Synthesis of Chiral<i>ansa</i>-Bridged Macrocyclic Lactams ([16]Metacyclophanes) Related to Geldanamycin
作者:Thorsten Bach、Aude Lemarchand
DOI:10.1055/s-2005-869970
日期:——
Two chiral ansa-bridged lactams ([16]metacyclophanes) 2a,b were synthesized starting from 2-methoxyhydroquinone diisopropyl ether (6) in 14 (2a, 3.9% overall) and 16 synthetic steps (2b, 0.6% overall). Both compounds contain typical features of geldanamycin (1) in the C-1 to C-9 part of the ansa chain, i.e. the α,β,γ,δ-unsaturated anilide (C-1 to C-5), the carbamate at the stereogenic carbon atom C-7 and the E-double bond between C-8 and C-9. While the rest of the ansa chain (C-10 to C-15) was an alkyl chain in compound 2a, a more polar CH2OCH2CH2OCH2 chain was installed in compound 2b. Key step of the sequence was a ring-closing metathesis in which the ansa compounds 3 were formed as a mixture of isomers. Deprotection and oxidation to the quinone failed for diisopropyl ether 2b but was successfully conducted with precursor 2a.
以2-甲氧基氢醌二异丙醚(6)为起始物,经过14步(2a,总收率3.9%)和16步(2b,总收率0.6%)合成,制得了两种手性ansa-桥连内酰胺([16]环烯)2a,b。两化合物在ansa链的C-1至C-9部分均含有格尔德霉素(1)的典型结构特征,即α,β,γ,δ-不饱和酰胺(C-1至C-5)、C-7手性碳上的氨基甲酸酯以及C-8和C-9之间E-型双键。而在ansa链的剩余部分(C-10至C-15),化合物2a为烷基链,化合物2b为极性更强的CH2OCH2CH2OCH2链。合成序列中的关键步骤是通过关环歧化反应生成了混合异构体的ansa化合物3。对二异丙醚2b实施脱保护及氧化为醌的反应失败,但对其前体2a则成功进行了这一反应。