Regioselectivity in the formation of di- and tri-6-O-mesitylenesulfonates of α-cyclodextrin

• Regioselectivity in mesitylenesulfonylation of α-CD in pyridine is discussed.
• The reaction gave less 6A,6C-isomer than 6A,6B-isomer.
• NMR analysis revealed Mess group on 6A sterically retards the substitution on 6C-OH.

The quantitative analysis of the reaction products for α-cyclodextrin (α-CD) with mesitylenesulfonyl chloride (MessCl) showed that di- and tri-mesitylenesulfonylation of the primary hydroxy groups of α-CD is regioselective. The reaction of mono-6-O-mesitylenesulfonyl-α-CD with MessCl in pyridine gave less 6A,6C-di-O-mesitylenesulfonyl-α-CD than 6A,6B-di-O-mesitylenesulfonyl-α-CD. The reaction of 6A,6D-di-O-mesitylenesulfonyl-α-CD with MessCl gave less 6A,6B,6E-tri-O-mesitylenesulfonyl-α-CD than 6A,6B,6D-tri-O-mesitylenesulfonyl-α-CD. These results indicate that the mesitylenesulfonyl group attached to glucopyranose-A (Glc-A) retards further mesitylenesulfonylation of the primary hydroxy group of Glc-C. The 1H NMR spectra of these modified α-CDs showed that the signal for the primary hydroxy and anomeric protons of Glc-C are significantly shifted upfield by the mesitylenesulfonyl group of Glc-A.

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