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

Abstract

The present study describes the biosynthesis and isolation of the major radiolabeled nicotine metabolites formed using phenobarbitone (PB)-induced rabbit hepatic homogenates (10,000 g fraction). The optimal incubation and extraction methods for cotinine formation from non-labeled nicotine were established. The biosynthesis and isolation of [5′-14C]cotinine and other radiolabeled metabolites such as [2′-14C]nornicotine and [4-14C]-(3-pyridyl)-4-oxobutyric acid, from commercially available [2′-14C]nicotine, were carried 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 acid, 3-hydroxycotinine, norcotinine, nicotine-1′-N-oxide and cotinine-1-N-oxide were also formed when PB-induced rabbit hepatic homogenates were used. Two further metabolites of unknown structure were detected. However, the isolation and further purification were only carried out on cotinine, nornicotine and 4-(3-pyridyl)-4-oxo-butyric acid. Copyright © 1999 John Wiley & Sons, Ltd.