Teucrolivin

From Teucrium oliverianum [34,68] the two C-10 hydroxylated neo-clerodane diterpenes were isolated, teucrolivins B (115) and A (116). Both possess a C-103 hydroxyl group appeared at 8 81.53 and 81.73, respectively, the 3-configuration of them was supported by NOE experiments, which showed that C-20 methyl group and the H-1 a proton must be close (3.7 % NOE enhancement in H-1 a when the Me-20 protons were irradiated). The NOE experiments summarized in Table 15 clearly revealed that the relative stereochemistry of the substituents of decalin ring of teucrolivin B is that depicted in its formula 115. 

From T. oliverianum [68,70] two neo-clerodanes with a P-oxygen function at C-10 were isolated. These compounds were named teucrolivin A (120) and teucrolivin F (121). 

The relative configuration of all the asymmetric centres of 120 was established by NOE experiments. This date clearly showed that C-6, C-8 and C-18 protons are on the same side of the plane, since irradiation at 5 5.26 (H-6p) caused NOE enhancement in the signals of H-8P and Hb-18 protons and vise versa. Also from the NOE data it was decided that Me-20 is c/5-oriented with respect to the H-la, H-7a, Me-17 and C-19 methylene protons with enhancements 5.7, 0.9, 1.7, 7.5%, respectively. The H and NMR spectra of teucrolivin F (121) were identical with those of teucrolivin A (120) except for the absence of the signals corresponding to the P-substituted furan ring and the downfield resonance of the C-12 carbon, which forms a 12, lOP-y-lactone in teucrolivin F (121) [Sc-12 173.09 5c-io 91.59 v 1790 cm i (y-lactone) and no hydroxyl absorptions] instead of the 12R, lOP-hemiacetal of 120 (5c-i2 100.77, 5c-io... 

Similar processes have been designed and utilized extensively by Barriault and coworkers for efforts in natural product synthesis. An impressive example of this strategy was utilized for the synthesis of the neo-clerodane skeleton of teucrolivin A. Thermal rearrangement of 92 under microwave irradiation results in a tandem sequence featuring an oxy-Cope rearrangement, followed by the Claisen rearrangement and subsequent ene reaction to give 93. 

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