Several novel betulin derivates were prepared using Mannich reactions as a key step. Starting from 3-ethynyl-3-hydroxy-lup-20(29)-ene derivatives, copper-catalyzed Mannich reactions yielded hydroxypropargyl ammonium hydrochlorides or their corresponding methiodides. All compounds were screened in a sulforhodamine B assay for their antitumor activity using a panel of 9 human cancer cell lines. Some of these compounds showed significant cytotoxicity; they act by triggering apoptotic cell death as shown by additional acridine orange/propidium iodide assays, Trypan blue tests, DNA laddering experiments, and investigations of the cell cycle.

Several triterpenoic acids display a remarkable cytotoxicity on tumor cells. Glycyrrhetinic acid – the main content of the licorice root – possesses an apoptotic effect on tumor cells. Previous studies pointed out the presence of a keto group at position C-11 in glycyrrhetinic acid derivatives as the main reason for its apoptotic activity. Several pairs of derivatives were synthesized differing only at position C-11. These compounds were tested in a sulforhodamine B colorimetric assay for cytotoxicity screening on 12 tumor cell lines and mouse embryonic fibroblasts (NIH3T3). Our results show that there is no direct relation between the existence of the C-11 keto group and the apoptotic activity of the compounds.

The extracts of the roots of licorice have been used in traditional and folk medicine to treat a broad variety of maladies. The main ingredient of these extracts is glycyrrhicinic acid. Its aglycon, glycyrrhetinic acid, has many biological activities, among them a pronounced cytotoxicity against tumor cells. In this study we varied glycyrrhetinic acid at position C-30 to get “simple” derivatives, for example esters, amides and a nitrile. The influence of these changes on the cytotoxic activity is noteworthy and was determined by a colorimetric sulphorhodamine B test using 7 human tumor cell lines and mouse embryonic fibroblasts (NIH3T3) for comparison. A Trypan blue test as well as an acridine orange/ethidium bromide test was used to discover the ability of the compounds to induce apoptosis.

Arglabin derivatives varied at the endo- or exo-cyclic double bond were synthesized and studied in a colorimetric sulforhodamine B assay for their cytotoxicity. Variations on the endocyclic double bond led to compounds of reduced cytotoxicity whereas derivatives from the reaction of the α-methylene-γ-butyrolactone moiety led to compounds of similar or only slightly reduced cytotoxicity but different, cell line-dependent selectivity. In addition, arglabin is an excellent starting material for the synthesis of the guaianolide arborescin.

Novel betulin derivatives were prepared and tested for their antitumor activity. Starting from 3-O-acetyl- or 3-O-methyl-betulinic aldehyde, the synthesis of C-28 ethynyl derivatives was performed; their subsequent transformation with several 1,3-dipolarophiles afforded pyrazoles and 1,2,3-triazoles. Their screening for antitumor activity was performed in a panel of 15 human cancer cell lines by a colorimetric SRB-assay. Thereby, several compounds revealed a higher cytotoxicity than betulinic acid. In addition, the encapsulation of the lead structure 7 into liposomes was investigated. The results from a dye exclusion test and from DNA laddering experiments provided evidence for an apoptotic cell death.

Glycyrrhetinic acid (GA) is a major ingredient of the dried extract of licorice roots; its antitumor activity is low compared to other members of the triterpenoic family. For example, oleanolic acid, betulin or betulinic acid are more cytotoxic with a pronounced activity for tumor cells. GA, however, is easily to earn, cheap and shows apoptotic effects on tumor cells – like the other triterpenoic acids. These facts bring GA and derivatives in the focus of our scientific interest. Here we tried to improve the poor cytotoxicity of GA by simple derivatization. Thus, we selected various glutamyl and aspartyl substituents for the synthesis of C(3) esters of GA methyl ester. A short (3-5 steps) synthesis was elaborated that allowed to access more effective compounds. One compound, methyl 3β 3-(O-benzyl-L-glutamyl)-11-oxo-olean-12-en-30-oate (5), having a glutamyl substituent with a benzyl protected side chain showed up to 67-fold higher cytoxicity and an up to 140-fold better selectivity towards tumor cells than parent GA. All compounds were evaluated by a sulforhodamine B assay as well as by a trypan blue test and extra acridine orange/ethidium bromide tests for apoptosis.

Selective monofluorination of the α-glycosidase inhibitor and antidiabetic agent miglitol at positions C(2′) or C(6) creates competitive inhibitors of glycosidases. Introducing a fluorine substituent at position C(6) results in a reduced binding to the enzyme whereas fluorination at C(2′) produces an inhibitor with an activity four times higher than the parent compound. This compound is selective for the α-galactosidase from green coffee beans. Its screening against a panel of human cell lines showed a low cytotoxicity, therefore, making this compound an interesting candidate for further clinical investigations.

Selective difluorination, introducing a lactame moiety (instead of an amine) and a double bond in a trihydroxy-2-thiaquinolizidine derivative reverses the selectivity of the glycosidase inhibitor – a selective inhibitor for an α-glucosidase is altered into an excellent, competitive inhibitor for a β-galactosidase.

The synthesis of dimeric compounds derived from quinazolin-2-one and 1,4-benzodiazepin-2-one possessing a piperazine or homopiperazine spacer was investigated. In addition, a piperazine spacered bis-isoalloxazine and a bis-riboflavin compound were prepared and their ability to interrupt the association of prion proteins and Alzheimer-specific Aβ peptides was investigated using a fast screening system based on flow cytometry. The bis-isoalloxazine 14 was identified as a new lead structure.

A series of triterpene endoperoxides was synthesized and screened for antitumor activity in a panel of 15 human cancer cell lines by a sulforhodamine-B (SRB) assay. The compounds induce apoptosis and show excellent antitumor activity.

Starting from substituted 9-chloroacridines, a series of quinacrine and spacered dimeric acridine compounds was prepared. Their ability to interrupt the protein association of prion- and Alzheimer-specific proteins and Ab peptides was explored using a fast screening system based on FACS analysis. The bis-acridines displayed a higher activity than the corresponding monomers. Among these derivatives, best results were obtained with the 2,4-dimethoxy-6-nitro compound 7h for Aβ-peptides and the 2-methoxy-6-nitro compound 7f for PrP.