کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
5228721 | 1383641 | 2008 | 11 صفحه PDF | دانلود رایگان |
Racemic trans 3-(9-fluorenylmethyloxycarbonylamino)-1-oxyl-2,2,5,5-tetramethylpyrrolidine-4-carboxylic acid (Fmoc-POAC-OH), prepared by conventional methods, was resolved upon esterification with (aR)-2,2â²-dihydroxy-1,1â²-binaphthyl. Separation of the obtained diastereomeric monoesters Fmoc-(±)-trans-POAC-O-(aR)-binaphthol by crystallization/chromatography, and removal of the chiral auxiliary by saponification of the aryl ester function furnished both enantiomers (+)-(3R,4R)-Fmoc-POAC-OH and (â)-(3S,4S)-Fmoc-POAC-OH. The absolute configuration of the asymmetric C3, C4 carbons of POAC were assigned from the induced circular dichroism of a flexible biphenyl probe present in the terminally protected dipeptide derivatives Boc-Bip-(+)-POAC-OMe and Boc-Bip-(â)-POAC-OMe (Bip, 2â²,1â²:1,2;1â³,2â³:3,4-dibenzcyclohepta-1,3-diene-6-amino-6-carboxylic acid). This assignment was confirmed by X-ray diffraction analysis of the diastereomeric monoester Fmoc-(+)-trans-POAC-O-(aR)-binaphthol, shown to be (aR,3R,4R). Solution synthesis of peptides to the hexamer level, based on the (3R,4R)-POAC enantiomer combined with (1S,2S)-2-aminocyclopentane-1-carboxylic acid, was carried out to examine coupling conditions at both C- and N-termini of the POAC residue, in view of further syntheses and 3D-structural investigations.
Racemic Fmoc-trans-POAC-OH was resolved upon esterification with (aR)-2,2â²-dihydroxy-1,1â²-binaphthyl and separation of the diastereomeric monoesters. Two pairs of enantiomers (+)-(3R,4R)-Fmoc-POAC-OH/(â)-(3S,4S)-Fmoc-POAC-OH and (+)-(3R,4R)-H-POAC-OMe/(â)-(3S,4S)-H-POAC-OMe were obtained. The absolute configuration was assigned from the CD curves of dipeptide derivatives and confirmed by X-ray diffraction analysis. Synthesis of peptides to the hexamer level, based on the (3R,4R)-POAC enantiomer combined with (1S,2S)-ACPC, was performed.
Journal: Tetrahedron - Volume 64, Issue 19, 5 May 2008, Pages 4416-4426