43 Zeorin及びLeucotylinの立体化学

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The stereochemical studies especially on rings D,E and ring E side chain of zeorin(5), leucotylin(6), and leucotylic acid(7), which were isolated from lichen, Parmelia leucotyliza Nyl., have been performed. It has been found at the beginning that leucotylin possesses an eoimeric hydroxyisopropyl side chain at C_<21> against zeorin, which has been believed to have hopane skeleton. Thus, a monoketone(15) derived from leucotylin has been found identical with a monoketone(24), obtainable from zeorin and being epimeric to it at C_<21>. Furthermore, a hydrocarbon(25) possessing the same carbon skeleton as zeorin has been proved identical with hopane, whereas a hydrocarbon(26) carrying the same carbon framework as leucotylin has been identified with isohopane (≡moretane). Since the fact that the widely co-existed triterpenes, zeorin and leucotylin, in the lichen have the epimeric carbon skeletons at C_<21> seemed quite interesting from the biogenetical view-point and it seemed worthwhile to search for the final proof on their stereostructures, the X-ray analysis of 6-keto-leucotylin-16β-O-p-bromobenzoate (28) has been done. Strikingly, it has been found that leucotylin in fact possesses α quasi-equatorial side chain at C_<21> (as in (6)) and consequently it follows that isohopane should be expressed by (26) with α isopropyl at C_<21> rather than β as believed before and in addition, zeorin and hopane must be formulated by (5) and (25) having β isopropyl side chain at C_<21> rather than α. Leucotylic acid has also been proved as (7) having β-hydroxyisopropyl side chain at C_<21> similarly as in zeorin based on its chemical and physicochemical behaviours.
天然有機化合物討論会の論文
1967-09-25

43 Zeorin及びLeucotylinの立体化学

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