A suspension of Example 15 (1.9 g, 3.77 mmol) in methanol-water (2:1) was made strongly basic with 5% aqueous NaOH and stirred at room temperature for 1.5 hours followed by gentle warming to complete the hydrolysis. The solution was then acidified to pH 4-5 with conc. HCl, the precipitated gum was washed with water and taken up in hot methanol. The suspension was made strongly acidic with conc. HCl resulting in a solution which was left to crystallize. The precipitated solid showed the presence of a substantial amount of the starting ester, presumed to be formed during the purification step. This material was redissolved in aqueous NaOH over 1 hour and acidified to pH 5, the precipitated gum was washed with 3 portions of water, taken up in hot methanol and treated with 3 equivalents of maleic acid. The presence of the reformed ester was again shown by TLC chloroform-methanol-acetic acid 15:5:1). The solid was washed successively with hot isopropanol then hot ethanol. The white solid thus isolated proved to be the free base of the desired compound. Suspension of the material in 75 ml 95% ethanol and treatment with enough maleic acid to give a clear solution followed by crystallization afforded the title compound in 1.44 g (63%) recovery, mp 170° C. (d) with softening at 135° C.
