Total synthesis of the ramoplanin A2 and ramoplanose aglycon

被引:59
作者
Jiang, WL
Wanner, J
Lee, RJ
Bounaud, PY
Boger, DL
机构
[1] Scripps Res Inst, Dept Chem, La Jolla, CA 92037 USA
[2] Scripps Res Inst, Skaggs Inst Chem Biol, La Jolla, CA 92037 USA
关键词
D O I
10.1021/ja020237q
中图分类号
O6 [化学];
学科分类号
0703 ;
摘要
A convergent total synthesis of the ramoplanin A2 and ramoplanose aglycon is disclosed. Three key subunits composed of residues 3-9 (heptapeptide 15), pentadepsipeptide 26, and pentapeptide 34 (residues 10-14) were prepared, sequentially coupled, and cyclized to provide the 49-membered depsipeptide core of the aglycon. Key to the preparation of the pentadepsipeptide 26 incorporating the backbone ester was the asymmetric synthesis of an orthogonally protected l-threo-β-hydroxyasparagine and the development of effective and near-racemization free conditions for esterification of its hindered alcohol (EDCI, DMAP, 0 °C). The coupling sites were chosen to maximize the convergency of the synthesis including that of the three subunits, to prevent late stage racemization of carboxylate-activated phenylglycine-derived residues, and to enlist β-sheet preorganization of an acyclic macrocyclization substrate for 49-membered ring closure. As such, macrocyclization at the chosen Phe9-d-Orn10 site may benefit from both β-sheet preorganization as well as closure at a d-amine terminus. Deliberate late stage incorporation of the subunit bearing the labile depsipeptide ester and a final stage Asn1 side chain introduction provides future access to analogues of the aglycons which themselves are reported to be equally potent or more potent than the natural products in antimicrobial assays. Copyright © 2002 American Chemical Society.
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页码:5288 / 5290
页数:3
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