Beta-boswellic acids are triterpenoids being generic to the plants of genus boswellia. Although they were shown to exhibit different biological activities, the cytotoxic potential of b-boswellic acid derivatives remained by and large unexploited. To expand the potential of these compounds we developed simple procedures for the interconversion of the most important b-boswellic acids 1-4 and prepared several other derivatives 5-48. These compounds were screened for their cytotoxic activity in sulforhodamine B assays employing several human tumor cell lines and nonmalignant mouse fibroblasts. One of these compounds, a difluoromethylester of 3-O-acetyl-11-keto-beta-boswellic acid 23, was cytotoxic for human breast adenocarcinoma cells MCF-7 (EC50 = 6.5 mM) while being significantly less cytotoxic for the mouse fibroblasts.
The aim of this study was to prepare 11-keto-β-boswellic acid derivatives modified at C-24 and to evaluate their in vitro cytotoxicity. Acetyl-11-keto-β-boswellic acid (AKBA) was isolated from frankincense and transformed into 11-keto-β-boswellic acid (KBA). Both compounds served as starting materials for the synthesis of several amides or hydrazides. The derivatives were fully characterized, and their cytotoxicity was evaluated in vitro using sulforhodamine B (SRB) assays employing two human tumor cell lines (A2780 and MCF7) as well as nonmalignant mouse fibroblasts (NIH 3T3). Nearly all of the compounds were more cytotoxic than their parent compounds. The highest cytotoxicity was observed for (3 α, 4 β) 3-acetyloxy-N-(3- aminopropyl)-11-oxo-urs-12-en-24-amide (15) and (3 α, 4 β) 3-acetyloxy-N-[4-(3-aminopropyl)piperazin-1-yl]- propyl-11-oxo-urs-12-en-24-amide (16) and the ovarian carcinoma cell line A2780. These compounds showed EC50 = 1.0-1.7 µM while being significantly less toxic for the mouse fibroblasts NIH 3T3 (EC50 = 9.3-16.3µM). Thus, compounds 15 and 16 have good antitumor effects and may serve as starting points for developing potential and selective antitumor agents
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