Selective Triisopropylsilylation of α-Amino Acids: Protection without Racemization
摘要:
The mono-, di- and trisilylation of alpha-amino acids with TIPSOTf is described. Treatment of the alpha-amino acids, proline and tryptophan with TIPSOTf in MeCN provides a quantitative yield of the corresponding ammonium salts of the O-TIPS esters (4). Employing two (2) equivalents of TIPSOTf/EDIPA produces N,O-bis-TIPS amino acid derivatives (2) without racemization as stable compounds (73-87%, 13 examples). Three (3) equivalents of this silylation mixture produces the corresponding tris-TIPS derivatives 6 (62-88%, 6 examples) from amino acids which contain protic functionality in their side chain. While this trisilylation procedure is ineffective for tryptophan, the N,O-bis-TIPS derivative 2m is easily prepared through this method, and the third silylation is achieved without racemization employing t-BuLi/R3SiX producing N-1-SiR3-N,O-bis-TIPS tryptophans (51-97%, 4 examples).
Selective Triisopropylsilylation of α-Amino Acids: Protection without Racemization
作者:John A. Soderquist、Buddy Soto-Cairoli、Iveliz Kock、Guang Yang、Jorge Justo de Pomar、José M. Guzmán、Javier R. González、Augie Antomattei
DOI:10.3987/com-09-s(s)37
日期:——
The mono-, di- and trisilylation of alpha-amino acids with TIPSOTf is described. Treatment of the alpha-amino acids, proline and tryptophan with TIPSOTf in MeCN provides a quantitative yield of the corresponding ammonium salts of the O-TIPS esters (4). Employing two (2) equivalents of TIPSOTf/EDIPA produces N,O-bis-TIPS amino acid derivatives (2) without racemization as stable compounds (73-87%, 13 examples). Three (3) equivalents of this silylation mixture produces the corresponding tris-TIPS derivatives 6 (62-88%, 6 examples) from amino acids which contain protic functionality in their side chain. While this trisilylation procedure is ineffective for tryptophan, the N,O-bis-TIPS derivative 2m is easily prepared through this method, and the third silylation is achieved without racemization employing t-BuLi/R3SiX producing N-1-SiR3-N,O-bis-TIPS tryptophans (51-97%, 4 examples).