6-Amino-2-thio- and 6-Aminouracils as Precursors for the Synthesis of Antiviral and Antimicrobial Methylenebis(2-thiouracils), Tricyclic Pyrimidines, and 6-Alkylthiopurine-2-ones

Synthesis, toxicological and in silico evaluation of novel spiro pyrimidines against Culex pipiens L. referring to chitinase enzyme

The exponential development of resistance to conventional chemical insecticides adds another important motive for the creation of novel insecticidal active agents. One of the keys to meeting this challenge is the exploration of novel classes of insecticidal molecules with different modes of action. Herein, a novel series of spiro pyrimidine derivatives was prepared using some green synthetic methodologies such as microwave irradiation, and sonication under ultrasound waves. Spiro pyrimidine aminonitrile 1 is a key starting material for the synthesis of targets 2-9 by reaction with different carbon electrophiles and nitrogen nucleophiles. The structures of all the newly synthesized compounds were approved using spectral data. The toxicological efficiency and biological impacts of the synthesized spiro pyrimidine derivatives were assessed against Culex pipiens L. larvae. The toxicity of synthesized compounds showed remarkable variations against the C. pipiens larvae. Where, 3, 4 and 2 were the most efficient compounds with LC50 values of 12.43, 16.29 and 21.73 µg/mL, respectively. While 1 was the least potent compound with an LC50 value of 95.18 µg/mL. As well, other compounds were arranged according to LC50 values as follows 5 > 7 > 6 > 9 > 8. In addition, 3 and 4 exhibited significant prolongation of the developmental duration and greatly inhibited adult emergence. Moreover, many morphological deformities were observed in all developmental stages. Furthermore, cytotoxicity of the most effective compounds was assessed against the normal human cells (WI-38) as non-target organisms, where compounds 2, 4 and 3 showed weak to non-toxic effects. The study of binding affinity and correlation between chemical structure and reactivity was carried out using molecular docking study and DFT calculations to investigate their mode of action. This study shed light on promising compounds with larvicidal activity and biological impacts on the C. pipiens life cycle.

Novel 2-Thioxanthine and Dipyrimidopyridine Derivatives: Synthesis and Antimicrobial Activity

Several fused imidazolopyrimidines were synthesized starting from 6-amino-1-methyl-2-thiouracil (1) followed by nitrosation, reduction and condensation with different aromatic aldehydes to give Schiff’s base. The dehydrocyclization of Schiff’s bases using iodine/DMF gave Compounds 5a–g. The methylation of 5a–g using a simple alkylating agent as dimethyl sulfate ((CH₃)₂SO₄) gave either monoalkylated imidazolopyrimidine 6a–g at room temperature or dialkylated derivatives 7a–g on heating 6a–g with ((CH₃)₂SO₄). On the other hand, treatment of 1 with different aromatic aldehydes in absolute ethanol in the presence of conc. hydrochloric acid at room temperature and/or reflux with acetic acid afforded bis-5,5′-diuracylmethylene 8a–e, which cyclized on heating with a mixture of acetic acid/HCl (1:1) to give 9a–e. Compounds 9a–e can be obtained directly by refluxing of Compound 1 with a mixture of acetic acid/HCl. The synthesized new compounds were screened for antimicrobial activity, and the MIC was measured.

Synthesis, antimicrobial, antioxidant activities of novel 6-aryl-5-cyano thiouracil derivatives

A series of 6-aryl-5-cyano thiouracil derivatives (2a-c to 11a-c) was synthesized from 6-aryl-4-hydrazino-2-thioxo-1,2-dihydropyrimidine-5-carbonitriles (1a-c). The products were characterized by analytical and spectral data (IR, (1)H NMR, (13)C NMR and mass spectra). All compounds were screened for their in-vitro antibacterial and antifungal activities. Compounds 7a, 7g and 9a-c showed pronounced antimicrobial activity than standards. Some of the newly synthesized compounds were evaluated for antioxidant activity. Compounds 1c, 5c and 8c displayed promising free radical scavenging activity and found to be more potent than standard, ascorbic acid (vitamin C).

Five pseudopolymorphs of 6-amino-2-thiouracil: absence of N-H...S hydrogen bonds

In order to study the preferred hydrogen-bonding pattern of 6-amino-2-thiouracil, C(4)H(5)N(3)OS, (I), crystallization experiments yielded five different pseudopolymorphs of (I), namely the dimethylformamide disolvate, C(4)H(5)N(3)OS·2C(3)H(7)NO, (Ia), the dimethylacetamide monosolvate, C(4)H(5)N(3)OS·C(4)H(9)NO, (Ib), the dimethylacetamide sesquisolvate, C(4)H(5)N(3)OS·1.5C(4)H(9)NO, (Ic), and two different 1-methylpyrrolidin-2-one sesquisolvates, C(4)H(5)N(3)OS·1.5C(5)H(9)NO, (Id) and (Ie). All structures contain R(2)(1)(6) N-H...O hydrogen-bond motifs. In the latter four structures, additional R(2)(2)(8) N-H...O hydrogen-bond motifs are present stabilizing homodimers of (I). No type of hydrogen bond other than N-H...O is observed. According to a search of the Cambridge Structural Database, most 2-thiouracil derivatives form homodimers stabilized by an R(2)(2)(8) hydrogen-bonding pattern, with (i) only N-H...O, (ii) only N-H...S or (iii) alternating pairs of N-H...O and N-H...S hydrogen bonds.