Sugar amino acids and related molecules: Some recent developments

To meet the growing demands for the development of new molecular entities for discovering new drugs and materials, organic chemists have started working on many new concepts that can help to assimilate knowledge-based structural diversities more efficiently than ever before. Emulating the basic principles followed by Nature to build its vast repertoire of biomolecules, organic chemists are developing many novel multifunctional building blocks and using them to create ‘nature-like’ and yet unnatural organic molecules. Sugar amino acids constitute an important class of such polyfunctional scaffolds where the carboxyl, amino and hydroxyl termini provide an excellent opportunity to organic chemists to create structural diversities akin to Nature’s molecular arsenal. In recent years, sugar amino acids have been used extensively in the area of peptidomimetic studies. Advances made in the area of combinatorial chemistry can provide the necessary technological support for rapid compilations of sugar amino acidbased libraries exploiting the diversities of their carbohydrate frameworks and well-developed solid-phase peptide synthesis methods. This perspective article chronicles some of the recent applications of various sugar amino acids, furan amino acids, pyrrole amino acids etc. and many other related building blocks in wide-ranging peptidomimetic studies     

Iodine-catalyzed efficient synthesis of azaarene substituted 3-hydroxy-2-oxindole derivatives through sp3 C–H functionalization

Iodine-catalyzed benzylic sp³ C–H bond functionalization of lutidines or picolines to isatins is described. This synthetic method provides a rapid entry towards biologically interesting 3-azaarene substituted 3-hydroxy-2-oxindole derivatives.     

A highly efficient regioselective one-pot synthesis of 2,3,6-trisubstituted pyridines and 2,7,7-trisubstituted tetrahydroquinolin-5-ones using K5CoW12O40·3H2O as a heterogeneous recyclable catalyst

A systematic investigation into the regioselective one-pot, three-component condensation of enaminones 1a–g, β-dicarbonyl compounds 2a–c, and ammonium acetate in the presence of a catalytic amount of K₅CoW₁₂O₄₀·3H₂O (0.01 equiv or 1.0 mol %) under solvent free conditions, as well as in refluxing isopropanol, has been reported. The reaction was highly efficient to produce 2,3,6-trisubstituted pyridines 3a–g, 4a–g, and novel 2,7,7-trisubstituted-5,6,7,8-tetrahydroquinoline-5-ones 5a–g in excellent yields. The present procedure offers advantages of short reaction time, simple work-up, and the catalyst exhibited remarkable reusable activity.     

Three-dimensional mesoporous gallosilicate with Pm3n symmetry and its unusual catalytic performances

Three-dimensional, mesoporous-cage-type, GaSBA-1 materials with different n(Si)/n(Ga) ratios have been successfully prepared for the first time by using a low hydrochloric acid to silicon (n(HCl)/n(Si)) molar ratio in the synthesis gel by templating with cetyltriethylammonium bromide as the structure-directing agent in a highly acidic medium. The obtained materials have been unambiguously characterized in detail by several sophisticated techniques including X-ray diffraction (XRD), N(2) adsorption, high-resolution transmission electron microscopy, high-resolution scanning electron microscopy, energy dispersive spectroscopy, elemental mapping, and (29)Si magic-angle-spinning NMR spectroscopy. XRD and nitrogen adsorption results reveal that the structures of the GaSBA-1 materials resemble that of SBA-1, which possesses a cubic, three-dimensional, cage-type structure with open windows. In addition, the specific surface area and the specific pore volume of the GaSBA-1 materials are much higher than those of the SBA-1 silica, which are very important for the catalytic applications. The amount of Ga cation in the SBA-1 silica framework has been found to play a critical role in controlling the morphology and the pore diameter of the materials. Finally, the catalytic activity in the tert-butylation of phenol with tert-butanol as the alkylating agent has been investigated and the results are compared with those of other mesoporous catalysts such as AlMCM-41, FeMCM-41, FeAl-MCM-41, and FeSBA-1. Moreover, the effect of various reaction parameters such as the reaction temperature, reactant feed ratio, and time-on-stream on the phenol conversion in the tert-butylation of phenol over GaSBA-1 catalysts has been demonstrated. Among the catalysts examined, GaSBA-1(17), in which the number in the parenthesis denotes the n(Si)/n(Ga) ratio, showed remarkable activity with a high conversion of phenol and selectivity to 4-tert-butylphenol; it was found to be superior over other mesoporous catalysts used in the study.     

Liquid Phase Acylation of Alcohols with Acetic Acid Over Zeolites

The liquid phase acylation of primary and secondary alcohols were carried out with acetic acid in the presence of zeolites. LaY zeolite is found to be the best catalyst.     

Study of optical and transport properties of K2CuCl4 · 2H2O single crystal

Optical absorption, transport properties and EPR of K₂CuCl₄ · 2H₂O single crystals have been studied. The optical absorption in UV, and visible region are characterized by a charge transfer band, and in the near infrared region at 3998, 4336, and 4480 cm⁻¹ are attributed to transitions between the stark levels of copper(II) ion in an extended octahedral crystal field. An anisotrophic ‘g’ value was observed with g_∥ = 2.12 and g_∥ = 2.24 by EPR method. The spin orbit coupling constant is found to be 500 cm₋₁. D.C. electrical conductivity measurements with temperature reveal an anisotropy characteristic of a two-dimensional layered structure and exhibit a first order irreversible structural phase-transition at 377 K, i.e. from tetragonal to monoclinic crystal system. X-ray diffraction studies and density calculations from the crystal structure data in both the phases suggest that the first order irreversible transition occurs following the loss of the two water molecules of hydration.     

Conformational studies of the linear homooligomers of a glucose-derived furanoid sugar amino acid

Conformational analysis of the linear tetramer of the glucose-derived furanoid sugar amino acid 1 by NMR and constrained molecular dynamics studies revealed that the fully protected tetramer 2a has a well-defined structure in CDCl₃ with repeating β-turns, each involving a 10-membered ring structure with intramolecular hydrogen bonds between NH_i → CO_i−2. Its deprotected versions 2b and 2c showed aggregation in organic solvents with structures similar to that of 2a.