L-iduronic acid, a major constituent of heparin

Abstract

Heparin has been degraded by a sequence of several reactions to give as the major identifiable products, 1,6-anhydro- l-idopyranose ( 2) and 2,5-anhydro- d-mannitol ( 3), these products being attributed originally to l-idosyluronic acid and the 2-amino-2-deoxy- d-glucopyranosyl residues, respectively. Products such as methyl α- d-glucopyranoside ( 4), derivable from d-glucosyluronic acid residues, were relatively minor, the ratio of 2 to 3 to 4 being approximately 5:5:1. These findings are supported by periodate-oxidation experiments, which have led to the detection of threitol (5 parts) and erythritol (1 part). The latter results show also that the l-idosyluronic (as well as the d-glucosyluronic) acid residues are substituted at position 4, and other evidence indicates that a hexosaminyl residue frequently is the 4-substituent. By reducing carboxyl groups of heparin (as methyl esters) with borohydride in tritiated water, evidence has been obtained to indicate that little, if any, of 2 is derived through isomerization of d-glucosyluronic acid residues. By contrast, and as required by the above information, the use of borohydride- t affords isotopically labelled 2. It is suggested that the presence of l-idosyluronic acid residues as major components of heparin helps to explain what heretofore has been regarded as an anomalously low positive rotation for the polymer.