4-Chloro-2-nitrophenyl esters

Aryl groups are widely employed as the protector. Some kinds of phenyl derivatives can be removed by b ic hydrolysis. The removal, particularly from phosphodiesters, frequendy requires high tempera-ture. For example, the 4-chloro-2-nitrophenyl ester (106 equation 63) is hydrolyzed by sodium... 

Two examples of aryl esters are given in Table 8.5, namely the 4-chloro-phenyl and 4-nitrophenyl esters of nicotinic acid (8.33). Under physiological conditions of pH and temperature, these two compounds were clearly much more susceptible to chemical hydrolysis than the alkyl and arylalkyl esters in Table 8.5. Their affinity for carboxylesterase and human plasma hydrolases, as assessed by the Michaelis constant Km, was generally higher, while nothing can be said regarding Vmax values. 

Boc amino acid thioesters 7 used in Boc-SPPS are prepared by reaction of Boc amino acid active esters such as the 4-nitrophenyl ester (ONp) or succinimide ester 6 (OSu) with thiols containing a carboxy group that can link to a resin (Scheme 3, Table 2). 1314 Amino acid thioesters 7 can also be prepared by reaction of Boc amino thiol acids 8 with a chloro, bromo, or hydroxy compound that also contains a carboxy group (Scheme 3, Table 2). 1516 ... 

In addition to the unsubstituted sulfene itself, the various substituted sulfenes used in the preparation of thietane 1,1-dioxides are listed in Table 4. Although the usual method for generating the sulfenes is by treatment of a methanesulfonyl chloride with triethylamine, sulfenes have been obtained by the reaction of phenyl-methanesulfonyl fluoride with phenyllithium, by treatment of a-chloro-ethanesulfinic acid with refluxing triethylamine,by treatment of 4-nitro-phenyl or 2-chloro-4-nitrophenyl, esters of arylmethanesulfonic acids with potassium t-butoxide or 2,6-dimethylpyridine, respectively, by treatment of diazoalkanes with sulfur dioxide" (e.g., to give 146) and by thermolysis of a Diels-Alder adduct of sulfene." ... 

Esters of 1,2,3-triazolecarboxylic acids are the most common derivatives of triazole (Section 5.01.9) therefore, their conversions to other, more useful, functionalities are of great importance. In an example given in Scheme 48, 4-triazolecarbocylic ester 317, obtained from a reaction of (3-ketoester 316 with 4-chloro-2-nitrophenyl azide, is hydrolyzed to free acid 318 (82% yield) by 4% KOH. Heated to reflux in DMF for 3 h, acid 318 undergoes decarboxylation to triazole derivative 319 with 81% isolated yield <2004FA397>. 

The ozonolysis reaction, followed by reductive workup with sulfur dioxide, as described in Part A of the present procedure, illustrates a general method which has been developed for the preparation of acetals. Application of the procedure is illustrated by conversion of the following olefins in alcoholic solution to the corresponding acetals (1) l-chloro-4-(o-nitrophenyl)-2-butene to o-nitrophenylacetaldehyde dimethyl acetal in 84% yield (2) l,4-dibromo-2-butene tobromoacetaldehyde dimethyl acetal in 67% yield (3) 3-butenoic acid to malonaldehydic acid diethyl acetal ethyl ester in 61% yield (4) cyclopentadiene to malonaldehyde bis(diethyl acetal) in 48% yield and (5)... 

Fig. 2. pH-rate profiles for three representative esters at 39°C, ionic strength 1.0, on adjusted scales. A, x I07 min for 2,4,6-trichlorophenyl phosphate , Ahyd x 10 min-1 for 2-chloro-4-nitrophenyl phosphate O, byd x I04 min- for 2,4-dinitrophenyl phosphate. 

Alcohols and phenols can be attached to support-bound alcohol linkers as carbonates [467,665,666], although few examples of this have been reported. For the preparation of carbonates, the support-bound alcohol needs to be converted into a reactive carbonic acid derivative by reaction with phosgene or a synthetic equivalent thereof, e.g. disuccinimidyl carbonate [665], carbonyl diimidazole [157], or 4-nitrophenyl chloro-formate [467] (see Section 14.7). The best results are usually obtained with support-bound chloroformates. The resulting intermediate is then treated with an alcohol and a base (DIPEA, DMAP, or DBU), which furnishes the unsymmetrical carbonate. Carbonates are generally more resistant towards nucleophilic cleavage than esters, but are less stable than carbamates. Aryl carbonates are easily cleaved by nucleophiles and are therefore of limited utility as linkers for phenols. 

See Dimethyl 2-chloro-4-nitrophenyl thionophosphate, above See other INDUCTION PERIOD INCIDENTS, PHOSPHORUS ESTERS... 

Aceto. See 3,5-Di-t-butyl-p-hydroxybenzoic acid o-Acetoacetanisidide, 2-((4-chloro-2-nitrophenyl) azo)-. See Pigment yellow 73 Acetoacetic acid, butyl ester. See Butyl acetoacetate... 

Reactions of arenesulphenyl chlorides with hydroxyl functions of nucleosides have been investigated with N phthalimido-2, 3 -0-isopropylideneadenosine, o-nitrophenyl sulphenyl chloride gave the 5 -0-sulphenyl ester, whilst other sulphenyl chlorides without an o-nitro group gave mixtures of sulphinate esters and 5 -deoxy-5 -chloro compound. Mechanisms were suggested. ... 

Symmetrical carbonates are synthesized by carbonylation of the alcohols 4-chloro-tetrafluorophenol and 4-nitrophenol with phosgene. In this way, active esters of carbonic acids, such as di(p-chlorotetrafiuorophenyl) carbonate (di-Tfc-carbotMte) 875 [634] and di(p-nitrophenyl) carbonate (di-Dnp-carbonate) 717 [503], are produced. Di-Tfc-carbonate 875 is used to prepare p-chlorotetrajluorophenyl esters of N-protected amino acids and offers an advantageous alternative to pentafiuorophenyl esters, because pentafluorophenol is too stable in waste. 

Besides the 0-glycosides mentioned so far, also attention has been paid to the synthesis of N- and S-analogues. The p-nitrophenyl N-glycoside of a-N-acetylneuraminic acid has been prepared by silver carbonate-promoted reaction of 4,7,8,9-tetra-0-acetyl-2-chloro-2-deoxy-p-N-acetylneuraminic acid methyl ester with p-nitroaniline and subsequent deprotection (Privalova and Khorlin 1969). Treatment of the same precursor with sodium azide, followed by de-esterification, led to the formation of 2-azido-2-deoxy-a-N-acetylneuraminic acid (Supp et al. 1980). The same authors reported also the preparation of the p-form. The azides can readily be converted into the 2-amino derivatives of N-acetylneuraminic acid. Subsequently, the amino function has been benzoylated. Data on the syntheses of the methyl and p-nitrophenyl S-glycosides of a-N-acetylneuraminic acid have been presented by Privalova and Khorlin (1969), whereas Ponpipom et al. (1980) have described a method for the synthesis of 5-acetamido-2-S-[6-(5-cholesten-3p-yloxy)hexyl]-3,5-dideoxy-2-thio-p-D-g/vccro-D-ga/acto-2-nonulopyranosonic acid. 

Privalova and Khorlin (1969) reported the synthesis of the p-nitrophenyl glycoside of a-N-acetylneuraminic acid. The substrate was obtained by glycosylation of p-nitrophenol with 4,7,8,9-tetra-0-acetyl-2-chloro-2-deoxy-p-N-acetylneuraminic acid methyl ester in chloroform in the presence of silver carbonate and Drierite, followed by 0-deacetylation and saponification. In enzymatic reactions, released p-nitrophenol can be determined spectrofoto-metrically. 

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