Synthesis and characterization of novel platinum(IV) complexes with non-functionalized acetylated carbohydrates

[PtMe3(Me2CO)3]BF4 (1) reacts in acetone with 1,2,3,4-tetraacetyl-beta-D-glucopyranose (C2), pentaacetyl-alpha-D-glucopyranose (C3), pentaacetyl-beta-D-mannopyranose (C4) and pentaacetyl-beta-D-galactopyranose (C5) to give trimethyl(carbohydrate)platinum tetrafluoroborate complexes [PtMe3L]BF4 (2-5) (2, L=C2; 3, L=C3; 4, L=C4; 5, L=C5). The platinum-carbohydrate complexes were isolated as white, air and moisture sensitive powders in moderate to good yields (26-87%), and their identities were confirmed by microanalysis, 1H-, 13C- and 195Pt-NMR spectroscopy and ESI mass spectrometry. The coordination modes of the tridentately bound carbohydrate ligands (2, OH+Oring+Oacetyl; 3, Oring+Oether+Oacetyl; 4,5, Oring+Oether+Oether where Oring is the oxygen of a pyranose ring and Oacetyl/ether is the acetyl and ether oxygen of an acetoxy substituent, respectively) were established by evaluating the chemical shifts and the 2J(Pt,H) coupling constants of the methyl ligands and by 2D-NOE experiments. Evaluation of the 3J(H,H) coupling constants shows that the pyranose rings are present in their 4C1 conformation. The results show that carbohydrates without anchoring groups and even without hydroxyl groups can coordinate to the metal center only through very weak donors such as oxygen atoms of pyranose rings and acetoxy substituents.