Proton magnetic resonance spectra of Trichosporonaculeatummannan and its borate complex and their relationship to chemical structure

Methylation–fragmentation and periodate oxidation studies show that the mannan of Trichosporonaculeatumis branched with 2-Oand 6-O-monosubstituted units and 2,6-di-O-substituted D-mannopyranosyl units. It contains up to five consecutive α-D-(1 → 2)-linkages. The proton magnetic resonance spectrum of the mannan (recorded in D2O at 70° using a VananHA-100 spectrometer) indicates structural differences from other yeast mannans. It contains four distinct H-1 signals, but more than four H-1 environments are present since addition of sodium tetraborate shifts two signals downfleld so that six signals are observed (Fig. 1). Two of the four signals in the mannan spectrum at τ 4.40, and τ 4.20 can be assigned to chemical structures. The former signal arises from nonreducing end units attached to the 2-positions of adjacent mannopyranose units and from 2,6-di-O-substituted units and the latter from 2-O-substituted mannopyranose units. These assignments are based on the above chemical evidence, comparison with H-1 chemical shifts of known compounds, and the magnitudes of the H-1 shifts on borate addition. Downfleld shifts of H-1 proton signals on borate addition to known mannopyranosides vary from a maximum with compounds that can form 2,3-borate complexes to virtually none with 2-O-substituted derivatives. The magnitude of the downfleld shifts observed with α-D-linked mannopyranose derivatives is greater than that of their β-linked counterparts.