Sodium Hydroxide → 6-(2,3-Di-p-tolyl-7,8-dihydropyrido[2,3-b]pyrazin-5(6H)-yl)hexanoic acid

A solution of ethyl 6-(2,3-di-p-tolyl-7,8-dihydropyrido[2,3-b]pyrazin-5(6H)-yl)hexanoate (step 1)(2.8 g, 6.12 mmol) in MeOH (50 ml) was treated with 1M sodium hydroxide (9.18 ml, 18.36 mmol) and the resulting white suspension was heated at 50° C. for 2 hours. The mixture was allowed to cool to room temperature and concentrated under reduced pressure. The residue was diluted with water, acidified (pH 4, 2N HCl) and extracted with DCM (×3). The combined organic extracts were dried (MgSO4) and concentrated under reduced pressure to afford an oil which crystallized to yield the titled compound as an off-white solid;