-benzylidene- 1,3-dimethylpyrimidine-2,4,6-trione was discovered. Scheme 1: Scheme 2: Chimica Techno Acta 2021, vol. 8(2), № 20218203 LETTER 4 of 4 References 1. Rashad AE, Shamroukh AH, Ali HS, Abdel-Megeid FME. Some New Pyrazole and Pyrazolopyrimidines: Synthesis and Anti- microbial Evaluation. J Heterocycl Chem. 2013;50:758-65. doi:10.1002/jhet.1550 2. Eweas AF, Swelam SA, Fathalla OA. Synthesis, anti-microbial evaluation, and molecular modeling of new pyrazolo[3,4- d]pyrimidine derivatives. Med Chem Res. 2012;21:3848-57. doi:10.1007/s00044-011-9911-y 3. Aggarwal R, Sumran G, Garg N, Aggarwal AA. 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