Specific degradation of pectins via a carbodiimide-mediated Lossen rearrangement of methyl esterified galacturonic acid residues

• Published in: Carbohydrate research Vol. 333; no. 1; pp. 47 - 58
• Main Authors: Needs, Paul W, Rigby, Neil M, Ring, Stephen G, MacDougall, Alistair J
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier Ltd 22.06.2001
• Subjects: Carbodiimide; Esterification; Ethyldimethylaminopropyl Carbodiimide; Galacturonic acid; Hexuronic Acids - chemistry; Hydroxamic Acids - chemistry; Hydroxylamine; Lossen rearrangement; Magnetic Resonance Spectroscopy; Methyl esterification; Oxidation-Reduction; Pectins; Pectins - chemistry; Specific degradation; Spectrometry, Mass, Electrospray Ionization; Lossen rearrangement; Galacturonic acid; Pectins; Carbodiimide; Specific degradation; Methyl esterification
• ISSN: 0008-6215; 1873-426X
• DOI: 10.1016/S0008-6215(01)00120-3

A specific, chemical degradation of the methyl esterified galacturonic acid residues of pectins is described. These residues are converted, with hydroxylamine, to hydroxamic acids, and then, with a carbodiimide, to isoureas; the latter undergo a Lossen rearrangement on alkaline hydrolysis. The isocyanates formed are hydrolysed to 5-aminoarabinopyranose derivatives, which spontaneously ring open to give 1,5-dialdehydes. The latter are reduced, in situ, to avoid peeling reactions, with sodium borohydride to give substituted arabitol residues. Thus, overall, partially esterified pectins are specifically cleaved to generate a series of oligogalacturonic acids bearing an arabitol residue as aglycone. Analysis of oligomers so generated discloses the pattern of contiguous nonesterification in a variety of pectins of differing degrees of esterification. Other potential applications are described. The methyl esterified galacturonic acid residues of pectins are converted to hydroxamic acid residues. These are specifically degraded via a carbodiimide-mediated Lossen rearrangement, to liberate the unesterified residues as oligomeric blocks. This allows a determination of the pattern of esterification of the pectin.