75(P-69) アロハイナペンBの全合成(ポスター発表の部)

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Arohynapenes are new anticoccidial agents, isolated from the fermentation broth of Penicillium sp. FO-2295 strain and their structures have been proposed as shown in Fig. 1. Although the absolute stereochemistry of arohynapenes are unclear, in comparison with the spectral data of an analogous natural product, tanzawaic acid A, the relative stereochemistry of arohynapene B is deduced to be cis. In this study, we planed the total synthesis of racemic arohynapene B starting from cis-3,5-dimethylcyclohexanone in order to confirm its relative stereochemistry. Treatment of cis-3,5-dimethylcyclohexanone (2), prepared from 3,5-dimethyl-2-cyclohexen-1-one (1) via stereoselective hydrogenation (H_2, Pd/C), with ethynylmagnesium bromide, followed by acetylation gave propargyl acetate derivative 3. Acetate 3 rearranges in benzene containing a catalytic amount of silver trifluoroacetate under reflux to afford 1,3-dienyl acetate 4, which underwent Diels-Alder reaction with dimethyl acetylenedicarboxylate. After heating in toluene under reflux for four days, the reaction mixture was treated with DBN to provide tetrahydronaphtalene-dicarboxylate derivative 5. With the tetrahydronaphthalene skeleton in hands, we next focused the elongation of the dienylcarboxylic acid side chain. After reduction of diester 5 with LAH, selective protection of the 2-hydroxymethyl group in diol 6 was investigated. Moderate selectivity was observed when TBSCl-imidazole/DMF was used for the protection condition. Oxidation of the remaining hydroxy group to aldehyde, followed by Horner-Wadsworth-Emmons reaction gave unsaturated ester 9, which was subjected to reduction, oxidation and HWE reaction afforded protected arohynapene B. Finally, hydrolysis of the ester moiety, followed by cleavage of the silyl ether under mild acidic condition furnished (±)-arohynapene B.
天然有機化合物討論会の論文
2004-10-01

75(P-69) アロハイナペンBの全合成(ポスター発表の部)

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