20 μl (112 μmol) of N,N-diisopropylethylamine were added to a solution of 60 mg (102 μmol) of the compound of Example 58A in 1 ml of THF. The mixture was cooled to 0° C., 18 mg (107 μmol) of 4-nitrophenyl formate were then added a little at a time and stirring was continued at 0° C. for 1 h. Since LC/MS analysis of the reaction mixture indicated the additional formation of an O-formylated byproduct, 408 μl of a 1 N solution of lithium hydroxide in water were added to the reaction mixture. Stirring of the mixture was then continued at RT overnight. The volatile components were then removed on a rotary evaporator. The residue was dissolved in a little DMSO and separated by preparative HPLC [Method 8]. The product-containing fraction was freed from the solvent on a rotary evaporator and the residue was dried under high vacuum. This gave 35 mg (59% of theory) of the title compound.
