P-3 海綿由来アデニン環含有ジテルペノイドの合成研究 : (±)-Agelasimine-Aおよび(±)-Agelasimine-Bの合成(ポスター発表の部)

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Agelasimine-A (1a) and agelasimine-B (2a) are novel adenine-related bicyclic diterpenoids isolated from the orange sponge Agelas mauritiana. Their chemical structures have been proposed on the basis of extensive spectral studies. In an attempt to confirm the correctness of these proposals by chemical synthesis, we set out the racemic syntheses of the candidate structures 1a and 2a. 1. Syntheses of the N(7)-Benzyl Analogues 1b and 2b (Scheme 1) Four-step synthetic routes from 3-methyladenine (5) to 1b and 2b, selected as models for 1a and 2a, respectively, were established. The key steps involved are regioselective methylations of 7 and 9. 2. Construction of the Diterpene Portion: Synthesis of the Diol (±)-4 (Scheme 2) The synthesis of the diterpene portion, a common structural unit of 1a and 1b, was accomplished as the diol (±)-4 through a route starting from 10 and proceeding via the intermediates 11, 12, 13, 14, 15, 18, 19, and 20. 3. Syntheses of (±)-Agelasimine-A [(±)-1a] and (±)-Agelasimine-B [(±)-2a] (Scheme 3) To complete the syntheses of (±)-1a and (±)-2a, the diol (±)-4 was converted to the corresponding bromide, and the succeeding steps were achieved according to synthetic routes parallel to those to the N(7)-benzyl analogues 1b and 2b. The identities of synthetic (±)-1a and (±)-2a with agelasimines-A and -B, respectively, established the structures and relative stereochemistries of these marine diterpenoids. 4. Acetylation of (±)-1a and (±)-2a: Synthesis of the Purino-diterpene (±)-3a The reaction of (±)-1a with acetic anhydride in pyridine was found to give the monocyclic imidazole derivative (±)-27a instead of the purine structure 28a proposed for diacetylagelasimine-A. A similar acetylation of (±)-2a produced the purino-diterpene (±)-3a, together with (±)-N^6-acetylagelasimine-B [(±)-29a] which was transformed to (±)-3a on treatment in boiling 50% aqueous EtOH. Therefore, the present results suggest that the artifact purino-diterpene 3a, isolated from the acetylated mixture of the crude extract of A. mauritiana, might have originated from agelasimine-B (2a) through N^6-acetylagelasimine-B (29a).
天然有機化合物討論会の論文
1995-09-01

P-3 海綿由来アデニン環含有ジテルペノイドの合成研究 : (±)-Agelasimine-Aおよび(±)-Agelasimine-Bの合成(ポスター発表の部)

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