The synthesis of chiral (2-substituted-2-aminoethyl)allylsilanes by cerium mediated trimethylsilylmethylmagnesium chloride addition to the ester group of non racemic chiral β-aminoesters is described.
Isolation and Structure Determination of Lyngbyastatin 3, a Lyngbyastatin 1 Homologue from the Marine Cyanobacterium <i>Lyngbya </i><i>m</i><i>ajuscula.</i> Determination of the Configuration of the 4-Amino-2,2-dimethyl-3-oxopentanoic Acid Unit in Majusculamide C, Dolastatin 12, Lyngbyastatin 1, and Lyngbyastatin 3 from Cyanobacteria
作者:Philip G. Williams、Richard E. Moore、Valerie J. Paul
DOI:10.1021/np0302145
日期:2003.10.1
The structure of lyngbyastatin 3 (1), including the configurations of the two unusual amino acid residues, viz., the 3-amino-2-methylhexanoic acid (Amha) and 4-amino-2,2-dimethyl-3-oxopentanoic acid units (Ibu), has been established by chemical degradation. Analysis of the cyanobacterial samples of lyngbyastatin 3 (1), lyngbyastatin 1 (2), and dolastatin 12 (3) demonstrated that they are mixtures of Ibu epimers [R (major) and S (minor)], whereas the structurally related majusculamide C (4) is a single diastereomer having an S-Ibu unit.
Diastereoselective synthesis of aziridine esters via amino selanyl esters
A synthesis of aziridine esters based on the cyclisation of amino selanyl esters induced by the selanyl group activation was developed with either the Meerwein salt or NBS. Twoasymmetricapproaches are proposed: the diastereoselective reductions of α-selanyl β-iminoesters derived from α-oxoesters, which lead to cis chiral aziridine esters 6 and 6′; and the diastereoselective conjugate additions of
The enantioselective total synthesis of (−)-indolizidine167B is described. The key step is the intramolecular cyclization of the chiral N-acyliminium ion 6. Indolizidine 167B was obtained in 7 steps and 17% yield from ethyl (R)-3-aminohexanoate, with an enantiomeric excess of 93%.