RESUMO
Diastereoselective addition of nitromethane to Boc-D-Phe-H in the presence of sodium hydride in diethyl ether/hexane containing 15-crown-5 and subsequent N,O-protection with 2,2-dimethoxypropane gave trans-oxazolidine in a diastereomeric ratio of >16:1. The oxazolidine was easily separated by column chromatography, which after Nef reaction was coupled to H-Leu-OtBu. The 8-step synthesis afforded (-)-bestatin in an overall yield of 24.7% after deprotection and ion exchange.
Assuntos
Leucina/análogos & derivados , Cromatografia Líquida de Alta Pressão , Leucina/síntese química , Leucina/química , Estrutura Molecular , EstereoisomerismoRESUMO
The title compound, C15H18NO3PS·C6H6, is a rare example of a crystallographically characterized exocyclic phosphiniminium-arene-sulfonate zwitterion, which crystallises as its benzene solvate. The crystal structure shows that the N atom is protonated and that the iminium H atom forms both intra- and inter-molecular hydrogen bonds to the single-bonded sulfonate O atom in an R 2 (2)(4) graph-set motif. The dihedral angle between the aromatic rings in the main molecule is 89.49â (8)°.