Validation of an HPLC method for the determination of alkaloids in a stem bark extract of Nauclea pobeguinii

Nauclea pobeguinii (Rubiaceae) is a tree from which the bark is widely used in African traditional medicine against malaria-like symptoms. Although the active compounds are not yet identified, alkaloids are expected to be responsible for the activity. One of these alkaloids is strictosamide, already known as the major constituent of this plant [1,2]. An HPLC method was developed and validated for the quantification of strictosamide in an 80% ethanol extract of the stem bark of N. pobeguinii. Because strictosamide is not commercially available, another alkaloid, ajmalicine.HCl, with comparable chromatographic properties was used as a secondary standard.

The method was validated according to the ICH guidelines. The response of ajmalicine.HCl was linear in a concentration range from 4.2 to 21.2µg/mL. The accuracy of the method was investigated by means of a recovery experiment (mean recovery of 92.2% (RSD of 9.4%). The method was shown to be precise with respect to the time (RSD of 2.2%, 3 days, n=6) and with respect to the concentration (RSD of 2.6%, 3 levels, n=6). The average concentration of strictosamide in the samples was 5.6% (w/w). The correction factor between ajmalicine.HCl and strictosamide was determined in order to compensate for the difference in detector response.

Based on these results it can be concluded that the newly developed method is suitable for its purpose, namely the determination of the alkaloids in extracts of the stem bark of N. pobeguinii.

References: 1. Zeches, M. et al. (1985)J Nat Prod 48:42–46

2. Abreu, P. et al. (2001) Nat Prod Lett 15:43–48