| Budget Amount *help |
¥2,800,000 (Direct Cost: ¥2,800,000)
Fiscal Year 1996: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 1995: ¥2,200,000 (Direct Cost: ¥2,200,000)
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| Research Abstract |
Abscisic acid (ABA) is an unique hormone protecting plants from environmental stresses. Analogues of ABA were synthesized to investigate the interaction between ABA and receptors.
(1) Role of the hydroxyl groups. The activity of 1'-deoxy-1'-fluoro-and 1'-deoxy-ABAs suggested that the 1'-hydroxyl group may interact with the receptor by means of an uncharged hydrogen bond. The activity of 8'-fluoro-ABA suggested that the 8'-hydroxyl group of 8'-hydroxy-ABA does not affect the acitivity of ABA,meaning that the activity of highly labile 8'-hydroxy-ABA is as strong as that of (+) -ABA.
(2) Examination of the pseudo-symmetry of ABA.7'-, 8'-and 9'-Methyl-, and 7'-, 8'-and 9'-ethyl analogues of ABA,whose pseudo-symmetry is decreased, were synthesized. The correlation of the decrease in the activity of (-) -7'-and 9'-alkyl-ABAs with that of (+) -9'-and 7'-alkyl-ABAs, respectively, seemed to agree with the hypothesis. The activity of the 8'-alkyl-ABAs indicated that the activity was relatively unaffected by the bulky group at C-8' of (+) -ABA.Alkylation of C-8' and C-9', especially that of C-8', of (-) -ABA markedly reduced the activity. C-8' of (-) -ABA would occupy the space facing the re-face of C-2' in natural (+) -ABA.The low activity of (-) -8'-alkyl-ABA suggests the presence of a strict steric requirement of the binding sites to occupy the re-face of C-2' in (+) -ABA.
(3) The active conformation The cyclopropane analogues and the achiral cyclohexadienone analogue of ABA were designed, and synthesized. The activiti of these analogues suggested that the axial substituent at the beta-side of the ring is fatal to the activity. The active conformation of abscisic acid would be a conformation where C-9' is equatorial and the side chain is between pseudo-axial and bisectional, that is, close to the favored half-chair with the side chain pseudo-axial rather than the less favored half-chair with the side chain pseudo-equatorial.
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