To a stirred mixture of 1.7 g (1.9 mmole) of the title product of Example 52 in 40 ml of methanol was added 10 ml of 10% aqueous potassium carbonate. After about 75 minutes the resultant solution was poured into a mixture of 150 ml of dichloromethane and 100 ml of 0.5M potassium bisulfate. The organic phase (containing the crude neutralized product) was separated and the aqueous layer was further extracted with dichloromethane. The combined organic layers were concentrated to dryness and purified by column chromatography, giving the analytically pure BOC-protected derivative of the title compound. [Analysis. Calcd. for C39H57N5O9S: C, 60.68; H, 7.44; N, 9.07; S, 4.15. Found: C, 60.64; H, 7.52; N, 8.90; S, 4.01.] The intermediate thus formed was converted to the title compound by the method described in Example 14. Structure Assignment was supported by elemental analysis.
