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Protective trichloroethyl esters

The use of protecting groups is common in penicillin chemistry the amino function is normally protected by a triryl, benzyloxycarbonyl. p-nitrobenzyloxycarbonyl. tridlloroethyloxycarbonyl. or trimethylsilyl group and the carboxylic acid is usually protected as a benzyl, p-nitrobenzyl. p-methoxybenzyl. or trichloroethyl ester. Acylations may thus be carried out... [Pg.125]

A scion of the small reductive-elimination orthogonal set is the phenacyl group which, like the 2,2,2-trichloroethyl ester (section 6.5.1), is useful for deprotect-ing the C-terminus of a peptide under conditions that retain such stalwart protecting groups as Fmoc, Boc, and Cbz (see section 8.3). Phenacyl esters are more labile towards nucleophilic attack than standard esters but they are stable towards acidic conditions typically employed for deprotection in peptide synthesis such as HF or trifluoroacetic acid. [Pg.402]

Protection of acids and phenols. Carboxylic acids can be protected as the p-bromophenacyl esters, prepared by the reaction of the carboxylate anion with p-bromophenacyl bromide in water or DMF. The protecting group is removed at room temperature by zinc in glacial or aqueous acetic acid. The new method is comparable to Woodward s protection of carboxylic acids as /3-trichloroethyl esters, which are also cleaved by zinc (see Trichloroethanol, this volume), y-Lactones are converted into y-hydroxy esters. [Pg.20]

Hydrolysis of 2-haloethyl esters. 2,2,2-Trichloroethyl esters have been used for protection of carboxyl groups because they are readily cleaved by zinc-acetic acid at 0° (3, 295-296). Ho has reported that 2-haloethyl esters can be cleaved by sodium trithiocarbonate in refluxing acetonitrUe in 75-85% yield. The suggested mechanism is formulated. ... [Pg.553]

Tee esters (OTce), R-CO-OCH2CHCL3, 2,2,2-trichloroethyl esters suitable for protection of the C-terminus in solution-phase peptide synthesis. They can be hydrolyzed under mild conditions that are compatible with acid-labile N -protecting groups [G. Just, K. Grozinger, Synthesis 1976, 457]. [Pg.365]

Protection of carboxyl groups as 2,2,2-trichloroethyl esters Reductive removal of the protective group... [Pg.287]

Protection and Deprotection.—N-Protected a-amino-acids are readily esterified by methanol or ethanol in 60—80% yield after reaction with an enamine (e.g. from isobutyraldehyde and piperidine) and t-butyl isocyanate. Such amino-acids can also be esterified efficiently with alkyl halides under phase-transfer conditions with no racemization. Direct esterification of a-amino-acids with ethyl toluene-p-sulphonate in boiling ethanol gives a-amino-acid ethyl esters in 80—90% yield as the sulphonate salts. The protection of acid functions by formation of the 2-chloro-(or bromo-)ethyl esters has been discussed. These derivatives survive exposure to both moderately acidic and basic conditions and are removable by conversion into the iodoethyl analogues followed by zinc reduction. Alternatively, they may be converted into hydrophilic ammonium or phosphonium salts which exhibit enhanced acid stability but which are cleaved by very dilute base. Yet another method for the removal of such groups using supernucleophilic Co phthalocyanin anions has been reviewed. Further routes to 2,2,2-trichloroethyl esters have been described, one of which employs an activated ester intermediate and is suited to acid-labile substrates. [Pg.134]


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See also in sourсe #XX -- [ Pg.837 ]




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Esters, protection

Trichloroethyl esters

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