Ethyl protection

Lipase from wheat germ l and Upase from Aspergillus niger selectively unmasked the methyl and (2-methoxyethoxy)ethyl protected C-terminals of nucleopeptides (Scheme 25). 

The silyl-based (methyldiphenylsilyl)ethyl protecting group is removed by treatment with TFA-phenol-Et3SiH (95 3 2) for 2 h at room temperature, and its application was illustrated by the synthesis of three peptides, one of them containing cysteine and methionine [114]. 

Ogawa T, Hosaka H, Makita T, Takaku H. Solid-phase synthesis of oligori-bonucleotides using 5 -9-fluorenylmethoxycarbonyl and 2 -l-(isopropoxyl)ethyl protection. Chem Lett 1169-1172, 1991. 

Sakatsume O, Yamaguchi T, Ishikawa M, Hirao I, Miura K, Takaku H. Solid-phase synthesis of oligoribonucleotides by the phosphoramidite approach using 2 -0-l-(2-chloroethoxy)ethyl protection. Tetrahedron 47 8717-8728, 1991. 

In a related process, triethylsilane plus SnCLr can expediently convert appropriately protected aldol products to fully protected 1,3-diols. Moreover, the synthesis of iyn-l,3-ethylidene acetals from l-(2-methoxyethoxy)ethyl-protected -hydroxy ketones with SnCLr and EtsSiH can occur with very high levels of diastereocontrol (eq 33). ... 

Full details of the total synthesis of ( )-pyrenophorin (107) have been published. The final cyclization was affected using di-imidazoyl-l-yl ketone as lactonizing reagent. The synthesis also features the use of the 2-(tolyl-/7-sulphonyl) ethyl protecting group for carboxylic acids selective removal of this group in the presence of other esters is easily achieved (DBN 25 °C). 

Scheme 5). The use of a 2-(p-nitrophenyl)ethyl protecting group at the 0-6 position of 2-fluoroguanosine derivatives allowed simultaneous 0-deprotection during amine substitution at C-2 [24], The SnAt reaction extends to alkoxy and thiol nucleophiles, as demonstrated on 2-fluoro-2, 3 -dideoxyadenosine [25],... 

Hamamoto, S, Shishido, Y, Furuta, M., Takaku, H, Kawashima, M, and Takaki, M. (1989) Use of the 2-(4-pyridyl)ethyl protecting group in the synthesis of DNA fragments via phosphoramidite intermediates Nucleosides Nucleotides 8, 317-326... 

Freshly distilled ethyl formate must be used. Commercial ethyl formate may be purified as follows. Allow the ethyl formate to stand for 1 hour with 16 per cent, of its weight of anhydrous potassium carbonate with occasional shaking. Decant the ester into a dry flask containing a little fresh anhydrous potassium carbonate and allow to stand for a further hour. Filter into a di flask and distil through an efficient fractionating column, and collect the fraction, b.p. 53-54° protect the receiver from atmospheric moisture. 

Tpte [2-[(4-tritylphenyl)thio]ethyl] Z = Cbz benzyloxycarbonyl protecting group... 

The benzoic acid derivative 457 is formed by the carbonylation of iodoben-zene in aqueous DMF (1 1) without using a phosphine ligand at room temperature and 1 atm[311]. As optimum conditions for the technical synthesis of the anthranilic acid derivative 458, it has been found that A-acetyl protection, which has a chelating effect, is important[312]. Phase-transfer catalysis is combined with the Pd-catalyzed carbonylation of halides[3l3]. Carbonylation of 1,1-dibromoalkenes in the presence of a phase-transfer catalyst gives the gem-inal dicarboxylic acid 459. Use of a polar solvent is important[314]. Interestingly, addition of trimethylsilyl chloride (2 equiv.) increased yield of the lactone 460 remarkabiy[3l5]. Formate esters as a CO source and NaOR are used for the carbonylation of aryl iodides under a nitrogen atmosphere without using CO[316]. Chlorobenzene coordinated by Cr(CO)j is carbonylated with ethyl formate[3l7]. 

Carboxyl groups of ammo acids and peptides are normally protected as esters Methyl and ethyl esters are prepared by Fischer esterification Deprotection of methyl and ethyl esters is accomplished by hydrolysis m base Benzyl esters are a popular choice because they can also be removed by hydrogenolysis Thus a synthetic peptide protected at both... 

Section 27 16 Carboxyl groups are normally protected as benzyl methyl or ethyl esters Hydrolysis m dilute base is normally used to deprotect methyl and ethyl esters Benzyl protecting groups are removed by hydrogenolysis... 

Remove the Z protecting group from the ethyl ester of Z Phe Gly by hydrogenolysis Cou pie with the p mtrophenyl ester of Z Leu then remove the Z group of the ethyl ester of Z Leu Phe Gly... 

Shipment, Stora.ge, ndPrices. Methyl vinyl ether is available in tank cars or cylinders, while the other vinyl ethers are available in tank cars, tank wagons, or dmms. Mild steel, stainless steel, and phenoHc-coated steel are suitable for shipment and storage. If protected from air, moisture, and acidic contamination, vinyl ethers are stable for years. United States bulk prices in 1991 for methyl vinyl ether, ethyl vinyl ether, and butyl vinyl ether were listed as about 5.78/kg, 6.28/kg, and 6.08/kg, respectively. 

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