54(PB1-3) クラブロン及びプナグランジンの全合成(ポスター発表の部)

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Marine eicosanoids such as clavulones and punaglandins are of unusual interest because of their relationship to prostaglandins, their antitumor activities and also the pathway of biosynthesis. In this presentation we wish to report novel syntheses of (+)-clavulone II (1) and (+)-punaglandin 4 (2) starting with either 1,2-bistrimethylsilyloxycyclopentene (6) or cyclopentanone. Both syntheses utilized the racemic hydroxy-ketone 5" as a key intermediate, which was easily derived from 1,2-bis-trimethylsilyloxycyclopentene (6) or cyclopentanone(Figure 3). The hydroxy-ketone 5" was efficiently converted to the cyclopentenone derivative 3' via allylic rearrangement of the mesylate derived from 17 in aqueous acetone (acetone-H_2O, 3: 1) (Figure 4). Aldol condensation of 3' with the optically active aldehyde 4 (R^2=Ac) synthesized from D-mannitol afforded the aldols 19 as a diastereomeric mixture, which was then treated with acetic anhydride in pyridine at 50℃, giving clavulone II (1) and 12-epi-clavulone II (20) (Figure 5). Similarly, the hydroxy-ketone 5" was also transformed into the α-chlorocyclopentenone derivative 8' through allylic rearrangement of 24 in 80% aqueous DMSO, which was subsequently condensed with the optically active aldehyde 9 derived from L-diethyl tartrate to provide 29 as a diastereomeric mixture (ca. 1: 1: 1: 1). The cyclopentenone 29 was converted to punaglandin 4 (2) in a three step (Figure 6 and 7). In order to improve the synthetic routes to 1 and 2, an asymmetric synthesis of the key intermediate 5" was undertaken. After several attempts, asymmetric reduction of 11 with lithium aluminum hydride partially decomposed by (-)-N-methylephedrine and 2-ethylaminopyridine was found to provide 12' with 96% e.e. in 91% yield, which was converted to the optically pure α-chlorocyclopentenone derivative 8 in the same route as described above.
天然有機化合物討論会の論文
1987-07-25

54(PB1-3) クラブロン及びプナグランジンの全合成(ポスター発表の部)

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