Nitrophenyl bonded phase

The most popular bonded phases for normal-phase chromatography are aminopropyl, cyanopropyl, and diol. Other polar bonded phases, including bonded ion exchangers, can be used as well. Another, less commonly used polar bonded phase is the nitrophenyl bonded phase. The retentivity of the aminopropyl and the diol phase is comparable to that of the oxides. Cyanopropyl and nitrophenyl phases have a smaller retentivity. Although differences in selectivity can be found for the different bonded phases, they are typically small. Thus the elution order of most members in a family of related compounds is largely preserved from packing to packing. For example, in a study of the elution behavior of steroids on silica, and aminopropyl and cyanopropyl bonded phases, an inversion in elution order was ol rved only for two to four pairs out of IS analytes (16). 

In order to accomplish the desired separation, the selection of appropriate stationary phase and eluent system is imperative. The most commonly used stationary phases in normal-phase chromatography are either (a) inorganic adsorbents such as silica and alumina or (b) moderately polar chemically bonded phases having functional groups such as aminopropyl, cyanopropyl, nitrophenyl, and diol that are chemically bonded on the silica gel support [16]. Other phases that are designed for particular types of analytes have also... 

Polar bonded phases for normal-phase separations have recently gained popularity. These include the dihydroxypropyl propyl ether (diol), aminopropyl, cyanopropyl, and nitrophenyl bonded silicas. These phases are advantageous to silica because they are less active and, yet, produce similar interactions, require shorter equilibration times, and are influenced less by the water content of the mobile phase. The retention of most analytes upon the diol and amino phases is similar to that of the parent silica and alumnia, whereas the cyanopropyl and nitrophenyl phases generally show less retention. 

More successful are solid-phase methods in which the linear precursor is attached through a labile ester bond (e.g. o-nitrophenyl) to a polymer. 

A high yielding synthesis of anthranil from 2-nitrobenZaldehyde makes use of zinc and allyl bromide as the reducing agent. The method has also been used for the preparation of 3-substituted anthranils from 2-nitrophenyl ketones <99H(51)1921>. A solid phase synthesis of 3-aminobenzisoxazoles 15 is based on the displacement of fluoride from 2-fluorobenzonitriles by the Kaiser oxime resin and subsequent hydrolysis of the C=N bond <99JOC4547>. A synthesis of 3-(2-dialkylaminoethyl)benzisoxazoles from oximes of 2-hydroxyphenyl ketones has also been described <99H(51)2139>. ... 

Solid-phase techniques can be applied to the N-activated esters.16 In the activated ester method, 4-nitrophenyl, 12 21-27 2,4-dinitrophenyl, 614 28 2,4,5-trichlorophenyl, 29 and penta-fluorophenyl 8 esters can be used, the amide bonds being formed with aminolytic release of the corresponding phenol (Scheme 4). For example, the use of pentafluorophenyl esters in the synthesis of pure azapeptides (named azatides for the first time) proved to be advantageous. 8 ... 

An approach to the stereospecific, solid phase synthesis of methylphosphonates has been developed whereby an appropriately protected, stereochemically pure J p or 5p 3 -(p-nitrophenyl methylphosphonate) ester (65) is coupled to an activated S -hydroxyl group of a support-bound nucleoside. The 5 -hydroxyl group is activated by the addition of a Grignard reagent in pyridine and the release of p-nitrophenol is accompanied by stereospecific intemucleotide bond... 

Alternatively, Schultz and coworkers [59] have proposed an approach related to that of Burgess which utilizes azido 4-nitrophenyl carbamates 98 as activated monomers. Carbamates 98 were prepared in four steps from alcohol 95. Mesylation of 95 followed by azide displacement afforded the A-Boc-protected azide in high yield (80-90%). Boc deprotection and treatment of the resulting free amine with / -nitrophenyl chloroformate in the presence of pyridine in THF provided 98 (50-90% for the two steps). Solid-phase urea bond formation was performed on a Rink amide resin by coupling 98 (5 equiv.) in CH2CI2 in the presence of DIEA (7 equiv.) for 4 h at room temperature. Support-bound azide 99 was reduced in less than 2 h using... 

New stationary phases were synthesized by binding substituted aromatic groups to silica. Their separation capacity was determined by using various native CDs and CD dal-vatives. The mobile phase for the gradient elution consisted of a mixture of MeCN, H2O, and formic acid. CDs were detected with a refractive index detector and ELSD. The measurements indicated that the N-(4-nitrophenyl)-carbamide group-bonded silica was the most effective. ... 

Zyss, J., Nicoud, J. R, and Coquillay, M., Chirality and hydrogen bonding in molecular crystals for phase-matched second-harmonic genaration A-(4-Nitrophenyl)-(L)-prolinol (NPP), J. Chem. 

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