The determination of a chlorinated benzofuran pharmaceutical intermediate by HPLC-MS with on-line derivatization

An HPLC-MS method for the analysis of 2-chloromethylbenzofuran, a pharmaceutical intermediate alkylating reagent employed in the preparation of a second generation HIV protease inhibitor, N-(2(R)-hydroxy-1(S)-indanyl)-2(R)-phenylmethyl-4(S)-hydroxy-5-(1-(4-(2-benzo[b]furanylmethyl)-2(S)-N'-9-t-butyl-carboxamido)-pipera zinyl))-pentaneamide, is described. Preliminary analysis of the protease inhibitor by HPLC-MS indicated that the quality of the drug substance was influenced by the composition of the chloromethylbenzofuran. Direct analysis of the chloromethylbenzofuran by LC-MS using atmospheric pressure ionization was unsuccessful, necessitating an alternative approach. The method described incorporated post-column derivatization of the chloromethyl benzofuran using a modification of the drug substance process chemistry yielding a derivative amenable to MS analysis using atmospheric pressure chemical ionization (APCI). This allowed measurement of an impurity in the chloromethylbenzofuran which was incorporated into the protease inhibitor. (C) 2000 Elsevier Science B.V. All rights reserved.