215182-76-6Relevant academic research and scientific papers
Alkyl substituent effects on pipecolyl amide isomer equilibrium: Efficient methodology for synthesizing enantiopure 6-alkylpipecolic acids and conformational analysis of their N-acetyl N'-methylamides
Swarbrick, Martin E.,Gosselin, Francis,Lubell, William D.
, p. 1993 - 2002 (2007/10/03)
Enantiopure 6-alkylpipecolic acid hydrochlorides 1a-e were synthesized in five steps and 15-59% overall yields from α-tert-butyl β-methyl N- (PhF)aspartate (3) via an approach featuring selective hydride reduction to the corresponding aspartate β-aldehyde 2, aldol condensations with the enolates of various methyl alkyl ketones, and diastereoselective intramolecular reductive aminations. The influence of the 6-position substituent on the equilibrium and the energy barrier for isomerization of the amide N-terminal to pipecolate was then explored via the synthesis of N- acetyl N'-methylpipecolinamide (16) and its (2S,6R)-6-tert- butylpipecolinamide counterpart 17, and their conformational analysis by proton NMR spectroscopy and coalescence experiments. The presence of the tert-butyl substituent augmented the population of the amide cis-isomer and lowered the barrier for pipecolyl amide isomerization in water. Compared with the results from our previous examination of N-acetyl-5-tert-butylproline N'- methylamides (Beausoleil, E.; Lubell, W. D. J. Am. Chem. Soc. 1996, 118, 12902), the consequences of the bulky 6-alkyl substituent on the acetamide geometry and isomerization barrier were less pronounced in the pipecolate series relative to the respective proline amides.
An olefination entry for the synthesis of enantiopure α,ω-diaminodicarboxylates and azabicyclo[X.Y.0]alkane amino acids
Gosselin, Francis,Lubell, William D.
, p. 7463 - 7471 (2007/10/03)
A new approach for synthesizing α,ω-diaminodicarboxylates of various chain lengths has opened the way for making a series of azabicyclo[X.Y.0]alkane amino acids of different ring sizes. β-Keto phosphonates 21-23 were synthesized in 71-90% yield by the addition of the lithium anion of dimethyl methyl phosphonate to the ω-methyl ester of α.-tert-butyl N-(PhF)aspartate 3, glutamate 9, and aminoadipate 12 (PhF = 9-phenylfluoren-9-yl). α,ω-Diaminodicarboxylates 24-26 of nine to eleven carbon chain lengths were prepared in 78-87% yield from the Horner-WadsworthEmmons olefination of α-tert-butyl .ZV-(PhF)aspartatc β-aldehyde (5) with aminodicarboxylate-derived β-keto phosphonates 21-23. The power of this approach for making azabicyclo[X.Y.0]alkane amino acid was then illustrated by the first synthesis of enantiopure indolizidin-9-one amino acid 2 in nine steps and >25% overall yield from inexpensive aspartic acid as chiral educt. Hydrogenation of (2S,8S)-di-tcrt-butyl 4-oxo-2,8-bis[N-(PhF)amino]non-4-enedioate (24) in 9:1 EtOH:AcOH furnished a 9:1 diastereomeric mixture of 6-alkylpipecolate 28 that was subsequently transformed into azabicyclo[4.3.0]alkane amino acid 2 via lactam cyclization and protecting group manipulations. Because α,ω-diaminodicarboxylates 25 and 26 may be similarly converted to heterocycles of larger ring sizes and because alkylation of similar ketones can be used to attach side-chains at different points on the heterocycle, this olefination strategy greatly expands our methodology for synthesizing azabicyclo[X.Y.0]alkane amino acids for the exploration of conformation-activity relationships of various biologically active peptides.
