Synthesis of a polymer-supported oxazolidine aldehyde for asymmetric chemistry

An expedient synthesis of the polymer-supported aldehyde 3, as a Garner aldehyde equivalent, is described. Oxazolidine 3 may be obtained through preformation of aldehyde linker 4 in solution and loaded onto amine-terminating resin under peptide-coupling conditions, or alternatively via oxidation of polymer-bound alcohol 14. The integrity of the serine-derived stereocenter is maintained through all steps of the synthesis.     

Kinetic modeling of liquid-phase esterification of acetic acid with n-butanol using heterogeneous poly(o-methylene p-toluene sulfonic acid) as catalyst

Liquid-phase esterification of acetic acid with n-butanol to n-butyl acetate is studied in the presence of a polymeric catalyst, that is, poly(o-methylene p-toluene sulfonic acid). The performance of the proposed catalyst is compared with the other commercially available homogeneous and heterogeneous catalysts in terms of its activity. Experiments are conducted in an isothermal stirred batch reactor to study the effects of speed of agitation, temperature, and catalyst loading on the rate of reaction. A concentration-based pseudo-homogeneous (PH) kinetic model and activity-based kinetic models such as PH, Eley-Rideal (ER), and Langmuir-Hinselwood-Hougen-Watson (LHHW) models are developed. All the models considered in this study resulted in similar percentage deviation close to 4%. Further, kinetic models are validated through additional experiments, and it is observed that the simple concentration-based PH model is able to predict experimental data with least deviation compared to activity-based PH, ER, and LHHW models. The developed kinetic models are also tested using the Fisher-Snedecor test (F-test) and are found to be acceptable. By incorporating both modeling data and validation data, the overall absolute average deviations of different models are found to be concentration-based PH model 4.354%, activity-based PH model 5.006%, ER I model 5.189%, ER II model 5.403%, ER III model 5.437%, and LHHW model 6.104%, illustrating the superiority of the simple concentration-based PH model.     

Enhanced cooperative binding of oligonucleotides to form DNA duplexes mediated by metal ion chelation

Metal chelating iminodiacetic acid moieties were appended to abutting ends of two 9-mer oligonucleotides designed to hybridize contiguously on an 18-mer target. Chelation of 1 equivalent of Gd3+ cooperatively increases affinities of the oligonucleotides to the single stranded DNA target as evidenced by a 15 degrees C increase in Tm of the complex.     

Novel Ferrocene-Appended β-Ketoimines and Related BF2 Derivatives with Significant Aggregation-Induced Emission and Second-Order Nonlinear Optical Properties

A series of new β-ketoimines containing a ferrocene moiety and their BF₂ complexes have been synthesized and structurally characterized. The solvatochromism of the β-ketoimines was studied, putting in evidence a redshift with increasing solvent polarity. This positive solvatochromism can be attributed to a more polarized excited state compared with the ground state, due to intramolecular charge transfer (ICT) transitions. The β-ketoimines exhibited weak emission, attributable to the excited-state intramolecular proton transfer (ESIPT) phenomenon. This ESIPT effect is suppressed upon restriction of the keto-enamine tautomerism, induced upon addition of BF₃ ⋅ OEt₂, which afforded the related BF₂ complexes, characterized by an enhancement of the fluorescence through the ICT effect. Both the β-ketoimines and BF₂ complexes exhibited significant aggregation-induced emission behavior in mixtures of CH₃CN/H₂O, due to restriction of intramolecular rotation in the aggregated state. The frontier molecular orbital levels, ground- and excited-state dipole moments (μ_g and μ_e), and the origin of electronic absorption spectra were studied by time-dependent DFT calculations. The second-order nonlinear optical (NLO) properties were determined by the electric-field-induced second-harmonic generation technique. The μβ₁₉₀₇ values of the β-ketoimines increased upon the formation of the related BF₂ complexes, mainly due to an enhancement of the ground-state dipole moment. The results presented here reveal that some of these novel compounds are excellent multifunctional candidates for NLO and luminescence applications.     

PNA forms an i-motif

A C-rich PNA hexanucleotide, p(C5T), has been shown to form an i-motif by nanoelectrospray ionization mass spectrometry coupled with H/D exchange, to have thermal stability comparable with its DNA analogue, but to exist over a much narrower pH range.     

InCl3-catalyzed four-component reaction: a novel synthesis of N-carbazolyl dihydropyridines

We have developed a simple, efficient, and environmentally benign microwave-assisted InCl₃-catalyzed synthesis of N-carbazolyldihydropyridines via a four-component reaction of 3-amino-9-ethylcarbazole, malononitrile, aromatic aldehydes, and acetylenic esters. The use of microwave heating allowed for reduced reaction times and resulted in higher yields. This four-component reaction is atom-efficient, high-yielding, and applicable to a wide variety of four-component reactions.     

Structural Investigations on 4-Chloro-6-Phenyl-7,8,9,14-Tetrahydroquinolino [2′,3′:7,6]cyclohept[<Emphasis Type="Italic">b</Emphasis>]indoles

Abstract  

Several 4-chloro-6-phenyl-7,8,9,14-tetrahydroquinolino[2′,3′:7,6]cyclohept[b]indole derivatives were obtained in one pot synthesis reactions via acid catalyzed condensation and cyclization of 1-oxo-1,2,3,4,5,10-hexahydrocyclohept[b]indoles with 2-amino-5-chlorobenzophenone in glacial acetic acid. Parent 4-chloro-6-phenyl-7,8,9,14-tetrahydroquinolino[2′,3′:7,6]cyclohept[b]indole and the 10, 11, 12 and 13-methyl derivatives all crystallize in the triclinic space group P[`1] \overline{1} . The 11-methyl derivative crystallizes with Z′ = 2, the 10 and 12-methyl isomers cocrystallize as a solid solution of the two molecules, and the 13-methyl derivative and the parent compound each with Z′ = 1. The unit cell parameters for the four structures are a = 10.1826(8), b = 12.3918(7), c = 16.3825(8)?, α = 91.626(1), β = 95.718(1), γ = 94.966(1)° and V = 2,047.7(2) ?³ for the 11 methyl derivative; a = 10.168(2), b = 10.304(2), c = 10.610(2)?, α = 89.169(3), β = 87.774(3), γ = 63.726(2)° and V = 996.0(3) ?³ for the solid solution of the 10 and 12-methyl derivative, a = 9.0412(5), b = 10.4926(6), c = 10.9093(6)?, α = 94.482(1), β = 102.181(1), γ = 95.812(1)° and V = 1,001.13(10) ?³ for the 13-methyl compound, and a = 9.6463(6), b = 10.2395(6), c = 10.6062(6)?, α = 91.7263(8), β = 94.7200(8), γ = 114.0812(7)° and 950.85(10) ?³ for the unsubstituted parent compound. The molecular shape of the molecules is not affected by the substitution pattern and all molecules exhibit the same conformation with very similar geometries. Intermolecular interactions are limited to weak C–H···Cl hydrogen bonds, a small number of π···π stacking interactions and several C–H···π interactions, which, in combination with shape recognition, dominate the packing of the quinolinocyclohept[b]indoles.     

Dynamic covalent chemistry on self-templating PNA oligomers: formation of a bimolecular PNA quadruplex

The tetramolecular PNA quadruplex motif has been probed using a dynamic covalent chemistry (DCC) approach to create and characterize a bimolecular PNA quadruplex.