Synthesis, structural and vibrational properties of 1-(4-Fluorobenzoyl)-3-(isomeric fluorophenyl)thioureas

Effect of Terminal Hydroxy Groups on the Structural Properties of Acyl Thioureas

The 1-acyl thiourea family [R1C(O)NHC(S)NR2R3] exhibits the flexibility to incorporate a wide variety of substituents into their structure. The structural attributes of these compounds are intricately tied to the type and extent of substitution. In the case of 3-mono-substituted thioureas (R2=H), the conformational behavior is predominantly shaped by the presence of an intramolecular N-H ⋅ ⋅ ⋅ O=C hydrogen bond. This study delves into the structural consequences stemming from the inclusion of substituents possessing hydrogen-donor capabilities within four novel 1-acyl-3-mono-substituted thiourea derivatives. A comprehensive suite of analytical techniques, encompassing FTIR, Raman spectroscopy, multinuclear (1H and 13C) NMR spectroscopy, single-crystal X-ray diffraction, and supported by computational methods, notably NBO (Natural Bond Orbital) population analysis, Hirshfeld analysis, and QTAIM (Quantum Theory of Atoms in Molecules), was harnessed to scrutinize and characterize these compounds. In the crystalline state, these compounds exhibit an intricate interplay of intermolecular interactions, prominently featuring an expansive network of hydrogen bonds between the hydroxy (-OH) groups and the carbonyl and thiocarbonyl bonds within the 1-acyl thiourea fragment. Notably, the topological analysis underscores significant distinctions in the properties of the acyl thiourea fragment and the intramolecular >C=O ⋅ ⋅ ⋅ H-N bond when transitioning from the isolated molecule to the crystalline environment.

Selenourea and thiourea derivatives of chiral and achiral enetetramines: Synthesis, characterization and enzyme inhibitory properties

A series of chiral and achiral cyclic seleno- and thiourea compounds bearing benzyl groups on N-atoms were prepared from enetetramines and appropriate Group VI elements in good yields. All the synthesized compounds were characterized by elemental analysis, FT-IR, ¹H NMR and ¹³C NMR spectroscopy, and the molecular and crystal structures of (R,R)-4b and (R,R)-5b were confirmed by the single-crystal X-ray diffraction method. These assayed for their activities against metabolic enzymes acetylcholinesterase, butyrylcholinesterase, and α-glycosidase. These selenourea and thiourea derivatives of chiral and achiral enetetramines effectively inhibit AChE and BChE with IC₅₀ values in the range of 3.32-11.36 and 1.47-9.73 µM, respectively. Also, these compounds inhibited α-glycosidase enzyme with IC₅₀ values varying between 1.37 and 8.53 µM. The results indicated that all the synthesized compounds exhibited excellent inhibitory activities against mentioned enzymes as compared with standard inhibitors. Representatively, the most potent compound against α-glycosidase enzyme, (S,S)-5b, was 12-times more potent than standard inhibitor acarbose; 7b and 8a as most potent compounds against cholinesterase enzymes, were around 5 and 13-times more potent than standard inhibitor tacrine against achethylcholinesterase (AChE) and butyrylcholinesterase (BChE), respectively.

Solving the enigma of weak fluorine contacts in the solid state: a periodic DFT study of fluorinated organic crystals

The nature and strength of weak interactions with organic fluorine in the solid state are revealed by periodic density functional theory (periodic DFT) calculations coupled with experimental data on the structure and sublimation thermodynamics of crystalline organofluorine compounds. To minimize other intermolecular interactions, several sets of crystals of perfluorinated and partially fluorinated organic molecules are considered. This allows us to establish the theoretical levels providing an adequate description of the metric and electron-density parameters of the C–F⋯F–C interactions and the sublimation enthalpy of crystalline perfluorinated compounds. A detailed comparison of the C–F⋯F–C and C–H⋯F–C interactions is performed using the relaxed molecular geometry in the studied crystals. The change in the crystalline packing of aromatic compounds during their partial fluorination points to the structure-directing role of C–H⋯F–C interactions due to the dominant electrostatic contribution to these contacts. C–H⋯F–C and C–H⋯O interactions are found to be identical in nature and comparable in energy. The factors that determine the contribution of these interactions to the crystal packing are revealed. The reliability of the results is confirmed by considering the superposition of the electrostatic potential and electron density gradient fields in the area of the investigated intermolecular interactions.

The nature and strength of weak C–H⋯F–C and C–F⋯F–C interactions and their role in organofluorine molecular crystals were studied using periodic DFT coupled with CSD data mining and experimental sublimation enthalpies.

Novel Guanidine Compound against Multidrug-Resistant Cystic Fibrosis-Associated Bacterial Species

Chronic pulmonary infection is a hallmark of lung disease in cystic fibrosis (CF). Infections dominated by non-fermentative Gram-negative bacilli are particularly difficult to treat and highlight an urgent need for the development of new class of agents to combat these infections. In this work, a small library comprising thiourea and guanidine derivatives with low molecular weight was designed; these derivatives were studied as antimicrobial agents against Gram-positive, Gram-negative, and a panel of drug-resistant clinical isolates recovered from patients with CF. One novel compound, a guanidine derivative bearing adamantane-1-carbonyl and 2-bromo-4,6-difluouro-phenyl substituents (H-BDF), showed potent bactericidal activity against the strains tested, at levels generally higher than those exhibited by tobramycin, ceftazimide and meropenem. The role that different substituents exert in the antimicrobial activity has been determined, highlighting the importance of the halo-phenyl group in the guanidine moiety. The new compound displays low levels of cytotoxicity against THP-1 and A549 cells with a selective index (SI) > 8 (patent application PCT/IB2017/054870, August 2017). Taken together, our results indicate that H-BDF can be considered as a promising antimicrobial agent.

Understanding the conformational changes and molecular structure of furoyl thioureas upon substitution

1-Acyl thioureas [R¹C(O)NHC(S)NR²R³] are shown to display conformational flexibility depending on the degree of substitution at the nitrogen atom. The conformational landscape and structural features for two closely related thioureas having R¹=2-furoyl have been studied. The un-substituted 2-furoyl thiourea (I) and its dimethyl analogue, i.e. 1-(2-furoyl)-3,3-dimethyl thiourea (II), have been synthesized and fully characterized by spectroscopic (FT-IR, ¹H and ¹³C NMR) and elemental analysis. According to single crystal X-ray diffraction analysis, compounds I and II crystallize in the monoclinic space group P21/c. In the compound I, the trans-cis geometry of the almost planar thiourea unit is stabilized by intramolecular NH⋯OC hydrogen bond between the H atom of the cis thioamide and the carbonyl O atom. In compound II, however, the acyl thiourea group is non-planar, in good agreement with the potential energy curve computed at the B3LYP/6-31+G(d,p) level of approximation. Centrosymmetric dimers generated by intermolecular NH⋯SC hydrogen bond forming R₂²(8) motif are present in the crystals. Intermolecular interactions have been rationalized in terms of topological partitions of the electron distributions and Hirshfeld surface analysis, which showed the occurrence of S⋯H, O⋯H and H⋯H contacts that display an important role to crystal packing stabilization of both thiourea derivatives.

Synthesis, X-ray crystal structure, thermal behavior and spectroscopic analysis of 1-(1-naphthoyl)-3-(halo-phenyl)-thioureas complemented with quantum chemical calculations

Two novel 1-(1-naphthoyl)-3-(halo-phenyl) substituted thioureas, namely 1-(1-naphthoyl)-3-(2,4-di-fluoro-phenyl)-thiourea (1) and 1-(1-naphthoyl)-3-(3-chloro-4-fluoro-phenyl)-thiourea (2), were synthesized and fully characterized. The X-ray crystal and molecular structures have been determined resulting in a planar acylthiourea group, with the C=O and C=S adopting a pseudo-antiperiplanar conformation. An intramolecular N-H⋯O=C hydrogen bond occurs between the thioamide and carbonyl groups. The crystal packing of both compounds is characterized by extended intermolecular N-H⋯S=C and N-H⋯O=C hydrogen-bonding interactions involving the acylthiourea moiety. Compound 2 is further stabilized by π-stacking between adjacent naphthalene and phenyl rings. The thermal behavior, as well as the vibrational properties, studied by infrared and Raman spectroscopy data complemented by quantum chemical calculations at the B3PW91/6-311++G(d,p) support the formation of these intra- and intermolecular hydrogen bonds. Furthermore, the UV-Vis spectrum is interpreted in terms of TD-DFT quantum chemical calculations with the shapes of the simulated absorption spectra in good accordance with the experimental data.

Intra- and intermolecular hydrogen bonding and conformation in 1-acyl thioureas: an experimental and theoretical approach on 1-(2-chlorobenzoyl)thiourea

The vibrational analysis (FT-IR and FT-Raman) for the new 1-(2-chlorobenzoyl)thiourea species suggests that strong intramolecular interactions affect the conformational properties. The X-ray structure determination corroborates that an intramolecular N-H⋯OC hydrogen bond occurs between the carbonyl (-CO) and thioamide (-NH2) groups. Moreover, periodic system electron density and topological analysis have been applied to characterize the intermolecular interactions in the crystal. Extended N-H⋯SC hydrogen-bonding networks between both the thioamide (N-H) and carbamide (NH2) groups and the thiocarbonyl bond (CS) determine the crystal packing. The Natural Bond Orbital (NBO) population analysis demonstrates that strong hyperconjugative remote interactions are responsible for both, intra and intermolecular interactions. The Atom in Molecule (AIM) results also show that the N-H⋯Cl intramolecular hydrogen bond between the 2-Cl-phenyl ring and the amide group characterized in the free molecule changes to an N⋯Cl interaction as a consequence of crystal packing.

Crystal structure of 1-benzoyl-3-(4-fluoro-phen-yl)thio-urea

The title compound, C14H11FN2OS, contains two mol-ecules (A and B) in the asymmetric unit, with different conformations. In mol-ecule A, the dihedral angles between the central thio-urea grouping and the phenyl and fluoro-benzene rings are 28.77 (8) and 41.82 (8)°, respectively, and the dihedral angle between the ring planes is 70.02 (9)°. Equivalent data for mol-ecule B are 8.46 (8), 47.78 (8) and 52.99 (9)°, respectively. Both mol-ecules feature an intra-molecular N-H⋯O hydrogen bond, which closes an S(6) ring. In the crystal, A+B dimers linked by pairs of N-H⋯S hydrogen bonds generate R 2 (2)(8) loops.

Synthesis, structural and vibrational properties of 1-(adamantane-1-carbonyl)-3-halophenyl thioureas

1-(Adamantane-1-carbonyl)-3-(2,4-dichlorophenyl)thiourea (1) and 1-(adamantane-1-carbonyl)-3-(2-bromo-4,6-difluorophenyl)thiourea (2) were synthesized by the reaction of adamantane-1-carbonyl chloride with ammonium thiocyanate to afford the adamantane-1-carbonylisothiocyanate in situ followed by treatment with suitable halogenated anilines. The structures of the products were established by elemental analyses, Fourier transform infrared spectroscopy (FTIR), (1)H, (13)C nuclear magnetic resonance (NMR), mass spectroscopy and single crystal X-ray diffraction study. Bond lengths and angles show the usual values. All of three condensed cyclohexane rings of the adamantane residues adopt the usual chair conformation. The molecular conformation of 1 and 2 is stabilized by an intramolecular (NH⋯OC) hydrogen bond which forms a pseudo-six-membered ring. Structural features have been complemented with the joint analysis of the FTIR and FT-Raman spectra along with quantum chemical calculations at the B3LYP/6-311++G level.