title: Analysis of 2,2'-azobis (2-amidinopropane) dihydrochloride degradation and hydrolysis in aqueous solutions.
abstract: 2,2'-Azobis(2-amidinopropane) dihydrochloride (AAPH), a free radical-generating azo compound, is gaining prominence as a model oxidant in small molecule and protein therapeutics, namely for its ability to initiate oxidation reactions via both nucleophilic and free radical mechanisms. To better understand its degradation pathways, AAPH was degraded at 40°C in aqueous solutions over a wide pH range. Samples were analyzed via liquid chromatography-ultraviolet spectroscopy and liquid chromatography-tandem mass spectrometry (LC-MS/MS). The thermal decomposition rate of AAPH to form radical species averaged 2.1 × 10(-6) s(-1) and did not vary significantly with pH. The hydrolysis rate increased exponentially with pH, showing hydroxide ion dependence. A mechanism for AAPH hydrolysis is proposed. The LC-MS/MS results provided evidence that the alkoxyl radical is a major radical species in solution. The LC-MS/MS results also showed a radical disproportionation reaction and enabled the generation of an overall reaction scheme showing the various side and termination products of AAPH degradation.
authors.affiliation: Late Stage Pharmaceutical Development, Genentech, Inc., South San Francisco, California 94080.
authors.forename: Jay
authors.initials: J
authors.lastname: Werber
authors.affiliation: Late Stage Pharmaceutical Development, Genentech, Inc., South San Francisco, California 94080.
authors.forename: Y John
authors.initials: YJ
authors.lastname: Wang
authors.affiliation: Late Stage Pharmaceutical Development, Genentech, Inc., South San Francisco, California 94080.
authors.forename: Michael
authors.initials: M
authors.lastname: Milligan
authors.affiliation: Drug Studies Unit, University of California, San Francisco, South San Francisco, California 94080.
authors.forename: Xiaohua
authors.initials: X
authors.lastname: Li
authors.affiliation: Late Stage Pharmaceutical Development, Genentech, Inc., South San Francisco, California 94080. Electronic address: ji.junyan@gene.com.
authors.forename: Junyan A
authors.initials: JA
authors.lastname: Ji
mesh_terms: D000578:Amidines / Q000737:chemistry*; D002853:Chromatography, Liquid; D003500:Cyclization; D005609:Free Radicals / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D015394:Molecular Structure; D016877:Oxidants / Q000737:chemistry*; D012996:Solutions; D013056:Spectrophotometry, Ultraviolet; D053719:Tandem Mass Spectrometry
chemical_list: D000578:Amidines; D005609:Free Radicals; D016877:Oxidants; D012996:Solutions; C046728:2,2'-azobis(2-amidinopropane)