Further<i>C</i>-Alkylations of Cyclotetrapeptides<i>via</i>Lithium and Phosphazenium (P4) Enolates: Discovery of a New Conformation
作者:Dieter Seebach、Olivier Bezençon、Bernhard Jaun、Thomas Pietzonka、Jennifer L. Matthews、Florian N. M. Kühnle、W. Bernd Schweizer
DOI:10.1002/hlca.19960790303
日期:1996.5.8
BnBr, primary allylic halides, aldehydes, CO2) can be employed. It is shown that the position, and thus the chirality sense, of the newly formed stereogenic centre in a given cyclotetrapeptide backbone is controlled by the positioning of N-methyl groups in the starting material (cf. cyclo(-MeLeu-Gly-D-Ala-Sar-) (3) and cyclo(-Leu-Sar-MeDAla-Gly-) (4) in Scheme 1). With Schwesinger's phosphazene P4-base
C-Alkylation of Sarcosine Residues in Cyclic Tetrapeptidesvia Lithium Enlates
作者:Scott A. Miller、Sian L. Griffiths、Dieter Seebach
DOI:10.1002/hlca.19930760138
日期:1993.2.10
introduced diastereoselectively (70 to > 98% ds) in yields ranging from 20 to 90%. The C-alkylatd products are all derived from a sarcosine-enolate moiety adjacent to another N-methylaminoacid. The structures of the resulting products are determined by NMR spectroscopy (DNOE and ROESY techniques) and by hydrolysis to the parent aminoacids, suitable derivatization, and analysis by chromatography on a chiral