Nitrophenacyl esters

The reaction between 4-nitrophenacyl esters and DMSO/diethylamine, described by Kallmayer et al., is also a halochromic reaction [39]. 

Maeda M, Tsuji A. Chemiluminescence with lucigenin as post-column reagent in high-performance liquid chromatography of corticosteroids and p-nitrophenacyl esters. J Chromatogr, 1986 352 213-29. 

Fig. 11.5.3. HPLC sqjaration of />-nitrophenacyl esters of selected prostaglandins. Chromatographic conditions column, silver ion-loaded Partisil SCX column (250X4.6 mm I.D.) mobile phase, 0.06% acetonitrile in dioxane detection, UV at 254 nm. Reproduced from Merritt and Bronson (1977), with permission.

A crown ether method has also been described for these esters. The acid(s) are again neutralized with methanolic KOH to phenolphthalein and the solution is evaporated to dryness. To the potassium salts is added 1.2 ml of a solution, in acetonitrile, of 43 mg of p-nitrophenacyl bromide and 56 mg of dicyclohexyl-18-crown-6. The mixture is refluxed for 1.5 hours, and the product is analysed by HPLC [93]. 

Fatty acids can be derivatized with p-bromophenacyl (73, 85, 86], phenacyl [87-89], naphthacyl [90, 91] or p-nitrophenacyl [74] bromide. To prepare p-bromophenacyl esters [73], fatty acids (0.001—0.5 mM) were dissolved in methanol or water and neutralized to a phenolphthalein end-point by methanolic KOH. The solvent was removed by either a rotary evaporator or lyophilization. A 3—10-fold molar excess of alkylating agent, p-bromophenacyl bromide/18-crown-6 (20 1) in acetonitrile, was then added. The mixture was stirred continuously in a sealed Reacti-Vial at 80 °C for 15 min. After cooling, the solution containing the derivatives was directly subjected to RP-HPLC with UV detection at 260 nm. The mobile phase was usually acetonitrile/ water [87, 92, 93], methanol/water [73, 88, 94, 95] or acetonitrile/methanol/water (86, 89], The separation of phenacyl derivatives of palmitoleic (Ci, ) and arachi-donic ( 20 4) acids was not achieved with the acetonitrile/ water system [87, 89], and elution with methanol/water could not resolve linolenic (Cig.3) and myristic (C]4.q) acids [88, 89]. A ternary mobile phase [89] containing a mixture of acetonitrile, methanol and water seemed to be best for the separation of phenacyl derivatives of fatty acids. 

Comparable phenacyl esters are synthesized with p-bromophenacyl bromide or p-nitrophenacyl bromide with a similar spectroscopic behavior (both p-Bondapak C18). Useful derivatization by tagging the COOH group can also be done with a-bromo-2 -acetonaphthone resulting in well-soluble and strongly UV-absorbing (254 nm) naphthanyl esters after a reaction time of only 10 min at ambient temperature (LiChrosorb Si-100). Furthermore, coumarin derivatives (substituted at position 7 for higher fluorescence quantum yields) are predestinated to... 

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