Abstract
The quantitative analysis of reaction products showed that the reaction of 6A,6D-di-O-trityl-α-cyclodextrin (CD), AD-isomer, with trityl chloride in pyridine at 55 °C gave 6A,6B,6E-tri-O-trityl-α-CD, the amount of which was only 25% of that of simultaneously formed 6A,6B,6D-tri-O-trityl-α-CD. This indicates that the bulky trityl groups of glucopyranose-A and -D (Glu-A and -D, respectively) in the AD-isomer mainly retard the additional tritylation of the C(6)-OH of the adjacent glucopyranoses in a counter-clockwise direction (Glu-F and -C, respectively). 1H NMR spectra of the AD-isomer showed that the O(6)-H and C(6)-H signals of Glu-C and -F are shifted upfield due to the ring current of the trityl groups. Thus, it is concluded that the bulky trityl groups on Glu-A and Glu-D are oriented to Glu-F and Glu-C, respectively, and sterically retard additional tritylation on Glu-F and Glu-C. Similar steric hindrance was also observed in the additional tritylations of mono-6-O-trityl-α-CD, 6A,6B-di- and 6A,6C-di-O-trityl-α-CD’s.
Highlights
It is concluded that the bulky trityl groups on
Regioselective modification and deprotection on the primary hydroxy side of cyclodextrins (CDs) are of great importance in supramolecular chemistry, as they allow the preparation of sophisticated concave molecules such as multi- or hetero-functionalized CD derivatives that are important intermediates for the preparation of enzyme mimics [1,2,3,4,5]
Mono, di, and tri-6-O-tritylates of α-CD were prepared by a reaction of α-CD with trityl chloride (TrCl) in pyridine at 55 °C according to the direction of literature [9], and separated by means of reversed-phase column chromatography
Summary
Regioselective modification and deprotection on the primary hydroxy side of cyclodextrins (CDs) are of great importance in supramolecular chemistry, as they allow the preparation of sophisticated concave molecules such as multi- or hetero-functionalized CD derivatives that are important intermediates for the preparation of enzyme mimics [1,2,3,4,5]. Four regioisomers of tri-6-O-trityl-α-CD gave well-separated peaks in the UFLC chromatography (Figure 2), when acetonitrile/methanol/water (40/45/15, v/v/v) was used as an eluent.
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