Hydrochloric Acid → Boc-Trp(Dmb)-OBzl

Participants

Reaction Steps

In dichloromethane (10 ml) was dissolved Boc-Trp-OBzl (789 mg, 2 mM), followed by addition of cetyltrimethylammonium chloride (6.4 mg, 0.02 mM) and crushed sodium hydroxide (200 mg, 5 mM). Then, a solution of 2,4-dimethoxybenzenesulfonyl chloride (710 mg, 3 mM) in dichloromethane (3 ml) was added dropwise to the above mixture. The reaction was conducted at room temperature for 30 minutes, after which it was cooled and brought to pH 2 with 1 N--HCl. Following addition of water (10 ml), the solution was shaken and the dichloromethane layer was separated, washed with water and dried over sodium sulfate. The solvent was then distilled off to give Boc-Trp(Dmb)-OBzl. This product was dissolved in ethanol (10 ml), and under ice-cooling, a 1--N aqueous solution of sodium hydroxide (2.2 ml) was added. The reaction was continued at room temperature for one hour. The ethanol was distilled off and the residual aqueous solution was diluted with water (20 ml) and extracted with ether (20 ml). The water layer was cooled and brought to pH 3 with 10% aqueous citric acid. The solution was then extracted with ethyl acetate and the ethyl acetate layer was washed with water and dried over sodium sulfate. The solvent was then distilled off and the residue was treated with petroleum ether to give Boc-Trp(Dmb)-OH as a solid product. Yield 737 mg; (73%); m.p. 100° C. (decomp.); [α]D22 -9.43° (c=0.5, DMF).

Provenance & Evidence