A Noncarbohydrate Based Approach to Polyhydroxylated Pyrrolidizines: Total Syntheses of the Natural Products Hyacinthacine A<sub>1</sub> and 1-Epiaustraline
作者:Timothy J. Donohoe、Herman O. Sintim、Jackie Hollinshead
DOI:10.1021/jo050977s
日期:2005.9.1
A flexible route to polyhydroxylated pyrrolizidinealkaloids is described, starting from commercially available N-Boc pyrrole and using a partial reduction as the key step. Tactics for varying the stereochemistry around the ring by choice of partial reduction conditions are discussed and methods for constructing the bicyclic ring system of the pyrrolizidine targets are examined. Intramolecular SN2
(+)-1-epiaustraline ((+)-1), a tetrahydroxypyrrolizidine alkaloid of the alexine/australine subclass, is described. The key step is a tandem intramolecular [4 + 2]/intermolecular [3 + 2] nitroalkenecycloaddition involving dienylsilyloxy nitroalkene3 and chiral vinyl ether 4, which establishes four of the five stereocenters present. The final center was installed by a diastereoselective dihydroxylation
Asymmetric synthesis of (+)-1-epiaustraline and attempted synthesis of australine
作者:Minyan Tang、Stephen G Pyne
DOI:10.1016/j.tet.2004.05.010
日期:2004.6
A diastereoselective synthesis of the pyrrolizidine alkaloid, (+)-1-epiaustraline has been achieved via a diastereoselective syn-dihydroxylation of a pyrrolo[1,2-c]oxazol-3-one precursor that was readily prepared by a RCM reaction. Attempts to extend this methodology to the synthesis of australine were not successful since the final pyrrolidine ring closure to produce the desired pyrrolizidine of the
通过吡咯并[1,2 - c ]恶唑-3-酮前体的非对映选择性顺式-二羟基化,可以通过RCM反应容易地制备吡咯并立啶生物碱((+)-1-epiaustraline)的非对映选择性合成。尝试将该方法扩展至合成奥曲林的尝试并未成功,因为最终的吡咯烷环闭合以产生目标分子所需的吡咯烷并没有生产力。
Stereocontrolled synthesis of 1,7a-diepialexine
作者:Nobuo Ikota
DOI:10.1016/s0040-4039(00)92240-8
日期:1992.4
(2R,5R)-Dihydroxymethyl-(3R,4S)-dihydroxypyrrolidine derivative 15, 1,7a-diepialexine 1, and 1,7,7a-triepialexine 2 have been synthesized from (S)-pyroglutamic acid derivative 4.
Isolated immunomodulatory (e.g. immunostimulatory) polyhydroxlated pyrrolizidine compounds having the formula
are disclosed. In these compounds R is selected from hydrogen, straight or branched, unsubstituted or substituted, saturated or unsaturated acyl, alkyl (e.g. cycloalkyl), alkenyl, alkynyl and aryl groups. The compounds are useful in therapy and prophylaxis, including increasing the Th1:Th2 response ratio, hemorestoration, alleviation of immunosuppression, cytokine stimulation, treatment of proliferative disorders (e.g. cancer), vaccination, stimulation of the innate immune response and boosting of the activity of endogenous NK cells.