In 13 ml of DMF was dissolved 826.0 mg of L-histidyl-L-prolinamide 2-
hydrobromide and then 2 ml of a DMF solution of 405.0 mg of triethylamine
was added to the solution under ice-cooling. After maintaining 30 min under
ice-cooling, the precipitates thus formed were filtered off to provide L-histidyl-
L-prolinamide.
In 10 ml of DMF was dissolved 230.0 mg of (S)-2-azetidinone-4-carboxylic
acid and then 351.0 mg of N-hydroxy-1,2,3-benzotriazole and 453.0 mg of
dicyclohexylcarbodiimide were added to the solution under ice-cooling. Then,
after stirring the mixture for 15 min, the reaction was maintained for 15 min
at room temperature. The reaction mixture was ice-cooled again and 15 ml of
a DMF solution of foregoing L-histidyl-L-prolinamide was added to the reaction
mixture followed by reaction overnight at 0°C. The precipitates thus formed
were filtered off, the filtrate was concentrated to dryness, the residue was
dissolved in 10 ml of chloroform-methanol (4:1) and subjected to silica gel
column chromatography. The eluates by chloroform-methanol (7:3) were
collected and concentrated to dryness to provide 509.0 mg of crude product.
When the product was subjected to silica gel column chromatography again
and eluted by a mixture of chloroform, methanol, and aqueous ammonia
(40:10:1) to provide 394.0 mg of pure Nepsilon-[(S)-2-azetidinone-4-carbonyl]-
L-histidyl-L-prolinamide, melting point 183°-185°C (crystallization from a
small amount of methanol).
