L-glutamic acid and L-alanine derivatives as building blocks for thesynthesis of a chiral monomer precursor of AABB-type polyamide

Abstract

The chiral monomer N-(1′-amino-2′-(S)-propyl)-5-oxo-2-(S)- tetrahydrofurancarboxy-amide hydrochloride (11), a precursor of a AABB-type stereoregular polyamide, has been synthesized from pentachlorophenyl 5-oxo-2-(S)-tetrahydrofurancarboxylate (2) and 2-(S)-amino-1-propanol (3). Compounds 2 and 3 are derivatives of the natural amino acids L-glutamic acid and L-alanine, respectively. The regioselective attack of the amino group of 3 to the ester function of 2 led to N-(1′-hydroxy-2′-(S)-propyl)-5-oxo- tetrahydrofurancarboxyamide (4) in 80% yield. However, the tosylation of the primary hydroxyl group of 4, and the subsequent substitution by azide to give 6, took place with low yields. Therefore, an alternative route was conducted starting from 3, which was selectively N-protected as the tert-butyloxycarbonyl derivative (N-Boc), O-tosylated and substituted by azide to afford 1-azido-2-(S)-N-(tert-butyloxycarbonyl)aminopropane (9) in 41% yield from 3. The amino group of 9 was deprotected by acid hydrolysis and the resulting amine 10 was regioselectively condensed with 2 to give the azide derivative 6. Hydrogenolysis of 6 afforded the desired monomer 11 in 69% yield from 2 and 10.