Utility of polymer-supported reagents in the total synthesis of lamellarins |
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Authors: | Ploypradith Poonsakdi Kagan Rachel Kirk Ruchirawat Somsak |
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Institution: | Laboratory of Medicinal Chemistry, Chulabhorn Research Institute, Vipavadee-Rangsit Highway, Bangkok 10210, Thailand. poonsakdi@tubtim.cri.or.th |
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Abstract: | Four solid-supported reagents have been utilized in the multistep synthesis of lamellarins. The use of Amberlyst A-26 Br(3)(-) and polymer bound pyridine hydrobromide perbromide (PVPHP) for keto alpha-bromination of the less studied ortho-substituted acetophenone derivatives selectively furnished the corresponding monobromination products (phenacyl bromide derivatives), which were used directly in condensation reactions with benzyldihydroisoquinoline mediated by Amberlyst A-26 NaCO(3)(-). The 2H-pyrrole carbonates subsequently underwent intramolecular Friedel-Crafts transacylation followed by lactonization to provide the lamellarin skeleton. Alternatively, Amberlyst A-26 NaCO(3)(-) effectively served as base in condensation reaction of benzyldihydroisoquinoline with alpha-nitrocinnamate derivatives to provide the corresponding 2-ethoxycarbonyl pyrroles, which smoothly underwent O-debenzylation reaction followed by lactonization to furnish the lamellarin skeleton. The novel Amberlyst-15 mediated lactonization reactions effectively combined the otherwise two separate steps into a single transformation. |
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