P-48 マンザシジンBの合成と相対・絶対配置の改定(ポスター発表の部)

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Manzacidin A-C, isolated from an Okinawan sponge Hymeniacidon sp., possess a unique structure consisting of an ester-linked bromopyrrolecarboxylic acid and a 3,4,5,6-tetrahydropyrimidine in which one of the amino groups attached to the C6 quarternary carbon center. The structures of manzacidin A (1) and C (3) have been confirmed as the C6 isomers with the same 4S configuration by our previous total synthesis of both 1 and 3. On the other hand, 4S,5S,6S configuration was assigned to the structure of manzacidin B (2) that was needed for the structural confirmation by the synthesis. We planned the syntheses of four possible diastereomers 4a-4d by stereochemically unambiguous processes starting with α-methyl Garner aldehyde (R)-5. The isomers, (4R,5S,6R)-4a and (4S,5R,6R)-4b, were synthesized from (E)-unsaturated ester 6a by the following sequence of transformations: (1) stereoselective dihydroxylation, (2) thionocarbonate formation followed by S_N2 azidation, and (3) reduction of the azide group, deprotection, amidination, and esterification with 4-bromopyrrolecarboxylate. Cu-catalyzed condensation of an isonitrile with (R)-5 was the key step for the synthesis of 4c,d. The reaction gave a 7: 1 mixture of trans-oxazolines 16a,b. Hydrolysis followed amidination-esterification gave a mixture of (4R,5R,6R)-4c (ent-2: major isomer) and (4S,5S,6R)-4d. Since the major isomer 4c, upon treatment with NaH, was isomerized to 4b, structures of 4c,d were assigned as above. Comparisons of the ^1H and ^<13>C NMR spectral data and sign of the optical rotation of 4a-d with those of natural product clearly indicated that (4S,5S,6R)-4d is identical in all respects with natural manzacidin B. Thus, the structure of manzacidin B was revised to 4d.
天然有機化合物討論会の論文
2006-09-15

P-48 マンザシジンBの合成と相対・絶対配置の改定(ポスター発表の部)

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