One-pot synthesis of helical aromatics: stereoselectivity, stability against racemization, and assignment of absolute configuration assisted by experimental and theoretical circular dichroism.

Helical aromatics (1) were synthesized via one step in good quantity by solvent-free condensation of N,N'-p-phenylenediamine (2) and various carboxylic acids in the presence of a Lewis acid. Microwave irradiation greatly facilitated the condensation reaction to furnish 1 with a 100% diastereo- and a 50% enantioselectivity, when a chiral carboxylic acid was utilized. 1f, derived from 2-methylglutaric acid, was quite stable, no racemization taking place even at 200 degrees C.

Crystal structure of achiral nonapeptide Boc-(Aib-DeltaZPhe)4-Aib-OMe at atomic resolution: evidence for a 3(10)-helix.

An x-ray crystallographic analysis was carried out for Boc-(Aib-DeltaZPhe)4-Aib-OMe (1: Boc = t-butoxycarbonyl; Aib = alpha-aminoisobutyric acid; DeltaZPhe = Z-alpha,beta-didehydrophenylalanine) to provide the precise conformational parameters of the octapeptide segment -(Aib-DeltaZPhe)4-. Peptide 1 adopted a typical 3(10)-helical conformation characterized by = +/-55.8 degrees (50 degrees -65 degrees), = +/-26.

Synthesis and structural analyses of 3-acetamido-1,4-di-O-acetyl-2,3,5-trideoxy-5-C-(isopropylphosphinyl)-D-erythro-pentopyranoses.

1H NMR spectroscopy of phosphorus containing hetero sugars (phospha sugars), revealed the alpha and beta configurations and chair conformations for 3-acetamido-1,4-di-O-acetyl-2,3,5-trideoxy-5-C-(isopropylphosphinyl)-alpha- and beta-D-erythro-pentopyranoses. The conformation of the title compounds was determined by 1H NMR as 1C4 in CDCl3 and the conformation was in accord with that in solid state determined by X-ray crystallographic analysis.