Development and validation of a stability-indicating RP-HPLC method for assay of alphamethylepoxide and estimation of its related compounds.

Alphamethylepoxide (16alpha-methyl-Delta1,4-pregnadiene-9beta-11beta-oxide-17alpha,21-diol-3,20-dione) is a key intermediate for the synthesis of various active pharmaceutical ingredients of steroid compounds. A stability-indicating reversed-phase high-performance liquid chromatographic (RP-HPLC) method for the assay of alphamethylepoxide and estimation of its related compounds has been developed and validated. It can accurately quantitate alphamethylepoxide in the presence of numerous structurally related compounds (including the beta-epimer, known as betamethylepoxide). This method can also adequately separate most of the impurities from each other and estimate their quantities in alphamethylepoxide samples. The stability-indicating capability of this method has been demonstrated by adequate separation of the degradation products from alphamethylepoxide in stress degraded and aged stability samples. A 15 cmx4.6 mm i.d. ACE C18 HPLC column is the primary column used in this method, and a 15 cmx4.6 mm i.d. A Develosil ODS UG column serves as the alternative column. The mobile phase consisted of 10 mM sodium sulfate, 0.05% (v/v) phosphoric acid, and acetonitrile. This method can accurately assay the content of alphamethylepoxide (in a given lot) with a % relative standard deviation of less than one. It can also estimate individual impurities down to 0.05% level compared with the alphamethylepoxide peak in the sample.