Structural basis for molecular recognition,theoretical studies and anti-bacterial properties of three bis-uracil derivatives

Three bis-pyrimidine compounds (1, 2 & 3) have been synthesized by the reaction of 6-[(dimethylamino)methyleneamino]-1,3-dimethyluracil with three different aldehydes viz. p-methoxybenzaldehyde, p-nitrobenzaldehyde, and 2-thiophenecarboxaldehyde in aqueous media in presence of ‘green surfactant’ followed by recrystallization in EtOH. The compounds are characterized by elemental analyses, NMR and single crystal X-ray diffraction. N–H?O hydrogen bonds and weak C–H?O interactions are the main non-bonding interactions in the molecular structures of the three compounds. Details of the synthesis, spectroscopic data and structures of the three compounds are presented. Furthermore, we have rationalized some relevant noncovalent interaction involving the aromatic moieties by means of DFT calculations. Finally, we have also analysed the anti-bacterial properties of compounds 1–3 and compared to Ofloxacin drug. The anti-bacterial activity has been tested against Klebsiella pneumoniae, Staphylococcus aureus and Pseudomonas aeruginosa. All compounds are found to possess from moderate to good anti-bacterial properties (MIC 25–100 μg/ml).     

Towards the real didemnaketal A: total syntheses of two C-21 stereoisomers of the proposed didemnaketal A

Two isomers (3 and 4) with a configuration at C-21 opposite to that proposed for didemnaketal A were synthesized through a process in which the longest linear sequence involved 29 steps. Comparative NMR analysis of these isomers and natural didemnaketal A suggests the possibility of misassignments at other stereocenters in the proposed structure of didemnaketal A.     

Synthesis,characterization, and initial reaction study of two new bicyclic hypervalent iodine(III) reagents

The synthesis of two new bicyclic hypervalent iodine(III) reagents 5 and 6 is described along with their corresponding X-ray crystal structures for the first time. A detailed comparison in the bond lengths and bond angles of reported bicyclic hypervalent iodine(III) reagents is also presented. Furthermore, an initial study shows that these two hypervalent iodine(III) reagents could promote the dipeptide coupling reaction.     

Characterization of process‐related impurities including forced degradation products of alogliptin benzoate and the development of the corresponding reversed‐phase high‐performance liquid chromatography method

The characterization of process‐related impurities and forced degradants of alogliptin benzoate (Alb) in bulk drugs and a stability‐indicating HPLC method for the separation and quantification of all the impurities were investigated. Alb was found to be unstable under acid and alkali stress conditions and two major degradation products (Imp‐F and Imp‐G) were observed. The optimum separation was achieved on Kromasil C₁₈ (250 × 4.6 mm, 5 μm) using 0.1% perchloric acid (pH adjusted to 3.0 with triethylamine) and acetonitrile as a mobile phase in gradient mode. The proposed method was found to be stability indicating, precise, linear (0.10–75.0 μg/mL), accurate, sensitive, and robust for the quantitation of Alb and its process‐related substances and degradation products. The structures of 11 impurities were characterized and confirmed by NMR spectroscopy, MS, and IR spectroscopy, and the most probable formation mechanisms of all impurities were proposed according to the synthesis route.     

Isolation and identification of two unknown impurities from the raw material of clindamycin hydrochloride

Clindamycin hydrochloride belongs to the antibiotic family of lincomycin. It has the same antibacterial spectrum as lincomycin, but the antibacterial activity is four to eight times stronger than that of lincomycin. There have been some adverse reactions in clinical use of clindamycin hydrochloride and its finished drug products. The impurities in drugs are directly related to their safety. In this study, two unknown impurities were isolated from the raw material of clindamycin hydrochloride through various chromatographic methods. Their structures were identified as clindamycin isomer (impurity 1) and dehydroclindamycin (impurity 2) by mass spectrometry and NMR spectroscopy. Both of them were found for the first time. The two impurities exhibit a similar but lower antibacterial activity compared with clindamycin hydrochloride.     

Effect of Hg2+doping and of the annealing temperature on the nanostructural properties of TiO2 thin films obtained by sol–gel method

This work is a study of Hg²⁺-doped TiO₂ thin films deposited on silicon substrates prepared by sol–gel method and treated at temperatures ranging between 600 to 1000 °C for 2 h. The structural and optical properties of thin films have been studied using different techniques. We analyzed the vibrations of the chemical bands by Fourier transform infrared (FTIR) spectroscopy and the optical properties by UV–Visible spectrophotometry (reflection mode) and photoluminescence (PL). The X-ray diffraction and Raman spectra of TiO₂ thin films confirmed the crystallization of the structure under the form of anatase, rutile, mercury titanate (HgTiO₃) as a function of the annealing temperature. The observation by scanning electron microscopy (SEM) showed the changing morphology, with respect to nanostructures, nanosheets, nanotubes, with the annealing temperature. The diameters of nanotubes ranged from 50 nm to 400 nm. The photoluminescence and reflectance spectra indicated that these structures should enhance photocatalytic activity.     

In‐situ cryocrystallization of 1,2‐dimethyl‐3‐nitrobenzene and 2,4‐dimethyl‐1‐nitrobenzene

The crystal structures of 1,2‐dimethyl‐3‐nitrobenzene, C₈H₉NO₂, and 2,4‐dimethyl‐1‐nitrobenzene, C₈H₉NO₂, which are liquids at room temperature, have been obtained through in‐situ cryocrystallization. Weak C—H...O and also π–π interactions are present in both crystal structures.     

Green analytical methodologies for the discovery of bioactive compounds from marine sources

The application of green analytical chemistry in search of bioactive compounds is of paramount importance, leading to the development of environmentally friendly methodologies for their isolation. This work provides an up-to-date overview of the analytical methodologies based on a green perspective for the discovery of bioactive compounds from marine sources, namely to their extraction and structural characterization. Both the characteristics of marine bioactive compounds and the sustainable evaluation of their bioactivity are also addressed.     

Minimax optimal procedures for testing the structure of multidimensional functions

We present a novel method for detecting some structural characteristics of multidimensional functions. We consider the multidimensional Gaussian white noise model with an anisotropic estimand. Using the relation between the Sobol decomposition and the geometry of multidimensional wavelet basis we can build test statistics for any of the Sobol functional components. We assess the asymptotical minimax optimality of these test statistics and show that they are optimal in presence of anisotropy with respect to the newly determined minimax rates of separation. An appropriate combination of these test statistics allows to test some general structural characteristics such as the atomic dimension or the presence of some variables. Numerical experiments show the potential of our method for studying spatio-temporal processes.     

On some structural sets and a quaternionic ‐hyperholomorphic function theory

Quaternionic analysis is regarded as a broadly accepted branch of classical analysis referring to many different types of extensions of the Cauchy‐Riemann equations to the quaternion skew field . It relies heavily on results on functions defined on domains in or with values in . This theory is centred around the concept of ψ‐hyperholomorphic functions related to a so‐called structural set ψ of or respectively. The main goal of this paper is to develop the nucleus of the ‐hyperholomorphic function theory, i.e., simultaneous null solutions of two Cauchy‐Riemann operators associated to a pair of structural sets of . Following a matrix approach, a generalized Borel‐Pompeiu formula and the corresponding Plemelj‐Sokhotzki formulae are established.