ZrCl4-Catalyzed C-O Bond to C-N Bond Formation: Synthesis of 1,2,3-Triazoles and Their Biological Evaluation

A simple and efficient protocol was developed for the synthesis of aryl azides directly from aryl carbinols using ZrCl₄ as a Lewis acid catalyst. The azides were converted to novel triazoles under click reaction conditions, which were evaluated for their antimicrobial activity against various strains.     

Fatty Acid Profiling During Microbial Lipid Production Under Varying pO2 and Impeller Tip Speeds

The fatty acid profile study was undertaken to study the effect of impeller tip speed-associated shear stress and dissolved oxygen saturation (DO) on the fatty acid composition variation and on total lipid content of the cells. The study was undertaken in a 5-l stirred tank bioreactor using Mucor sp. RRL001. To study the interaction of parameters and their effects, a central composite design was used. The fatty acid profiling during the course of study suggested that oleic acid and palmitic acid were two major components with their composition varying between 34-47% and 29-39.1%, respectively, of the total lipid content. The GLA content varied between 3% and 9% of the total lipid. The lipid profile study also revealed the presence of a minor amount of fatty acids of chain length C:12, C:20, C:22, and C:24. The modeling of lipid accumulation suggested that it follows a quadratic model with both impeller tip speed (p = 0.0166) and dissolved oxygen concentration (p = 0.0098) following the quadratic order of effect. The fermenter run based on the optimum production zone in response surface plot resulted in the maximum 4.8 g l(-1) lipid compared with the model-predicted value of 4.49 g l(-1). The present study suggests that dissolved oxygen saturation is a more significant contributor to total lipid accumulation. However, the study also suggests that the fatty acid profile of fungal lipid is not directly associated with the shear stress or oxygen availability in Mucor sp. RRL001.     

Noncovalent interaction of 5,10,15,20-tetrakis(4-N-methylpyridyl)porphyrin with Cucurbit[7]uril: a supramolecular architecture

Noncovalent interaction of two water-soluble synthetic macromolecules, Cucurbit[7]uril (CB7) and 5,10,15,20-tetrakis(4- N-methylpyridyl)porphyrin (TMPyP), has been studied from the viewpoint of organizing them through supramolecular interactions and thereby modulating their functional activities. Steady-state and time-resolved fluorescence measurements along with NMR results establish that CB7 crowns the N-methylpyridyl group of the TMPyP in a 1:4 stoichiometry. The overall binding constant was evaluated to be approximately 4.5 x 10 (19) M (-4). The high binding affinity, promoting a stable and extendable molecular assembly in aqueous solution, could open new frontiers in the design and synthesis of higher-order supramolecular structures with photofunctional moieties and project their utility in therapeutic applications.     

Interaction of a new surface sensitive probe compound with anionic surfactants of varying hydrophobic chain length

The amide derivative of a bis-phenylethynyl compound meta linked to 2,6-pyridine (BPEAP) poses inherent equilibrium between its neutral and zwitterionic forms in the excited state. BPEAP has been found to bind to the surface of anionic micelles instead of penetrating inside. This phenomenon has been exploited to attempt controlling the process of equilibrium using sodium dodecyl sulfate (SDS) at its pre-micellar and near-micellar aggregation concentrations. The anionic surfactant has been found to alter the equilibrium between the said forms of BPEAP depending on its concentration in solution. The process has been further verified by using sodium decyl sulfate (SDeS), which has smaller hydrophobic chain length than SDS as also varies in the critical micellar concentration (CMC) and aggregation number. The binding constant of the probe to the surfactant aggregates varies depending on the extent of surface available to the fluorophore for attachment.     

A concise approach towards the synthesis of WS75624 A and WS75624 B via the cross-metathesis of vinyl-functionalized thiazoles

Synthetic approach towards precursors of WS75624 A and WS75624 B, two potent endothelin converting enzyme (ECE) inhibitors and potential antihypertensive agents, is reported featuring a key cross-metathesis between a vinyl-functionalized thiazole and a terminal olefin. As the two natural products only differ by the nature of their hydroxyalkyl side-chain, our convergent strategy enable the synthesis of key intermediates of both molecules in a limited amount of steps.     

Modulation of Excited‐State Proton Transfer of 2‐(2′‐Hydroxyphenyl)benzimidazole in a Macrocyclic Cucurbit[7]uril Host Cavity: Dual Emission Behavior and pKa Shift

The effect of the macrocyclic host, cucurbit[7]uril (CB7), on the photophysical properties of the 2‐(2′‐hydroxyphenyl)benzimidazole (HPBI) dye have been investigated in aqueous solution by using ground‐state absorption and steady‐state and time‐resolved fluorescence measurements. All three prototropic forms of the dye (cationic, neutral, and anionic) form inclusion complexes with CB7, with the largest binding constant found for the cationic form (K≈2.4×10⁶ M ^?1). At pH≈4, the appearance of a blue emission band upon excitation of the HPBI cation in the presence of CB7 indicates that encapsulation into the CB7 cavity retards the deprotonation process of the excited cation, and hence reduces its subsequent conversion to the keto form. Excitation of the neutral form (pH≈8.5), however, leads to an increase in the keto form fluorescence, indicating an enhanced excited‐state intramolecular proton‐transfer process for the encapsulated dye. In both the ground and excited states, the two pK_a values of the HPBI dye show upward shifts in the presence of CB7. The prototropic equilibrium of the CB7‐complexed dye is represented by a six‐state model, and the pH‐dependent changes in the binding constants have been analyzed accordingly. It has been observed that the calculated pK_a values using this six‐state model match well with the values obtained experimentally. The changes in the pK_a values in the presence of CB7 have been corroborated with the modulation of the proton‐transfer process of the dye within the host cavity.     

Highly conductive and transparent laser ablated nanostructured Al: ZnO thin films

Al doped ZnO thin films are prepared by pulsed laser deposition on quartz substrate at substrate temperature 873 K under a background oxygen pressure of 0.02 mbar. The films are systematically analyzed using X-ray diffraction, atomic force microscopy, micro-Raman spectroscopy, UV-vis spectroscopy, photoluminescence spectroscopy, z-scan and temperature-dependent electrical resistivity measurements in the temperature range 70-300 K. XRD patterns show that all the films are well crystallized with hexagonal wurtzite structure with preferred orientation along (0 0 2) plane. Particle size calculations based on XRD analysis show that all the films are nanocrystalline in nature with the size of the quantum dots ranging from 8 to 17 nm. The presence of high frequency E₂ mode and longitudinal optical A₁ (LO) modes in the Raman spectra suggest a hexagonal wurtzite structure for the films. AFM analysis reveals the agglomerated growth mode in the doped films and it reduces the nucleation barrier of ZnO by Al doping. The 1% Al doped ZnO film presents high transmittance of ∼75% in the visible and near infrared region and low dc electrical resistivity of 5.94 × 10⁻⁶ Ω m. PL spectra show emissions corresponding to the near band edge (NBE) ultra violet emission and deep level emission in the visible region. Nonlinear optical measurements using the z-scan technique shows optical limiting behavior for the 5% Al doped ZnO film.     

Formal synthesis of Pellasoren – A

A convergent and highly stereoselective formal synthesis of Pellasoren – A is described. The salient features of the synthesis are the utilization of enzymatic desymmetrization, Crimmin’s non-Evans syn aldol, Lindlar’s and Wittig reaction.     

An easy access to gamma-lactone-fused cyclopentanoids

The tricyclic alpha-keto hemiacetals 3a,b and 8a-d obtained from ruthenium-catalyzed oxidation of tetrahalonorbornyl derivatives possessing a pendant hydroxymethyl group were cleaved using Pb(OAc)(4) or alkaline H(2)O(2) to give gamma-lactone-fused cyclopentane derivatives 5a,b and 9a-d. The alpha-keto hemiacetal 3b has also been elaborated to spiroepoxide derivative 25. The stable hydrate 4 formed from ruthenium-catalyzed oxidation of acrolein adduct 10 furnished an intramolecular hemiacetal 11 upon cleavage with Pb(OAc)(4). The alpha-halo ester moiety in 5a was transformed smoothly in a highly regio- and stereoselective manner to alpha-hydroxy esters through a lactone-assisted intermediate to furnish 18.     

Acid Catalyzed Multicomponent Reaction to Access Functionalized N-Benzhydryl Amides: A Tandem Ritter Reaction

Acid catalyzed multicomponent reaction (MCR) for the synthesis of N-benzhydryl amide derivatives from aldehydes, N,N-disubstituted arylamines and nitriles is reported. The reaction is compatible with electronically differentiating aryl/heteroaryl aldehydes/acetals, different nucleophiles (cyclic and acyclic N,N-disubstituted arylamines,β-naphthols, 1,3 dicarbonyl, 1,3,5-trimethoxy benzene), alkyl nitriles, aryl/heteroaryl nitriles in catalytic TFA/TfOH through tandem Ritter reaction. The one-pot MCR with broad substrate scope generated a wide variety of sterically hindered N-substituted amides and is successfully applied for the synthesis of isoindolinone.