34 ネジキの有毒主成分Lyoniol-A(Lyoniatoxin)の構造研究

抄録

Lyoniol-A (I) contains one acetoxyl group, four hydroxyl groups and an ethereal oxygen atom. Alkaline hydrolysis of lyoniol-A afforded deacetyl derivative, lyoniol-B (II). Lyonibl-B consumed one mole of sodium periodate, but lyoniol-A did not. Thus, the acetoxyl group must be located vicinal to a hydroxyl group. Oxidation of lyoniol-A with chromic acid gave a monoketone (V). Reduction of lyoniol-A with LiAlH_4 yielded dihydrolyoniol-B, a hexahydric alcohol (VII). This result suggested that the ethereal oxygen atom converted into a hydroxyl group and the cyclic ether must be an epoxide. Dihydrolyoniol-B was treated with p-tolu-enesulfonic acid in acetone to yield a monoacetonide (IX) and two monoanhydromonoacetonide (X) and (XI). The compound (X) gave a cyclopentanone derivative (XII) with chromic acid oxidation. Thus, the epoxide ring must be situated in the cyclopentane ring. The structure of lyoniol-A was suggested to be (I) from above results and by the analogy of grayanotoxin-I and rhodojaponin-II. The A,B-ring juncture was proved as trans by ORD measurement of 10-ketocompound derived from lyoniol-A. The cis and trans configuration of 3-ketocompound show a small difference in their octant frameworks (fig. 3). But 10-ketocompounds show a remarkable difference between their cis and trans configuration (fig. 4). The cis form is predicted to have slightly positive Cotton effect and the trans form negative. The observed ORD curve of 10-keto-compound derived from lyoniol-A (fig. 5) and grayanotoxin-II (fig. 6) have typical negative Cotton effects. Thus, the A,B-ring juncture of lyoniol-A and grayanotoxin-II must be trans.