Galacturonic acid derivatives .8. Synthesis of N-(D-galacturonoyl) amino acids and dipeptides

D-Galacturonic acid derivatives, amide-linked to amino acids or dipeptides, have been synthesized. These glycoconjugates exhibit stability when the uronic acid residue is protected with isopropylidene and acetyl groups or is in its pyranoside form. The formation of the amide or peptide linkages was best achieved by the EDCI/HOBt coupling method; an alternative method employing the 1,2;3,4-di-O-isopropylidene-alpha-D-galactopyranuronosyl chloride 2 furnished only moderate yields of the conjugates. The use of NMR spectroscopy to detect racemization of the amino acid moiety is also discussed herein.