Classification models for neocryptolepine derivatives as inhibitors of the ß-haematin formation.

This paper describes the construction of a QSAR model to relate the structures of various derivatives of neocryptolepine to their anti-malarial activities. QSAR classification models were build using Linear Discriminant Analysis (LDA), Quadratic Discriminant Analysis (QDA), Classification and Regression Trees (CART), Partial Least Squares-Discriminant Analysis (PLS-DA), Orthogonal Projections to Latent Structures-Discriminant Analysis (OPLS-DA), and Support Vector Machines for Classification (SVM-C), using four sets of molecular descriptors as explanatory variables. Prior to classification, the molecules were divided into a training and a test set using the duplex algorithm. The different classification models were compared regarding their predictive ability, simplicity, and interpretability. Both binary and multi-class classification models were constructed. For classification into three classes, CART and One-Against-One (OAO)-SVM-C were found to be the best predictive methods, while for classification into two classes, LDA, QDA and CART were.

Development and validation of an HPLC-method for the determination of alkaloids in the stem bark extract of Nauclea pobeguinii.

A new method was developed and validated for the quantification of strictosamide in the extract of the stem bark of Nauclea pobeguinii. This plant belongs to the Rubiaceae family and is widely used in the African traditional medicine against malaria and malaria-like symptoms. Alkaloids are suspected to be responsible for the antimalarial activity. One of these alkaloids is strictosamide, already reported to be the major constituent in the root bark of this plant. Because strictosamide was not commercially available another alkaloid, ajmalicine HCl, with comparable properties was used as a secondary standard. The samples of the dried 80% ethanol extract from the stem bark of N. pobeguinii were purified on C(18) solid phase extraction cartridges and analysed using HPLC-UV. The strictosamide used for the validation of the correction factor for response was isolated and purified by means of preparative HPLC and TLC. Although the relative standard deviation (R.S.D.) of 2.6% was still acceptable, the response factor was determined for every analysis based on the ratio of the peak area of strictosamide compared to the peak area of ajmalicine HCl in a concentration of 0.01 mg/ml. The precision of the method according to the time and the concentration, had a R.S.D. value of 2.2% and 2.6%, respectively. The recovery of the method was 92.2% (R.S.D. of 9.4%) which was acceptable. The method has been proven to be suitable for the determination of alkaloids in the extract of the stem bark of N. pobeguinii, according to the ICH guidelines on the validation of analytical methods.

A new decomposition product of dihydroartemisinin.

After prolonged storage, samples of dihydroartemisinin were found to contain a decomposition product with a molecular weight of 238, as evidenced by MS analysis, the formation of which was accelerated by heating at 60 degrees C for several days. This decomposition product was isolated and identified as 2-(3-oxobutyl)-3-methyl-6-(2-propanal)-cyclohexanon, known to be formed by thermolysis of dihydroartemisinin at 190 degrees C. However, during work-up of this compound a hitherto unknown decomposition product of dihydroartemisinin with a molecular weight of 210 was obtained and identified by 1H, 13C and two-dimensional NMR spectroscopy as 2-(3-oxobutyl)-3-methyl-6-ethyl-cyclohexanon. Most probably this product was formed by oxidation of the aldehyde functionality of the former decomposition product and subsequent decarboxylation.