Proton magnetic resonance spectra of Trichosporon aculeatum mannan and its borate complex and their relationship to chemical structure

Methylation–fragmentation and periodate oxidation studies show that the mannan of Trichosporon aculeatum is branched with 2-O and 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.