Synthesis of Heterocyclic Triterpene Derivatives with Biological Activities via Click Reaction

Grignard reactions were applied to synthesize 2-ethynyl-2-hydroxylallobetulin 5 from 2-oxoallobetulin 4. The compound plays an important role as starting material to synthesize heterocyclic triterpenes using the click reaction. A series of new 1,2,3-triazole derivatives derived from 2-oxoallobetulin were successfully obtained. Under similar reaction conditions, only one compound 6 kept the hydroxyl functional group, while in the other compounds 7, 8 and 9, water was eliminated. The structures of obtained compounds were confirmed by 2D-NMR spectroscopy. The X-ray analysis of 5 indicated that only one isomer was obtained and in this compound, the hydroxyl group is situated on the same side as the ether group, the ethynyl group being situated at the opposite side. All products were also evaluated for their cytostatic activity in cell culture including L1210, CEM and Hela. Several compounds showed measurable cytostatic activity in the micromolar range.