Herbal plants used in TCM as a source of compounds with ... - Bora

Results and discussionWith the exception of five carbons, the vinylic plus one other, the carbon shifts for compound C2are very similar to the shifts seen for C6 (see Table 4.4). It is therefore reasonable to expect thetwo compounds to have some similarities. Since the carbonyls in the two compounds haveidentical shift values, it is assumed that C2 also includes an acid. The difference in molecularmass of C6 and C2 is 32 amu, which corresponds to two oxygens. This is consistent with thetwo carbon signals at 82.2 ppm and 79.8 ppm. These could arise from two carbons bound toone oxygen each. These assumptions would give a molecular formula of C 20 H 30 O 4 , which has 6degrees of unsaturation. The carbonyl and vinylic group uses two unsaturations. Thesimilarities of the carbon shift between C6 and C2 would indicate a similar tricyclic nucleus,which then leaves one unsaturation. If one double bond in C6 has been replaced by twooxygens and the only difference in the molecular formula is the two oxygens and no hydrogens,the two oxygens have to bind with each other, forming an epidioxy bridge. This adds up the lastunsaturation.Yang et al’s. (2008) review article on diterpenes from Abies species [10] shows a compoundthat match the description, a 9,13 -epidioxy-8(14)-abieten-18-oic acid. The NMR- data for C2was compared to data from earlier work on 9,13-epidioxy-8(14)-abieten-18-oic acid, andconfirmed to be 9,13(β)-epidioxy-8(14)-abieten-18-oic acid and the peaks were assignedaccording to this.[25]-54-