The role of substituents in the molecular and crystal structure of 1-(adamantane-1-carbonyl)-3-(mono)- and 3,3-(di) substituted thioureas

Novel adamantyl clubbed iminothiazolidinones as promising elastase inhibitors: design, synthesis, molecular docking, ADMET and DFT studies

Porcine Pancreatic Elastase (PPE) is a serine protease that is homologous to trypsin and chymotrypsin that are involved in various pathologies like inflammatory disease, Chronic Obstructive Pulmonary Disease (COPD), acute respiratory distress syndrome, cystic fibrosis, and atherosclerosis. PPE if remained uninhibited would lead to digestion of important connective tissue. We developed new structurally diverse series of adamantyl-iminothiazolidinone hybrids to divulge elastase inhibition assay. To identify potent derivatives, in silico screening was conducted and in vitro studies disclosed that the compounds 5a, 5f, 5g, and 5h showed excellent binding energies and low IC₅₀ values. In silico studies including molecular docking, DFT studies (using the B3LYP/SVP basis set in the gas phase) drug likeness scores and molecular dynamic simulation studies were conducted to evaluate protein–ligand interactions and to determine the stability of top ranked conformation. In silico studies further supported the results of in vitro experiments and suggest these derivatives as novel inhibitors of elastase enzyme.

Structurally diverse adamantyl-iminothiazolidinone conjugates were synthesized, evaluated for elastase inhibition, and subjected to in silico ADMET prediction. The inhibition studies revealed compounds 5a, 5f, 5g, and 5h to show significant activity.

Supramolecular Self-Assembly Mediated by Multiple Hydrogen Bonds and the Importance of C-S···N Chalcogen Bonds in N'-(Adamantan-2-ylidene)hydrazide Derivatives

The present article comprehensively examines six N'-(adamantan-2-ylidene)hydrazide derivatives using the Hirshfeld surface analysis, PIXEL energy for molecular dimers, lattice energies for crystal packing, and topological analysis for intramolecular and intermolecular interactions. The crystal structure of one of the N'-(adamantan-2-ylidene)hydrazide derivatives, namely, N'-(adamantan-2-ylidene)-5-bromothiophene-2-carbohydrazide 1, C15H17N2OSBr, has been determined and analyzed in detail along with five closely related structures. The molecular conformation of 1 is locked by an intramolecular C-S···N chalcogen bond as found in one of its closely related structure, namely, N'-(adamantan-2-ylidene)thiophene-2-carbohydrazide. Furthermore, a detailed potential energy surface scan analysis has been performed to highlight the importance of a chalcogen bond. Two of these compounds possess syn-orientation for amide units, whereas the corresponding moiety exhibits anti-conformations in the remaining four structures. The Hirshfeld surface and its decomposed fingerprint plots provide a qualitative picture of acyl substituent effects on the intermolecular interactions toward crystal packing of these six structures. Intermolecular interaction energies for dimers observed in these structures calculated by density functional theory (B97D3/def2-TZVP) and PIXEL (MP2/6-31G**) methods are comparable. This study also identifies that multiple hydrogen bonds, including N/C-H···O/N and C-H···π interactions, are collectively responsible for a self-assembled synthon. The nature and strength of these interactions have been studied using atoms in molecule topological analysis. The in vitro antiproliferative activity of compound 1 was assessed against five human tumor cell lines and showed marked antiproliferative activity.

Probing the Effect of Halogen Substituents (Br, Cl, and F) on the Non-covalent Interactions in 1-(Adamantan-1-yl)-3-arylthiourea Derivatives: A Theoretical Study

The effect of halogen substituents (X = Br, Cl, and F) on the crystal packing and intra- and intermolecular interactions in four adamantane-thiourea hybrid derivatives is investigated using different theoretical tools. The bromo and chloro derivatives exhibit 3D isostructurality as evident from lattice parameters, molecular conformation, and crystal packing. The density functional theory study suggests that the molecular conformation of the parent (unsubstituted) and fluoro derivatives exhibits a stable low energy anti-syn conformation. In contrast, bromo and chloro derivatives adopt stable and relatively high energy minima on their potential energy surfaces. Hirshfeld surface analysis reveals the effect of halogen substituents on the intermolecular contacts. The halogen atoms mainly reduce the contribution of H···H contacts toward crystal packing. PIXEL energy analysis indicates the strong dimer formed by N-H···S hydrogen bonds in all four structures. It also revealed that a vast number of H···H contacts observed in different dimers of these structures either presented along with other conventional interactions or solely stabilize the dimeric topology. The topological parameters for intermolecular interactions in these structures suggest an intermediate bonding character between shared and closed-shell interactions for N-H···S hydrogen bonds in the parent and chloro derivatives. In contrast, the N-H···S hydrogen bond in other structures is of a closed-shell interaction. Among four derivatives, the fluoro derivative is weakly packed in the solid state based on the PIXEL method's lattice energy calculation.

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.

Structural and energetic aspects of adamantane and memantine derivatives of sulfonamide molecular crystals: experimental and theoretical characterisation

A number of new sulfonamide compounds with adamantane and memantine fragments were synthesised and characterised.

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.

Intermolecular interactions in crystalline 1-(adamantane-1-carbonyl)-3-substituted thioureas with Hirshfeld surface analysis

The 1-acyl thiourea synthon is characterized through a complete Hirshfeld surface analysis for a series of six closely related 1-(adamantane-1-carbonyl) thioureas.