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Benzyl esters selectivity

The carboxamidomethyl ester was prepared for use in peptide synthesis. It is formed from the cesium salt of an A-protected amino acid and a-chloroacetamide (60-85% yield). It is cleaved with 0.5 M NaOH or NaHCOa in DMF/H2O. It is stable to the conditions required to remove BOC, Cbz, Fmoc, and r-butyl esters. It cannot be selectively cleaved in the presence of a benzyl ester of aspartic acid. ... [Pg.239]

Catalytic hydrogenolysis of an O-benzyl protective group is a mild, selective method introduced by Bergmann and Zervas to cleave a benzyl carbamate (>NC0-0CH2C6H5 —> >NH) prepared to protect an amino group during peptide syntheses. The method has also been used to cleave alkyl benzyl ethers, stable compounds prepared to protect alkyl alcohols benzyl esters are cleaved by catalytic hydrogenolysis under neutral conditions. [Pg.2]

PhCH20COCl, Na2C03, H20,0°, 30 min, 72% yield. Alpha-omega diamines can be protected somewhat selectively with this reagent at a pH between 3.5 and 4.5, but the selectivity decreases as the chain length increases [H2N(CH2) NH2, n = 2, 71% mono n = l, 29% mono]. Hindered amino acids are protected in DMSO (DMAP, TEA, heat, 47-82% yield). These conditions also convert a carboxylic acid to the benzyl ester. ... [Pg.531]

Alcalase selectively catalyses the hydrolysis of D,L-amino add methyl and benzyl esters to provide L-amino adds and D-amino add esters with high optical purity (Figure A8.10). [Pg.285]

Although these Boc derivatives underwent methylation with poor selectivity (compared to 3-amino-N-benzoyl butanoates [106] and Z-protected methyl 4-phen-yl-3-aminobutanoate [107]), epimers were succesfully separated by preparative HPLC or by flash chromatography. However, saponification of the methyl ester caused partial epimerization of the a-stereocenter and a two-step (epimerization free) procedure involving titanate-mediated transesterification to the corresponding benzyl esters and hydrogenation was used instead to recover the required Boc-y9 -amino acids in enantiomerically pure form [104, 105]. N-Boc-protected amino acids 19 and 20 for incorporation into water-soluble /9-peptides were pre-... [Pg.42]

Lord and Pawliszyn" developed a related technique called in-tube SPME in which analytes partition into a polymer coated on the inside of a fused-silica capillary. In automated SPME/HPLC the sample is injected directly into the SPME tube and the analyte is selectively eluted with either the mobile phase or a desorption solution of choice. A mixture of six phenylurea pesticides and eight carbamate pesticides was analyzed using this technique. Lee etal. utilized a novel technique of diazomethane gas-phase methylation post-SPE for the determination of acidic herbicides in water, and Nilsson et al. used SPME post-derivatization to extract benzyl ester herbicides. The successful analysis of volatile analytes indicates a potential for the analysis of fumigant pesticides such as formaldehyde, methyl bromide and phosphine. [Pg.732]

The benzyl ester group was selectively hydrogenolyzed on 10% Pd/C in EtOH-H20 (9 1) at 15 psi H2 for 15 hours without concomitant removal of the imidazoyl benzyl moiety (Scheme 4.88).337... [Pg.169]

This procedure was also compatible with the benzyl ester, as demonstrated in Scheme 8.24 by selective deprotection of compound 66 (67 was isolated in 70% yield by chromatography after 20 min irradiation at 75 °C (30 W) in the Synthewave 402 reactor). [Pg.267]

The Pyoc group is stable to acids and bases, but may be selectively removed after conversion into the jV-methylpyridinium form and subsequent treatment with morpholine, to give 146. Treatment of 146 with acetic anhydride in pyridine gave 147. Hydrogenolysis of the benzyl ester group of 147 followed by methanolysis catalyzed by hydrazine afforded (44,73) the de-protected derivative 148. [Pg.298]

Table V. Carboxymethylation of Benzyl Bromide -Selectivity to Ester(a)... Table V. Carboxymethylation of Benzyl Bromide -Selectivity to Ester(a)...
In the initial phase of our work we prepared a set of benzyl esters of the 3-(2,2-dichloroethenyl)-2,2-dimethylcyclopropanecarboxylic acid (DVA) which were monosubstituted in the meta position. The substituents were chosen to cover a broad spectrum of physicochemical parameter space by selecting them from Hansch s cluster sets( ). In addition, substituents with no bridging group, one atom and two atom bridges were included to probe the need for a bridging atom. [Pg.301]

The diastereoselective cycloaddition of 2-phenyl-4-dimethylamino-l-thia-3-azabuta-l,3-diene with a choice of dienophiles and in the presence of a Lewis acid provides a convenient route to 5,6-dihydro-4//-l,3-thiazines <2002TL6067, 2004T1827>. The more stable /ra r-adducts are produced exclusively. The approach using (4A)-3-acryloyl-4-benzyloxazolidin-2-one 198 provides access to the chiral 5,6-dihydro-4//-l,3-thiazine 199 <2004T1827>. The exceptional level of selectivity is only achieved when magnesium bromide is used. The chiral auxiliary was removed by reaction with lithium benzoxide to give the benzyl ester 200, and reaction with catalytic amount of samarium triflate and methanol provides the methyl ester 201 (Scheme 21). 2-Substituted-5,6-dihydro-l,3-thiazines are conveniently synthesized from nitriles or thiocyanates and 4-mercapto-2-methylbutan-2-ol to produce... [Pg.591]

Derivatization of a-aminosuberic acid to produce selectively protected derivatives such as Z-L-Asu(OtBu)-OH 16 is performed as outlined in Scheme 6. Using Z-l-Asu-OH 13 as starting material, conversion into a-benzyl ester 14 by treatment with Bzl-Br, followed by reaction with isobutene/H2S04 and saponification of the benzyl ester 15 leads to the desired product 16 as the piperazine salt.124 ... [Pg.228]

An electron-withdrawing group, such as nitro, at 4 - position of the benzyl ester determined a significant enhancement of both affinity and selectivity (compound MRS 1334). Any other modifications, including heterocycles at the 4-position, aminoalkyl or thioalkyl groups at the 3- and 5-positions, appeared detrimental in term of both affinity and selectivity. [Pg.124]

Derivative formation is essential for analysis of gibberel-lins because they only absorb radiation below 230 nm, which is an extremely nonspecific region. Benzyl esters (49) and p-nitro-benzyl esters (60) of gibberellins have successfully been synthesized prior to injection to permit their detection as they elute from HPLC columns. Unfortunately, these derivatives have added little selectivity to the analytical procedure. The derivatives are monitored at 254 or 265 nm which, as previously mentioned, is a nonspecific region. [Pg.233]


See other pages where Benzyl esters selectivity is mentioned: [Pg.65]    [Pg.259]    [Pg.426]    [Pg.697]    [Pg.213]    [Pg.156]    [Pg.71]    [Pg.288]    [Pg.70]    [Pg.126]    [Pg.677]    [Pg.149]    [Pg.165]    [Pg.450]    [Pg.200]    [Pg.7]    [Pg.448]    [Pg.145]    [Pg.151]    [Pg.550]    [Pg.55]    [Pg.268]    [Pg.287]    [Pg.63]    [Pg.173]    [Pg.846]    [Pg.48]    [Pg.156]    [Pg.905]    [Pg.389]    [Pg.298]    [Pg.287]    [Pg.63]    [Pg.8]   
See also in sourсe #XX -- [ Pg.522 ]




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Benzyl Ester

Ester benzylic

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