The biosynthesis of [5'-C-14]cotinine and other radiolabeled nicotine metabolites

The present study. describes the biosynthesis and isolation of the major ra diolabeled nicotine metabolites formed using phenobarbitone (PB)-induced ra bbit hepatic homogenates (10,000g fraction). The optimal incubation and ext raction methods for cotinine formation from non-labeled nicotine were estab lished. The biosynthesis and isolation of [5'-C-14]cotinine and other radio labeled metabolites such as [2'-C-14]nornicotine and [4-C-14]-(3-pyridyl)-4 -oxobutyric acid, from commercially available [2'-C-14]nicotine, were carri ed out using the developed methods. Cotinine was isolated using preparative silica gel TLC, whereas the other metabolites were obtained using a cation -exchange HPLC method. This study showed that in addition to the two major metabolites (i.e. cotinine and nornicotine), 4-(3-pyridyl)-4-oxo-butyric ac id, 3-hydroxycotinine, norcotinine, nicotine-1'-N-oxide and cotinine-1-N-ox ide were also formed when PB-induced rabbit hepatic homogenates were used. Two further metabolites of unknown structure were detected. However, the is olation and further purification were only carried out on cotinine, nornico tine and 4-(3-pyridyl)-4-oxo-butyric acid.