Solid-Phase Synthesis of Oligonucleotide Glycoconjugates Bearing Three Different Glycosyl Groups: Orthogonally Protected Bis(hydroxymethyl)-<i>N,N</i><i>‘</i>-bis(3-hydroxypropyl)malondiamide Phosphoramidite as Key Building Block
O‘-(methoxymethylene)bis(hydroxymethyl)malonate (3) was observed to undergo a stepwise aminolysis when treated with 3-aminopropanol. This allowed convenient preparation of bis(hydroxymethyl)-N,N‘-bis(3-hydroxypropyl)malondiamide bearing orthogonal levulinyl (Lev) and tert-butyldiphenylsilyl (TBDPS) protections at the two N-hydroxypropyl groups (8). One of the hydroxylmethyl functions was then protected with a 4,4‘-dimethoxytrityl