SYNTHESIS AND CONFORMATIONAL STUDIES OF A NUMBER OF SATURATED BICYCLIC SIX-MEMBERED RING PHOSPHITES

Abstract

An ¹H NMR study of the conformation of the dioxaphosphorinane ring of a number of diastereoisomeric bicyclic saturated six-membered ring phosphites (3ab-10ab) has been performed. The dioxaphosphorinane ring of these phosphites is transannelated with a tetrahydrofuran, cyclopen-tane, tetrahydropyran or cyclohexane ring. The substituent on the phosphorus atom is a methoxy or phenoxy group. It is shown that the cis isomers 3a-10a prefer a chair conformation of the dioxaphosphorinane ring, independent of the substituent on the phosphorus atom and of the nature of the transannelated ring. In contrast, for the trans isomers 3b-10b a twist rather than a chair conformation of the dioxaphosphorinane ring is preferred. The fraction of the twist conformer in the trans isomers is mainly determined by the substituent on phosphorus. The size and composition of the transannelated ring are relatively unimportant in this respect. For both cis and trans isomers the preferred geometry is solvent-independent. The measured ^3JPOCH couplings of the cis isomers 3a-10a are used to formulate an expression for the dependence of such couplings upon dihedral angles in bicyclic phosphites.     

Potentiometric Liquid Membrane Sensors That Discriminate Linear Homologs and Geometrical/Positional Isomers of Dicarboxylates

Abstract

Potentiometric discrimination of series of linear homologs (4-7), geometrical isomers (8,9), and positional isomers (10-12) of dicarboxylate guests by a liquid membrane sensor containing Iipophiiic macrocyclic polyamine 1 as a sensory element is described. the pH conditions were carefully set so that the potentiometric response to the dianionic forms of the guests could be specifically observed. Whereas only small discrimination was observed for the flexible linear homologs (4-7), marked discrimination was observed, for the geometrical isomers (8,9) and positional isomers (10-12) having rigid structures. the selectivities of the potentiometric response were found to correlate well with the reported selectivities of host-guest complexation in water displayed by macrocyclic polyamines having the structures related to 1.     

The HSnPh3 Free Radical Mediated Cyclization of 4,9-Dioxa-1,6-dodecadien-11-yne

We report the triphenyltin hydride radical mediated cyclization of 4,9-dioxa-1,6-dodecadien-11-yne 2. The reaction proceeds under very mild conditions and in good chemical yield (59%), giving a mixture of products 5 (mixture of isomers in a 1:2 ratio) and 6 (mixture of isomers in a 1:3 ratio).     

Molecular Recognition of Dihydroxybenzenes by Macrocyclic Polyamines in Langmuir Films and PVC Matrix

Lipophilic polyamines 1 and 2 form stable monolayers at the air–water interface. The shapes of the isotherms show a strong pH-dependence due to different stages of polyamine protonation. For all isomers of dihydroxybenzene the strong interaction with 1 and 2 can be observed at pH 4, 6, and 8. Polyamines 1and 2 in the PVC liquid membrane act as the sensory element of the potentiometric sensor for selective determination of catechol in the presence of other isomers of dihydroxybenzenes.     

Theoretical study on structures and stability of HC2P isomers

 The structures and isomerization pathways of various HC₂P isomers in both singlet and triplet states are investigated at the B3LYP/6-311G(d,p), QCISD/6-311G(d,p) (for isomers only) and single-point CCSD(T)/6-311G(d,p)//B3LYP/6-311G(d,p) levels. At the CCSD(T)/6-311G(d,p)//B3LYP/6-311G(d,p) level, the lowest-lying isomer is a linear HCCP structure ³ 1 in the ³∑⁻ state. The second low-lying isomer has a CPC ring with exocyclic CH bonding ¹ 5 in a singlet state at 10.5 kcal/mol. The following third and fourth low-lying isomers are a singlet bent HCCP structure ¹ 1 at 20.9 kcal/mol and a bent singlet HPCC structure ¹ 3 at 35.8 kcal/mol, respectively. Investigation of the HC₂P potential-energy surface indicates that in addition to the experimentally known isomer ³ 1, the other isomers ¹ 1, ¹ 3 and ¹ 5 also have considerable kinetic stability and may thus be observable. However, the singlet and triplet bent isomers HCPC ¹ 2 and ³ 2 as well as the triplet bent isomer HPCC ³ 3 are not only high-lying but are also kinetically unstable, in sharp contrast to the situation of the analogous HCNC and HNCC species that are both kinetically stable and that have been observed experimentally. Furthermore, the reactivity of various HC₂P isomers towards oxygen atoms is briefly discussed. The results presented here may be useful for future identification of the completely unknown yet kinetically stable HC₂P isomers ¹ 1, ¹ 3 and ¹ 5 either in the laboratory or in interstellar space. Received: 5 November 2000 / Accepted: 25 November 2001 / Published online: 8 April 2002     

Ab initio Molecular Orbital Study of Dithiopyrrolopyrrole and Its Structural Isomers

Abstract

Ab initio molecular orbital calculations at HF/6-31G*, HF/6-311+G**, and B3LYP/6-311+G** levels of theory for geometry optimization are reported for 1,4-dithiopyrrolo[3,4-c]pyrrole (DtPP, 1) and its twelve structural isomers (2–13). Compounds 1–3 include 2 C─CH and 2 NH─CS structural units. Structural isomers 4–7 include 2 C–CH units, together with 2 NH and 2 C–S groups. Isomers 8–13 possess 2 CH, 2 C, 2 NH, and 2 C─S fragments. According to these calculations, isomers 2, 4, and 8, are more stable than 1.     

Synthesis of a phloroacetophenon[4]arene consisting of four isomers via the one-pot,acid-catalysed condensation of phloroacetophenone with benzaldehyde

A phloroacetophenon[4]arene (3) consisting of four isomers was synthesised for the first time via the condensation of phloroacetophenone and benzaldehyde in a one-pot reaction with refluxing toluene in the presence of catalytic amounts of TsOH·H₂O for a maximum yield of 64%. The conformational elucidation of four isomers (3a–d) by ¹H NMR spectroscopy and X-ray crystal structure analysis showed them to be cone, partial cone, 1,3-alternate and 1,2-alternate types of conformations, respectively.     

The Determination of Optical Isomers of 2-[3-(2-Chloro-Penoxyphenyl)]-Propionic Acid in Rat Plasma by High Performance Liquid Chromatography

Abstract

The optical isomers of dl-2-[3-(2-chlorophenoxy-phenyl)]-propionic acid in rat plasma is converted to the diastereomeric derivatives with (+)-2-aminobutane and then determined by high performance liquid chromatography using a Nucleosil NH₂ (10 μm) column and cyclohexane-ethyl acetate (5:1) as a mobile phase.

The time course of the optical isomers of this drug in rat plasma after oral administration was measured.

The proposed method is specific and reproducible for the determination of the optical isomers of this drug.     

6,8-di-C-glycosyl flavones with β-furanoarabinose from Scutellaria baicalensis and their anti-inflammatory activities

Two flavone di-C-glycosides, a pair of isomers, were isolated from Scutellaria baicalensis. The structures of compounds 1 and 2 were elucidated by means of physical data, including 1D and 2D NMR and HR-ESI-MS. Supporting theoretical calculations of the compound conformational landscape has also been conducted for geometry optimization. This is the first report of the natural occurrence of β-furanoarabinoside. In addition, the effects of compounds 1 and 2 on NO, pro-inflammatory cytokines, PGE2 and COX-2 levels were measured in lipopolysaccharide (LPS)-stimulated RAW264.7 macrophage cells. The pair of isomers exhibited significant inhibitory effects on inflammation.     

Excess Molar Enthalpies for Isomeric Chlorobutanes with Isomeric Butanols

Abstract

Excess molar enthalpies for mixtures of each of the isomers of chlorobutane with each of the isomers of butanol were determined at the temperature 298.15 K and atmospheric pressure. Excess molar enthalpies are positive for all the mixtures. The results are discussed in terms of molecular interactions.     

ELECTROCHEMICAL ISOMERIZATION OF SULFINE

Abstract

Electrochemical isomerization of 1-phenyl-2, 2-dimethylpropane-1-thione S-oxide (phenyl-t-butylsulfine, E and Z form, 1a and 1b) was studied. Anodic isomerization of 1a gave the two isomers of the sulfine only, but cathodic reductive isomerization of 1a gave pivalophenone and 1-cyano-2-phenyl-3, 3-dimethyl-1-butene in addition to the E and Z isomers. This is the first example of an electrochemical reaction of a sulfine.     

The Separation of 2-, 3- and 4-Cyclopentylphenol by Thin-Layer Chromatography

Abstract

A TLC system is described for the resolution of the three positional isomers of cyclopentylphenol. Quantitation of the 3- and 4- isomers in 2-cyclopentylphenol at a sensitivity of 0.1% may be achieved.     

CHEMISTRY OF CIS- AND TRANS-9-PHENYLSELENOXANTHENE-N-ARYLSULFONYLSELENILIMINES1

Abstract

cis- and trans-9-Phenylselenoxanthene-N-(arylsulfonyl)selenilimines were synthesized and isolated. Their stereochemistry was ascertained from the NMR spectra. Cis isomers reacted with chloramine-T or -B by an S_N 2 type substitution to form trans isomers, but the reverse reaction did not take place. When trans isomers were refluxed in toluene they underwent intermolecular 1,4 rearrangement to give 9-arylsulfonamido-9-phenylselenoxanthene. The cis isomers neither rearranged nor isomerized. On treatment with DABCO, both isomers rearranged intermolecularly to 9-(N-arylsulfonamido)selenoxanthenes at room temperature. Hydrolysis of both isomers yielded trans-9-phenylselenoxanthene 10-oxide. Reactions with p-methoxyphenylmagnesium bromide or methylmagnesium iodide afforded 9-(p-methoxyphenyl)-9-phenylselenoxanthene or 9-phenylselenoxanthene as a main product, respectively.     

Separation of Optical Isomers as Diastereomeric Derivatives by High Performance Liquid Chromatography

Abstract

Optical isomers occuring widely in nature, display different biochemical and pharmacological effects against their enantiomeric isomers. Therefore, it is very important to distinguish or resolve enantiomers, especially in biochemical and pharmaceutical applications.     

Synthesis and properties of optically active 1,3-diols and their derivatives as chiral dopants for ferroelectric liquid crystals

Abstract

New chiral dopants β-hydroxy ketones 1, 1,3-diols 2, 1,3-dioxanes 3 and 1,3-dioxan-2-ones 4 were designed and synthesized. Reaction of (R)-1,2-epoxyoctane with carbanions derived from 2-(4-substituted phenyl)-1,3-dithianes followed by hydrolysis of the resulting hydroxy dithianes afforded 1. Reduction of 1 gave the diols 2, which yielded 3 upon acetalization and 4 upon carbonation. The syn isomers of 2, 3, and 4 exhibited larger spontaneous polarizations, when applied as chiral dopants, than the anti isomers or hydroxy ketones 1.     

Preparation and Characterization of 61,6n-DI-O-(α-D-Galactopyranosyl)Cyclomaltooctaoses

ABSTRACT

Four positional isomers of 6¹,6ⁿ-di-O-(D-galactopyranosyl)cyclomaltooctaoses (cG₈s, γ-cyclodextrins) (n = 2?5) were chemically synthesized using the trichloroacetimidate method. The desired compounds having two α-(1→6)-linkages were isolated from a mixture of configurational isomers by HPLC, and their structures were confirmed by ¹³C NMR spectroscopy and FAB-high resolution mass spectra (HRMS). The elution behavior of their four positional isomers on an ODS column by HPLC is discussed.     

Isolation of Gram Quantities of Configurational Isomers of Cyclic Nitrosamines by Preparative Liquid Chromatography

Abstract

Substituted cyclic nitrosamines, e.g., 2,6-dimethyl-N-nitrosomorpholine and 3,5-dimethyl-N-nitrosopiperidine are separable into their component configurational isomers by preparative hplc. Gram quantities of the individual isomers sufficient for animal testing were obtained. The identification of contaminants in commercial 2,6-dimethylmorpholine of purported 99% is discussed.     

Stereoselective Synthesis of the Optical Isomers of a New Muscarinic Receptor Antagonist,HL‐031120

We present here a practical stereoselective synthetic method to produce enantiopure isomers of a new muscarinic receptor antagonist, HL‐031120 (3‐quinuclidinyl‐2′‐cyclopentyl‐2′‐hydroxy‐2′‐phenylacetate, I). Four optical isomers were effectively by stereoselective synthesized using pivaldehyde as steric hindrance agent from the chiral starting material, (S) or (R)‐mandelic acid. The isomers were obtained with 70–76% yields in 98–99% e.e.     

High Performance Liquid Chromatography of Uroporphyrin Isomers

Abstract

The separation of uroporphyrin I and III isomers by reversed-phase high performance liquid chromatography on ODS-Hypersil with ammonium acetate buffer-acetonitrile solvent systems is described. The effects of buffer concentration, pH, organic modifier proportion and different organic modifiers on the resolution are studied. The optimum conditions for the separation were 12–13% acetonitrile in 1M ammonium acetate buffer pH 5.10–5.20. The method also separated uroporphyrin I and III from the II isomers but the resolution of uroporphyrin III and IV isomers was not achieved.     

Theoretical study on structures and stability of triplet SiC<Subscript>3</Subscript>O isomers

Various levels of calculations are carried out~for exploring the potential energy surface (PES) of triplet SiC₃O, a molecule of potential interest in interstellar chemistry. A total of 38 isomers are located on the PES including chain-like, cyclic and cage-like structures, which are connected by 87 interconversion transition states at the DFT/B3LYP/6-311G(d) level. The structures of the most relevant isomers and transition states are further optimized at the QCISD/6-311G(d) level followed by CCSD(T)/6-311+G(2df) single-point energy calculations. At the QCISD level, the lowest lying isomer is a linear SiCCCO 1 (0.0 kcal/mol) with the ³ ∑ electronic state, which possesses great kinetic stability of 59.5 kcal/mol and predominant resonant structure . In addition, the bent isomers CSiCCO 2 (68.3 kcal/mol) and OSiCCC 5 (60.1 kcal/mol) with considerable kinetic stability are also predicted to be candidates for future experimental and astrophysical detection. The bond natures and possible formation pathways in interstellar space of the three stable isomers are discussed. The predicted structures and spectroscopic properties for the relevant isomers are expected to be informative for the identification of SiC₃O and even larger SiC _n O species in laboratory and interstellar medium. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.