Radioiodination and preliminary in vivo investigation of the alkaloid cryptolepine

In this paper we report the successful labelling of cryptolepine with ¹³¹I using the chloramine T method. Quality control by ITLC of the labelled product showed 80% labelling but when the mixture was equilibrated with some amberlite (Cl⁻) anion resin to exchange the excess free iodide, the radiochemical purity was raised to >90%. Preliminary biodistribution in a rat did not show specific localisation of the tracer; rather, rapid clearance from the blood was indicated. It appears that its main excretory pathway is the hepatobiliary tract despite its relatively small molecular weight of 365. Also, despite i.v. administration, an appreciable 8% uptake was found in the stomach at 1 h post injection, indicating the process of enterohepatic reflux. These findings may have some bearings on the antimicrobial property of the plant.