29. アブシシン酸が有する電子親和性の生理活性における重要性

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Abscisic acid (ABA, 1) possesses electrophilicity derived from the conjugated dienecarboxyl group in the side chain. In the cathodic reaction, ABA is reduced to give a derivative with a three-membered ring. The electrophilicity of ABA may play an important role in expression of physiological function through its binding to the receptor. We synthesized ABA derivatives in which the side chains are partially or completely reduced, and tested the biological activity of the derivatives to examine the relationship between the electrophilicity and biological activity. ABA derivatives possessing partially reduced side chains were synthesized by cathodic reaction. In the cathodic reaction of ABA, an added electron localizes at C-5 and then C-5 attacks C-2' with low electron density. To prevent this intramolecular conjugate addition, (+)-1', 4'-trans-diol-ABA methyl ester (2) was reduced at a cathode in an aqueous 20% CH_3CN solution. The products were oxidized with MnO_2, and hydrolyzed to give (+)-2, 5-dihydro-ABA (3), (3R, 1'S)- and (3S, 1'S)-(+)-2, 3-dihydro-ABAs (4a and 4b, respectively). The absolute configuration at C-3 of 4a and 4b was elucidated by ozonolysis which gave (2R)-(+)- and (2S)-(-)-metylsuccinic acids, respectively. Hydrogenation of (+)-ABA gave (3S, 1'S)- and (3R, 1'S)-(+)-2, 3, 4, 5-tetrahydro-ABAs (5a and 5b, respectively). The absolute configuration of 5a and 5b was determined by HPLC analysis of 4a and 4b reduced by hydrogenation. These derivatives were new compounds. Inhibitory activity of 3, 4a, 4b, 5a and 5b was 1/30 to 1/1000 of (+)-ABA in germination of lettuce seed and elongation of rice seed. This result suggests importance of the electrophilic side chain of ABA for the biological activity.
植物化学調節学会の論文
2004-10-13

29. アブシシン酸が有する電子親和性の生理活性における重要性

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