Synthesis, characterization and reactivity of carbohydrate platinum(iv) complexes with thioglycoside ligands

Abstract

Reactions of fac-[PtMe₃(4,4′-R₂bpy)(Me₂CO)][BF₄] (R = H, 1a; ^tBu, 1b) and fac-[PtMe₃(OAc-κ²O,O′)(Me₂CO)] (2), respectively, with thioglycosides containing thioethyl (ch-SEt) and thioimidate (ch-STaz, Taz = thiazoline-2-yl) anomeric groups led to the formation of the carbohydrate platinum(IV) complexes fac-[PtMe₃(4,4′-R₂bpy)(ch*)][BF₄] (ch* = ch-SEt, 8–14; ch-STaz, 15–23) and fac-[PtMe₃(OAc-κ²O,O′)(ch*)] (ch* = ch-SEt, 24–28; ch-STaz = 29–35), respectively. NMR (¹H, ¹³C, ¹⁹⁵Pt) spectroscopic investigations and a single-crystal X-ray diffraction analysis of 19 (ch-STaz = 2-thiazolinyl 2,3,4,6-tetra-O-benzoyl-1-thio-β-D-galactopyranose) revealed the S coordination of the ch-SEt glycosides and the N coordination of the ch-STaz glycosides. Furthermore, X-ray structure analyses of the two decomposition products fac-[PtMe₃(bpy)(STazH-κS)][BF₄] (21a) and 1,6-anhydro-2,3,4-tri-O-benzoyl-β-D-glucopyranose (23a), where a cleavage of the anomeric C–S bond had occurred in both cases, gave rise to the assumption that this decomposition was mediated due to coordination of the thioglycosides to the high electrophilic platinum(IV) atom, in non-strictly dried solutions. Reactions of fac-[PtMe₃(Me₂CO)₃][BF₄] (3) with ch-SEt as well as with ch-SPT and ch-Sbpy thioglycosides (PT = 4-(pyridine-2-yl)-thiazole-2-yl; bpy = 2,2′-bipyridine-6-yl), having N,S and N,N heteroaryl anomeric groups, respectively, led to the formation of platinum(IV) complexes of the type fac-[PtMe₃(ch*)][BF₄] (ch* = ch-SEt, 36–40, ch-SPT 42–44, ch-Sbpy 45, 46). The thioglycosides were found to be coordinated in a tridentate κS,κ²O,O′, κS,κN,κO and κS,κ²N,N′ coordination mode, respectively. Analogous reactions with ch-STaz ligands succeeded for 2-thiazolinyl 2,3,4-tri-O-benzyl-6-O-(2,2′-bipyridine-6-yl)-1-thio-β-D-glucopyranoside (5h) resulting in fac-[PtMe₃(ch-STaz)][BF₄] (41, ch-STaz = 5h), having a κ³N,N′,N′′coordinated thioglycoside ligand.