氨基酸保护

Carboxylic acid protection - [Bn ester] [Pfp ester] [Me ester] [Allyl ester] [tButyl ester] [PMB ester] [MEM ester]

Amine protection (carbamates) - [Fmoc] [Boc] [Cbz] [Troc]

Side Chain protections- [Boc]

t Bu - (tert-butyl) ester

Standard Protection Procedure

To a solution of the N-protected amino acid, 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.

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.

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