[S-(R*,R*)]-Hexahydro-6-[[2-(acetylthio)-1-oxo-3-phenylpropyl]amino]-2,2-dimethyl-7-oxo-1H-azepine-1-acetic acid, ethyl ester (2.0 g, 4.46 mmole) [prepared as described in Example 66 (g) of U.S. Pat. No. 5,552,397] was dissolved in methanol (9 ml) in a 100-ml flask equipped with an addition funnel, internal temperature probe and argon inlet. To the solution was added DL-dithiothreitol (34 mg, 0.22 mmole). The solution was sparged with argon for 15 minutes and then kept under argon. The resulting solution was cooled to 0° C. in an ice-bath. In the addition funnel, 1N sodium hydroxide (26.8 ml, 26.8 mmole) was sparged with argon for 30 minutes. The sparged sodium hydroxide solution was added to the reaction flask over 30 minutes so that the internal temperature did not exceed 5° C. The reaction was allowed to stir at 0° C. for 30 minutes and then the ice-bath was removed to allow the reaction to warm to room temperature over one hour. The reaction was stirred at room temperature for an additional 1.5 hours at which time TLC showed that the reaction was complete. A pH probe was attached to the reaction flask. The reaction was acidified with previously sparged 3N HCl to a pH of 6. A few seed crytals were added and the mixture was stirred for 5 minutes. The mixture was then further acidified to pH 2. The resulting slurry was stirred at room temperature for one hour. The product was collected by filtration and washed with distilled water until the wash-water tested negative for chloride with silver nitrate solution. The product was air-dried for 30 minutes, washed with t-butyl methyl ether (2×4 ml) and hexane (2×4 ml), air-dried, and dried under a high vacuum to give 1.5 g of title product as a white crystalline solid (890% yield),
