An ice cold, stirred mixture of the product of Example 2, Step 1 (0.22 g, 0.50 mmol) in tetrahydrofuran (THF; 15 mL), under nitrogen, is treated dropwise during 2 minutes, with a lM solution of tetrabutylammonium fluoride in THF (1.5 mL). The mixture is kept in the ice bath for 10 minutes and at ambient temperature (24° C.) for 1 hour 25 minutes, diluted with ethyl acetate, washed with water and brine, dried (Na2SO4) and concentrated. Chromatography of the residue on silica gel with mixtures of 25 methanol-methylene chloride containing 3-6% methanol gave 0.15 g of the alcohol, a compound of formula 9 (Scheme 1) where R is hydrogen: MS(ES) m/z 324 (M+H+). A stirred suspension of the alcohol (0.15 g, 0.46 mmol) in methylene chloride (15 mL) and THF (8 mL), under nitrogen, is treated with triethylamine (0.5 mL, 1.4 mmol) and then portionwise during 1 minute at ambient temperature, with 0.14 g (0.56 mmol) of m-nitrobenzenesulfonyl chloride. The mixture is stirred for 90 minutes, mixed with additional methylene chloride (10 mL) to give a solution and kept at ambient temperature for 1 hour. It is then kept for several days at -11° C., diluted with methylene chloride, washed with saturated sodium bicarbonate, water and brine, dried (Na2SO4) and concentrated to give 0.21 g of the m-nitrobenzenesulfonate, a compound of formula 10 (Scheme 1). A stirred mixture of the m-nitrobenzenesulfonate (0.21 g, 0.44 mmol), acetonitrile (10 mL), 2-propanol (10 mL) and 29% ammonium hydroxide (10 mL) is warmed at 45-50° C. under a Dry Ice-acetone condenser for 4.5 hours and kept at ambient temperature for 18 hours. Additional ammonium hydroxide (5 mL) is added and the mixture is warmed at 45-50° C. for 4.5 hours, kept at ambient temperature for 1 hour, treated with 5 mL of ammonium hydroxide and kept at ambient temperature for 18 hours. It is then concentrated to give a yellow solid which is chromatographed on silica gel with mixtures of methanol-methylene chloride containing 5-7.5% methanol followed by 8% methanol-0.2% ammonium hydroxide-methylene chloride to give the titled product.
