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C. Ruiz-Ruiz, H. Amer, C. Stanetty, I. Beseda, L. Czollner, P. Shah, U. Jordis, B. Küenburg, D. Classen-Houben, A. Hofinger, P. Kosma:
"Efficient synthesis of glycyrrhetinic acid glycoside/glucuronide derivatives using silver zeolite as promoter";
Carbohydrate Research, 344 (2009), 9; 1063 - 1071.

3-O-Glycopyranosides of glycyrrhetinic acid have been synthesized in good to high yields and excellent
stereoselectivity using glycosyl bromide donors and silver zeolite as promoter. In addition to the preparation
of glycosides containing b-linked glucosyl, 2-deoxy-2-trichloroacetamido-glucosyl, galactosyl, cellobiosyl
and lactosyl residues, also the deactivated acetylated methyl glucopyranosyluronate bromide
donor could be coupled to triterpene aglycon ester derivatives in good yields. The ester protecting group
located at C-30 of the oleanolic acid scaffold exerted an influence on the overall yield, with the methylester-
protected glycosyl acceptor giving better yields compared to the allyl, benzyl as well as diphenylmethyl
ester aglycon. The acetyl-protected glucuronides were differently deblocked in high yields via
Zemplén deacetylation or via hydrogenolysis followed by Zemplén deacetylation, and alkaline hydrolysis,
respectively, to allow for a selective liberation of the ester groups from either the glucuronide or the glycyrrhetinic
acid unit, respectively. The target glycosides/glucuronides serve as probes for pharmaceutical
studies aimed at defining structure-activity relationships of glycoside/glucuronide triterpenes.
2009 Elsevier Ltd. All rights reserved.

Triterpene, Saponin, Glucuronic acid, Glycyrrhizin, Glycosylation, Silver zeolite

http://dx.doi.org/10.1016/j.carres.2009.04.015