Regioselective Synthesis Of Cyclodextrins Derivatives

Cyclodextrins are a series of cyclic oligosaccharides consisting several glucoseunits linked through a-1,4-linkages.The glucose unit contains one primary hydroxyl group at C-6 position,two secondary hydroxyl groups at C-2 and C-3 position,the structure of these three hydroxyl groups are perfectly ordered,and easy to be decorated.In this paper,the C-6 regioselective systhesis and trimethylsilylation of cyclodextrin is studied and discussed.1.Firstly,hexaki(2,3-di-O-benzyl)-a-CD,which is perbenzylated on the secondary OH-side,reacts wih bromoalkane in the presence of catalyst NaH affording 6?-?-Penta-O-alkyl-2?-?,3?-?-di-O-benzyl-a-CD with about 70%yield.The remaining C6-OH on 6?-?-Penta-O-alkyl-2?-?,3?-?-di-O-benzyl-a-CD can be further modificated by reacting with cis-butenedioic anhydride,the yield is about 80%.2.Reaction of cyclodextrin with TMSCI in pyridine with the existence of HMDS gives pertrimethylsilylated and 2,6-di-O-trimethylsilylated cyclodextrin derivatives.The results are influenced by reacting time and the native structure of cyclodextrins.2,6-di-O-trimethylsilylated cyclodextrin derivatives are abtained in 10 mins;while pertrimethylsilylated cyclodextrin derivatives are obtained when the reaction time is up to 48 h.Pertrimethylsilylated a-cyclodextrin is twisted during to its steric-hindrance.