To a cooled solution of the appropriate methyl ester (1.0 eq.) in a mixture of MeOH and CH2Cl2 (2/1 (v/v)) over an ice bath, NaOH (40 eq.) and hydroxylamine (50% in H2O) (30 eq.) were added in one portion. The reaction mixture was stirred for 30 min at 0 °C before it was allowed to warm up to room temperature. The reaction was stirred for 2-8 hours at room temperature until full conversion of the ester was observed by HPLC. The solvents were evaporated under reduced pressure. 10 mL of water was added to the residue and the mixture was neutralized with 6 M hydrochloric acid. The formed precipitate was filtered out and washed with cold water and Et2O and either purified by preparative HPLC or flash chromatography (C18-reversed phase, 5-95% MeCN/H2O) or used without further purification.