| Abstract
| - Pentacyclic triterpenes from the 11-keto-boswellic acid series were identified as the active principalingredients of Boswellia resin, inhibiting the key enzyme of leukotriene biosynthesis, 5-lipoxygenase (5-LO). Of the genuine boswellic acids hitherto characterized, 3-O-acetyl-11-keto-β-boswellic acid, AKBA(1), proved to be the most potent inhibitor of 5-LO. In the course of purification of further boswellic acidderivatives from Boswellia resin, we observed the degradation of the natural compound 3-O-acetyl-11-hydroxy-β-boswellic acid (2) to the thermodynamically more stable product 3-O-acetyl-9,11-dehydro-β-boswellic acid (4). The metastable intermediate of this conversion, under moderate conditions of workupin methanolic solutions, was identified as 3-O-acetyl-11-methoxy-β-boswellic acid (3). The novel artifactualboswellic acid derivatives inhibited 5-LO product formation in intact cells with different characteristics: 4 almost totally abolished 5-LO activity, with an IC50 of 0.75 μM, whereas 3 and 9,11-dehydro-β-boswellicacid (5), the deacetylated analogue of 4, were incomplete inhibitors. The data suggest that the conditionschosen for the workup of Boswellia extracts could significantly influence the potency of their biologicalactions and their potential therapeutic effectiveness.
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