ENANTIOSELECTIVE SYNTHESIS OF NATURAL PRODUCTS

下一个奖助金期的主要目标是进一步发展

A major goal for the next grant period is the further development of methods for the enantioselective conversion of aromatic carboxylic acid derivatives to chiral intermediates for use in organic synthesis. These methods will be applied to the synthesis of natural products that possess biological and/or medicinal activity; it is expected that an enantioselective total synthesis of the Windaus-Grundmann ketone, an important vitamin D synthetic intermediate will be completed during the next grant period. We will begin an enantioselective total synthesis of (+)-quassin, a member of the quassinoid family of triterpenes of interest because of their wide spectrum of biological properties, including antileukemic activity. When completed the total synthesis of (+)-quassin will demonstrate the utility of the enantioselective Birch reductive alkylation strategy as applied to an unusually demanding synthesis target. An enantioselective total synthesis of hasbanane alkaloid (+)-cepharamine will demonstrate an intramolecular 1+5 aromatic ring construction at an angular carbon atom, a process that should have general utility in complex alkaloid and terpenoid construction. An enantioselective total synthesis of (-)delta9,12-capnellene features a novel utilization of the tandem intramolecular Diels-Alder cycloaddition and oxa-di-pi-methane photorearrangement. It is expected that our recently reported stereoselective conjugate addition methodology will be applied to new cycloalkenones, as well as heterocyclic systems and acyclic enones. This method for asymmetric synthesis along with other projects initiated during the past grant period will be examined within the context of alkaloid and terpenoid synthesis. Another major goal for the next grant period is the development of methods for preparation and utilization of chiral biaryl derivatives to be obtained in enantiomerically pure form by photorearrangement of derivatives of the morphine alkaloids. It is proposed that C(2) symmetric bidentate ligands with increasing degrees of steric hindrance at positions flanking the 2,2'-dihydroxy-1,1'-biaryl unit will be available by simple modifications of commercial codeine and thebaine. The chiral ligands will be examined in asymmetric Lewis acid promoted Diels-Alder cycloadditions, ene reactions, and Claisen rearrangements.