Novel amphiphilic cyclodextrins: Graft-synthesis of heptakis(6-alkylthio-6-deoxy)-beta-cyclodextrin 2-oligo(ethylene glycol) conjugates and their omega-halo derivatives

Novel amphiphilic cyclodextrins were synthesised by grafting oligo(ethylene glycol) units onto the secondary side of heptakis(6-alkylthio-6-deoxy)-bet a -cyclodextrins (alkyl = ethyl, hexyl, dodecyl and hexadecyl). The oligo(e thylene glycol) substituents were introduced by reaction of heptakis(6-alky lthio-6-deoxy)-beta -cyclodextrins with ethylene carbonate in the presence of potassium carbonate at elevated temperatures. The resulting oligo(ethyle ne glycol)-cyclodextrin conjugates were characterised by H-1 NMR and C-13 N MR, COSY and HSQC spectroscopy, and mass spectrometry. Addition of ethylene carbonate occurs exclusively at OH2 and results in a degree of substitutio n of 8-22 ethylene glycol units per cyclodextrin. Also, the omega -bromo an d omega -iodo derivatives of heptakis[6-deoxy-6-hexylthio-2-oligo(ethylene glycol)]-beta -cyclodextrin were prepared as strategic synthetic intermedia tes. The observation that seven halogen atoms are introduced per cyclodextr in provides strong evidence for the grafting of oligo(ethylene glycol) to e ach of the seven glucose units in the cyclodextrin ring.