New Method of Orthoesterification Under Kinetic Control

Convergent synthesis of a tetrasaccharide repeating unit of the O-specific polysaccharide from the cell wall lipopolysaccharide of Azospirillum brasilense strain Sp7

“…The transformation of 2-azidoethyl β-D-galactopyranoside ( 6 ) [ 36 ] into 2-azidoethyl 2,6-di- O -acetyl-β-D-galactopyranoside ( 7 ) was carried out in 72% yield by using the reaction sequence consisting of 3,4- O -isopropylidenation with 2,2-dimethoxypropane in the presence of p -toluenesulfonic acid [ 37 ], conventional acetylation of the free hydroxy groups followed by acidic hydrolysis of the acetonide functionality. Selective acetylation of compound 7 by the formation of an orthoester intermediate [ 38 ] resulted in the formation of 2-azidoethyl 2,4,6-tri- O -acetyl-β-D-galactopyranoside ( 2 ) in 74% yield ( Scheme 1 ).…”

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“…The value of cyclic orthoesters as intermediates for selective acylation of carbohydrates has been demonstrated 25 . For example, methyl α-D-glucopyranoside on treatment with trimethylorthoacetate or 1, 1-dimethoxyethene in N,N-dimethylformamide (DMF) in the presence of p-toluenesulphonic acid is known to afford the corresponding 4,6-cyclic orthoester derivative, which on hydrolysis afforded the corresponding 6acetate as the major and 4-acetate as the minor compound 26 .…”

“…Acid-Daunomycin Conjugate: Daunomycin (25) has been conjugated with HA, using ε-aminocaproic acid spacer arm. The carboxyl group of the hyaluronic acid was activated using N-hydroxysuccinimide and EDC, the excess was decomposed by dipottasium phosphate buffer and then treated with ε-aminocaproic acid to afford the intermediate HA-5'-ε-aminocaproic acid amide, which was then treated with Daunomycin C in water, pyridine and N,N-dimethylformamide (DMF) in the presence of EDC.…”