Department of Biochemistry, University of Wisconsin-Madison, 433 Babcock Drive, Madison, WI 53706, USA.
Bioorg Med Chem. 2011 Dec 1;19(23):7205-20. doi: 10.1016/j.bmc.2011.09.048. Epub 2011 Oct 2.
As a continuation of our studies focused on the vitamin D compounds lacking the C,D-hydrindane system, 13,13-dimethyl-des-C,D analogues of (20S)-1α,25-dihydroxy-2-methylene-19-norvitamin D(3) (2, 2MD) were prepared by total synthesis. The known cyclohexanone 30, a precursor of the desired A-ring phosphine oxide 11, was synthesized starting with the keto acetal 13, whereas the aldehyde 12, constituting an acyclic 'upper' building block, was obtained from the isomeric esters 34, prepared previously in our laboratory. The commercial 1,4-cyclohexanedione monoethylene ketal (13) was enantioselectively α-hydroxylated utilizing the α-aminoxylation process catalyzed by l-proline, and the introduced hydroxy group was protected as a TBS, TPDPS, and SEM ether. Then the keto group in the obtained compounds 15-17 was methylenated and the allylic hydroxylation was performed with selenium dioxide and pyridine N-oxide. After separation of the isomers, the newly introduced hydroxy group was protected and the ketal group hydrolyzed to yield the corresponding protected (3R,5R)-3,5-dihydroxycyclohexanones 30-32. The esters 34, starting compounds for the C,D-fragment 12, were first α-methylated, then reduced and the resulted primary alcohols 36 were deoxygenated using the Barton-McCombie protocol. Primary hydroxy group in the obtained diether 38 was deprotected and oxidized to furnish the aldehyde 12. The Wittig-Horner coupling of the latter with the anion of the phosphine oxide 11, followed by hydroxyl deprotection furnished two isomeric 13,13-dimethyl-des-C,D analogues of 2MD (compounds 10 and 42) differing in configuration of their 7,8-double bond. Pure vitamin D analogues were isolated by HPLC and their biological activity was examined. The in vitro tests indicated that, compared to the analogue 7, unsubstituted at C-13, the synthesized vitamin D analogue 10 showed markedly improved VDR binding ability, significantly enhanced HL-60 differentiation activity as well as increased transcriptional potency. Docking simulations provided a rational explanation for the observed binding affinity of these ligands to the VDR. Biological in vivo tests proved that des-C,D compound 10 retained some intestinal activity. Its geometrical isomer 42 was devoid of any biological activity.
作为我们对缺乏 C,D-氢化茚系统的维生素 D 化合物研究的延续，通过全合成制备了（20S）-1α,25-二羟基-2-亚甲基-19-降维 D（3）（2,2MD）的 13,13-二甲基-去 C,D 类似物。已知的环己酮 30 是所需 A 环膦氧化物 11 的前体，它是从酮缩醇 13 开始合成的，而醛 12 则是无环的“上部”构建块，是由我们实验室以前制备的异构酯 34 获得的。商业的 1,4-环己二酮单缩乙二醇酮（13）利用 l-脯氨酸催化的α-氨氧化过程进行对映选择性α-羟化，引入的羟基被保护为 TBS、TPDPS 和 SEM 醚。然后，在获得的化合物 15-17 中，酮基被亚甲基化，并且用二氧化硒和吡啶 N-氧化物进行烯丙基羟化。异构体分离后，新引入的羟基被保护，缩酮基水解得到相应的保护（3R,5R）-3,5-二羟基环己酮 30-32。酯 34 是 C,D-片段 12 的起始化合物，首先进行α-甲基化，然后还原，得到的一级醇 36 用 Barton-McCombie 方案脱氧。得到的二醚 38 中的伯羟基被脱保护并氧化为醛 12。后者与磷氧化物 11 的阴离子的 Wittig-Horner 偶联，然后羟基脱保护得到两个 2MD 的 13,13-二甲基-去 C,D 类似物（化合物 10 和 42），它们在 7,8-双键的构型上有所不同。通过 HPLC 分离得到纯维生素 D 类似物，并对其生物活性进行了测试。体外测试表明，与在 C-13 位未取代的类似物 7 相比，合成的维生素 D 类似物 10 表现出明显改善的 VDR 结合能力、显著增强的 HL-60 分化活性以及增加的转录效力。对接模拟为这些配体与 VDR 的观察到的结合亲和力提供了合理的解释。体内生物测试证明，去 C,D 化合物 10 保留了一些肠道活性。它的几何异构体 42 没有任何生物活性。
