A mixture of 142 mg (0.25 mmoles) of (2S, 4S, 5S)-5-{N-[N-(t-butoxycarbonyl)-3-(4-thiazolyl)-L-alanyl]}amino-4-hydroxy-2-(1-hydroxy-1-methylethyl)-7-methyl-N-[2(RS)-methylbutyl]octanamide (prepared as described in Example 6) in 5 ml of a 4N solution of hydrogen chloride in dioxane was stirred at room temperature for 30 minutes. At the end of this time, the solvent was removed by distillation under reduced pressure. Diethyl ether was then added to the residue, and the solvent was removed again by distillation under reduced pressure. This operation was repeated in total three times, after which the residue was dried under vacuum for 8 hours. At the end of this time, the dried material was suspended in 10 ml of anhydrous tetrahydrofuran, and 99.9 mg (0.32 mmoles) of N-t-butoxycarbonyl-3-(1 naphthyl)-L-alanine were added to the resulting suspension, followed by 0.05 ml (0.33 mmoles) of 95% diethyl cyanophosphate and 0.12 ml (0.86 mmoles) of triethylamine, all whilst ice-cooling and under an atmosphere of nitrogen, The mixture was then stirred for 8 hours, after which the solvent was removed by distillation under reduced pressure, and the residue was purified by silica gel thin layer chromatography (using a 10:1 by volume mixture of methylene chloride and methanol as developing solvent), to give 181 mg (yield 95%) of the title compound as white crystals, melting at 90°-92° C.
