Characterization of Microbial Degradation Products of Steviol Glycosides.

Steviol glycosides were subjected to bacteria present in a soil sample collected from a Stevia plantation in Paraguay. During the incubation experiments, next to the aglycon steviol, steviol degradation products were also formed. X-ray analysis and NMR methods in combination with chemical synthesis and GIAO NMR calculations were used to fully characterize the structure of these compounds as a tricyclic ketone and the corresponding reduced form. They were nicknamed monicanone and monicanol. The latter has the (S)-configuration at the alcohol site.

Synthesis of triterpenoid triazine derivatives from allobetulone and betulonic acid with biological activities.

The synthetic transformation and modification of natural products with the aim to improve the biological properties is an area of current interest. The triterpenoids betulin and betulinic acid are very abundant in nature and now are commercially available. In our study, starting from betulin and betulinic acid, we obtained allobetulone and betulonic acid in a few synthetic steps. The ketone function at the A-ring was used as the starting point for the synthesis of a series of 1,2,4-triazine-fused triterpenoids. The alkylation and Liebeskind-Srogl coupling were used for further substitution of 1,2,4-triazines, and the intramolecular hetero Diels-Alder reaction leads to interesting fused thienopyridine derivatives. All new compounds were tested for their cytostatic activities against murine leukemia L1210, human cervix carcinoma HeLa and human lymphoblast CEM tumor cells. The results show that some triterpenoid triazine betulonic acid derivatives have a promising cytostatic activity in vitro and could be used as potential leads for the development of new type of anti-cancer agents. Several compounds were also endowed with anti-HCMV activity in the low micromolar range.