Teucrium lactone

Vandewalle et al. have also used oxidative ring opening of one side of a norbomanone to prepare a number of iridoids, culminating in a synthesis and correction of the structure of specionin. At first they described the synthesis of teucrium lactone (425) and a loganin precursor (472) from the Diels-Alder adduct 473 of cyclopentadiene and methyl ( )-crotonate (Scheme 44). The same paper describes the preparation of the all-enafo-isomer 474 of ketone 475, from... 

The parent compound of the secoiridoids is secologa-nin (see secoiridoids), the most important intermediate in the biogenesis of alkaloids that are not derived from an amino acid. This includes most indole alkaloids, the ipecac, the Cinchona, and the pyrroloquinoline alkaloids as well as simple monoterpene alkaloids The best known biological property of the I. is their bitter taste. However, bitter principles are mostly not used as pure substances, instead alcoholic extracts are preferred to stimulate appetite (increased secretion of gastric juice). Furthermore, bitter substances are used to modify the taste of pharmaceutical products. Some I. exert various effects on the central nervous system as a consequence of their volatility and lipophilicity, e.g., nepetalactone, iridodial, teucrium lactones, and valepotriates. 

Teucrium lactones. C, o- Iridoids occurring in the germander species Teucrium marum (Lamiaceae), aplant indigenous to the Mediterranean region, the essential oil of which has strong lacrimatory properties (e.g., T, 1. A-D, CioHmOj, Mr 166.22). 

Teuflin, from Teucrium flavum (Labiatae) has been assigned the stereochemistry (39) epimeric at C-10 to teucvidin on the basis of an X-ray analysis. Isocrotocaudin (40) from Croton caudatus (Euphorbiaceae) is an 11(12)-dehydro-derivative which is similar to crotocaudin and teucvidin. The c.d. curves of the a/3-unsaturated lactones have been used to assign the absolute stereochemistry in this series. Plaunol A (41) and plaunol B (42) are anti-ulcer diterpenoid lactones which have been isolated from the Thai medicinal drug Croton sublyratus (Euphorbiaceae). Baccharis genistelloides (Compositae) has afforded a clerodane dilactone (43) similar to that isolated previously from B. trimera. 

In Teucrium diterpenoids C-6 position is also very important. Almost all of the neo-clerodane diterpenes have an oxygen function at that location, either as a hydroxyl, acetyl or a ketone, and sometimes as an ether function. In somecases, C-6 hydroxyl group forms a lactone with C-18 methylene group as in compounds 7, 14, 16. The hydroxyl or the acetyl groups could possess a or P stereochemistry. When the literature is studied, there are some discrepancies for the chemical shifts of the C-6 proton, either a or 3, it appears in the lowfield or highfield, as observed in compounds 77 and 78. 

---