P-56 オルトキノンの環化付加反応を利用したクレオミスコシンCの合成研究(ポスター発表の部)
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Cleomiscosin C (aquillochin, 1) and the regioisomer cleomiscosin D (2) were isolated from seeds of Cleome viscose and they were shown to exhibit lipid peroxidation inhibitory activity and antibacterial activities. The feature of their structure is the hybrid framework of 1,4-benzodioxane and coumarin. In conjunction of our interest in the cycloaddition reaction for construction of 1,4-benzodioxanes, we have embarked on syntheses of natural products including the moiety. In the presentation, we wish to report our efforts toward a synthesis of 1, along with investigations into problems of the cycloaddition reaction. It was recently reported by us that the cycloaddition reaction of o-quinone 3 and protected sinapyl alcohol 4 gave 1,4-benzodioxanes 5 and 5'. However, two problems remained unsolved: (1) The regioselectivity was not so high. (5A/5'A=2/1) (2) The substitution patterns of the resulted adducts were not clear by NMR analysis. To overcome problem (1), we found that introduction of alkoxy group to the o-quinone increased the regioselectivity and that the selectivity was reversed depending on the position of the alkoxy group. To clear problem (2), we developed two novel procedures which confirmed the structure of the adducts based on the partial ring cleavage of the 1,4-benzodioxane. Synthesis of 1 commenced with selective protection of 2',4'-dihydroxyacetophenone (13). Conversion of the protecting group of 14 and sequential introduction of bromine afforded 16. After protection of ketone of 16, resulted 17 was converted to arylsilane 18 by intramolecular transposition of the TBS group. Oxidation of 18 with IBX afforded o-quinone 19. In the oxidation, only 3F was produced from 22. [X=Br, CHO, CH(SCH_2)_2] Cycloaddition of 19 and 4 proceeded smoothly to give a predicted cycloadduct 23 as a single isomer. Conversion of silyl group of 23 to methoxy group of 26 was achieved by way of iodination and subsequent Ullmann reaction.
- 天然有機化合物討論会の論文
- 2006-09-15
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