Some chemical and analytical aspects of polysaccharide modifications. II. A high‐yielding, specific method for the chemical derivatization of galactose‐containing polysaccharides: Oxidation with galactose oxidase followed by reductive amination
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Medientyp:
E-Artikel
Titel:
Some chemical and analytical aspects of polysaccharide modifications. II. A high‐yielding, specific method for the chemical derivatization of galactose‐containing polysaccharides: Oxidation with galactose oxidase followed by reductive amination
Beteiligte:
Yalpani, Manssur;
Hall, Laurance D.
Erschienen:
Wiley, 1982
Erschienen in:
Journal of Polymer Science: Polymer Chemistry Edition, 20 (1982) 12, Seite 3399-3420
Beschreibung:
<jats:title>Abstract</jats:title><jats:p>A versatile and high‐yielding method was developed for specifically modifying galactose‐containing polysaccharides, exemplified here by two representative galactomannans, guar gum<jats:bold>1</jats:bold>and locust bean gum<jats:bold>5</jats:bold>. Oxidation of the primary alcohol functions of<jats:bold>1</jats:bold>and<jats:bold>5</jats:bold>with galactose oxidase produced the corresponding aldehyde derivatives<jats:bold>2</jats:bold>and<jats:bold>6</jats:bold>which were subsequently derivatized in several ways. Reductive amination with sodium cyanoborohydride of<jats:bold>2</jats:bold>and<jats:bold>6</jats:bold>proceeded smoothly (60–90% yields) and led to stable amine derivatives (<jats:bold>4</jats:bold>,<jats:bold>7–11</jats:bold>), which included hydroxyalkylamine‐ (<jats:bold>8</jats:bold>), glycine‐ (<jats:bold>9</jats:bold>), and BSA‐ (<jats:bold>11</jats:bold>) derivatives. The cationic primary amine derivative<jats:bold>12</jats:bold>was similarly reductively alkylated with lactose to yield a product<jats:bold>13</jats:bold>with extended carbohydrate side chains. Oxidation of<jats:bold>2</jats:bold>produced the anionic carboxy derivative<jats:bold>14</jats:bold>, whereas reduction of<jats:bold>2</jats:bold>and<jats:bold>6</jats:bold>with sodium borodeuteride yielded the deuterium labeled neutral species<jats:bold>15</jats:bold>and<jats:bold>16</jats:bold>. The undegraded gums and some of their derivatives were studied by high resolution<jats:sup>13</jats:sup>C‐NMR (100.6 MHz) at 30°C, and the proposed chemical shift assignments were in good qualitative agreement with those of earlier studies. ESR spectroscopy was used to follow the chemical reactions and to derive information about the galactose distribution of<jats:bold>1</jats:bold>and<jats:bold>5</jats:bold>. Mean nearest neighbor distances (<jats:italic>r̄</jats:italic>) between nitroxides attached to<jats:bold>1</jats:bold>and<jats:bold>5</jats:bold>were 1.36 nm (±5%) for<jats:bold>4</jats:bold>and 1.75 nm (±5%) for<jats:bold>7</jats:bold>. These<jats:italic>r̄</jats:italic>values agree favorably with the structural models recently proposed elsewhere, excluding earlier suggestions of homogeneous galactose distributions or regularly alternating blocks of branched and unbranched mannose units. The solution properties, such as viscosity and salt‐ and organic solvent‐compatibility, of some of the guar derivatives appear to be unique and interesting. An alternative oxidation procedure of the galactose residues of<jats:bold>1</jats:bold>and<jats:bold>5</jats:bold>with sodium periodate has been evaluated.</jats:p>