A suspension of the product of Example 7 (2.6 g., 6.5 mmol.) in 4.25 mL of concentrated ammonium hydroxide and 9.3 mL of water was stirred at room temperature under argon for 12-15 minutes. The resulting solution was acidified with 200 mL of 5% potassium hydrogen sulfate and extracted with ethyl acetate (5×50 mL). The combined ethyl acetate extract was washed with brine, dried (MgSO4) and evaporated to give 2.4 g. of a light yellow solid. This material was combined with an additional 80 mg. of compound and flash chromatographed on 300 g. of silica gel eluting with methylene chloride:methanol:acetic acid, 40:1:1 to give 2.3 g. of white solid. This solid was triturated with toluene containing approximately 5% ethyl acetate, and 1.25 g. of white crystalline solid was collected by filtration. The filtrate was evaporated to dryness and the residue was triturated in a similar fashion to produce an additional 560 mg. of material which was combined with the initial 1.25 g. crop to yield 1.81 g. of title isomer A compound as a white crystalline solid; m.p. 148.5°-150.5° C., TLC Rf =0.48 (300:100:1 ethyl acetate:hexanes:acetic acid), [α]D =-10.3° (c=1.00, methanol).
