Preparation of optically active cyclohexenones: Chirons for the lipophilic moiety of flowery- and woody-like odorant ketones

Optically active 2,5,6,6- and 2,4,4,5-tetraalkylcyclohex-2-en-1-ones ((+)- 2a – d and (?)- 5a – d ), important building blocks for flowery- and woody-like odorants, have been prepared. Compounds (+)- 2a – d and (?)- 5a – d were obtained by ozonolysis of the corresponding cyclopentenic precursors, followed by intramolecular aldol condensation. Alternatively, enones (+)- 2a – d were reduced to the corresponding allylic alcohols ad converted to enones (-)- 5a – d via acidic isomerization and oxidation. ¹³C-NMR assignments are presented.     

The Potential of BioArena in the Study of the Formaldehydome

JPC – Journal of Planar Chromatography – Modern TLC - New results with BioArena as a complex separation and detection (evaluation) system support earlier observations that formaldehyde...     

On the origin of Turing instability

A reaction–diffusion system consisting of one, two or three chemical species and taking place in an arbitrary number of spatial dimensions cannot exhibit Turing instability if none of the reaction steps express cross‐inhibition. A corollary of this result – obtained by elementary calculations – underlines the importance of nonlinearity in the formation of stationary structures, a kind of self‐organization on a chemical basis. Relations to global stability of reaction–diffusion systems, and results on multispecies systems are also mentioned. The statements are not restricted to mass action type models. As a by‐product, the solution of a basic inverse problem of formal kinetics is also presented which extends a previous result by Hárs and Tóth (1981) to models with arbitrary – including rational – functions as reaction rates so often occurring, e.g., in enzyme kinetics.     

Syntheses of the Macrocyclic Spermine Alkaloids (±)‐Budmunchiamine A – C

The syntheses of four macrocyclic spermine alkaloids, (±)‐budmunchiamine A – C ( 1a – c ) and (±)‐budmunchiamine L4 ( 1 ), were accomplished by Michael addition of spermine to the α,β‐unsaturated esters 3a – d , followed by cyclization of the resulting α,ω‐tetraamino esters 4a – d with triethoxyantimony; N‐methylation of the amino lactams 6a – c yielded the budmunchiamines A – C ( 1a – c ).     

Thermal Reactions of Epoxyenones and Epoxydienes in the Ionone Series

On flash vaccum thermolysis at temperatures between 390 and 585°, the epoxyenones 1 – 9 and the epoxydienes 10 – 12 undergo various types of reactions involving C? C and/or C? O bond cleavage in the oxirane ring. Thus, the compounds 1 , 4 – 9 , 11 , and 12 were transformed to the divinyl ethers 13 , 20 , 21 , 24 , 25 , 29 , and 38 by a reversible [1,5] homosigmatropic H-shift. On thermolysis of the epoxides 1 – 12 , several products formed via carbonyl-ylide intermediates were also isolated. The extent of the formation of ylide products is clearly related to the conjugating ability of the functional groups neighboring the oxirane. Thus, the epoxides 3 , 5 , and 7 – 10 , bearing a C(3)?C(4) bond, a 5-oxo function, a 3,4-epoxy or a 3,4-methano group, preferentially underwent reactions via a carbonyl-ylide intermediate. As a further reaction pathway, the epoxides 1 – 12 undergo cleavage of the C–O bonds of the oxirane, which, however, is presumably an acid-catalyzed rather than a thermal reaction.     

Comparative Studies on the Analytical and Antioxidant Activities of the Medicinally Important Stem Bark of Holoptelea integrifolia

JPC – Journal of Planar Chromatography – Modern TLC - Holoptelea integrifolia (Sanskrit: chirivilva, Hindi: chilbil, family: Ulmaceae) is a large deciduous tree, growing up to 18 m...     

An HPTLC-AMD Method for Understanding the Metabolic Behavior of Microorganisms in the Presence of Mixed Carbon Sources. The Case of Bifidobacterium adolescentis MB 239

JPC – Journal of Planar Chromatography – Modern TLC - The intestinal microflora Bifidobacteria has been adapted to utilize, as a source of energy, complex carbohydrates that escape...     

Investigation of the Flavonoids in Croatian Propolis by Thin-Layer Chromatography

JPC – Journal of Planar Chromatography – Modern TLC - Flavonoids and phenolic acids with a variety of biological activity are considered to be the main compounds in propolis–a...     

Laser-Induced Hydrogen Radical Removal in UV MALDI-MS Allows for the Differentiation of Flavonoid Monoglycoside Isomers

Negative-ion matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass spectra and tandem mass spectra of flavonoid mono-O-glycosides showed the irregular signals that were 1 and/or 2 Da smaller than the parent deprotonated molecules ([M – H]^–) and the sugar-unit lost fragment ions ([M – Sugar – H]^–). The 1 and/or 2 Da mass shifts are generated with the removing of a neutral hydrogen radical (H*), and/or with the homolytic cleavage of the glycosidic bond, such as [M – H* – H]^–, [M – Sugar – H* – H]^–, and [M – Sugar – 2H* – H]^–. It was revealed that the hydrogen radical removes from the phenolic hydroxy groups on the flavonoids, not from the sugar moiety, because the flavonoid backbones themselves absorb the laser. The glycosyl positions depend on the extent of the hydrogen radical removals and that of the homolytic cleavage of the glycosidic bonds. Flavonoid mono-glycoside isomers were distinguished according to their TOF MS and tandem mass spectra.

New Approach for the Construction of the Coumarin Frame and Application in the Total Synthesis of Natural Products

A new synthetic approach is described for building the coumarin scaffold through the Lewis acid‐promoted cyclization of novel aryl 3‐(dimethylamino)prop‐2‐enoates 2a – 2f . The latter precursors were prepared via aminomethylenation of the corresponding aryl acetates 4a – 4f with the Bredereck reagent. This approach was used for the synthesis of biologically active natural compounds 1a – 1f , through a three‐step procedure starting from the corresponding phenols.     

The origin of the [M – 1]+ ion in the mass spectra of N,N-dialkylbenzamides. A reinvestigation of the mechanism

A reinvestigation of the mechanism of formation of the [M – 1]⁺ ion in a series of N,N-dialkylbenzamides suggests that previous mechanisms put forward to account for the formation of the [M – 1]⁺ ion are deficient. A new mechanism is proposed which accounts for the data observed previously, as well as our results for a series of N,N-dialkyl-2-chlorobenzamides, 4-substituted N,N-dimethylbenzamides and some related compounds. For the N,N-dialkyl-2-chlorobenzamides, comparison of the abundances of the [M – 1]⁺ ion with the [M – 35]⁺ ion suggests that a concurrent reaction is occurring, besides loss of the ortho aromatic hydrogen atom. A study of substituent effects on the intensity ratio [M – 1]⁺/[M]⁺ shows an upward concave plot of this against σ⁺, suggesting that two competing mechanisms occur for the formation of the [M – 1]⁺ ion.     

Application of SPE-HPLC-DAD and SPE-HPTLC-DAD to the Analysis of Pesticides in Lake Water

JPC – Journal of Planar Chromatography – Modern TLC - The objective of this paper is to present a new procedure for analysis of pesticides in water by use of solid-phase extraction...     

Molecular engineering of liquid crystal polymers by living polymerization. II. Living cationic polymerization of 11-[(4-cyano-4′-biphenyl) oxy] undecanyl vinyl ether and the mesomorphic behavior of the resulting polymers

The synthesis and living cationic polymerization of 11-[(4-cyano-4′-biphenyl)oxy]-undecanyl vinyl ether ( 6 – 11 ) are described. The mesomorphic phase behavior of poly( 6 – 11 ) with different degrees of polymerization was compared to that of 6 – 11 and of 11-[(4-cyano-4′-biphenyl) oxy] undecanyl ethyl ether ( 8 – 11 ) which is the model compound of the monomeric structural unit of poly( 6 – 11 ). 6 – 11 displays a monotropic S_A and a monotropic nematic mesophase while 8 – 11 an enantiotropic S_A mesophase. Poly( 6 – 11 ) with low degrees of polymerization exhibits an enantiotropic S_A mesophase. Poly( 6 – 8 ) with high degrees of polymerization displays an enantiotropic S_X (i. e., an unidentified smectic phase) and an enantiotropic S_C mesophase. These results demonstrate that the transformation of the nematic mesophase of the monomer into a smectic mesophase after polymerization, occurs at the level of monomeric structural unit.     

Design of Experiment Approach for the Development and Validation of a Stability-Indicating High-Performance Thin-Layer Chromatography Method for the Estimation of Metformin Hydrochloride and Ursodeoxycholic Acid in Pharmaceutical Dosage Form

JPC – Journal of Planar Chromatography – Modern TLC - In the present study, a design of experiment (DoE) approach was used to optimize chromatographic conditions for the development of...     

Determination of the Yields of meso-Tetraphenylporphyrins by Densitometry

JPC – Journal of Planar Chromatography – Modern TLC - Thin-layer chromatography with densitometric detection has been used to monitor different compounds produced by condensation of...     

HPTLC Method for Chemical Standardization of Sida Species and Estimation of the Alkaloid Ephedrine

JPC – Journal of Planar Chromatography – Modern TLC - The roots of Sida cordifolia, known as ‘Bala’ in the Ayurvedic system of medicine, are used to treat a variety of...     

Application of HPTLC to the Analysis of Horminone in Sphacele chamaedryoides (Balbis) Briq.

JPC – Journal of Planar Chromatography – Modern TLC - Royleanones are diterpene quinones ubiquitous in plants belonging to the Lamiaceae family. Sphacele chamaedryoides is a plant used...     

Compliance of Retention Data on Inorganic Oxide Adsorbents with the Solvation Parameter Model

JPC – Journal of Planar Chromatography – Modern TLC - The solvation parameter model has been used to characterize the retention properties of a varied group of solutes in silica gel...     

Erratum to: Analysis of the Yperite Block Fished up from the Baltic Sea

JPC – Journal of Planar Chromatography – Modern TLC -     

Intra-Specific Variation of Precocene I in the Wild Population of Ageratum conyzoides L. from the Western Himalayas

JPC – Journal of Planar Chromatography – Modern TLC -