Procedures for the synthesis of branched Xylβ(1→3)[Galβ(1→2)]‐Glc and Xylβ(1→3)[Galβ(1→2)]‐GlcUA trisaccharides β‐linked to the 3‐O of cholesterol, cholestanol, and friedelanol, respectively, were developed. To this end, β‐selective glucosylation of cholesterol with glucosyl donors giving selective access to 2‐O, 3‐O, and 6‐O was studied. This way intermediates 10 and 21 having 2‐O‐acyl, 3‐O‐benzyl and 4,6‐O‐benzylidene or also benzyl protection were obtained. Removal of the 2‐O‐acyl group and then galactosylation afforded β(1→2)‐linked disaccharide intermediates 14 and 23. Standard manipulations with the O‐benzylidene and/or O‐benzyl protecting groups gave selective access to the 3‐O of the glucosyl residue, thus affording with a xylosyl donor the trisaccharide β‐linked to the cholesteryl residue (compound 18) as decisive intermediate. Also an alternative procedure to this compound via attachement of a Xylβ(1→3)Glc residue to cholesterol and then galactosylation could be developed. Total deprotection of 18 or regioselective introduction of a sulfate group and of a dodecylcarbamoyl residue at 6a‐O furnished saponins 34, 36, and 38, respectively. Hydrogenation of cholesteryl disaccharide 23 led directly to a 3a‐O‐unprotected cholestanyl disaccharide 39. β‐Selective xylosylation and transformation of the liberated glucose hydroxymethyl group into a carboxylic group afforded target molecule 1b having the desired Xyl(1→3)[Gal(1→2)]‐GlcUA β‐linked to cholestanol. Similarly, a saponin analog was obtained having an α‐linked L‐rhamnosyl residue instead of the β‐linked D‐xylosyl residue. Application of the glycosylation sequence, as worked out for cholesterol, to friedelanol led to attachment of the Xylβ(1→3)[Galβ(1→2)]‐Glc residue to the 3‐O (compound 54). Complete O‐deacylation led to saponin 55; oxidation of the hydroxymethyl group of the glucose residue to the carboxylic group and then deprotection afforded target molecule 2 containing the same trisaccharide residue as 1b. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Procedures for the synthesis of branched Xylβ(1–3)[Galβ(1–2)]Glc and Xylβ(1–3)[Galβ(1–2)]GlcA trisaccharides β‐linked to the 3‐O moieties of allobetulin and glycyrrhetic acid, respectively, were developed. To this end, β‐selective glucosylation of the two triterpenes with a glucosyl donor permitting selective access to 2a‐O, 3a‐O, and 6a‐O, was studied; this led to glucoside intermediates. Xylosylation of the 2a,3a‐O‐unprotected glucoside was straightforward because, under inverse procedure conditions, exclusively 3a‐O‐reaction was observed. Subsequent 2a‐O‐galactosylation followed by 4a,6a‐O‐debenzylidenation and chemoselective oxidation of the glucose hydroxymethyl group gave the target molecule 1 in high yield after deprotection. The high nucleophilicity of the glycyrrhetinate keto group required a variation in the sequential attachment of the galactosyl and xylosyl residues, so the 2a‐O‐unprotected glucoside was selected. Initial 2a‐O‐galactosylation, affording mainly a disaccharide, and subsequent protecting group manipulation and 3a‐O‐xylosylation gave the target molecule 2b after deprotection. Transformation of the glucose residue in the trisaccharide intermediate into a glucuronate residue furnished target molecule 2a, with the Xylβ(1–3)[Galβ(1–2)]GlcA β‐linked to 3‐O of the glycyrrhetic acid. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)