Stereoisomeric probes

Nagahara, S., et ah (1992). Spin-labeled oligonucleotides site specifically labeled at the internucleotide linkage—Separation of stereoisomeric probes and EPR spectroscopical detection of hybrid formation in solution. Nucleosides Nucleotides 11, 889—901. 

Various aspects of structure activity relationships in 4,5-epoxymorphinans have been reviewed,(201,46 U467) and specific consideration has been given to quantum chemical studies with particular reference to polar group variation,(468) stereoisomeric ligands as receptor probes, 469 partition and distribution coefficients, 470 471 and antagonists. 145 ... 

A considerable number of chiral natural compounds has been investigated under photooxygenation conditions, mostly terpenoids and steroids. Of these compounds, ( + )-limonene (1) has been utilized as a popular probe for singlet oxygen in view of the fact that it gives a characteristic pattern of regio- and stereoisomeric allylic hydroperoxides which were reduced to the alcohols 2-4 as products22-24. 

By studying the migratory aptitudes of different substituted aryl groups it was possible to probe the electronic character of the -carbon. It was found that the migratory aptitude of 4-cyanophenyl versus phenyl is 14 1 (formation of 10 and 11) while that observed for 4-methoxyphenyl versus phenyl is 10-15 1 (formation of 12 and 13). The ratio of the stereoisomeric ketones was dependent on the length of the irradiation. Thus, it appears that the initial photoproduct has the two aryl groups in a trans relationship, the cw-isomer arising from further irradiation. ... 

The second step in the analysis involves evaluating coimectively identical nuclei for their possible chemical nonequivalency. This is done by a substitution test in which it is supposed that a hydrogen nucleus is replaced with a probe nucleus that can be distinguished from other nuclei in the same set. The stereoisomeric relationship between such substituted species is then assessed. 

Stereoisomerism and Connectivity 300 Total Synthesis of an Antibiotic with a Staggering Number of Stereocenters 303 The Descriptors for the Amino Acids Can Lead to Confusion 307 Chiral Shift Reagents 308 C2 Ligands in Asymmetric Synthesis 313 Enzymatic Reactions, Molecular Imprints, and Enantiotopic Discrimination 320 Biological Knots—DNA and Proteins 325 Polypropylene Structure and the Mass of the Universe 331 Controlling Polymer Tacticity—The Metallocenes 332 CD Used to Distinguish a-Helices from [3-Sheets 335 Creating Chiral Phosphates for Use as Mechanistic Probes 335... 

The most studied reaction in liquid crystalline solvents is the NorishA ang type II reaction of alkyl and aryl alkyl ketones (Scheme 1). This reaction has been used extensively, mainly by Weiss and coworkers, to probe the properties of liquid crystals, since the distribution of fragmentation and cyclization products and the distribution of stereoisomeric trans- and cw-cyclobutanols are sensitive to the dynamics and conformational equilibria of the 1,4-biradical intermediate produced in the primary photochemical decay process of the ketone [352, 353, 360, 368-376]. Generally, in liquid crystals there is a preference for fragmentation over cyclization of the biradical, due to a preference for the biradical conformer that can only react by fragmentation. When cy-... 

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