- Asymmetric synthesis of (?)- and (+)-neodichroine/hydrachine A from (+)- and (?)-febrifugine
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A new asymmetric approach to both enantiomers of the quinazolinone-containing natural product febrifugine is reported. Utilising a proline-mediated aminooxylation-Horner-Wadsworth-Emmons sequence provides the key optically active 2,3-disubstituted piperidine intermediate 7 in high enantioselectivity but poor overall yield (7 steps, 3%, 98% ee). This intermediate has been used to prepare both naturally occurring (+)-febrifugine (1) and its (?)-enantiomer. In turn, each were then used to synthesise, for the first time, both enantiomers of the claimed natural product neodichroine/hydrachine A. Spectroscopic data for the synthetic compound matched the claimed structure. However, the specific rotation differed in both magnitude and sign from the isolation work.
- Smullen, Shaun,Evans, Paul
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p. 1627 - 1629
(2018/03/29)
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- An asymmetric synthesis of febrifugine, halofuginone and their hemiketal isomers
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A new synthesis of both enantiomers of naturally occurring febrifugine (1) and its analogue halofuginone (3) are reported. This robust route relies on an enzymatic kinetic resolution (EKR)-cross metathesis (CM) sequence, performed on allylic alcohol 8. A diastereoselective Lewis acid-mediated cyclisation of resultant enone 6 affords piperidine 12. In relation to its enantiomeric excess, values of 87 and 88% e.e were obtained for both enantiomers of 12 and for (?)-12 this was increased to 98% e.e by conducting the resolution process twice. A bromination (featuring an in situ temporary alcohol protection), alkylation and amino-deprotection sequence finally afforded the target compounds (+)- and (?)-1, and (+)- and (?)-3. Studies demonstrate that, as their ammonium salts, the compounds are stereochemically stable. However, as their free-bases, particularly in chloroform, C-2 isomerisation occurs. This isomerisation has been taken advantage of synthetically to provide enantioenriched (+)-isofebrifugine (2) and both enantiomers of isohalofuginone (14).
- Smullen, Shaun,Evans, Paul
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p. 5493 - 5499
(2017/08/22)
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- Dihydroxylation of vinyl sulfones: Stereoselective synthesis of (+)- and (-)-febrifugine and halofuginone
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(Chemical Equation Presented) The asymmetric dihydroxylation of amino-functionalized vinyl sulfone 19 has been used for the 3-step preparation of 3-hydroxylpiperidine 24 in 86% enantiomeric excess. This enantiomerically enriched building block was used then to synthesize the naturally occurring antimalarial alkaloid febrifugine 1 and its antiangiogenic analogue, halofuginone 3.
- McLaughlin, Noel P.,Evans, Paul
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supporting information; experimental part
p. 518 - 521
(2010/03/30)
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