Synthesis of Duocarmycin SA by Way of Methyl 4-(Methoxycarbonyl)oxy-3H-pyrrolo[3,2-f] quinoline-2-carboxylate as a Tricyclic Heteroaromatic Intermediate.
作者:Hideaki MURATAKE、Miyuki TONEGAWA、Mitsutaka NATSUME
DOI:10.1248/cpb.46.400
日期:——
Formal syntheses of (±)-duocarmycin SA, natural (+)-duocarmycin SA and unnatural (-)-duocarmycin SA were accomplished by way of a tricyclic heteroaromatic compound 10b. For the preparation of 10, an N-oxide route aiming at a process 20 in Chart 3 was first investigated by synthesizing 19, derived from Stille coupling products 13 between bromopyrrole 7a and 3-(tributylstannyl)pyridines 12, but without success. As the second approach, Stille coupling products 9a-c were prepared by condensation between 7a and 2-substituted 3-(trialkylstannyl)pyridines 8a-f. Both 9b and 35, derived from 9c, were converted to their silyl enol ethers and then subjected to a palladium-catalyzed methyl ketone-arylation reaction in the presence of tributyltin fluoride and lithium chloride, affording 10a and 10b in excellent yields, especially from 35. Application to 10b of three successive operations, i.e., i) partial reduction of 10b to dihydropyridine derivatives 11a and 11b, ii) dihydroxylation of the double bonds formed to give 58 and 59, and iii) reductive elimination of the hydroxy groups adjacent to the nitrogen function and the aromatic ring, afforded 6 in fairly good yield. Compound 6 was readily converted to relay compounds 64 and 67, completing total syntheses of (±)-, (+)-, and (-)-duocarmycin SA. Both Sharpless asymmetric dihydroxylation (AD) and Jacobsen's asymmetric epoxidation were applied to 11a and 11b. At the best, 81% ee was observed in the AD reaction of 11a using 2, 5-diphenyl-4, 6-bis(9-O-dihydroquinyl)pyrimidine [(DHQ)2PYR], but the resulting 58 possessed an unnatural absolute configuration.
通过三环杂芳香族化合物 10b 正式合成了(±)-杜羧霉素 SA、天然(+)-杜羧霉素 SA 和非天然(-)-杜羧霉素 SA。为了制备 10,首先研究了 N-氧化物路线,目的是制备图 3 中的过程 20,合成了 19,它来自溴吡咯 7a 和 3-(三丁基锡)吡啶 12 之间的斯蒂尔偶联产物 13,但没有成功。第二种方法是通过 7a 和 2-取代的 3-(三烷基锡)吡啶 8a-f 缩合制备斯蒂尔偶联产物 9a-c。由 9c 制得的 9b 和 35 被转化为它们的硅基烯醇醚,然后在三丁基氟化锡和氯化锂存在下进行钯催化的甲基酮芳基化反应,以极好的收率得到 10a 和 10b,尤其是 35。对 10b 连续进行三次操作,即 i) 将 10b 部分还原为二氢吡啶衍生物 11a 和 11b;ii) 对形成的双键进行二羟基化反应,得到 58 和 59;iii) 还原消除邻近氮功能和芳香环的羟基,得到产率相当高的化合物 6。化合物 6 很容易转化为中继化合物 64 和 67,从而完成了 (±)-、(+)- 和 (-)- 二胭脂虫霉素 SA 的全部合成。对 11a 和 11b 采用了 Sharpless 不对称二羟基化(AD)和 Jacobsen 不对称环氧化反应。在使用 2,5-二苯基-4,6-双(9-O-二氢喹基)嘧啶[(DHQ)2PYR]对 11a 进行 AD 反应时,ee 值最高可达 81%,但生成的 58 具有非自然的绝对构型。