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wjw2005至尊木虫 (著名写手)
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氨基的各种保护已有1人参与
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氨基的各种保护 tBu - (tert-butyl) ester Standard Protection Procedure To a solution of the N-protected aminoacid, DMAP (0.5 eq), and tBuOH (1.2 eq) in dry DCM at 0° under an inert atmosphere, is added EDCI (1.1. eq) and stirred for 2 h. The mixture is then stirred at room temperature until complete by TLC (usually 14 h) and concentrated in vacuo. The residue is redissolved in ethyl acetate and extracted twice with water, then twice with aqueous saturated sodium bicarbonate. The organic solution is dried (magnesium sulfate) and concentrated in vacuo. The residue is purified by flash chromatography (SiO2) if necessary. Removal The compound is dissolved in formic acid and stirred at room temperature until the reaction is complete by TLC (usually 12 hours). The solution is then concentrated and coconcentrated several times with toluene. The resulting residue can then be purified by flash chromatography (SiO2) if necessary. References J. Chem. Soc., Perkin Trans. 1, 1996, 985-993. JOC, 1982, 47, 1962-1965. [Back to Top] [Back to Synthetic Procedures] -------------------------------------------------------------------------------- Bn - (benzyl) ester Standard Protection Procedure The amino acid is stirred with dry THF and O-benzyl-N,N'-diisopropylisourea (see ref. for synthesis) at room temperature under an inert atmosphere until complete by TLC (usually 2 days). The mixture is cooled to -20 C and filtered. The filtrate is concentrated in vacuo and purified by flash chromatography (SiO2) if necessary. Removal The amino acid derivative is dissolved in 1:1 methanol:t-butanol and Pd(OH)2-C is added under a hydrogen atmosphere. The mixture is allowed to stir until complete by TLC (usually >3 h), then filtered and concentrated. The resulting residue can then be purified by flash chromatography (SiO2) if necessary. References Macromolecules, 1978, 534-539. [Back to Top] [Back to Synthetic Procedures] -------------------------------------------------------------------------------- Allyl - (allyl) ester Standard Protection Procedure The compound is dissolved in dry DCM and allyl alcohol (1.1 eq) is added. The solution is stirred under an inert atmosphere at 0° and dicyclohexylcarbodiimide (1 eq) is added followed by 4-N,N-dimethylaminopyridine (0.05 eq). The reaction is allowed to warm to room temperature and is stirred until complete by TLC (usually 1-2 days). Ethyl acetate is added and the resulting precipitate is removed by filtration. The filtrate is concentrated in vacuo and purified by flash chromatography (SiO2) if necessary. Removal The amino acid and pyrrolidine (1.2 eq) are dissolved in methylene chloride and cooled to -15°. Triphenylphosphine (0.2 eq) and Tetrakis(triphenylphosphine)palladium (0) (0.05 eq) are added and stirred under an inert atmosphere for approx. 1 h. Water and acetonitrile are added and the resulting mixture is extracted twice with petroleum ether. The acetonitrile layer is evaporated and purified by flash chromatography (SiO2) if necessary. References Tetrahedron, 1996, 52, 12839-12852. [Back to Top] [Back to Synthetic Procedures] -------------------------------------------------------------------------------- PfP - (pentafluorophenyl) ester Standard Protection Procedure The acid is dissolved in ethyl acetate and pentafluorophenol (1.2 eq) is added. The solution is cooled to 0° and DCC (1.2 eq) is added. The reaction is allowed to warm to room temperature and stir until complete by TLC (usually overnight, if not complete more DCC may be added). The solution is then filtered through celite, rinsed several times with EtOAc, and concentrated in vacuo. The resulting residue can then be purified by flash chromatography (SiO2) if necessary. References J. Chem. Soc., Perkin Trans. 1, 1996, 985-993. [ Last edited by wjw2005 on 2007-6-1 at 23:10 ] |
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