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A new phosphonic acid, (2-oxo-2-(thiophen-2-yl)ethyl) phosphonic acid (OTEPA), was synthesized and its molecular and crystal structures investigated using several experimental techniques complemented by different types of calculations. The experimental techniques used include infrared and Raman spectroscopies and single crystal X-ray crystallography. Calculations were performed at both molecular mechanics and DFT(B3LYP)/6–311++G(d,p) levels of approximation, for the isolated molecule. The conformational space of OTEPA was investigated and the most stable conformers characterized both structurally and spectroscopically. It was found that in the lower energy conformers of OTEPA an intramolecular H-bond exists between one of the OH groups of the phosphonic acid fragment and the carbonyl oxygen atom. The two lowest energy conformers have the sulphur atom of the thiophene ring eclipsed with the carbonyl oxygen atom, allowing for the establishment of an O⋯S stabilizing contact, similar to the N⋯S type contact found previously in other molecular systems. Noteworthy, in the crystalline phase the OTEPA molecules do not assume one of the most stable conformations for the isolated molecule, but exist in a conformation similar to that of high-energy conformers, which have predicted energies relative to the conformational ground state higher than 13 kJ mol−1. The infrared spectra of the monomeric molecules of the compound isolated in a low temperature solid argon matrix and of the crystal of the neat compound were also investigated and assigned, together with the Raman spectrum of the crystalline compound.

Pyrenes bear a propensity to form fluorescent excimers, and thus this chromophore is often found in sensors and fluorescent probes. 2-FunctionaIized pyrenes are of particular interest, however the preparation of these scaffolds is not trivial, involving synthetic routes that require 4,5,9,10-tetrahydropyrene as a key intermediate. Herein, the development and optimization of routes for the synthesis of 2-functionalized pyrene-derived building blocks, with potential to be used as tags in the preparation of fluorescent probes, is described. Additionally, the crystal structures of ethyl 4,5,9,10-tetrahydro-2-pyrene-5-oxopentanoate and 2-acetyl-4,5,9,10-tetrahydropyrene revealed distinct conformations of the saturated tetrahydropyrene rings. (C) 2017 Elsevier Ltd. All rights reserved. FEDER [PTDC/QUI-BIQ/112943/2009, PTDC/MAR-BIO/4132/2014, UID/Multi/04326/2013, UID/FIS/04564/2016] Fundacao para a Ciencia e a Tecnologia (FCT), Portugal info:eu-repo/semantics/publishedVersion

Furans were explored as scaffold for the synthesis of a range of heterocyclic compounds, exploring the dienophilic behaviour towards nitroso- and azoalkenes as the first step. Acid-catalysed rearrangements of these cycloadducts, 4a,7a-dihydro-4H-furo[2,3-e][1,2]oxazines and 1,4,4a,7a-tetrahydrofuro[3,2-c]pyridazines, were studied. Using 1 equivalent of TFA, the bicyclic heterocycles derived from furan and 2-methylfuran, are converted into furans bearing side-chains incorporating oxime and hydrazone groups by ring-opening of the six-membered ring with the concomitant aromatization of the furan ring. The use of TFA as solvent can lead to rearrangements via the generation of spirocyclic intermediates followed by furan ring-opening to afford functionalized isoxazoles or pyrazoles. Furthermore, furo-oxazines derived from 2,5-dimethylfuran, where furan aromatization is precluded, are converted efficiently into 6H-1,2-oxazines via a furan ring-opening reaction upon thermolysis in presence of a catalytic amount of p-toluenesulfonic acid. Tetrahydrofuro[3,2-c]pyridazines derived from furan and dimethylfuran undergo acid-catalyzed addition reaction, leading to 6-substitued-hexahydrofuro[3,2-c]pyridazines, when in presence of alcohols or water.

The synthesis of a new hydrazone, 2-oxoacenaphthylen-1(2H)-ylidene nicotinohydrazide, and its structural and spectroscopic characterization is reported. The obtained powder was recrystallized from DMSO and ethanol that afforded small crystals used for single-crystal X-ray diffraction studies. The compound was found to crystallize in two polymorphs, depending on the crystallization conditions. One of the polymorphs (form I) crystallizes in the centrosymmetric P21/c monoclinic space group, the other (form II) crystallizes in the non-centrosymmetric, but achiral, orthorhombic space group P212121. Conformation of the molecules is similar in both polymorphs, but the network of weak intermolecular interactions determining the crystal packing is different. In form II an additional C-H⋯O bond connects molecules related by the screw-axis running parallel to the a-axis. Crystals of both polymorphs were also screened by FT-IR and Raman microscopy; a detailed analysis of the spectra and comparison with those of the isolated molecule calculated by ab-initio HF/MP2 and DFT/B3LYP methods using a correlation consistent cc-pVDZ basis set is presented. In addition, UV-vis and NMR studies were performed in solution.

Three novel copper(I) complexes with three methyl 4-aryl-6-methyl-3,4-dihydropyrimidine-2(1H)-thione-5-carboxylate ligands were synthesized and fully characterized by elemental analysis, magnetic susceptibility, molar conductivity, ESI-MS, FTIR, UV–Vis and NMR. The difference between the three ligands is located in the aryl group: 4-(tert-butyl)phenyl (HL1), 2,6-dichlorophenyl (HL2) and 2,4-dichlorophenyl (HL3). Two ligands and complex 2 were characterized by single-crystal X-ray diffraction. The complex [CuCl(HL2)2]·dmso exhibits an almost perfect trigonal planar coordination geometry crystallizing in a space group P21/n, through the two sulfur atoms of the ligands, one chlorine atom bonded to the copper(I) and solvated with one molecule of dimethyl sulfoxide. The anticancer activity was evaluated in vitro against human colorectal cancer (CRC) cell line (Caco-2). The complexes have cytotoxic effect with IC50 values of 28.46, 25.03 and 38.83 μM respectively. Moreover, complexes 1 and 2 are able to strongly induce apoptosis in this CRC in vitro model.

The sodium salt of 5-acetic acid hydantoin (5AAH) was synthesized, and its crystal structure determined by single crystal X-ray diffraction. The material was found to exhibit rather unusual structural features. Firstly, contrarily to what is most common for hydantoins, the 5AAH molecules in the crystal bind the sodium ions through coordination via its oxygen atoms (instead of via a deprotonated ring nitrogen). In second place, the molecular formula of the salt is Na(5AAH)2, i.e., the formal charge of the hydantoin in the crystal is −0.5 e. Finally, the conformation adopted by the 5AAH molecules in the crystal of the salt is neither the most stable conformer for the isolated molecule (and observed before in the gas phase of the compound), nor that present in the neat crystalline compound (most stable polymorph at room temperature). These results show that 5AAH is a structurally very versatile molecule, which is able to participate in strong intermolecular interactions that can supersede the intrinsic higher structural stability of the individual molecules and lead to selection of different higher energy conformers on formation of a crystalline phase. The Raman spectrum of the newly synthesized salt was also obtained and used to extract further structural details of the crystal, in particular on the prevalent intermolecular interactions. The results (both structural and spectroscopic) obtained for the studied sodium salt of 5AAH are also compared with those relative to the neat 5AAH most stable crystalline polymorph at room temperature. To help the interpretation of the spectra, DFT(B3LYP)/6–311++G(d,p) calculations were undertaken on simple models based on the structural elements of the crystals.

Reports showing that the copper concentration is considerably higher in neoplasms than in normal tissues prompted the need to develop selective copper chelators. We disclosed recently that some N-linked tetrazole-saccharinates bind selectively to copper, forming complexes that are highly cytotoxic towards cancer cells. Because tetrazole-saccharinates are photolabile, due to the photoreactivity of tetrazoles, we proposed thiadiazolyl-saccharinates as an alternative. Herein we describe the synthesis, structure, and monomeric photochemistry of a sulphanyl-bridged thiadiazolyl-saccharinate, 3-[(5-methyl-1,3,4-thiadiazol-2-yl)sulphanyl]-1,2-benzothiazole 1,1-dioxide (MTSB). The monomeric structure, charge density analysis, and characteristic infrared spectrum of MTSB were investigated theoretically, using quantum chemical calculations, and also experimentally, using matrix-isolation infrared spectroscopy. The crystal structure was investigated by combining X-ray crystallography with infrared and Raman spectroscopies. Results show that the structure of isolated MTSB is similar to that found in the crystal, with an S⋅⋅⋅N interaction clearly contributing to the structure of the molecule and of the crystal. Matrix irradiation revealed a high photostability of MTSB, compared to parent tetrazole-saccharinates and to the 5-methyl-1,3,4-thiadiazole building block, emphasizing the photostabilizing effect of the saccharyl system. Finally, in vitro toxicity assays of MTSB showed a copper concentration-dependent toxicity against cancer cells, without affecting normal cells. In particular, MTSB was most effective towards the hepatic (HepG2), neuroblastoma (SH-SY5), and lymphoma cell lines (U937). Thus, MTSB represents a promising lead for cancer chemotherapy based on chelating agents.

In a previous study [Nogueira, B.A.; Ildiz, G.O.; Canotilho, J.; Eusebio, M. E. S.; Fausto, R. J. Phys. Chem. A, 2014, 118, 5994-6008], two different polymorphs of 1-methylhydantoin (1-MH, C4H6N2O2) were identified using infrared spectroscopy, differential scanning calorimetry and polarized-light thermal microscopy. Unfortunately, at that time it was not possible to structurally characterize in detail the second polymorph (polymorph II) of the compound, due to lack of suitable crystals for X-ray diffraction structure determination. In this article, a throughout investigation of the polymorphism of 1-MH is presented. Screening for polymorphs was performed by recrystallization from different solvents, and the structure of polymorph II was determined for the first time by single crystal X-ray diffraction. The spectroscopic characterization of this polymorph was also undertaken, by Raman spectroscopy, which was also used to follow the phase transition between the two polymorphs (the well-known polymorph I, and the newly described polymorph II), showing that even though their structures are significantly distinct, the transition is a non-destructive one. (C) 2017 Elsevier B.V. All rights reserved.

The molecular structure, vibrational spectra and photochemistry of 5-methylhydantoin (C4H6N2O2; 5-MH) were studied by matrix isolation infrared spectroscopy and theoretical calculations at the DFT(B3LYP)/6-311++G(d,p) theory level. The natural bond orbital (NBO) analysis approach was used to study in detail the electronic structure of the minimum energy structure of 5-MH, namely the specific characteristics of the sigma and pi electronic systems of the molecule and the stabilizing orbital interactions. UV irradiation of 5-MH isolated in argon matrix resulted in its photofragmentation through a single photochemical pathway, yielding isocyanic acid, ethanimine, and carbon monoxide, thus following a pattern already observed before for the parent hydantoin and 1-methylhydantoin molecules. The investigation of the thermal properties of 5-MH was undertaken by differential scanning calorimetry (DSC), polarized light thermal microscopy (PLTM) and Raman spectroscopy. Four different polymorphs of 5-MH were identified. The crystal structure of one of the polymorphs, for which it was possible to grow up suitable crystals, was determined by X-ray diffraction (XRD). Two of the additional polymorphs were characterized by powder XRD, which confirmed the molecules pack in different crystallographic arrangements.

(1H-Tetrazol-5-yl)-allenes have been prepared for the first time, and their reactivity toward aziridines explored. Reaction of a (1-benzyl-1H-tetrazol-5-yl)-phosphonium chloride and acyl chlorides in the presence of triethylamine afforded the target allenes via Wittig reaction of the in situ generated phosphorus ylide and ketenes. 1-(1-Benzyl-1H-tetrazol-5-yl)propa-1,2-diene and 3-methyl-, 3-ethyl- and 3-benzyl derivatives undergo microwave-induced formal [3 + 2] cycloaddition with cis-N-benzyl-2-benzoyl-3-phenylaziridine, through C-N bond cleavage, to give selectively tetrasubstituted pyrroles. In contrast, with (1H-tetrazol-5-yl)-allenes bearing bulkier substituents at C-3, such as i-propyl or a tert-butyl, 4-methylenepyrrolidines were obtained exclusively via [3 + 2] cycloaddition of the in situ generated azomethine ylide. The latter allenes also gave 4-methylenepyrrolidines on reacting with cis-2-benzoyl-N-cyclohexyl-3-phenylaziridine, whereas with the other allenes, pyrroles were obtained as major products together with the formation of 4-methylenepyrrolidines. All the studied (1H-tetrazol-5-yl)-allenes reacted with N-benzyl-cis-3-phenylaziridine-2-carboxylate to give the corresponding 4-methylenepyrrolidines exclusively.

The role of copper in the proliferation of cancer cells is under investigation and has been explored in the context of cancer chemotherapy. The evidence that proliferation of cancer cells requires a higher abundance of Cu(II) than their normal counterparts has prompted the development of new copper chelators that can avidly bind copper ions, forming redox active metal complexes that ultimately lead to harmful reactive oxygen species (ROS) in neoplasms. In this context, the mandatory properties of the chelators for medical applications are safety (neglectable cytotoxicity), high binding affinity and selectivity towards Cu(II). We report the synthesis, structure (calculations and single crystal X-ray diffraction), spectroscopic (IR; UV-Vis) and magnetic properties of two novel copper(II) complexes based on 5-(3-aminosaccharyl)-tetrazoles (TS and 2MTS), as well as their in vitro cytotoxicity against the human hepatic carcinoma cell line HepG2. Quite interestingly, we found that the saccharinate-tetrazoles tested exhibit strong binding selectivity to Cu(II), over Fe(II) and Ca(II). Additionally, the corresponding copper complexes have shown a huge increase in the in vitro cytotoxicity against tumoral cells, compared to the corresponding nontoxic ligands. Thus, the new ligands may be viewed as potential precursors of selective cytotoxic agents, acting as non-cytotoxic pro-drugs that can be activated inside neoplastic cells, known to be richer in Cu(II) than the corresponding normal cells.