Hydrochloric Acid → AHPBA 38a

Participants

Reaction Steps

0.6 ml of 1N aqueous hydrochloric acid was added to a solution of 300 mg (0.48 mmol) of (4S)-1-[(2S,3S)-3-(N2 -benzyloxycarbonyl-L-asparaginyl)amino-2-hydroxy-4-phenylbutyryl]-N-t-butyl-4-chloro-L-prolinamide (prepared as described in Example 1) in methanol, and a stream of hydrogen was bubbled through the mixture at atmospheric pressure for 3 hours in the presence of 60 mg of 10% w/w palladium-on-charcoal, to remove the benzyloxycarbonyl group. The whole of the resulting (4S)-1-[(2S,3S)-3--asparaginylamino-2-hydroxy-4-phenylbutyryl]-N-t-butyl-4-chloroprolinamide hydrochloride and 99 mg (0.57 mmol) of 2-quinoxalinecarboxylic acid were dissolved in 5 ml of dimethylformamide, and 93 mg (0.57 mmol) of diethyl cyanophosphate and 144 mg (1.44 mmol) of triethylamine under ice-cooling were added to this solution. The resulting mixture was stirred for 3 hours, after which it was concentrated by evaporation under reduced pressure. The residue was mixed with a 10% w/v aqueous solution of sodium hydrogencarbonate and then extracted with ethyl acetate. The organic extract was washed with a saturated aqueous solution of sodium chloride and then dried over anhydrous sodium sulfate. The solvent was removed by distillation under reduced pressure, and the resulting residue was purified by preparative thin layer chromatography, using a 10:1 by volume mixture of methylene chloride and methanol as the developing solvent, to give 140 mg of the title compound as a colorless powder, melting at 132°-134° C.

Provenance & Evidence