A review on oxime functionality: an ordinary functional group with significant impacts in supramolecular chemistry

The oxime functional group is pivotal in chemistry, finding extensive applications in medical science, catalysis, organic functional group transformations, and the recognition of essential and toxic analytes. While the coordination chemistry of oxime derivatives has been thoroughly explored and several reviews have been published on this topic in reputable journals, a comprehensive review encompassing various aspects such as crystal engineering, cation and anion recognition, as well as coordination chemistry activities, is still in demand. This feature article highlights the diverse applications of oxime derivatives across multiple domains of chemistry, including medicine, agriculture, crystal engineering, coordination chemistry, and molecular recognition studies. Each of the oxime derivatives in this feature article are meticulously described in terms of their medicinal applications, crop protection, crystal engineering attributes, analyte recognition capabilities, and coordination chemistry aspects. By providing a comprehensive overview of their versatile applications, this article aims to inspire researchers to explore and develop novel oxime-based derivatives for future applications.

Combination of Hydrogen and Halogen Bonds in the Crystal Structures of 5-Halogeno-1H-isatin-3-oximes: Involvement of the Oxime Functionality in Halogen Bonding

Various functional groups have been considered as acceptors for halogen bonds, but the oxime functionality has received very little attention in this context. In this study, we focus on the analysis of the hydrogen and halogen bond preferences observed in the crystal structures of 5-halogeno-1H-isatin-3-oximes. These molecules can be involved in various non-covalent interactions, and the competition between these interactions has a decisive influence on their self-organization. In particular, we were interested to see whether the crystal structures of 5-halogeno-1H-isatin-3-oximes, especially bromine- and iodine-substituted ones, are characterized by the presence of halogen bonds formed with the oxime functionality. The oxime group proved its ability to compete with the other strong donor and acceptor sites by participating in the formation of cyclic hydrogen-bonded heterosynthons oxime∙∙∙amide and Ooxime∙∙∙Br/I halogen bonds.

OxymaPure Coupling Reagents: Beyond Solid-Phase Peptide Synthesis

OxymaPure [ethyl 2-cyano-2-(hydroxyimino)acetate] is an exceptional reagent with which to suppress racemization and enhance coupling efficiency during amide bond formation. The tremendous popularity of OxymaPure has led to the development of several Oxyma-based reagents. OxymaPure and its derived reagents are widely used in solid- and solution-phase peptide chemistry. This review summarizes the recent developments and applications of OxymaPure and Oxyma-based reagents in peptide chemistry, in particular in solution-phase chemistry. Moreover, the side reaction associated with OxymaPure is also discussed.

1 Introduction

2 Oxyma-Based Coupling Reagents

2.1 Aminium/Uronium Salts of OxymaPure

2.2 Phosphonium Salts of OxymaPure

2.3 Oxyma-Based Phosphates

2.4 Sulfonate Esters of OxymaPure

2.5 Benzoate Esters of OxymaPure

2.6 Carbonates of OxymaPure Derivatives

3 OxymaPure Derivatives

4 Other Oxime-Based Additives and Coupling Reagents

5 Side Reactions Using OxymaPure Derivatives

6 Conclusion

7 List of Abbreviations

Different substituent effects on the supramolecular arrays in some (E)-halo- and nitro-benzaldehyde oximes: confirmation of attractive π(C=N)···π(phenyl) interactions

The crystal structures and Hirshfeld surface analyses are reported for four aldoximes, (E)-X–C6H4CH=N–OH [X = 3-Cl (1), 4-F (2), 2-O2N (3) and 4-O2N (4)]. The strong classical O–H · · · N hydrogen bonds involving the oxime group generate C(3) chains in compound 1, in contrast to the R2 2(6) dimers formed in compounds 2–4; such arrangements have been shown to be the most frequently found for oximes other than salicylaldoximes (2-hydroxybenzaldehyde oximes). In general, weaker intermolecular interactions involving the X substituents, as well as C–H · · · O and π · · · π interactions have significant effects on the supramolecular arrays generated in the aggegation. A further important interaction in compound 1, and to a lesser extent in compound 4, is a π(C=N) · · · π(phenyl) molecular stacking. A data base search has indicated that short Cg(C=N) · · · Cg(phenyl) distances, <3.3 Å (Cg = centre of gravity), have been found in various compounds, including other oximes. A theoretical study was carried out starting from the crystal structure data of compound 1, with optimisation at the BLYP-D3/def2-DZVP level, as well as at the higher PBE0/ma-def2-TZVP level. Breakdown of the interaction energy into separate contributions was achieved using SAPT (using the jun-cc-pvdz basis set). Overall, the calculations indicate that the π(C=N) ·· · π(phenyl) interaction is attractive, with a magnitude of 14–18 kJ mol−1.

A Fragment-Based Approach for the Development of G-Quadruplex Ligands: Role of the Amidoxime Moiety

G-quadruplex (G4) nucleic acid structures have been reported to be involved in several human pathologies, including cancer, neurodegenerative disorders and infectious diseases; however, G4 targeting compounds still need implementation in terms of drug-like properties and selectivity in order to reach the clinical use. So far, G4 ligands have been mainly identified through high-throughput screening methods or design of molecules with pre-set features. Here, we describe the development of new heterocyclic ligands through a fragment-based drug discovery (FBDD) approach. The ligands were designed against the major G4 present in the long terminal repeat (LTR) promoter region of the human immunodeficiency virus-1 (HIV-1), the stabilization of which has been shown to suppress viral gene expression and replication. Our method is based on the generation of molecular fragment small libraries, screened against the target to further elaborate them into lead compounds. We screened 150 small molecules, composed by structurally and chemically different fragments, selected from commercially available and in-house compounds; synthetic elaboration yielded several G4 ligands and two final G4 binders, both embedding an amidoxime moiety; one of these two compounds showed preferential binding for the HIV-1 LTR G4. This work presents the discovery of a novel potential pharmacophore and highlights the possibility to apply a fragment-based approach to develop G4 ligands with unexpected chemical features.

Crystal structures of (E)-1-naphthaldehyde oxime and (E)-phenanthrene-9-carbaldehyde oxime

The aldoximes C11H9NO (I) and C15H11NO (II), synthesized in ca 90% yield, by treatment of 1-naphthaldehyde or phenanthrene-9-carbaldehyde, respectively, with hydroxyl-amine hydro-chloride and sodium carbonate, have been characterized by IR, 1H, 13C and DEPT-135 NMR spectroscopies, and also by single-crystal X-ray diffraction analysis. The mol-ecules of (I) and (II) are conformationally similar, with the aldoxime substituent groups lying outside the planes of the naphthalene or phenanthrene rings, forming dihedral angles with them of 23.9 (4) and 27.9 (6)°, respectively. The crystal structures of both (I) and (II) are similar with a single inter-molecular O-H⋯N hydrogen-bonding inter-action, giving rise to the formation of one-dimensional polymeric chains extending along the 21 (b) screw axes in each.

Different self-assemblies and absorption–emission properties of the picrate salts of aromatic amine or heterocycle linked oximes

Different sub-assemblies and fluorescence quenching in picrate salts of an aromatic amine and of three different heterocycle tethered aldoximes are described.

Formation of ionic co-crystals of amphoteric azoles directed by the ionic liquid co-former 1-ethyl-3-methylimidazolium acetate

The ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate was utilized as a liquid-state crystallization agent to form ionic co-crystals using amphoteric azoles selected as model compounds for active pharmaceutical ingredients. Weakly acidic azoles crystallize the IL relatively quickly, while stronger acidic azoles undergo slower ion exchange with the IL to form salts.

Reconstruction of Block Copolymer Micelles to Long-Range Ordered Dense Nanopatterns Via Light-Tunable Hydrogen-Bonding Association

Controlling the orientation and long-range order of nanostructures is a key issue in the self-assembly of block copolymer micelles. Herein, a versatile strategy is presented to transform one-component oxime-based block copolymer micelles into long-range ordered dense nanopatterns. Photoisomerization provides a straightforward and versatile approach to convert the hydrogen-bonding association from inward dimerization (E-type oxime motifs, slightly desolvated in ethyl acetate) into outward interchain association (Z-type ones, highly desolvated in ethyl acetate). This increases the glass transition temperature in bulk and converts swollen micelles into compact spherical micelles in solution. The reconstruction of these micelles on various substrates demonstrates that the phase transformation enables reconstruction of spherical micelles into mesoscopic sheets, nanorods, nanoworms, nanowires, networks, and eventually into long-range ordered and densely packed textile-like and lamellar nanopatterns on a macroscopic scale by adjusting E/Z-oxime ratio and solvent-evaporation rate.

Metal complexes derived from hydrazoneoxime ligands: V. Spectral and structural studies on diacetylmonoxime n-alkanoylhydrazones and their nickel(II) and copper(II) complexes

A series of diacetylmonoxime n-alkanoylhydrazones (H₂L(n), n=4, 5, 6, 12 and 16) were prepared by the condensation of diacetylmonoxime with the corresponding n-alkanoylhydrazine in ethanol. The X-ray crystal structure of diacetylmonoxime octadecanoyl hydrazone has been solved and its molecular and supramolecular structures have been discussed. Both neutral dinuclear Cu(II) and Ni(II) complexes, [{M(L(n))}₂] (M=Cu, Ni and n=4, 5, 6, 12 and 16) as well as cationic dinuclear Cu(II) complexes, [Cu₂(L(n))(HL(n))]NO₃ (n=12 and 16) have been also prepared and characterized by elemental analyses, FD- and ESI-mass spectra as well as IR, UV-Vis, (1)H NMR, (13)C NMR spectra. Variable temperature magnetic susceptibility measurements for dinuclear Cu(II) complexes have been also discussed.

A study on fluoride detection and assembly of hydroxyaromatic aldoximes caused by tetrabutylammonium fluoride

Different assemblies formed by the interactions of tetrabutylammonium fluoride with hydroxy-aromatic oximes show characteristic optical properties.

Evidence for hydrogen-bonded ammonia wire influencing the ESMPT process of the 7-hydroxy-4-methylcoumarin·(NH3)3 cluster

The different types of excited-state hydrogen-bonded dynamics mechanisms orderly provide two driving forces for the excited-state multiple proton transfer (ESMPT) reaction of the 7H4MC·(NH₃)₃ cluster.

Complexation of formaldoxime with water. Infrared matrix isolation and theoretical studies

The 1:1, 1:2 and 2:1 formaldoxime-water complexes isolated in the argon matrices have been studied by help of FTIR spectroscopy and MP2/6-311++G(2d,2p) method. The calculations predicted the stability of the three CH(2)NOH···H(2)O isomeric complexes, three CH(2)NOH···(H(2)O)(2) ones and one (CH(2)NOH)(2)···H(2)O complex. The analysis of the experimental spectra and their comparison with theoretical ones indicated that both the 1:1 and 1:2 complexes trapped in solid argon have the most stable cyclic structures stabilized by the O-H···O and O-H···N bonds between the formaldoxime and water molecules. In the 1:2 complex formaldoxime interacts with the water dimer, one H(2)O molecule acts as a proton acceptor for the OH group of formaldoxime whereas the second H(2)O molecule acts as a proton donor toward the nitrogen atom of the formaldoxime molecule. In the (CH(2)NOH)(2)···H(2)O complex the OH group of the water molecule acts as a proton donor toward one of the oxygen atoms of the formaldoxime cyclic dimer.

Experimental and theoretical investigations of benzamide oxime

The FT-IR (4000-400 cm(-1)) and FT-Raman (4000-100 cm(-1)) spectral measurements of benzamide oxime and complete assignments of the observed spectra have been proposed. Ab initio and DFT calculations have been performed giving energies, optimized structures, harmonic vibrational frequencies, depolarization ratios, IR intensities, Raman activities and atomic displacements. Furthermore, force field calculations have been performed by normal coordinate analysis. Force field calculations showed that several normal modes are mixed in terms of the internal coordinates. A complete assignment of the observed spectra, based on spectral correlations, electronic structure calculations and normal coordinate analysis, has been provided.

Oxime decorated cavitands functionalized through solvent-assisted grinding

In order to assemble supramolecular capsules, there is a need for reliable and effective synthetic methods for decorating cavitand-based host structures with appropriate functional groups. The synthesis of four different cavitands of significantly different depth and interior volume functionalized with four aldoxime groups capable of forming homomeric or heteromeric capsules through hydrogen bonding is reported. The final step in each synthesis, the aldehyde to oxime transformation, has been achieved in excellent yields through 'solvent assisted grinding'.

Different hydrogen-bonding modes in two closely related oximes

Two closely related oximes, namely 1-chloroacetyl-3-ethyl-2,6-diphenylpiperidin-4-one oxime, C(21)H(23)ClN(2)O(2), (I), and 1-chloroacetyl-2,6-diphenyl-3-(propan-2-yl)piperidin-4-one oxime, C(22)H(25)ClN(2)O(2), (II), despite their identical sets of hydrogen-bond donors and acceptors, display basically different hydrogen-bonding patterns in their crystal structures. While the molecules of (I) are organized into typical centrosymmetric dimers, created by oxime-oxime O-H...N hydrogen bonds, in the structure of (II) there are infinite chains of molecules connected by O-H...O hydrogen bonds, in which the carbonyl O atom from the chloroacetyl group acts as the hydrogen-bond acceptor. Despite the differences in the hydrogen-bond schemes, the -OH groups are always in typical anti positions (C-N-O-H torsion angles of ca 180 degrees ). The oxime group in (I) is disordered, with the hydroxy groups occupying two distinct positions and C-C-N-O torsion angles of approximately 0 and 180 degrees for the two alternatives. This disorder, even though the site-occupancy factor of the less occupied position is as low as ca 0.06, is also observed at lower temperatures, which seems to favour the statistical and not the dynamic nature of this phenomenon.

Benzamide oxime

In the crystal structure of the title compound, C₇H₈N₂O, mol­ecules are connected via inter­molecular N—H⋯O and O—H⋯N hydrogen bonds to form a two-dimensional supra­molecular structure. The oxime group has an E configuration and the dihedral angle between the mean planes of the benzene ring and the amidoxime grouping is 20.2 (3)°.

Mechanochemical preparation of molecular and supramolecular organometallic materials and coordination networks

This Dalton Perspective deals with solvent-free reactions taking place within solids or between solids or involving a solid and a vapour. The focus is on reactions involving organometallic and coordination compounds and occurring via reassembling of non-covalent bonding, e.g. hydrogen bonds, and/or formation of ligand-metal coordination bonds. It is argued that reactions activated by mechanical mixing of solid reactants as well as those obtained by exposing a crystalline solid to a vapour can be exploited to "make crystals", which is the quintessence of crystal engineering. It is demonstrated through a number of examples that solvent-free methods, such as co-grinding, kneading, milling of molecular solids, or reactions of solid with vapours represent viable alternative, when not unique, routes for the preparation of novel molecular and supramolecular solids as well as for the preparation of polymorphic or solvate modifications of a same species. The structural characterization of the products requires the preparation of single crystals suitable for X-ray diffraction, a goal often achieved by seeding.

4-(Tetrahydro-4H-thiopyran-1-oxide-4-ylidene)-cyclohexanone oxime in the solid-state. A two-dimensional network of enantiomorphous chains interconnected by weak hydrogen bonds

From a saturated C6H6 solution of racemic 4-(tetrahydro-4H-thiopyran-1-oxide-4-ylidene)-cyclohexanone oxime [1(1-R/1-S)] the co-crystal is crystallized. Single crystal X-ray analysis showed that (1)4.C6H6 (P1 space group) in the solid-state consists of enantiomorphous, non-covalent polymer-like chains that contain, in an alternating fashion, the crystallographically independent enantiomers 1-R and 1-R' or 1-S and 1-S'', respectively. Within each chain the enantiomers are linked by 'head-to-tail' intermolecular oxime-sulfoxide hydrogen bonding [D(2) motif]. Neighbouring chains consist of enantiomers with opposite configuration and possess opposite molecular 'head-to-tail' alignments. The enantiomorphous chains are interconnected by weak intermolecular C-HO hydrogen bonds involving centrosymmetric C-Hoxime [R(12)] and C-Hsulfoxide [R(8)] motifs between the 1-R and 1-S molecules in neighbouring chains; a nearly planar two-dimensional hydrogen bonding network motif is obtained. In the crystallographic direction [1 0 0] the layers stack in such a fashion that chains occupying successive layers with an identical 'head-to-tail' alignment are positioned on top of each other. Concomitantly, channels with areas of ca. 25 Angstroms(2) are obtained, which are occupied by C6H6 solvent molecules. A comparison of the IR and Raman spectra of with those obtained for native 1 that does not contain C6H6, indicates that intermolecular oxime-sulfoxide hydrogen bonding [D(2) motif] also occurs for native 1 in the solid-state.