The Influence of Fluoroalkyl-Group Electronegativity on Stereocontrol in the Synthesis of <i>Ψ</i>[CH(R<sub>F</sub>)NH]Gly Peptides
作者:Alessandro Volonterio、Matteo Zanda、Serena Bigotti
DOI:10.1055/s-2008-1072653
日期:——
New peptidomimetics featuring CH(RF)NH units, having different degree of fluorination, as peptide-bond surrogates have been synthesized. The key step in the synthesis consists of a stereoselective aza-Michael addition of chiral α-amino acid esters to β-fluoroalkyl-α-nitroethenes. The diastereoselection of the process was influenced by the electronegativity, rather than by the steric bulk, of the fluorinated residue RF in β-position of the nitroalkene acceptors. Replacement of a single F atom of RF by a hydrogen or methyl group brings about a dramatic drop of stereocontrol, whereas Br, Cl, and CF3, albeit bulkier than F, provide poorer results in terms of stereocontrol.
新型肽类仿生物分子已合成,这些分子具有不同氟化程度的CH(RF)NH单元,作为肽键的替代物。合成的关键步骤是选择性地将手性α-氨基酸酯与β-氟烷基-α-硝基乙烯进行氮的迈克尔加成。该过程的反式选择性受到氟化基团RF在β位的电负性影响,而非空间位阻的影响。当将RF的单个氟原子替换为氢或甲基时,立体控制能力急剧下降,而Br、Cl和CF3虽然比F体积更大,但在立体控制方面的结果更差。