Dehydrative Substitution Reaction in Water for the Preparation of Unsymmetrically Substituted Triarylmethanes: Synthesis, Aggregation-Enhanced Emission, and Mechanofluorochromism.

Water as a reaction media in chemical transformations has several advantages in terms of safety and non-toxicity. However, dehydrative substitution reaction in water is a highly challenging operation. In this paper, we have reported a sulfamic acid-mediated dehydrative substitution reaction of benzofuryl alcohols with several nucleophiles in water towards the scalable, easily isolable, synthesis of unsymmetrically substituted triarylmethanes (TRAMs) in good to excellent yields (up to 92 %). Moreover, we have demonstrated that rationally designed propellor-shaped triarylmethanes promote aggregation-induced emission (AIE) through restricted intramolecular rotation with irreversible mechanoflurochromic property.

Exciton-tryptophan coupling pulse behaviour along with corona formation, binding analysis, and interaction study of ZnO nanorod-serum albumin protein bioconjugate.

The bioconjugate of bovine serum albumin (BSA) and zinc oxide nanorods (ZnO NRs) is investigated to explore the behaviour of the tryptophan (Trp)-exciton coupling and corona formation. The pulse like nature of the coupled system between Trp of BSA and exciton of ZnO NRs has been observed after analysis of the optical parameters such as refractive index, susceptibility, and optical dielectric constant. The time constant for tryptophan, exciton surface binding (t1 ) and reorganization (t2 ) are found to be (t1 ) 8 min, 7 min and (t2 ) 150 min, 114.5 min, respectively. The close proximity binding of BSA with ZnO NRs via tryptophan as well as exciton is responsible for bioconjugate formation. The aggregated structure of BSA is observed from small-angle X-ray scattering study in interaction with ZnO NRs. The change in secondary structure and tertiary deformation of the serum protein have been studied from Fourier transform infrared and emission quenching analyses. The number of binding sites (n) signified to the enhancement of the cooperative binding. The binding has been found to be endothermic and favoured using unfavourable positive enthalpy with a favourable entropy change from the result of the isothermal titration calorimetry.

Design and Development of Axially Chiral Bis(naphthofuran) Luminogens as Fluorescent Probes for Cell Imaging.

Designing chiral AIEgens without aggregation-induced emission (AIE)-active molecules externally tagged to the chiral scaffold remains a long-standing challenge for the scientific community. The inherent aggregation-caused quenching phenomenon associated with the axially chiral (R)-[1,1'-binaphthalene]-2,2'-diol ((R)-BINOL) scaffold, together with its marginal Stokes shift, limits its application as a chiral AIE-active material. Here, in our effort to design chiral luminogens, we have developed a design strategy in which 2-substituted furans, when appropriately fused with the BINOL scaffold, will generate solid-state emissive materials with high thermal and photostability as well as colour-tunable properties. The excellent biocompatibility, together with the high fluorescence quantum yield and large Stokes shift, of one of the luminogens stimulated us to investigate its cell-imaging potential. The luminogen was observed to be well internalised and uniformly dispersed within the cytoplasm of MDA-MB-231 cancer cells, showing high fluorescence intensity.

Characterization of zinc oxide nanocrystals with different morphology for application in ultraviolet-light photocatalytic performances on rhodamine B.

ZnO nanostructures of different morphology (nanorods, nano-leaf, nanotubes) were favourably grown using a chemical precipitation process. The prepared ZnO nanostructures were characterized systematically using absorption spectroscopy, emission spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared studies. XRD results showed the hexagonal wurtzite phase of the synthesized ZnO nanostructures. Structural properties such as average crystallite size, lattice constants, volume of the unit cell, atomic fraction, and structural bonds were also studied. The optical band gap of the synthesized ZnO nanocrystals varied from 3.52 eV to 3.69 eV with high quantum yield of the blue emission (~420 nm). Urbach energy for ZnO nanocrystals was calculated to be 0.702 eV, 0.901 eV, and 0.993 eV for nanorods, nano-leaf, and tube like ZnO crystals, respectively. Morphology of the fabricated nanostructures was investigated using SEM. Photocatalytic degradation of rhodamine B (Rh B) in solution under UV irradiation was explored with different ZnO morphology. Photocatalytic experiments showed that ZnO nano-leaf had a higher degradation rate of photocatalytic activity of photodegrading Rh B compared with the other tube shape and rods shape nanostructures. The Rh B dye degraded considerably by ∼79.05%, 74.41%, and 69.8% within 120 min in the presence of the as-fabricated fern nano-leaf, nanotubes, and nanorods of the ZnO nanocrystals at room temperature.

Screening of Esophageal Varices by Noninvasive Means in Chronic Liver Disease.

INTRODUCTION: Noninvasive assessment of esophageal varices (EV) decreases the medical and financial burden related to screening and helps in the management of patients with chronic liver diseases (CLDs). In this study, our aim was to assess the utility of the platelet count/spleen diameter index for the noninvasive evaluation of EV. MATERIALS AND METHODS: In this cross-sectional observational study, a total of 100 CLD patients underwent screening endoscopy for EV in Medicine and Gastroenterology Department, Sylhet MAG Osmani Medical College Hospital, Sylhet, Bangladesh. Platelet count/spleen diameter ratio was assessed in all patients and its diagnostic implication was calculated. RESULTS: Upper gastrointestinal endoscopy revealed that 45 (45.0%) patients had medium EV followed by 27 (27.0%) that had small EV and 19 (19.0%) patients had large EV. Receiver operator characteristic (ROC) curve was constructed using platelet count/spleen index, which gave a cut-off value of >905. The validity of platelet count/spleen index evaluation of CLD was: Sensitivity 92.3%, specificity 66.7%, accuracy 90.0%, positive predictive value (PPV) and negative predictive value (NPV) were 96.6 and 46.2% respectively. True positive was 84 cases, false positive 3 cases, false negative 7 cases, and true negative 6 cases. If we consider cut-off value as 909 in the evaluation of EV in CLD, then true positive was 85 cases, false positive 3 cases, false negative 6 cases, and true negative 6 cases. From this, by calculation, sensitivity was 93.4%, specificity 66.7%, accuracy 91%, PPV 96.6%, and NPV 50%. CONCLUSION: The platelet count/spleen index may be proposed to be a safe and reliable mean of screening of EV in CLD patients; however, case-control study would be required to validate this.How to cite this article: Hossain E, Ahammed F, Saha SK, Foez SA, Rahim MA, Noor-e-Alam SM, Abdullah AS. Screening of Esophageal Varices by Noninvasive Means in Chronic Liver Disease. Euroasian J Hepato-Gastroenterol 2018;8(1):18-22.

Scope and advances in the catalytic propargylic substitution reaction.

Nucleophilic displacement of the propargylic alcohol is one of the sought-after methods in the current scenario. The highly nucleophilic alkyne functional moiety along with its considerably acidic terminal hydrogen atom allows the propargylic unit to play a crucial role in organic synthesis by offering a handle for further synthetic transformations. Until 2000, the most fundamental propargylic substitution reaction was the Nicolas reaction, a multi-step transformation, developed in 1972, which involved cobalt as a stoichiometric promoter. Therefore, the direct catalytic substitution of propargylic alcohols was a highly desirable method for development. The pioneering work on the Ru-catalyzed propargylic substitution reaction in 2000 encouraged many researchers to develop several novel catalytic propargylic substitution reactions, which have made rapid progress since then. The purpose of this review is to emphasise the involvement of diverse types of Lewis acid, transition metal and Brønsted acid catalysts in the propargylic substitution reaction and provide an updated summary of the recent developments in this field. The selected examples presented here are the most significant and relevant ones and we believe that this will help the readers to comprehend the scope of the propargylic substitution reaction with diverse types of catalysts and will envisage the scientific community for the future developments in this field.

Directing group assisted nucleophilic substitution of propargylic alcohols via o-quinone methide intermediates: Brønsted acid catalyzed, highly enantio- and diastereoselective synthesis of 7-alkynyl-12a-acetamido-substituted benzoxanthenes.

BINOL-based, chiral phosphoric acids catalyze the substitution of 1-(o-hydroxyphenyl)propargylic alcohols with enamides to furnish 7-alkynyl-12a-acetamido-substituted benzo[c]xanthenes and related heterocycles in a one-pot operation with excellent diastereo- and enantioselectivity. Ambient reaction temperature, operationally simple reaction conditions, low catalyst loading, high yields, and excellent stereocontrol are attractive features of this process and make it a highly practical and versatile transformation.

Brønsted acid-catalyzed, highly enantioselective addition of enamides to in situ-generated ortho-quinone methides: a domino approach to complex acetamidotetrahydroxanthenes.

The highly enantioselective conjugate addition of enamides and enecarbamates to in situ-generated ortho-quinone methides, upon subsequent N,O-acetalization, gives rise to acetamido-substituted tetrahydroxanthenes with generally excellent enantio- and diastereoselectivities. A chiral BINOL-based phosphoric acid catalyst controls the enantioselectivity of the carbon-carbon bond-forming event. The products are readily converted into other xanthene-based heterocycles.

Chiral Brønsted acid-catalyzed Friedel-Crafts alkylation of electron-rich arenes with in situ-generated ortho-quinone methides: highly enantioselective synthesis of diarylindolylmethanes and triarylmethanes.

We disclose herein a highly enantioselective protocol for the Brønsted acid-catalyzed addition of indoles and phenols to in situ-generated ortho-quinone methides which deliver broadly substituted diarylindolylmethanes and triarylmethanes, respectively, in a one-pot reaction under very mild conditions. A chiral phosphoric acid catalyst has been developed for this process serving to convert the starting ortho-hydroxybenzhydryl alcohols into the reactive ortho-quinone methides and to control the enantioselectivity of the carbon-carbon bond-forming event via hydrogen-bonding.

Enantioselective organocatalytic Biginelli reaction: dependence of the catalyst on sterics, hydrogen bonding, and reinforced chirality.

From a systematic investigation involving the synthesis of a series of catalysts and screening studies, the organocatalyst 16, which is sterically hindered, contains a strong hydrogen-bonding site, and is endowed with reinforced chirality, is shown to promote the Biginelli cyclocondensation of aromatic as well as aliphatic aldehydes with ethyl acetoacetate and urea in a remarkably high enantioselectivity (ee ca. 94-99%).

Intramolecular O-H...O hydrogen-bond-mediated reversal in the partitioning of conformationally restricted triplet 1,4-biradicals and amplification of diastereodifferentiation in their lifetimes.

The photoreactivity and nanosecond transient phenomena have been investigated for a rationally designed set of ketones 4-9 in order to gain comprehensive insights concerning the influence of intramolecular hydrogen bonding on (i) the lifetimes of triplet 1,4-biradicals and (ii) the partitioning of the latter between cyclization and elimination. Comparisons of the photochemical results and lifetime data for the biradicals of ketones 6 versus 8 and 7 versus 9 revealed a remarkable influence of hydrogen bonding when superimposed upon steric factors: while 6 and 7 yielded cyclobutanols in poor yields, cyclization was found to be overwhelmingly predominant for 8-anti and moderately so for 9-anti, with a high stereoselectivity in the formation of cyclobutanols (>95% for 8-anti). The diastereochemistry in the case of 8 permitted the occurrence of fragmentation or cyclization almost exclusively (>90% cyclization for 8-anti and >75% elimination for 8-syn). Significantly, the intramolecular hydrogen bonding in the biradicals of 8 and 9 was found to reverse their partitioning between cyclization and elimination compared with the behavior of the biradicals of ketones 3; the ketones 8-anti and 9-anti underwent cyclization in benzene, predominantly leading to cyclobutanols with syn stereochemistry between the C2 and C3 substituents. In accordance with photoproduct profiles, an unprecedented approximately 2-fold difference in the lifetimes of the intermediate diastereomeric triplet biradicals of ketones 8 in nonpolar solvents (e.g., tau(syn) = 123 ns and tau(anti) = 235 ns in cyclohexane) was observed via nanosecond laser flash photolysis, while no such difference in lifetimes was found for the triplet biradicals of acetoxy ketones 9. The intriguing diastereodifferentiation in the lifetimes of the diastereomeric triplet 1,4-biradicals of 8 and the product profiles of ketones 6, 7, and 9 are best reconciled via a unified mechanistic picture in which superposition of steric factors over varying magnitudes of O-H...O hydrogen bonding selectively facilitates a particular pathway. In particular, the diastereodifferentiation in the photochemical outcomes for the diastereomers of ketone 8 and in the lifetimes of their triplet biradicals can be understood on the basis of rapid deactivation of the 8-syn triplet biradical via fragmentation and slow cyclization of the 8-anti triplet biradical from chair- and twist-boat-like hydrogen-bonded conformations, respectively. The photolysis in polar aprotic solvents such as DMSO and pyridine was found to reverse the chemoselectivity, yielding reactivity paralleling that of ketones 3, for which the steric factors between the C2 and C3 substituents control the photochemical outcome.