Deacylation of 4-nitrophenyl acetate by 6A-(ω-aminoalkyl)amino-6A-deoxy-β-cyclodextrins

Abstract

The deacylation of 4-nitrophenyl acetate (pNPA) in aqueous solution to give 4-nitrophenolate is significantly accelerated by the 6A-(ω-aminoalkyl)amino-6A-deoxy-β-cyclodextrins [βCDNH(CH2)nNH2] which are themselves acylated to give predominantly βCDNH(CH2)nNHCOCH3. The deacylation is characterised by kdK = 27.4, 35.5, 24.5 and 16.0 dm3 mol-1 s-1 at 298.2 K in aqueous 0.05 mol dm-3 borate buffer and I = 0.10 mol dm-3 (NaClO4) when n = 2, 3, 4 and 6, respectively, where kd (s-1) is the rate constant for pNPA deacylation through a βCDNH-(CH2)nNH2·pNPA complex characterised by a stability constant K (dm3 mol-1). The inhibition of the deacylation by adamantane-1-carboxylate (AC-) is consistent with a mechanism where AC competes with pNPA in entering the βCDNH(CH2)nNH2 annulus through the formation of a βCDNH(CH2)nNH2·AC- complex. The latter complex has been qualitatively studied by 1H NMR ROESY methods, and its structure and that of βCDNH(CH2)nNH2· pNPA have also been force-field modelled. The possibility of the operation of an SN2 mechanism as an alternative explanation for the deacylation data is also considered.