A stirred mixture of (S)-2-(3,5-diamino-6-chloropyrazine-2-carboxamido)-3-phenylpropionic acid (1.8 g.), 1-β-aminoethylamino-3-α-naphthyloxypropan-2-ol (1.43 g.), 2-isobutoxy-1-isobutoxycarbonyl-1,2-dihydroquinoline (1.5 g.) and dimethylsulphoxide (30 ml.) was heated at 75° C. for 18 hours, cooled and poured into ice-water (600 ml.). Aqueous 6% w/v sodium bicarbonate solution (50 ml.) was added, the mixture was filtered and the solid product was washed with diethylether (100 ml.). There was thus obtained as solid product 3,5-diamino-6-chloro-N-{1-[N-β-(2-hydroxy-3-α-naphthyloxypropylamino)ethylcarbamoyl]-2-phenylethyl}pyrazine-2-carboxamide, m.p. 142°-146° C.
