Synthesen von Galactose‐Cluster‐haltigen Steroid‐Derivaten

Synthesis of Galactose‐Cluster‐Containing Steroid Derivatives The synthesis of galactose clusters that are linked to a steroid moiety by a peptide‐like spacer unit is described. The galactose cluster is obtained by Koenigs‐Knorr glycosylation of TRIS‐Gly‐Fmoc ( 2b ) under Helferich conditions. Peptide and ester bonds are formed after activation of carboxylic acids as diphenylthiophene dioxide (TDO) esters. 6a is synthesized in a convergent way by coupling of (Ac 4 Gal) 3 ‐TRIS‐Gly ( 3e ) with cholesteryl TDO succinate ( 5b) . Coupling of (Ac 4 Gal) 3 ‐TRIS‐Gly hydrogen succinate ( 3f ) with Gly‐O‐Chol ( 5d ) by means of EEDQ yields 6d . Reaction of (Ac 4 Gal) 3 ‐TRIS‐Gly‐SUCC‐O‐TDO ( 3g ) with 25‐hydroxycholesterol leads in a linear sequence to the oxysterol derivative 6f . Selective cleavage of the acetyl groups from galactose units yields the known compound 6b and the new derivatives 6e and 6g .